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Preparation and Properties of Poly(imide-siloxane) Copolymer Composite Films with Micro-Al2O3 Particles

Preparation and Properties of Poly(imide-siloxane) Copolymer Composite Films with Micro-Al2O3... applied sciences Article Preparation and Properties of Poly(imide-siloxane) Copolymer Composite Films with Micro-Al O Particles 2 3 1 1 1 1 1 Ju-Young Choi , Kyeong-Nam Nam , Seung-Won Jin , Dong-Min Kim , In-Ho Song , 2 1 1 , 2 , Hyeong-Joo Park , Sungjin Park and Chan-Moon Chung * Department of Chemistry, Yonsei University, Wonju, Gangwon-do 26493, Korea; cjy0510@yonsei.ac.kr (J.-Y.C.); nkn001@yonsei.ac.kr (K.-N.N.); jinsw0906@yonsei.ac.kr (S.-W.J.); dmkimr@yonsei.ac.kr (D.-M.K.); segunda@yonsei.ac.kr (I.-H.S.); sjpsi@yonsei.ac.kr (S.P.) Department of Chemistry and Medical Chemistry, Yonsei University, Wonju, Gangwon-do 26493, Korea; hyeongjoo1016@yonsei.ac.kr * Correspondence: cmchung@yonsei.ac.kr; Tel.: +82-033-760-2266 Received: 11 January 2019; Accepted: 1 February 2019; Published: 6 February 2019 Abstract: In the current study, poly(imide-siloxane) copolymers (PIs) with different siloxane contents were synthesized and used as a matrix material for PI/Al O composites. The PIs were characterized 2 3 via their molecular weight, film quality, and thermal stability. Among the PI films, free-standing and flexible PI films were selected and used to prepare PI/Al O composite films, with different 2 3 Al O loadings. The thermal conductivity, thermal stability, mechanical property, film flexibility, 2 3 and morphology of the PI/Al O composite films were investigated for their application as 2 3 heat-dissipating material. Keywords: poly(imide-siloxane) copolymer; Al O ; thermal conductivity; heat-dissipating 2 3 1. Introduction Recent electronic devices such as smart applications and laptops are becoming smaller and lighter with developments in the electronics industry [1–3]. To ensure the proper operation of smaller devices, unwanted heat that is generated in electronic devices must be removed. The dissipation of heat has attracted increasing attention, and is an important issue that reqiuires resolution [4,5]. Currently, polymer composite materials containing ceramic powder are widely used as heat dissipation materials in electronic devices [6,7]. Among the polymer materials, polysiloxane has some advantages and is used as a heat-dissipating polymer matrix [8–10]. It is composed of a linear Si-O-Si moiety with a bond-angle between 104 and 180 , which introduces flexibility to the polymer [11,12]. In addition, polysiloxane can be used permanently without any change at 150 C, it is able to withstand 200 C for 1000 h, and 350 C for shorter periods of time [13,14]. However, some studies on the long-term reliability of silicone rubber suggest that commercial high-temperature silicones, which are being aged at 250 C could suffer from severe thermal decomposition [15–17]. Polyimides have widely been used in display, vehicle, aerospace, and microelectronic industries as high-performance material owing to their good mechanical properties, excellent thermal stability, flexibility, low dielectric permittivity, and good chemical resistance [4,18–21]. Polyimides are also good candidates for use as thermal conductive composite materials that can be operated at high temperatures, due to their high thermal stability [22–27]. By introducing siloxane chain segments to the polyimide backbone structure, adhesion between the polyimide and inorganic materials can be improved, including the adhesion of the metal materials and other substrates [28–31]. Previously, Appl. Sci. 2019, 9, 548; doi:10.3390/app9030548 www.mdpi.com/journal/applsci Appl. Sci. 2019, 9, 548 2 of 11 poly(imide-siloxane) copolymers (PIs) have been studied for applications in aerospace, separation, and microelectronics [32–35]. On the other hand, alumina (Al O ) fillers are used as thermally conductive 2 3 material embedded in the polymer matrix [36–40]. Alumina is commercially very inexpensive and often employed to improve the dissipation of polymer materials’ heat properties due to its better insulating qualities and higher thermal conductivity [40]. In this paper, we first report the preparation method and properties of PI composite films containing Al O particles, for their application as heat dissipating material. We report the 2 3 preparation and properties of PIs with varyingmolar ratio of two diamines (an aromatic diamine and bis(3-aminopropyl)-terminated polydimethylsiloxane). Furthermore, PI/Al O composite films 2 3 were prepared by adding various Al O contents into the PI matrix. Then the thermal conductivity, 2 3 thermal stability, mechanical properties, film flexibility, and morphology of the composite films were investigated according to the change in Al O loadings. 2 3 2. Materials and Methods 2.1. Materials 0 0 4,4 -(Hexafluoroisopropylidene) diphthalic anhydride (6FDA), 4,4 -methylenedianiline (MDA), and bis(3-aminopropyl)-terminated polydimethylsiloxane (PDMS) (M ~2500) were purchased from Sigma-Aldrich Korea (Seoul, Korea), and were used as received. Tetrahydrofuran (THF) was purchased from Samchun Chemicals (Seoul, Korea), distilled from N /benzophenone, and stored under nitrogen until use. 1-Methyl-2-pyrrolidinone (NMP) was purchased from Duksan Pure Chemical (Seoul, Korea), distilled in reduced pressure, and kept under nitrogen until use. Polygonal alumina (Al O ; average 2 3 particle size = 4 m) was purchased from Denka Co. Ltd. (Seoul, Korea) and was dried at 120 C in an oven for 24 h to remove the adsorbed water before use. Tetrahydrofuran-d (THF-d ) was purchased 8 8 from Acros Organics BVBA (Geel, Belgium). 2.2. Characterization Proton nuclear magnetic resonance ( H NMR) spectra of samples dissolved in THF-d were acquired using a Bruker Avance II 400 MHz spectrometer (Bruker Corporation, Billerica, MA, USA). Gel permeation chromatography (GPC; Waters Corporation, Milford, MA, USA) analysis was carried out in refractive index mode using a doubly connected Showa Denko Shodex KF-806L column at 100 C and an eluent of 0.05 mol/L LiBr in NMP at a flow rate of 1.0 mL/min; the results were calibrated with respect to polystyrene standards. Fourier Transform Infrared (FT-IR) spectroscopy was carried out using a Spectrum One B FT-IR spectrometer (PerkinElmer, Inc., Waltham, MA, USA) using the KBr pellet technique with the following scan parameters: scan range 500–4000 cm ; number of scan 1; resolution 4 cm . Thermal analyses were carried out under a nitrogen atmosphere with a balance flow rate of 40 mL/min and a furnace flow rate of 60 mL/min using a Discovery TGA 55 (TA instrument, Inc., New Castle, DE, USA) at a heating rate of 10 C/min. The thickness of the polyimide films was measured using a 293–348 IP65 digimatic outside micrometer (Mitutoyo Corporation, Kawasaki, Japan). Thermal conductivities (in-plane) of the composite films were measured using a LFA 467 Nanoflash (NETZSCH Korea Co., Ltd., Koyang, Korea). A universal testing machine (UTM) (QC-505M1, Daeha Trading Co., Seoul, Korea) was used to determine tensile properties. A 3-cm gauge and a strain rate of 2 cm/min were used. Film specimen measurements were performed at room temperature using 0.5 cm wide, 6 cm long, and ca. 0.3 mm thick films. An average of five individual determinations were used for each sample. Field emission scanning electron microscopy (FE-SEM) was carried out using a SU-70 (Hitachi, Ltd., Tokyo, Japan), with an acceleration voltage of 30 kV and a working distance in the range of 10 to 11.6 mm. The samples were sputter-coated with platinum. Appl. Sci. 2019, 9, 548 3 of 11 Appl. Sci. 2018, 8, x FOR PEER REVIEW 3 of 11 2.3. Preparation of Poly(amic acid-siloxane)s (PAAs) 2.3. Preparation of poly(amic acid-siloxane)s (PAAs) Scheme 1 shows the general method of copolyimide synthesis. A representative example for the Scheme 1 shows the general method of copolyimide synthesis. A representative example for the synthesis of poly(amic acid-siloxane)-4 (PAA-4) (molar feed ratio of 6FDA:MDA:PDMS was 1:0.5:0.5) is synthesis of poly(amic acid-siloxane)-4 (PAA-4) (molar feed ratio of 6FDA:MDA:PDMS was 1:0.5:0.5) described below. A dried 50-mL flask was charged with MDA (0.002 mol, 0.198 g) and PDMS (0.002 mol, is described below. A dried 50-mL flask was charged with MDA (0.002 mol, 0.198 g) and PDMS (0.002 2.500 g) in THF (14.3 mL) under a nitrogen atmosphere. After 6FDA (0.004 mol, 0.888 g) was added, mol, 2.500 g) in THF (14.3 mL) under a nitrogen atmosphere. After 6FDA (0.004 mol, 0.888 g) was the resulting solution was stirred at 0 C for 1 h, and then further stirred at room temperature for 23 h added, the resulting solution was stirred at 0 °C for 1 h, and then further stirred at room temperature to yield a clear viscous PAA-4 solution. The other PAA solutions were prepared in a similar fashion for 23 h to yield a clear viscous PAA-4 solution. The other PAA solutions were prepared in a similar by favarying shion bythe var molar ying tfeed he mratio olar f of eed the radiamines. tio of the d As iami ann exception, es. As an e NMP xceptwas ion, used NMP w in the as usynthesis sed in the of synthesis of PAA-1 with a molar feed ratio of 6FDA:MDA:PDMS of 1:1:0. The PAA solutions was PAA-1 with a molar feed ratio of 6FDA:MDA:PDMS of 1:1:0. The PAA solutions was used to prepare used to prepare PI films, powders, and composite films (see below). PI films, powders, and composite films (see below). Scheme 1. Synthesis of PIs and their composites. Scheme 1. Synthesis of PIs and their composites. 2.4. Preparation of PI Films 2.4. Preparation of PI Films The PAA-4 solution obtained above was drop-cast onto slide glasses and the solution was The PAA-4 solution obtained above was drop-cast onto slide glasses and the solution was stepwisely heated (at 50, 100, and 150 C). The solution was allowed to stand at each temperature stepwisely heated (at 50, 100, and 150 °C). The solution was allowed to stand at each temperature for for 1 h. The resulting films were finally heated at 250 C for 2 h, and PI-4 films were obtained. 1 h. The resulting films were finally heated at 250 °C for 2 h, and PI-4 films were obtained. The PI-4 The PI-4 films were cooled to room temperature and put in a water bath for 1 h to allow easy peel off. films were cooled to room temperature and put in a water bath for 1 h to allow easy peel off. The The resultant films were dried in a vacuum oven at 100 C for 1 h. The other PI films were prepared in resultant films were dried in a vacuum oven at 100 °C for 1 h. The other PI films were prepared in a a similar manner by varying the molar feed ratio of the diamines. similar manner by varying the molar feed ratio of the diamines. 2.5. Preparation of PI Powders 2.5. Preparation of PI Powders The PAA-4 solution obtained above was poured into distilled water, forming a precipitate that was The PAA-4 solution obtained above was poured into distilled water, forming a precipitate that collected via filtration. The precipitate was washed with distilled water and then dried in a vacuum was collected via filtration. The precipitate was washed with distilled water and then dried in a oven, yielding a PAA-4 powder. The PAA-4 was thermally imidized by stepwise heating in a furnace vacuum oven, yielding a PAA-4 powder. The PAA-4 was thermally imidized by stepwise heating in (50, 100, and 150 C). The powder was kept for 1 h at each temperature and finally heated at 250 C a furnace (50, 100, and 150 °C). The powder was kept for 1 h at each temperature and finally heated for 2 h to obtain PI-4 powder. The other PAA and PI powders were prepared in a similar manner by at 250 °C for 2 h to obtain PI-4 powder. The other PAA and PI powders were prepared in a similar varying the molar feed ratio of the diamines. The prepared PAA and PI powders were used in FT-IR manner by varying the molar feed ratio of the diamines. The prepared PAA and PI powders were spectroscopy and GPC. used in FT-IR spectroscopy and GPC. Appl. Sci. 2019, 9, 548 4 of 11 2.6. Preparation of PI Composite Films Al O powder (30, 60, 75, or 80 wt%) was added to the PAA-4 solution obtained above. 2 3 The mixture was ultrasonicated using an ultrasonic device (VCX750, Sonics & Materials, Newtown, CT, USA), with an output power of 150 W and a frequency of 20 kHz for 1 h to yield a milky suspension. The suspension was drop-cast onto slide glasses, and then heated in a stepwise manner (at 50, 100, and 150 C). The suspension was allowed to stand at each temperature for 1 h and finally heated at 250 C for 2 h to obtain PI/Al O composite films (PI-4-30, PI-4-60, PI-4-75, and PI-4-80). The obtained 2 3 films were cooled to room temperature and put in a water bath for 1 h to facilitate peeling it off. The resultant composite films were dried in a vacuum oven at 100 C for 1 h. 3. Results and Discussion 3.1. Preparation of PIs and Their Composite Films The preparation of poly(imide-siloxane) copolymers (PIs) is illustrated in Scheme 1. The PIs were synthesized according to a conventional two-step procedure. During typical conventional polyimide synthesis, aprotic polar solvents such as NMP, dimethylacetamide (DMAc), or dimethylformamide (DMF) are usually used. However, the siloxane group underwent microphase separation when aprotic solvents were used during the copolymerization. To overcome this problem, the preparation of PIs required the use of a co-solvent system or THF [41,42]. In this work, 6FDA, MDA, and PDMS were copolymerized using THF as a solvent (Table 1), except for PAA-1 which was prepared without the PDMS moiety and used NMP as a solvent. 6FDA and mixed diamines (MDA and PDMS) were first polymerized to prepare poly(amic acid-siloxane)s (PAA-1–PAA-7). The diamine molar feed ratio was controlled as summarized in Table 1. The PDMS content of PAA copolymers was determined by H NMR (Table 1 and Figure S1). The mole percent of PDMS was calculated from the ratio of the integration values of the methyl groups in PDMS and the methylene groups of MDA. It was found that the determined values agreed well with those corresponding to PDMS contents in the feeds. The PAA solutions were drop-cast onto slide glasses and then PAAs were converted to PI-1–PI-7 films by thermal imidization. The PAA and PI powders were also prepared for characterization via FT-IR spectroscopy and GPC. Table 1 lists the molecular weights and polydispersity indexes (PDIs) of the PAAs measured by GPC. In addition, PI/Al O 2 3 composites were prepared by adding various amount of Al O powder to PAA solutions. The resulting 2 3 suspensions were drop-cast onto galss slides and subsequent thermal imidization was carried out to obtain PI/Al O composite films. 2 3 Table 1. Molar feed ratios and molecular weights of PAAs. Molar Feed Ratio PDMS Content M M n w a c PAA Code PDI b 4 4 (6FDA:MDA:PDMS) (mol%) (10 g/mol) (10 g/mol) PAA-1 1:1:0 - 1.03 2.32 2.2 PAA-2 1:0.9:0.1 13 10.8 37.8 3.5 PAA-3 1:0.7:0.3 32 10.8 18.1 1.6 PAA-4 1:0.5:0.5 49 3.73 13.2 3.5 PAA-5 1:0.3:0.7 70 21.1 48.8 2.3 PAA-6 1:0.1:0.9 89 16.3 50.9 3.1 PAA-7 1:0:1 - 7.92 25.1 3.2 a b 1 c PAA: poly(amic acid-siloxane); Calculated from H NMR integrations of PAA copolymers; Polydispersity index (M /M ). w n 3.2. Characterization of PAAs and PIs The structures of PAAs and PIs were confirmed by FT-IR spectroscopy (Figure 1). FT-IR spectra of PAA-4 and PI-4 showed absorption bands at 1021 and 1095 cm , respectively, due to Si-O-Si stretching in the structure of PDMS. The absorption band at 1259 cm was also attributed to the symmetric Appl. Sci. 2019, 9, 548 5 of 11 Appl. Sci. 2018, 8, x FOR PEER REVIEW 5 of 11 deformation of the –CH group in –Si(CH ) -, and the absorption band at 803 cm was assigned −1 to 3 3 2 symmetric deformation of the –CH3 group in –Si(CH3)2-, and the absorption band at 803 cm was the Si-C vibration [11,41,43–45]. The FT-IR spectrum of PAA-4 showed bands at 1721 cm (carboxyl) −1 assigned to the Si-C vibration [11,41,43–45]. The FT-IR spectrum of PAA-4 showed bands at 1721 cm 1 1 and 1660 cm (amide)−owing 1 to C=O stretching, and at 1545 cm owing−to 1 C-N stretching (amide), (carboxyl) and 1660 cm (amide) owing to C=O stretching, and at 1545 cm owing to C-N stretching suggesting the formation of PAA (Figure 1a) [11,34,46]. PI-4 exhibited absorption bands at 1785 cm (amide), suggesting the formation of PAA (Figure 1a) [11,34,46]. PI-4 exhibited absorption bands at owing to−1imide C=O asymmetric stretching, 1726 cm owing to−1imide C=O symmetric stretching, 1785 cm owing to imide C=O asymmetric stretching, 1726 cm owing to imide C=O symmetric and 1375 cm owing to−1 imide C–N stretching (Figure 1b) [11,34,46–48]. FT-IR spectra of the other stretching, and 1375 cm owing to imide C–N stretching (Figure 1b) [11,34,46–48]. FT-IR spectra of PAAs and PIs are shown in Figures S2–S7. the other PAAs and PIs are shown in Figures S2–S7. Figure 1. FT-IR spectra of (a) PAA-4, and (b) PI-4. Figure 1. FT-IR spectra of (a) PAA-4, and (b) PI-4. 3.3. Properties of PI Films 3.3. Properties of PI Films Thermal stability of PIs was investigated by thermogravimetric analysis (TGA) (Table 2 and Thermal stability of PIs was investigated by thermogravimetric analysis (TGA) (Table 2 and Figure 2). TGA was conducted to study the effects of the molar ratio of diamines on decomposition Fig temperatur ure 2). TG e (T A was cond and T ) and ucted to study the effects char yield of PIs. T and of T the molar ratio of di values of the PIs ranged amines on decomposition from 373 to 505 and 5 10 5 10 temperature (T5 and T10) and char yield of PIs. T5 and T10 values of the PIs ranged from 373 to 505 and 419 to 528 C, respectively, and the decomposition temperature decreased with increasing PDMS molar 41 ratio. 9 toNevertheless, 528°C, respect PIs’ ively decomposition , and the decom temperatur position t esemperature were much decreased higher than with incre those ofa silicone sing PDM [17S ]. molar ratio. Nevertheless, PIs’ decomposition temperatures were much higher than those of silicone The char yield at 800 C of PI-1 without siloxane moiety was the highest (62.4%) and the other char yields [17]. The wer cha e much r yield lower at 80 . 0 °C of PI-1 without siloxane moiety was the highest (62.4%) and the other char yields were much lower. Table 2. Film quality and thermal properties of PIs. Flexible and free-standing PI films (PI-3, PI-4, and PI-5) could be prepared from PAA-3, PAA-4, and PAA-5, respectively (Table 2 and Figure 3). When the films were bent, twisted, rolled-up, or a  b  c d PI Code Film Quality T ( C) T ( C) Char Yield (%) 5 10 wrapped on the 3-mm diameter bar numerous times, their appearance was almost unchanged (no PI-1 Brittle 505 528 62.4 damage occurred). However, PI-1 and PI-2 films were brittle due to their rigid chemical structures. PI-2 Brittle 446 473 28.2 On the other hand, PI-6 and PI-7 films were sticky due to the very high PDMS group contents. PI-3 Flexible 438 454 16.7 PI-4 Flexible 428 443 0.7 PI-5 Table 2. Flexible Film quality and ther 423 mal properties 441 of PIs. 2.1 PI-6 Sticky 403 426 4.3 a b c d PI Code Film Quality T5 (°C) T10 (°C) Char Yield (%) PI-7 Sticky 373 419 3.2 a PI-1 Brittle 505 b 528 62.4 PI-1–PI-7 were prepared from PAA-1–PAA-7, respectively; The temperature at which a sample exhibits 5 wt% decomposition in a nitrogen atmosphere; The temperature at which a sample exhibits 10 wt% decomposition in a PI-2 Brittle 446 473 28.2 nitrogen atmosphere; Char yield at 800 C in a nitrogen atmosphere. PI-3 Flexible 438 454 16.7 PI-4 Flexible 428 443 0.7 PI-5 Flexible 423 441 2.1 PI-6 Sticky 403 426 4.3 PI-7 Sticky 373 419 3.2 a b PI-1–PI-7 were prepared from PAA-1–PAA-7, respectively; The temperature at which a sample exhibits 5 wt% decomposition in a nitrogen atmosphere; The temperature at which a sample exhibits 10 wt% decomposition in a nitrogen atmosphere; Char yield at 800 °C in a nitrogen atmosphere. Appl. Sci. 2018, 8, x FOR PEER REVIEW 6 of 11 Appl. Sci. 2019, 9, 548 6 of 11 Appl. Sci. 2018, 8, x FOR PEER REVIEW 6 of 11 Figure 2. TGA curves of PIs. Figure 2. TGA curves of PIs. Flexible and free-standing PI films (PI-3, PI-4, and PI-5) could be prepared from PAA-3, PAA-4, and PAA-5, respectively (Table 2 and Figure 3). When the films were bent, twisted, rolled-up, or wrapped on the 3-mm diameter bar numerous times, their appearance was almost unchanged (no damage occurred). However, PI-1 and PI-2 films were brittle due to their rigid chemical structures. Figure 2. TGA curves of PIs. On the other hand, PI-6 and PI-7 films were sticky due to the very high PDMS group contents. Figure 3. Photographs of (a) PI-3; (b) PI-4; (c) PI-5 films. 3.4. Properties of PI/Al2O3 Composite Films Because the PI-3, PI-4, and PI-5 films were free-standing and flexible, they were used to prepare Figure 3. Photographs of (a) PI-3; (b) PI-4; (c) PI-5 films. PI/Al2O3 composite films. Figure 4 shows the thermal conducting properties of neat PI films and Figure 3. Photographs of (a) PI-3; (b) PI-4; (c) PI-5 films. 3.4. Properties of PI/Al O Composite Films 2 3 PI/Al2O3 composite films, with different Al2O3 loadings along an in-plane direction (D ) at room 3.4. Properties of PI/Al2O3 Composite Films temperature (see Because the PI-3, Table PI-4, s S1 and –S3PI-5 ). The filmsfilm wer s’ t e frhee-standing ermal diffusiv andity flexible, (α) wthey as dwer etermined e used toat prroom epare temperature PI/Al O composite and under films. ambient pressure. From Figure 4 shows the the equation K thermal conducting = α × ρpr × operties Cp, the thermal of neat conducti PI filmsvi and ty 2 3 Because the PI-3, PI-4, and PI-5 films were free-standing and flexible, they were used to prepare (K) PI/Al value O ca composite n be calculfilms, ated. In t with he e dif qu fer atent ion, Alρ is the O loadings measured along filman density in-plane , and dir Cection p is the (speci D ) at ficr he oom at 2 3 2 3 PI/Al2O3 composite films. Figure 4 shows the thermal conducting properties of neat PI films and ca temperatur pacity of the fi e (seelm Tables [5,49S1–S3). ]. The thermal The films’ conducti thermal vities diffusivity of neat PI- ( ) 3 was , PI-4 determined , and PI-5 at were room 0.11 temperat , 0.13, and ure PI/Al2O3 composite films, with different Al2O3 loadings along an in-plane direction (D ) at room 0. and 14 W/ underm·ambient K, respect pressur ivelye.. It From is k then equation own thKat thermal =  $  conducti C , the thermal vities of polyi conductivitymi(K) de a value nd temperature (see Tables S1–S3). The films’ thermal diffusivity (α) was determined at room p can olydim be calculated. ethylsiloxa Inne theare equation, 0.11 and $ is the 0.25 measur W/m· ed K a film t room density t,eand mperat C ure is the , res specific pectively [ heat capacity 22]. The of temperature and under ambient pressure. From the equation K = α × ρ × Cp, the thermal conductivity incorporat the film [5ion ,49]. of The Althermal 2O3 fillers conductivities increased therma of neatl di PI-3, ffuPI-4, sivity and and t PI-5hermal cond were 0.11, 0.13, uctivity o and 0.14 f PI W/m /Al2OK, 3 (K) value can be calculated. In the equation, ρ is the measured film density, and Cp is the specific heat composit respectively e fil .m Its (F is known igure 4a that ,b). thermal When thconductivities e Al2O3 loading of was polyimide 80 wt%, and PI-3polydimethylsiloxane and PI-4 composites sar howe e 0.11 d capacity of the film [5,49]. The thermal conductivities of neat PI-3, PI-4, and PI-5 were 0.11, 0.13, and hi and gh therm 0.25 W/m al conducti K at room vity temperatur values, grea e,ter tha respectively n 1.3 W/ [22 m·K. The t ]. The incorporation hermal diffu of siv Al ity and O fillers conduc incrteased ivity 2 3 0.14 W/m·K, respectively. It is known that thermal conductivities of polyimide and data ar thermal e quite reproduc diffusivity and ible thermal as presented conductivity in Tabof les S1 PI/Al –S3.O composite films (Figure 4a,b). When the 2 3 polydimethylsiloxane are 0.11 and 0.25 W/m·K at room temperature, respectively [22]. The incorporation of Al2O3 fillers increased thermal diffusivity and thermal conductivity of PI/Al2O3 composite films (Figure 4a,b). When the Al2O3 loading was 80 wt%, PI-3 and PI-4 composites showed high thermal conductivity values, greater than 1.3 W/m·K. The thermal diffusivity and conductivity data are quite reproducible as presented in Tables S1–S3. Appl. Sci. 2019, 9, 548 7 of 11 Al O loading was 80 wt%, PI-3 and PI-4 composites showed high thermal conductivity values, greater 2 3 than 1.3 W/mK. The thermal diffusivity and conductivity data are quite reproducible as presented in Appl. Sci. 2018, 8, x FOR PEER REVIEW 7 of 11 Tables S1–S3. Figure 4. (a) Thermal diffusivity (D ), and (b) thermal conductivity (D ) of the PI and PI/Al O 2 3 ? ? Figure 4. (a) Thermal diffusivity (D ), and (b) thermal conductivity (D ) of the PI and PI/Al2O3 ┴ ┴ composite films with different Al O loadings. 2 3 composite films with different Al2O3 loadings. In addition, thermal and mechanical properties of the PI/Al O composite films were studied 2 3 In addition, thermal and mechanical properties of the PI/Al2O3 composite films were studied (Table 3 and Figures S8 and S9). Among the flexible PI films, PI-3 was selected because it (Table 3 and Figures S8 and S9). Among the flexible PI films, PI-3 was selected because it exhibited exhibited the best thermal conducting properties. The T and T values of the neat PI-3 and 5 10 the best thermal conducting properties. The T5 and T10 values of the neat PI-3  and PI-3/Al2O3 PI-3/Al O composite films ranged from 437 to 454 C and 456 to 474 C, respectively. Generally the 2 3 composite films ranged from 437 to 454 °C and 456 to 474 °C, respectively. Generally the decomposition temperatures of the PI/Al O composite films were higher than those of the neat PI 2 3 decomposition temperatures of the PI/Al2O3 composite films were higher than those of the neat PI film. The improvement in thermal stability can be attributed to restrained polymer chain mobility by film. The improvement in thermal stability can be attributed to restrained polymer chain mobility by Al O particles [17]. Furthermore, it should be noted that the PI/Al O composites showed much 2 3 2 3 Al2O3 particles [17]. Furthermore, it should be noted that the PI/Al2O3 composites showed much higher thermal stability compared to polysiloxane/Al O composites [17,50]. From the char yield data, 2 3 higher thermal stability compared to po  lysiloxane/Al2O3 composites [17,50]. From the char yield data, each mass value retained around 800 C and was almost identical to the corresponding Al O content 2 3 each mass value retained around 800 °C and was almost identical to the corresponding Al2O3 content in each composite. in each composite. The neat PI-3 film showed a tensile strength of 14.6 ± 2.7 MPa, and a high elongation at a break Table 3. Thermal and mechanical properties of the PI-3/Al O composite films. 2 3 of 210.4 ± 38.4%. However, the PI/Al2O3 composite films exhibited decreased tensile strength and Char Yield Tensile Strength Elongation at Break a  b  c PI/Al O Composite Code T ( C) T ( C) elongati2on 3 at break, and the mechanical 10 properties decreased with increasing Al2O3 loadings. It is 5 d (%) (MPa) (%) well known that the incorporation of an inorganic filler to the polymer matrix reduces the polymer’s PI-3 438 461 16.7 14.6  2.7 210.4  38.4 flexibility. Furthermore, the polymer’s strength is reduced if there are no binding sites between the PI-3-30 440 456 30.7 7.3  0.2 41.7  2.8 PI-3-60 454 469 61.3 6.5  0.4 10.4  0.6 polymer phase and inorganic material phase [51]. Nevertheless, the composite films with up to 75 PI-3-75 450 474 75.2 5.7  0.5 4.8  0.6 wt% Al2O3 are sufficiently flexible, as shown in Figure 5. They may be useful as a flexible heat- PI-3-80 437 471 79.1 5.2  0.5 3.7  0.6 radiating film in flexible electronic devices requiring a high operating temperature. Even though the a b PI-3, PI-3-30, PI-3-60, PI-3-75, and PI-3-80 films have Al O loadings of 0, 30, 60, 75, and 80 wt%, respectively; The 2 3 composite temperatur films with e at which 80 a sample wt% Al exhibits 2O 53wt% loadecomposition ding are not f in a l nitr exi ogen ble, the atmospher y co e;uld Thealtemperatur so be us ee atd which in high- a sample exhibits 10 wt% decomposition in a nitrogen atmosphere; Char yield at 800 C in a nitrogen atmosphere. temperature electronic devices. The neat PI-3 Table 3. filmThermal and me showed a tensile chanical pr strength opertie of 14.6 s of the PI-3/Al 2.7 MPa, 2O and 3 com a high posite fi elongation lms. at a break of 210.4  38.4%. However, the PI/Al O composite films exhibited decreased tensile strength and 2 3 Char Yield Tensile Strength Elongation at Break a b c PI/Al2O3 Composite Code T5 (°C) T10 (°C) elongation at break, and the mechanical properties decreased with increasing Al O loadings. It is 2 3 (%) (MPa) (%) well known that the incorporation of an inorganic filler to the polymer matrix reduces the polymer ’s PI-3 438 461 16.7 14.6 ± 2.7 210.4 ± 38.4 flexibility. Furthermore, the polymer ’s strength is reduced if there are no binding sites between the PI-3-30 440 456 30.7 7.3 ± 0.2 41.7 ± 2.8 polymer phase PI-3-60 and inorganic material 454 phase 469 [51]. Nevertheless, 61.3 the6.5 ± composite 0.4 films with 10.4 ± up 0.6 to 75 wt% PI-3-75 450 474 75.2 5.7 ± 0.5 4.8 ± 0.6 Al O are sufficiently flexible, as shown in Figure 5. They may be useful as a flexible heat-radiating 2 3 PI-3-80 437 471 79.1 5.2 ± 0.5 3.7 ± 0.6 film in flexible electronic devices requiring a high operating temperature. Even though the composite PI-3, PI-3-30, PI-3-60, PI-3-75, and PI-3-80 films have Al2O3 loadings of 0, 30, 60, 75, and 80 wt%, films with 80 wt% Al O loading are not flexible, they could also be used in high-temperature 2 3 respectively; The temperature at which a sample exhibits 5 wt% decomposition in a nitrogen electronic devices. atmosphere; The temperature at which a sample exhibits 10 wt% decomposition in a nitrogen atmosphere; Char yield at 800 °C in a nitrogen atmosphere. Appl. Sci. 2019, 9, 548 8 of 11 Appl. Sci. 2018, 8, x FOR PEER REVIEW 8 of 11 Appl. Sci. 2018, 8, x FOR PEER REVIEW 8 of 11 Figure 5. Photographs of PI composite films containing different Al2O3 contents. Figure 5. Photographs of PI composite films containing different Al O contents. 2 3 Figure 5. Photographs of PI composite films containing different Al2O3 contents. Scanning electron microscopy (SEM) was carried out to investigate the morphology of the Scanning electron microscopy (SEM) was carried out to investigate the morphology of the Scanning electron microscopy (SEM) was carried out to investigate the morphology of the PI/Al O composite films. Figure 6a shows the SEM image of micro-Al O particles. The particles PI/Al2O3 composite films. Figure 6a shows the SEM image of micro-Al2O3 particles. The particles are 2 3 2 3 PI/Al2O3 composite films. Figure 6a shows the SEM image of micro-Al2O3 particles. The particles are are irregularly shaped with 4 m average size. The neat PI-3 film before Al O addition showed a irregularly shaped with 4 μm average size. The neat PI-3 film before Al2O3 addition showed a very 2 3 irregularly shaped with 4 μm average size. The neat PI-3 film before Al2O3 addition showed a very very smooth surface (Figure 6b). As shown in Figure 6c, Al O particles were well dispersed in the smooth surface (Figure 6b). As shown in Figure 6c, Al2O3 particles were well dispersed in the PI/Al2O3 2 3 smooth surface (Figure 6b). As shown in Figure 6c, Al2O3 particles were well dispersed in the PI/Al2O3 PI/Al O composite film and no significant fractures were observed across the film’s surface. composite film and no significant fractures were observed across the film’s surface. 2 3 composite film and no significant fractures were observed across the film’s surface. Figure 6. SEM images of (a) Al O particles; (b) PI-3 film; (c) PI-3-75 film. 2 3 Figure 6. SEM images of (a) Al2O3 particles; (b) PI-3 film; (c) PI-3-75 film. Figure 6. SEM images of (a) Al2O3 particles; (b) PI-3 film; (c) PI-3-75 film. 4. Conclusions 4. Conclusions 4. Conclusions The PIs with different siloxane contents were prepared using 6FDA, MDA, and The PIs with different siloxane contents were prepared using 6FDA, MDA, and PDMS. Free- The PIs with different siloxane contents were prepared using 6FDA, MDA, and PDMS. Free- PDMS.Free-standing, flexible films of PI-3, PI-4, and PI-5 were obtained, and the PIs were used standing, flexible films of PI-3, PI-4, and PI-5 were obtained, and the PIs were used to prepare standing, flexible films of PI-3, PI-4, and PI-5 were obtained, and the PIs were used to prepare to prepare PI/Al O composite films. The thermal conductivities of the composite films increased with 2 3 PI/Al2O3 composite films. The thermal conductivities of the composite films increased with increasing PI/Al2O3 composite films. The thermal conductivities of the composite films increased with increasing increasing Al O content. It was demonstrated that the composite films with up to 75 wt% Al O 2 3 2 3 Al2O3 content. It was demonstrated that the composite films with up to 75 wt% Al2O3 were both free- Al2O3 content. It was demonstrated that the composite films with up to 75 wt% Al2O3 were both free- were both free-standing and flexible. The composite films with 80 wt% Al O loading showed a 2 3 st standin anding g an and d flex flexiible. The ble. The composit composite fi e films wit lms withh 8 800 wt wt% Al % Al 2O 2O 3 lo 3 lo adin adin g showe g showe dd a re a re lat lat ive ive lyly good good relatively good thermal conductivity, higher than 1.3 W/mK. Besides, PI/Al O composite films 2 3 therma thermal conducti l conductivi vity, higher th ty, higher than an 1. 1.3 W/ 3 W/m m··K. K. Be Besi sides, des, PI/ PI/A Al2lO 2O 3 composite films 3 composite films exhibited high exhibited high er er exhibited higher thermal stability compared to conventional polysiloxane/Al O composites. The 2 3 thermal stability compared to conventional polysiloxane/Al2O3 composites. The PI/Al2O3 composite thermal stability compared to conventional polysiloxane/Al2O3 composites. The PI/Al2O3 composite PI/Al O composite films could be used as a heat-radiating film in electronic devices requiring high 2 3 film films c s coouulld d be u be ussed ed a ass a h a heeat at--rrad adiiaattiing ng f film ilm in in elect electrronic onic de devices vices re requ quiriirinng h g high igh ope ope ratrat ing ing operating temperatures. temperatures. temperatures. Supplementary Materials: The following are available online at http://www.mdpi.com/2076-3417/9/3/548/s1, Supplementary Materials: The following are available online at www.mdpi.com/xxx/s1, Figure S1: FT-IR Figur Supplementary Materials: e S1: FT-IR spectra of (a The following a ) PAA-1, and (b) r PI-1; e available online at Figure S2: FT-IR spectra www.mdpi.com/xxx/ of (a) PAA-2, and s1, Figure S1: (b) PI-2; Figur FT-IR e S3: FT-IR spectra of (a) PAA-3, and (b) PI-3; Figure S4: FT-IR spectra of (a) PAA-5, and (b) PI-5; Figure S5: FT-IR spectra of (a) PAA-1, and (b) PI-1; Figure S2: FT-IR spectra of (a) PAA-2, and (b) PI-2; Figure S3: FT-IR spectra spectra of (a) PAA-1, and (b) PI-1; Figure S2: FT-IR spectra of (a) PAA-2, and (b) PI-2; Figure S3: FT-IR spectra spectra of (a) PAA-6, and (b) PI-6; Figure S6: FT-IR spectra of (a) PAA-7 and (b) PI-7; Figure S7: TGA curves of of (a) PAA-3, and (b) PI-3; Figure S4: FT-IR spectra of (a) PAA-5, and (b) PI-5; Figure S5: FT-IR spectra of (a) of (a) PAA-3, and (b) PI-3; Figure S4: FT-IR spectra of (a) PAA-5, and (b) PI-5; Figure S5: FT-IR spectra of (a) PI-3 and PI-3/Al O composite films; Figure S8: Stress–strain curves of PI-3 and PI-3/Al O composite films; 2 3 2 3 PAA-6, and (b) PI-6; Figure S6: FT-IR spectra of (a) PAA-7 and (b) PI-7; Figure S7: TGA curves of PI-3 and PI- PAA-6, and (b) PI-6; Figure S6: FT-IR spectra of (a) PAA-7 and (b) PI-7; Figure S7: TGA curves of PI-3 and PI- Table S1: Thermal diffusivity and thermal conductivity values of the PI-3 and PI-3/Al O composite films; 2 3 3/Al2O3 composite films; Figure S8: Stress–strain curves of PI-3 and PI-3/Al2O3 composite films; Table S1: 3/Al2O3 composite films; Figure S8: Stress–strain curves of PI-3 and PI-3/Al2O3 composite films; Table S1: Table S2: Thermal diffusivity and thermal conductivity values of the PI-4 and PI-4/Al O composite films; 2 3 Thermal diffusivity and thermal conductivity values of the PI-3 and PI-3/Al2O3 composite films; Table S2: T Thermal diffusivity and thermal conducti able S3: Thermal diffusivity and thermal conductivity vity values of t values he PI-3 and PI-3/Al of the PI-5 and PI-5/Al 2O3 composite O composite films; Ta films. ble S2: 2 3 Thermal diffusivity and thermal conductivity values of the PI-4 and PI-4/Al2O3 composite films; Table S3: Thermal diffusivity and thermal conductivity values of the PI-4 and PI-4/Al2O3 composite films; Table S3: Thermal diffusivity and thermal conductivity values of the PI-5 and PI-5/Al2O3 composite films. Thermal diffusivity and thermal conductivity values of the PI-5 and PI-5/Al2O3 composite films. Appl. Sci. 2019, 9, 548 9 of 11 Author Contributions: Conceptualization, J.-Y.C., S.P., and C.-M.C.; methodology, J.-Y.C.; formal analysis, J.-Y.C., K.-N.N., and S.-W.J.; investigation, D.-M.K., I.-H.S., and H.-J.P.; writing—original draft preparation, J.-Y.C. and C.-M.C.; writing—review and editing, C.-M.C.; supervision, C.-M.C. Conflicts of Interest: The authors declare no conflict of interest. References 1. Gutfleisch, O.; Willard, M.A.; Bruck, E.; Chen, C.H.; Sankar, S.G.; Liu, J.P. Magnetic materials and devices for the 21st century: Stronger, lighter, and more energy efficient. Adv. Mater. 2011, 23, 821–842. [CrossRef] [PubMed] 2. Jayaprakash, N.; Das, S.K.; Archer, L.A. The rechargeable aluminum-ion battery. Chem. Commun. 2011, 47, 12610–12612. [CrossRef] [PubMed] 3. Gain, A.K.; Fouzder, T.; Chan, Y.C.; Sharif, A.; Wong, N.B.; Yung, W.K.C. The influence of addition of al nano-particles on the microstructure and shear strength of eutectic Sn–Ag–Cu solder on Au/Ni metallized Cu pads. J. Alloys Comp. 2010, 506, 216–223. [CrossRef] 4. Li, T.-L.; Hsu, S.L.-C. Enhanced thermal conductivity of polyimide films via a hybrid of micro-and nano-sized boron nitride. J. Phys. Chem. B 2010, 114, 6825–6829. [CrossRef] [PubMed] 5. Wang, M.; Jiao, Z.; Chen, Y.; Hou, X.; Fu, L.; Wu, Y.; Li, S.; Jiang, N.; Yu, J. Enhanced thermal conductivity of poly(vinylidene fluoride)/boron nitride nanosheet composites at low filler content. Compos. Part A Appl. Sci. Manuf. 2018, 109, 321–329. [CrossRef] 6. Han, Z.; Fina, A. Thermal conductivity of carbon nanotubes and their polymer nanocomposites: A review. Prog. Polym. Sci. 2011, 36, 914–944. [CrossRef] 7. Huang, X.; Jiang, P.; Tanaka, T. A review of dielectric polymer composites with high thermal conductivity. IEEE Trans. Dielectr. Electr. Insul. 2011, 27, 8–16. [CrossRef] 8. Fang, H.; Zhang, X.; Zhao, Y.; Bai, S.-L. Dense graphene foam and hexagonal boron nitride filled PDMS composites with high thermal conductivity and breakdown strength. Compos. Sci. Technol. 2017, 152, 243–253. [CrossRef] 9. He, X.; Huang, Y.; Liu, Y.; Zheng, X.; Kormakov, S.; Sun, J.; Zhuang, J.; Gao, X.; Wu, D.J. Improved thermal conductivity of polydimethylsiloxane/short carbon fiber composites prepared by spatial confining forced network assembly. J. Mater. Sci. 2018, 53, 14299–14310. [CrossRef] 10. Kim, Y.; Hwang, S.; So, J.I.; Kim, C.L.; Kim, M.; Shim, S.E. Treatment of atmospheric-pressure radio frequency plasma on boron nitride for improving thermal conductivity of polydimethylsiloxane composites. Macromol. Res. 2018, 26, 864–867. [CrossRef] 11. Feng, L.; Iroh, J.O. Polyimide-b-polysiloxane copolymers: Synthesis and properties. J. Inorg. Organomet Polym. Mater. 2013, 23, 477–488. [CrossRef] 12. Barry, A.; Beck, H. Inorganic Polymers; Academic Press: New York, NY, USA, 1962. 13. Valentini, L.; Bittolo Bon, S.; Pugno, N.M. Severe graphene nanoplatelets aggregation as building block for the preparation of negative temperature coefficient and healable silicone rubber composites. Compos. Sci. Tech. 2016, 134, 125–131. [CrossRef] 14. Clarson, S.J. Silicones and silicone-modified materials: A concise overview. ChemInform 2004, 35, 1–10. [CrossRef] 15. Yao, Y.; Chen, Z.; Lu, G.; Boroyevich, D.; Ngo, K.D.T. Characterization of encapsulants for high-voltage high-temperature power electronic packaging. IEEE Trans. Compon. Packag. Manuf. Technol. 2012, 2, 539–547. [CrossRef] 16. Scofield, J.D.; Merrett, J.N.; Richmond, J.; Agarwal, A.; Leslie, S. Performance and Reliability Characteristics of 1200 V, 100 A, 200 C Half-Bridge SIC MOSFET-JBS Diode Power Modules. In Proceedings of the International Conference on High Temperature Electronics, International Microelectronics & Packaging Society, Albuquerque, NM, USA, 11–13 May 2010; pp. 000289–000296. 17. Yao, Y.; Lu, G.-Q.; Boroyevich, D.; Ngo, K.D.T. Effect of Al O fibers on the high-temperature stability of 2 3 silicone elastomer. Polymer 2014, 55, 4232–4240. [CrossRef] 18. Nakanishi, F. Photoreaction of amphiphilic diolefins in monolayers formed on an air-water interface. J. Polym. Sci. Part C Polym. Lett. 1988, 26, 159–163. [CrossRef] Appl. Sci. 2019, 9, 548 10 of 11 19. Liaw, D.-J.; Liaw, B.-Y.; Li, L.-J.; Sillion, B.; Mercier, R.; Thiria, R.; Sekiguchi, H. Synthesis and characterization 0 0 of new soluble polyimides from 3,3 ,4,4 -benzhydrol tetracarboxylic dianhydride and various diamines. Chem. Mater. 1998, 10, 734–739. [CrossRef] 20. Mathews, A.S.; Kim, I.; Ha, C.S. Fully aliphatic polyimides from adamantane-based diamines for enhanced thermal stability, solubility, transparency, and low dielectric constant. J. Appl. Polym. Sci. 2006, 102, 3316–3326. [CrossRef] 21. Wachsman, E.D.; Frank, C.W. Effect of cure history on the morphology of polyimide: Fluorescence spectroscopy as a method for determining the degree of cure. Polymer 1988, 29, 1191–1197. [CrossRef] 22. Ngo, I.-L.; Jeon, S.; Byon, C. Thermal conductivity of transparent and flexible polymers containing fillers: A literature review. Int. J. Heat Mass Transf. 2016, 98, 219–226. [CrossRef] 23. Kato, R.; Maesono, A.; Tye, R.P. Thermal conductivity measurement of submicron-thick films deposited on substrates by modified ac calorimetry (laser-heating Çngstrom method). Int. J. Thermophys. 2001, 22, 617–629. [CrossRef] 24. Kurabayashi, K.; Asheghi, M.; Touzelbaev, M.; Goodson, K.E. Measurement of the thermal conductivity anisotropy in polyimide films. J. Microelectromech. Syst. 1999, 8, 180–191. [CrossRef] 25. Irwin, P.C.; Cao, Y.; Bansal, A.; Schadler, L.S. Thermal and mechanical properties of polyimide nanocomposites. In Proceedings of the 2003 IEEE Annual Report Conference on Electrical Insulation and Dielectric Phenomena, Albuquerque, NM, USA, 19–22 October 2003; pp. 120–123. 26. Guo, Y.; Xu, G.; Yang, X.; Ruan, K.; Ma, T.; Zhang, Q.; Gu, J.; Wu, Y.; Liu, H.; Guo, Z. Significantly enhanced and precisely modeled thermal conductivity in polyimide nanocomposites with chemically modified graphene via in situ polymerization and electrospinning-hot press technology. J. Mater. Chem. C 2018, 6, 3004–3015. [CrossRef] 27. Wang, T.; Wang, M.; Fu, L.; Duan, Z.; Chen, Y.; Hou, X.; Wu, Y.; Li, S.; Guo, L.; Kang, R.; et al. Enhanced thermal conductivity of polyimide composites with boron nitride nanosheets. Sci. Rep. 2018, 8, 1557. [CrossRef] [PubMed] 28. You, L. Preparation and thermal properties of silicon-containing polyimide composite films. Chem. Eng. Trans. 2017, 59, 1051–1056. 29. Lupinski, J.H.; Moore, R.S. Polymeric Materials for Electronics Packaging and Interconnection; American Chemical Society: Washington, DC, USA, 1989; Volume 407, p. 516. 30. Mahoney, C.M.; Gardella, J.A.; Rosenfeld, J.C. Surface characterization and adhesive properties of poly (imidesiloxane) copolymers containing multiple siloxane segment lengths. Marcromolecules 2002, 35, 5256–5266. [CrossRef] 31. Homma, T.; Yamaguchi, M.; Kutsuzawa, Y.; Otsuka, N. Electrical stability of polyimide siloxane films for interlayer dielectrics in multilevel interconnections. Thin Solid Films 1999, 340, 237–241. [CrossRef] 32. Rogers, M.E.; Rodrigues, D.; Wilkes, G.L.; McGrath, J.E.; Brennan, A. Perfectly alternating segmented polyimide siloxane copolymers. In Advances in New Materials; Springer: Boston, MA, USA, 1992; pp. 47–55. 33. McGrath, J.E.; Dunson, D.L.; Mecham, S.J.; Hedrick, J.L. Synthesis and characterization of segmented polyimide-polyorganosiloxane copolymers. In Progress in Polyimide Chemistry I; Springer: Berlin/Heidelberg, Germany, 1999; pp. 61–105. 34. Zou, L.; Anthamatten, M. Synthesis and characterization of polyimide-polysiloxane segmented copolymers for fuel cell applications. J. Polym. Sci. Part A Polym. Chem. 2007, 45, 3747–3758. [CrossRef] 35. Pechar, T.W.; Kim, S.; Vaughan, B.; Marand, E.; Baranauskas, V.; Riffle, J.; Jeong, H.K.; Tsapatsis, M. Preparation and characterization of a poly(imide siloxane) and zeolite L mixed matrix membrane. J. Memb. Sci. 2006, 277, 210–218. [CrossRef] 36. Bujard, P.; Kuhnlein, G.; Ino, S.; Shiobara, T. Thermal conductivity of molding compounds for plastic packaging. IEEE Trans. Compon. Packag. Manuf. Technol. 1994, 17, 527–532. [CrossRef] 37. Droval, G.; Feller, J.-F.; Salagnac, P.; Glouannec, P. Thermal conductivity enhancement of electrically insulating syndiotactic poly(styrene) matrix for diphasic conductive polymer composites. Polym. Adv. Technol. 2006, 17, 732–745. [CrossRef] 38. Shimazaki, Y.; Hojo, F.; Takezawa, Y. Preparation and characterization of thermoconductive polymer nanocomposite with branched alumina nanofiber. Appl. Phys. Lett. 2008, 92, 133309. [CrossRef] 39. Shimazaki, Y.; Hojo, F.; Takezawa, Y. Highly thermoconductive polymer nanocomposite with a nanoporous -alumina sheet. ACS Appl. Mater. Interfaces 2009, 1, 225–227. [CrossRef] Appl. Sci. 2019, 9, 548 11 of 11 40. Li, H.; Liu, G.; Liu, B.; Chen, W.; Chen, S. Dielectric properties of polyimide/Al O hybrids synthesized by 2 3 in-situ polymerization. Mater. Lett. 2007, 61, 1507–1511. [CrossRef] 41. Ha, S.Y.; Oh, B.-K.; Lee, Y.M. Preparation of poly(amideimide siloxane) from trimellitic anhydride chloride, oxylene diamine and oligo(dimethylsiloxane) diamine. Polymer 1995, 36, 3549–3553. [CrossRef] 42. Bowens, A.D. Synthesis and Characterization of Poly (Siloxane Imide) Block Copolymers and End-Functional Polyimides for Interphase Applications; Virginia Tech: Blacksburg, VA, USA, 1999. 43. Deng, X.; Luo, R.; Chen, H.; Liu, B.; Feng, Y.; Sun, Y. Synthesis and surface properties of pdms–acrylate emulsion with gemini surfactant as co-emulsifier. Colloid Polym. Sci. 2007, 285, 923–930. [CrossRef] 44. Téllez, L.; Rubio, J.; Rubio, F.; Morales, E.; Oteo, J.L. FT-IR study of the hydrolysis and polymerization of tetraethyl orthosilicate and polydimethyl siloxane in the presence of tetrabutyl orthotitanate. Spectrosc. Lett. 2004, 37, 11–31. [CrossRef] 45. Li, K.; Zeng, X.; Li, H.; Lai, X.; Xie, H. Effects of calcination temperature on the microstructure and wetting behavior of superhydrophobic polydimethylsiloxane/silica coating. Colloids Surf. A Physicochem. Eng. Asp. 2014, 445, 111–118. [CrossRef] 46. Zhang, K.; Yu, Q.; Zhu, L.; Liu, S.; Chi, Z.; Chen, X.; Zhang, Y.; Xu, J. The Preparations and Water Vapor Barrier Properties of Polyimide Films Containing Amide Moieties. Polymers 2017, 9, 677. [CrossRef] 47. Yu, H.-C.; Choi, J.-Y.; Jeong, J.-W.; Kim, B.-J.; Chung, C.-M. Simple and easy recycling of poly(Amic Acid) gels through microwave irradiation. J. Polym. Sci. Part A Polym. Chem. 2017, 55, 981–987. [CrossRef] 48. Choi, J.-Y.; Yu, H.-C.; Lee, J.; Jeon, J.; Im, J.; Jang, J.; Jin, S.-W.; Kim, K.-K.; Cho, S.; Chung, C.-M. Preparation of polyimide/graphene oxide nanocomposite and its application to nonvolatile resistive memory device. Polymers 2018, 10, 901. [CrossRef] 49. Muratov, D.S.; Kuznetsov, D.V.; Il’inykh, I.A.; Burmistrov, I.N.; Mazov, I.N. Thermal conductivity of polypropylene composites filled with silane-modified hexagonal BN. Compos. Sci. Technol. 2015, 111, 40–43. [CrossRef] 50. Cinausero, N.; Azema, N.; Cochez, M.; Ferriol, M.; Essahli, M.; Ganachaud, F.; Lopez-Cuesta, J.M. Influence of the surface modification of alumina nanoparticles on the thermal stability and fire reaction of PMMA composites. Polym. Adv. Technol. 2008, 19, 701–709. [CrossRef] 51. Chen, Y.; Iroh, J.O. Synthesis and characterization of polyimide/silica hybrid composites. Chem. Mater. 1999, 11, 1218–1222. [CrossRef] © 2019 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/). http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Applied Sciences Multidisciplinary Digital Publishing Institute

Preparation and Properties of Poly(imide-siloxane) Copolymer Composite Films with Micro-Al2O3 Particles

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applied sciences Article Preparation and Properties of Poly(imide-siloxane) Copolymer Composite Films with Micro-Al O Particles 2 3 1 1 1 1 1 Ju-Young Choi , Kyeong-Nam Nam , Seung-Won Jin , Dong-Min Kim , In-Ho Song , 2 1 1 , 2 , Hyeong-Joo Park , Sungjin Park and Chan-Moon Chung * Department of Chemistry, Yonsei University, Wonju, Gangwon-do 26493, Korea; cjy0510@yonsei.ac.kr (J.-Y.C.); nkn001@yonsei.ac.kr (K.-N.N.); jinsw0906@yonsei.ac.kr (S.-W.J.); dmkimr@yonsei.ac.kr (D.-M.K.); segunda@yonsei.ac.kr (I.-H.S.); sjpsi@yonsei.ac.kr (S.P.) Department of Chemistry and Medical Chemistry, Yonsei University, Wonju, Gangwon-do 26493, Korea; hyeongjoo1016@yonsei.ac.kr * Correspondence: cmchung@yonsei.ac.kr; Tel.: +82-033-760-2266 Received: 11 January 2019; Accepted: 1 February 2019; Published: 6 February 2019 Abstract: In the current study, poly(imide-siloxane) copolymers (PIs) with different siloxane contents were synthesized and used as a matrix material for PI/Al O composites. The PIs were characterized 2 3 via their molecular weight, film quality, and thermal stability. Among the PI films, free-standing and flexible PI films were selected and used to prepare PI/Al O composite films, with different 2 3 Al O loadings. The thermal conductivity, thermal stability, mechanical property, film flexibility, 2 3 and morphology of the PI/Al O composite films were investigated for their application as 2 3 heat-dissipating material. Keywords: poly(imide-siloxane) copolymer; Al O ; thermal conductivity; heat-dissipating 2 3 1. Introduction Recent electronic devices such as smart applications and laptops are becoming smaller and lighter with developments in the electronics industry [1–3]. To ensure the proper operation of smaller devices, unwanted heat that is generated in electronic devices must be removed. The dissipation of heat has attracted increasing attention, and is an important issue that reqiuires resolution [4,5]. Currently, polymer composite materials containing ceramic powder are widely used as heat dissipation materials in electronic devices [6,7]. Among the polymer materials, polysiloxane has some advantages and is used as a heat-dissipating polymer matrix [8–10]. It is composed of a linear Si-O-Si moiety with a bond-angle between 104 and 180 , which introduces flexibility to the polymer [11,12]. In addition, polysiloxane can be used permanently without any change at 150 C, it is able to withstand 200 C for 1000 h, and 350 C for shorter periods of time [13,14]. However, some studies on the long-term reliability of silicone rubber suggest that commercial high-temperature silicones, which are being aged at 250 C could suffer from severe thermal decomposition [15–17]. Polyimides have widely been used in display, vehicle, aerospace, and microelectronic industries as high-performance material owing to their good mechanical properties, excellent thermal stability, flexibility, low dielectric permittivity, and good chemical resistance [4,18–21]. Polyimides are also good candidates for use as thermal conductive composite materials that can be operated at high temperatures, due to their high thermal stability [22–27]. By introducing siloxane chain segments to the polyimide backbone structure, adhesion between the polyimide and inorganic materials can be improved, including the adhesion of the metal materials and other substrates [28–31]. Previously, Appl. Sci. 2019, 9, 548; doi:10.3390/app9030548 www.mdpi.com/journal/applsci Appl. Sci. 2019, 9, 548 2 of 11 poly(imide-siloxane) copolymers (PIs) have been studied for applications in aerospace, separation, and microelectronics [32–35]. On the other hand, alumina (Al O ) fillers are used as thermally conductive 2 3 material embedded in the polymer matrix [36–40]. Alumina is commercially very inexpensive and often employed to improve the dissipation of polymer materials’ heat properties due to its better insulating qualities and higher thermal conductivity [40]. In this paper, we first report the preparation method and properties of PI composite films containing Al O particles, for their application as heat dissipating material. We report the 2 3 preparation and properties of PIs with varyingmolar ratio of two diamines (an aromatic diamine and bis(3-aminopropyl)-terminated polydimethylsiloxane). Furthermore, PI/Al O composite films 2 3 were prepared by adding various Al O contents into the PI matrix. Then the thermal conductivity, 2 3 thermal stability, mechanical properties, film flexibility, and morphology of the composite films were investigated according to the change in Al O loadings. 2 3 2. Materials and Methods 2.1. Materials 0 0 4,4 -(Hexafluoroisopropylidene) diphthalic anhydride (6FDA), 4,4 -methylenedianiline (MDA), and bis(3-aminopropyl)-terminated polydimethylsiloxane (PDMS) (M ~2500) were purchased from Sigma-Aldrich Korea (Seoul, Korea), and were used as received. Tetrahydrofuran (THF) was purchased from Samchun Chemicals (Seoul, Korea), distilled from N /benzophenone, and stored under nitrogen until use. 1-Methyl-2-pyrrolidinone (NMP) was purchased from Duksan Pure Chemical (Seoul, Korea), distilled in reduced pressure, and kept under nitrogen until use. Polygonal alumina (Al O ; average 2 3 particle size = 4 m) was purchased from Denka Co. Ltd. (Seoul, Korea) and was dried at 120 C in an oven for 24 h to remove the adsorbed water before use. Tetrahydrofuran-d (THF-d ) was purchased 8 8 from Acros Organics BVBA (Geel, Belgium). 2.2. Characterization Proton nuclear magnetic resonance ( H NMR) spectra of samples dissolved in THF-d were acquired using a Bruker Avance II 400 MHz spectrometer (Bruker Corporation, Billerica, MA, USA). Gel permeation chromatography (GPC; Waters Corporation, Milford, MA, USA) analysis was carried out in refractive index mode using a doubly connected Showa Denko Shodex KF-806L column at 100 C and an eluent of 0.05 mol/L LiBr in NMP at a flow rate of 1.0 mL/min; the results were calibrated with respect to polystyrene standards. Fourier Transform Infrared (FT-IR) spectroscopy was carried out using a Spectrum One B FT-IR spectrometer (PerkinElmer, Inc., Waltham, MA, USA) using the KBr pellet technique with the following scan parameters: scan range 500–4000 cm ; number of scan 1; resolution 4 cm . Thermal analyses were carried out under a nitrogen atmosphere with a balance flow rate of 40 mL/min and a furnace flow rate of 60 mL/min using a Discovery TGA 55 (TA instrument, Inc., New Castle, DE, USA) at a heating rate of 10 C/min. The thickness of the polyimide films was measured using a 293–348 IP65 digimatic outside micrometer (Mitutoyo Corporation, Kawasaki, Japan). Thermal conductivities (in-plane) of the composite films were measured using a LFA 467 Nanoflash (NETZSCH Korea Co., Ltd., Koyang, Korea). A universal testing machine (UTM) (QC-505M1, Daeha Trading Co., Seoul, Korea) was used to determine tensile properties. A 3-cm gauge and a strain rate of 2 cm/min were used. Film specimen measurements were performed at room temperature using 0.5 cm wide, 6 cm long, and ca. 0.3 mm thick films. An average of five individual determinations were used for each sample. Field emission scanning electron microscopy (FE-SEM) was carried out using a SU-70 (Hitachi, Ltd., Tokyo, Japan), with an acceleration voltage of 30 kV and a working distance in the range of 10 to 11.6 mm. The samples were sputter-coated with platinum. Appl. Sci. 2019, 9, 548 3 of 11 Appl. Sci. 2018, 8, x FOR PEER REVIEW 3 of 11 2.3. Preparation of Poly(amic acid-siloxane)s (PAAs) 2.3. Preparation of poly(amic acid-siloxane)s (PAAs) Scheme 1 shows the general method of copolyimide synthesis. A representative example for the Scheme 1 shows the general method of copolyimide synthesis. A representative example for the synthesis of poly(amic acid-siloxane)-4 (PAA-4) (molar feed ratio of 6FDA:MDA:PDMS was 1:0.5:0.5) is synthesis of poly(amic acid-siloxane)-4 (PAA-4) (molar feed ratio of 6FDA:MDA:PDMS was 1:0.5:0.5) described below. A dried 50-mL flask was charged with MDA (0.002 mol, 0.198 g) and PDMS (0.002 mol, is described below. A dried 50-mL flask was charged with MDA (0.002 mol, 0.198 g) and PDMS (0.002 2.500 g) in THF (14.3 mL) under a nitrogen atmosphere. After 6FDA (0.004 mol, 0.888 g) was added, mol, 2.500 g) in THF (14.3 mL) under a nitrogen atmosphere. After 6FDA (0.004 mol, 0.888 g) was the resulting solution was stirred at 0 C for 1 h, and then further stirred at room temperature for 23 h added, the resulting solution was stirred at 0 °C for 1 h, and then further stirred at room temperature to yield a clear viscous PAA-4 solution. The other PAA solutions were prepared in a similar fashion for 23 h to yield a clear viscous PAA-4 solution. The other PAA solutions were prepared in a similar by favarying shion bythe var molar ying tfeed he mratio olar f of eed the radiamines. tio of the d As iami ann exception, es. As an e NMP xceptwas ion, used NMP w in the as usynthesis sed in the of synthesis of PAA-1 with a molar feed ratio of 6FDA:MDA:PDMS of 1:1:0. The PAA solutions was PAA-1 with a molar feed ratio of 6FDA:MDA:PDMS of 1:1:0. The PAA solutions was used to prepare used to prepare PI films, powders, and composite films (see below). PI films, powders, and composite films (see below). Scheme 1. Synthesis of PIs and their composites. Scheme 1. Synthesis of PIs and their composites. 2.4. Preparation of PI Films 2.4. Preparation of PI Films The PAA-4 solution obtained above was drop-cast onto slide glasses and the solution was The PAA-4 solution obtained above was drop-cast onto slide glasses and the solution was stepwisely heated (at 50, 100, and 150 C). The solution was allowed to stand at each temperature stepwisely heated (at 50, 100, and 150 °C). The solution was allowed to stand at each temperature for for 1 h. The resulting films were finally heated at 250 C for 2 h, and PI-4 films were obtained. 1 h. The resulting films were finally heated at 250 °C for 2 h, and PI-4 films were obtained. The PI-4 The PI-4 films were cooled to room temperature and put in a water bath for 1 h to allow easy peel off. films were cooled to room temperature and put in a water bath for 1 h to allow easy peel off. The The resultant films were dried in a vacuum oven at 100 C for 1 h. The other PI films were prepared in resultant films were dried in a vacuum oven at 100 °C for 1 h. The other PI films were prepared in a a similar manner by varying the molar feed ratio of the diamines. similar manner by varying the molar feed ratio of the diamines. 2.5. Preparation of PI Powders 2.5. Preparation of PI Powders The PAA-4 solution obtained above was poured into distilled water, forming a precipitate that was The PAA-4 solution obtained above was poured into distilled water, forming a precipitate that collected via filtration. The precipitate was washed with distilled water and then dried in a vacuum was collected via filtration. The precipitate was washed with distilled water and then dried in a oven, yielding a PAA-4 powder. The PAA-4 was thermally imidized by stepwise heating in a furnace vacuum oven, yielding a PAA-4 powder. The PAA-4 was thermally imidized by stepwise heating in (50, 100, and 150 C). The powder was kept for 1 h at each temperature and finally heated at 250 C a furnace (50, 100, and 150 °C). The powder was kept for 1 h at each temperature and finally heated for 2 h to obtain PI-4 powder. The other PAA and PI powders were prepared in a similar manner by at 250 °C for 2 h to obtain PI-4 powder. The other PAA and PI powders were prepared in a similar varying the molar feed ratio of the diamines. The prepared PAA and PI powders were used in FT-IR manner by varying the molar feed ratio of the diamines. The prepared PAA and PI powders were spectroscopy and GPC. used in FT-IR spectroscopy and GPC. Appl. Sci. 2019, 9, 548 4 of 11 2.6. Preparation of PI Composite Films Al O powder (30, 60, 75, or 80 wt%) was added to the PAA-4 solution obtained above. 2 3 The mixture was ultrasonicated using an ultrasonic device (VCX750, Sonics & Materials, Newtown, CT, USA), with an output power of 150 W and a frequency of 20 kHz for 1 h to yield a milky suspension. The suspension was drop-cast onto slide glasses, and then heated in a stepwise manner (at 50, 100, and 150 C). The suspension was allowed to stand at each temperature for 1 h and finally heated at 250 C for 2 h to obtain PI/Al O composite films (PI-4-30, PI-4-60, PI-4-75, and PI-4-80). The obtained 2 3 films were cooled to room temperature and put in a water bath for 1 h to facilitate peeling it off. The resultant composite films were dried in a vacuum oven at 100 C for 1 h. 3. Results and Discussion 3.1. Preparation of PIs and Their Composite Films The preparation of poly(imide-siloxane) copolymers (PIs) is illustrated in Scheme 1. The PIs were synthesized according to a conventional two-step procedure. During typical conventional polyimide synthesis, aprotic polar solvents such as NMP, dimethylacetamide (DMAc), or dimethylformamide (DMF) are usually used. However, the siloxane group underwent microphase separation when aprotic solvents were used during the copolymerization. To overcome this problem, the preparation of PIs required the use of a co-solvent system or THF [41,42]. In this work, 6FDA, MDA, and PDMS were copolymerized using THF as a solvent (Table 1), except for PAA-1 which was prepared without the PDMS moiety and used NMP as a solvent. 6FDA and mixed diamines (MDA and PDMS) were first polymerized to prepare poly(amic acid-siloxane)s (PAA-1–PAA-7). The diamine molar feed ratio was controlled as summarized in Table 1. The PDMS content of PAA copolymers was determined by H NMR (Table 1 and Figure S1). The mole percent of PDMS was calculated from the ratio of the integration values of the methyl groups in PDMS and the methylene groups of MDA. It was found that the determined values agreed well with those corresponding to PDMS contents in the feeds. The PAA solutions were drop-cast onto slide glasses and then PAAs were converted to PI-1–PI-7 films by thermal imidization. The PAA and PI powders were also prepared for characterization via FT-IR spectroscopy and GPC. Table 1 lists the molecular weights and polydispersity indexes (PDIs) of the PAAs measured by GPC. In addition, PI/Al O 2 3 composites were prepared by adding various amount of Al O powder to PAA solutions. The resulting 2 3 suspensions were drop-cast onto galss slides and subsequent thermal imidization was carried out to obtain PI/Al O composite films. 2 3 Table 1. Molar feed ratios and molecular weights of PAAs. Molar Feed Ratio PDMS Content M M n w a c PAA Code PDI b 4 4 (6FDA:MDA:PDMS) (mol%) (10 g/mol) (10 g/mol) PAA-1 1:1:0 - 1.03 2.32 2.2 PAA-2 1:0.9:0.1 13 10.8 37.8 3.5 PAA-3 1:0.7:0.3 32 10.8 18.1 1.6 PAA-4 1:0.5:0.5 49 3.73 13.2 3.5 PAA-5 1:0.3:0.7 70 21.1 48.8 2.3 PAA-6 1:0.1:0.9 89 16.3 50.9 3.1 PAA-7 1:0:1 - 7.92 25.1 3.2 a b 1 c PAA: poly(amic acid-siloxane); Calculated from H NMR integrations of PAA copolymers; Polydispersity index (M /M ). w n 3.2. Characterization of PAAs and PIs The structures of PAAs and PIs were confirmed by FT-IR spectroscopy (Figure 1). FT-IR spectra of PAA-4 and PI-4 showed absorption bands at 1021 and 1095 cm , respectively, due to Si-O-Si stretching in the structure of PDMS. The absorption band at 1259 cm was also attributed to the symmetric Appl. Sci. 2019, 9, 548 5 of 11 Appl. Sci. 2018, 8, x FOR PEER REVIEW 5 of 11 deformation of the –CH group in –Si(CH ) -, and the absorption band at 803 cm was assigned −1 to 3 3 2 symmetric deformation of the –CH3 group in –Si(CH3)2-, and the absorption band at 803 cm was the Si-C vibration [11,41,43–45]. The FT-IR spectrum of PAA-4 showed bands at 1721 cm (carboxyl) −1 assigned to the Si-C vibration [11,41,43–45]. The FT-IR spectrum of PAA-4 showed bands at 1721 cm 1 1 and 1660 cm (amide)−owing 1 to C=O stretching, and at 1545 cm owing−to 1 C-N stretching (amide), (carboxyl) and 1660 cm (amide) owing to C=O stretching, and at 1545 cm owing to C-N stretching suggesting the formation of PAA (Figure 1a) [11,34,46]. PI-4 exhibited absorption bands at 1785 cm (amide), suggesting the formation of PAA (Figure 1a) [11,34,46]. PI-4 exhibited absorption bands at owing to−1imide C=O asymmetric stretching, 1726 cm owing to−1imide C=O symmetric stretching, 1785 cm owing to imide C=O asymmetric stretching, 1726 cm owing to imide C=O symmetric and 1375 cm owing to−1 imide C–N stretching (Figure 1b) [11,34,46–48]. FT-IR spectra of the other stretching, and 1375 cm owing to imide C–N stretching (Figure 1b) [11,34,46–48]. FT-IR spectra of PAAs and PIs are shown in Figures S2–S7. the other PAAs and PIs are shown in Figures S2–S7. Figure 1. FT-IR spectra of (a) PAA-4, and (b) PI-4. Figure 1. FT-IR spectra of (a) PAA-4, and (b) PI-4. 3.3. Properties of PI Films 3.3. Properties of PI Films Thermal stability of PIs was investigated by thermogravimetric analysis (TGA) (Table 2 and Thermal stability of PIs was investigated by thermogravimetric analysis (TGA) (Table 2 and Figure 2). TGA was conducted to study the effects of the molar ratio of diamines on decomposition Fig temperatur ure 2). TG e (T A was cond and T ) and ucted to study the effects char yield of PIs. T and of T the molar ratio of di values of the PIs ranged amines on decomposition from 373 to 505 and 5 10 5 10 temperature (T5 and T10) and char yield of PIs. T5 and T10 values of the PIs ranged from 373 to 505 and 419 to 528 C, respectively, and the decomposition temperature decreased with increasing PDMS molar 41 ratio. 9 toNevertheless, 528°C, respect PIs’ ively decomposition , and the decom temperatur position t esemperature were much decreased higher than with incre those ofa silicone sing PDM [17S ]. molar ratio. Nevertheless, PIs’ decomposition temperatures were much higher than those of silicone The char yield at 800 C of PI-1 without siloxane moiety was the highest (62.4%) and the other char yields [17]. The wer cha e much r yield lower at 80 . 0 °C of PI-1 without siloxane moiety was the highest (62.4%) and the other char yields were much lower. Table 2. Film quality and thermal properties of PIs. Flexible and free-standing PI films (PI-3, PI-4, and PI-5) could be prepared from PAA-3, PAA-4, and PAA-5, respectively (Table 2 and Figure 3). When the films were bent, twisted, rolled-up, or a  b  c d PI Code Film Quality T ( C) T ( C) Char Yield (%) 5 10 wrapped on the 3-mm diameter bar numerous times, their appearance was almost unchanged (no PI-1 Brittle 505 528 62.4 damage occurred). However, PI-1 and PI-2 films were brittle due to their rigid chemical structures. PI-2 Brittle 446 473 28.2 On the other hand, PI-6 and PI-7 films were sticky due to the very high PDMS group contents. PI-3 Flexible 438 454 16.7 PI-4 Flexible 428 443 0.7 PI-5 Table 2. Flexible Film quality and ther 423 mal properties 441 of PIs. 2.1 PI-6 Sticky 403 426 4.3 a b c d PI Code Film Quality T5 (°C) T10 (°C) Char Yield (%) PI-7 Sticky 373 419 3.2 a PI-1 Brittle 505 b 528 62.4 PI-1–PI-7 were prepared from PAA-1–PAA-7, respectively; The temperature at which a sample exhibits 5 wt% decomposition in a nitrogen atmosphere; The temperature at which a sample exhibits 10 wt% decomposition in a PI-2 Brittle 446 473 28.2 nitrogen atmosphere; Char yield at 800 C in a nitrogen atmosphere. PI-3 Flexible 438 454 16.7 PI-4 Flexible 428 443 0.7 PI-5 Flexible 423 441 2.1 PI-6 Sticky 403 426 4.3 PI-7 Sticky 373 419 3.2 a b PI-1–PI-7 were prepared from PAA-1–PAA-7, respectively; The temperature at which a sample exhibits 5 wt% decomposition in a nitrogen atmosphere; The temperature at which a sample exhibits 10 wt% decomposition in a nitrogen atmosphere; Char yield at 800 °C in a nitrogen atmosphere. Appl. Sci. 2018, 8, x FOR PEER REVIEW 6 of 11 Appl. Sci. 2019, 9, 548 6 of 11 Appl. Sci. 2018, 8, x FOR PEER REVIEW 6 of 11 Figure 2. TGA curves of PIs. Figure 2. TGA curves of PIs. Flexible and free-standing PI films (PI-3, PI-4, and PI-5) could be prepared from PAA-3, PAA-4, and PAA-5, respectively (Table 2 and Figure 3). When the films were bent, twisted, rolled-up, or wrapped on the 3-mm diameter bar numerous times, their appearance was almost unchanged (no damage occurred). However, PI-1 and PI-2 films were brittle due to their rigid chemical structures. Figure 2. TGA curves of PIs. On the other hand, PI-6 and PI-7 films were sticky due to the very high PDMS group contents. Figure 3. Photographs of (a) PI-3; (b) PI-4; (c) PI-5 films. 3.4. Properties of PI/Al2O3 Composite Films Because the PI-3, PI-4, and PI-5 films were free-standing and flexible, they were used to prepare Figure 3. Photographs of (a) PI-3; (b) PI-4; (c) PI-5 films. PI/Al2O3 composite films. Figure 4 shows the thermal conducting properties of neat PI films and Figure 3. Photographs of (a) PI-3; (b) PI-4; (c) PI-5 films. 3.4. Properties of PI/Al O Composite Films 2 3 PI/Al2O3 composite films, with different Al2O3 loadings along an in-plane direction (D ) at room 3.4. Properties of PI/Al2O3 Composite Films temperature (see Because the PI-3, Table PI-4, s S1 and –S3PI-5 ). The filmsfilm wer s’ t e frhee-standing ermal diffusiv andity flexible, (α) wthey as dwer etermined e used toat prroom epare temperature PI/Al O composite and under films. ambient pressure. From Figure 4 shows the the equation K thermal conducting = α × ρpr × operties Cp, the thermal of neat conducti PI filmsvi and ty 2 3 Because the PI-3, PI-4, and PI-5 films were free-standing and flexible, they were used to prepare (K) PI/Al value O ca composite n be calculfilms, ated. In t with he e dif qu fer atent ion, Alρ is the O loadings measured along filman density in-plane , and dir Cection p is the (speci D ) at ficr he oom at 2 3 2 3 PI/Al2O3 composite films. Figure 4 shows the thermal conducting properties of neat PI films and ca temperatur pacity of the fi e (seelm Tables [5,49S1–S3). ]. The thermal The films’ conducti thermal vities diffusivity of neat PI- ( ) 3 was , PI-4 determined , and PI-5 at were room 0.11 temperat , 0.13, and ure PI/Al2O3 composite films, with different Al2O3 loadings along an in-plane direction (D ) at room 0. and 14 W/ underm·ambient K, respect pressur ivelye.. It From is k then equation own thKat thermal =  $  conducti C , the thermal vities of polyi conductivitymi(K) de a value nd temperature (see Tables S1–S3). The films’ thermal diffusivity (α) was determined at room p can olydim be calculated. ethylsiloxa Inne theare equation, 0.11 and $ is the 0.25 measur W/m· ed K a film t room density t,eand mperat C ure is the , res specific pectively [ heat capacity 22]. The of temperature and under ambient pressure. From the equation K = α × ρ × Cp, the thermal conductivity incorporat the film [5ion ,49]. of The Althermal 2O3 fillers conductivities increased therma of neatl di PI-3, ffuPI-4, sivity and and t PI-5hermal cond were 0.11, 0.13, uctivity o and 0.14 f PI W/m /Al2OK, 3 (K) value can be calculated. In the equation, ρ is the measured film density, and Cp is the specific heat composit respectively e fil .m Its (F is known igure 4a that ,b). thermal When thconductivities e Al2O3 loading of was polyimide 80 wt%, and PI-3polydimethylsiloxane and PI-4 composites sar howe e 0.11 d capacity of the film [5,49]. The thermal conductivities of neat PI-3, PI-4, and PI-5 were 0.11, 0.13, and hi and gh therm 0.25 W/m al conducti K at room vity temperatur values, grea e,ter tha respectively n 1.3 W/ [22 m·K. The t ]. The incorporation hermal diffu of siv Al ity and O fillers conduc incrteased ivity 2 3 0.14 W/m·K, respectively. It is known that thermal conductivities of polyimide and data ar thermal e quite reproduc diffusivity and ible thermal as presented conductivity in Tabof les S1 PI/Al –S3.O composite films (Figure 4a,b). When the 2 3 polydimethylsiloxane are 0.11 and 0.25 W/m·K at room temperature, respectively [22]. The incorporation of Al2O3 fillers increased thermal diffusivity and thermal conductivity of PI/Al2O3 composite films (Figure 4a,b). When the Al2O3 loading was 80 wt%, PI-3 and PI-4 composites showed high thermal conductivity values, greater than 1.3 W/m·K. The thermal diffusivity and conductivity data are quite reproducible as presented in Tables S1–S3. Appl. Sci. 2019, 9, 548 7 of 11 Al O loading was 80 wt%, PI-3 and PI-4 composites showed high thermal conductivity values, greater 2 3 than 1.3 W/mK. The thermal diffusivity and conductivity data are quite reproducible as presented in Appl. Sci. 2018, 8, x FOR PEER REVIEW 7 of 11 Tables S1–S3. Figure 4. (a) Thermal diffusivity (D ), and (b) thermal conductivity (D ) of the PI and PI/Al O 2 3 ? ? Figure 4. (a) Thermal diffusivity (D ), and (b) thermal conductivity (D ) of the PI and PI/Al2O3 ┴ ┴ composite films with different Al O loadings. 2 3 composite films with different Al2O3 loadings. In addition, thermal and mechanical properties of the PI/Al O composite films were studied 2 3 In addition, thermal and mechanical properties of the PI/Al2O3 composite films were studied (Table 3 and Figures S8 and S9). Among the flexible PI films, PI-3 was selected because it (Table 3 and Figures S8 and S9). Among the flexible PI films, PI-3 was selected because it exhibited exhibited the best thermal conducting properties. The T and T values of the neat PI-3 and 5 10 the best thermal conducting properties. The T5 and T10 values of the neat PI-3  and PI-3/Al2O3 PI-3/Al O composite films ranged from 437 to 454 C and 456 to 474 C, respectively. Generally the 2 3 composite films ranged from 437 to 454 °C and 456 to 474 °C, respectively. Generally the decomposition temperatures of the PI/Al O composite films were higher than those of the neat PI 2 3 decomposition temperatures of the PI/Al2O3 composite films were higher than those of the neat PI film. The improvement in thermal stability can be attributed to restrained polymer chain mobility by film. The improvement in thermal stability can be attributed to restrained polymer chain mobility by Al O particles [17]. Furthermore, it should be noted that the PI/Al O composites showed much 2 3 2 3 Al2O3 particles [17]. Furthermore, it should be noted that the PI/Al2O3 composites showed much higher thermal stability compared to polysiloxane/Al O composites [17,50]. From the char yield data, 2 3 higher thermal stability compared to po  lysiloxane/Al2O3 composites [17,50]. From the char yield data, each mass value retained around 800 C and was almost identical to the corresponding Al O content 2 3 each mass value retained around 800 °C and was almost identical to the corresponding Al2O3 content in each composite. in each composite. The neat PI-3 film showed a tensile strength of 14.6 ± 2.7 MPa, and a high elongation at a break Table 3. Thermal and mechanical properties of the PI-3/Al O composite films. 2 3 of 210.4 ± 38.4%. However, the PI/Al2O3 composite films exhibited decreased tensile strength and Char Yield Tensile Strength Elongation at Break a  b  c PI/Al O Composite Code T ( C) T ( C) elongati2on 3 at break, and the mechanical 10 properties decreased with increasing Al2O3 loadings. It is 5 d (%) (MPa) (%) well known that the incorporation of an inorganic filler to the polymer matrix reduces the polymer’s PI-3 438 461 16.7 14.6  2.7 210.4  38.4 flexibility. Furthermore, the polymer’s strength is reduced if there are no binding sites between the PI-3-30 440 456 30.7 7.3  0.2 41.7  2.8 PI-3-60 454 469 61.3 6.5  0.4 10.4  0.6 polymer phase and inorganic material phase [51]. Nevertheless, the composite films with up to 75 PI-3-75 450 474 75.2 5.7  0.5 4.8  0.6 wt% Al2O3 are sufficiently flexible, as shown in Figure 5. They may be useful as a flexible heat- PI-3-80 437 471 79.1 5.2  0.5 3.7  0.6 radiating film in flexible electronic devices requiring a high operating temperature. Even though the a b PI-3, PI-3-30, PI-3-60, PI-3-75, and PI-3-80 films have Al O loadings of 0, 30, 60, 75, and 80 wt%, respectively; The 2 3 composite temperatur films with e at which 80 a sample wt% Al exhibits 2O 53wt% loadecomposition ding are not f in a l nitr exi ogen ble, the atmospher y co e;uld Thealtemperatur so be us ee atd which in high- a sample exhibits 10 wt% decomposition in a nitrogen atmosphere; Char yield at 800 C in a nitrogen atmosphere. temperature electronic devices. The neat PI-3 Table 3. filmThermal and me showed a tensile chanical pr strength opertie of 14.6 s of the PI-3/Al 2.7 MPa, 2O and 3 com a high posite fi elongation lms. at a break of 210.4  38.4%. However, the PI/Al O composite films exhibited decreased tensile strength and 2 3 Char Yield Tensile Strength Elongation at Break a b c PI/Al2O3 Composite Code T5 (°C) T10 (°C) elongation at break, and the mechanical properties decreased with increasing Al O loadings. It is 2 3 (%) (MPa) (%) well known that the incorporation of an inorganic filler to the polymer matrix reduces the polymer ’s PI-3 438 461 16.7 14.6 ± 2.7 210.4 ± 38.4 flexibility. Furthermore, the polymer ’s strength is reduced if there are no binding sites between the PI-3-30 440 456 30.7 7.3 ± 0.2 41.7 ± 2.8 polymer phase PI-3-60 and inorganic material 454 phase 469 [51]. Nevertheless, 61.3 the6.5 ± composite 0.4 films with 10.4 ± up 0.6 to 75 wt% PI-3-75 450 474 75.2 5.7 ± 0.5 4.8 ± 0.6 Al O are sufficiently flexible, as shown in Figure 5. They may be useful as a flexible heat-radiating 2 3 PI-3-80 437 471 79.1 5.2 ± 0.5 3.7 ± 0.6 film in flexible electronic devices requiring a high operating temperature. Even though the composite PI-3, PI-3-30, PI-3-60, PI-3-75, and PI-3-80 films have Al2O3 loadings of 0, 30, 60, 75, and 80 wt%, films with 80 wt% Al O loading are not flexible, they could also be used in high-temperature 2 3 respectively; The temperature at which a sample exhibits 5 wt% decomposition in a nitrogen electronic devices. atmosphere; The temperature at which a sample exhibits 10 wt% decomposition in a nitrogen atmosphere; Char yield at 800 °C in a nitrogen atmosphere. Appl. Sci. 2019, 9, 548 8 of 11 Appl. Sci. 2018, 8, x FOR PEER REVIEW 8 of 11 Appl. Sci. 2018, 8, x FOR PEER REVIEW 8 of 11 Figure 5. Photographs of PI composite films containing different Al2O3 contents. Figure 5. Photographs of PI composite films containing different Al O contents. 2 3 Figure 5. Photographs of PI composite films containing different Al2O3 contents. Scanning electron microscopy (SEM) was carried out to investigate the morphology of the Scanning electron microscopy (SEM) was carried out to investigate the morphology of the Scanning electron microscopy (SEM) was carried out to investigate the morphology of the PI/Al O composite films. Figure 6a shows the SEM image of micro-Al O particles. The particles PI/Al2O3 composite films. Figure 6a shows the SEM image of micro-Al2O3 particles. The particles are 2 3 2 3 PI/Al2O3 composite films. Figure 6a shows the SEM image of micro-Al2O3 particles. The particles are are irregularly shaped with 4 m average size. The neat PI-3 film before Al O addition showed a irregularly shaped with 4 μm average size. The neat PI-3 film before Al2O3 addition showed a very 2 3 irregularly shaped with 4 μm average size. The neat PI-3 film before Al2O3 addition showed a very very smooth surface (Figure 6b). As shown in Figure 6c, Al O particles were well dispersed in the smooth surface (Figure 6b). As shown in Figure 6c, Al2O3 particles were well dispersed in the PI/Al2O3 2 3 smooth surface (Figure 6b). As shown in Figure 6c, Al2O3 particles were well dispersed in the PI/Al2O3 PI/Al O composite film and no significant fractures were observed across the film’s surface. composite film and no significant fractures were observed across the film’s surface. 2 3 composite film and no significant fractures were observed across the film’s surface. Figure 6. SEM images of (a) Al O particles; (b) PI-3 film; (c) PI-3-75 film. 2 3 Figure 6. SEM images of (a) Al2O3 particles; (b) PI-3 film; (c) PI-3-75 film. Figure 6. SEM images of (a) Al2O3 particles; (b) PI-3 film; (c) PI-3-75 film. 4. Conclusions 4. Conclusions 4. Conclusions The PIs with different siloxane contents were prepared using 6FDA, MDA, and The PIs with different siloxane contents were prepared using 6FDA, MDA, and PDMS. Free- The PIs with different siloxane contents were prepared using 6FDA, MDA, and PDMS. Free- PDMS.Free-standing, flexible films of PI-3, PI-4, and PI-5 were obtained, and the PIs were used standing, flexible films of PI-3, PI-4, and PI-5 were obtained, and the PIs were used to prepare standing, flexible films of PI-3, PI-4, and PI-5 were obtained, and the PIs were used to prepare to prepare PI/Al O composite films. The thermal conductivities of the composite films increased with 2 3 PI/Al2O3 composite films. The thermal conductivities of the composite films increased with increasing PI/Al2O3 composite films. The thermal conductivities of the composite films increased with increasing increasing Al O content. It was demonstrated that the composite films with up to 75 wt% Al O 2 3 2 3 Al2O3 content. It was demonstrated that the composite films with up to 75 wt% Al2O3 were both free- Al2O3 content. It was demonstrated that the composite films with up to 75 wt% Al2O3 were both free- were both free-standing and flexible. The composite films with 80 wt% Al O loading showed a 2 3 st standin anding g an and d flex flexiible. The ble. The composit composite fi e films wit lms withh 8 800 wt wt% Al % Al 2O 2O 3 lo 3 lo adin adin g showe g showe dd a re a re lat lat ive ive lyly good good relatively good thermal conductivity, higher than 1.3 W/mK. Besides, PI/Al O composite films 2 3 therma thermal conducti l conductivi vity, higher th ty, higher than an 1. 1.3 W/ 3 W/m m··K. K. Be Besi sides, des, PI/ PI/A Al2lO 2O 3 composite films 3 composite films exhibited high exhibited high er er exhibited higher thermal stability compared to conventional polysiloxane/Al O composites. The 2 3 thermal stability compared to conventional polysiloxane/Al2O3 composites. The PI/Al2O3 composite thermal stability compared to conventional polysiloxane/Al2O3 composites. The PI/Al2O3 composite PI/Al O composite films could be used as a heat-radiating film in electronic devices requiring high 2 3 film films c s coouulld d be u be ussed ed a ass a h a heeat at--rrad adiiaattiing ng f film ilm in in elect electrronic onic de devices vices re requ quiriirinng h g high igh ope ope ratrat ing ing operating temperatures. temperatures. temperatures. Supplementary Materials: The following are available online at http://www.mdpi.com/2076-3417/9/3/548/s1, Supplementary Materials: The following are available online at www.mdpi.com/xxx/s1, Figure S1: FT-IR Figur Supplementary Materials: e S1: FT-IR spectra of (a The following a ) PAA-1, and (b) r PI-1; e available online at Figure S2: FT-IR spectra www.mdpi.com/xxx/ of (a) PAA-2, and s1, Figure S1: (b) PI-2; Figur FT-IR e S3: FT-IR spectra of (a) PAA-3, and (b) PI-3; Figure S4: FT-IR spectra of (a) PAA-5, and (b) PI-5; Figure S5: FT-IR spectra of (a) PAA-1, and (b) PI-1; Figure S2: FT-IR spectra of (a) PAA-2, and (b) PI-2; Figure S3: FT-IR spectra spectra of (a) PAA-1, and (b) PI-1; Figure S2: FT-IR spectra of (a) PAA-2, and (b) PI-2; Figure S3: FT-IR spectra spectra of (a) PAA-6, and (b) PI-6; Figure S6: FT-IR spectra of (a) PAA-7 and (b) PI-7; Figure S7: TGA curves of of (a) PAA-3, and (b) PI-3; Figure S4: FT-IR spectra of (a) PAA-5, and (b) PI-5; Figure S5: FT-IR spectra of (a) of (a) PAA-3, and (b) PI-3; Figure S4: FT-IR spectra of (a) PAA-5, and (b) PI-5; Figure S5: FT-IR spectra of (a) PI-3 and PI-3/Al O composite films; Figure S8: Stress–strain curves of PI-3 and PI-3/Al O composite films; 2 3 2 3 PAA-6, and (b) PI-6; Figure S6: FT-IR spectra of (a) PAA-7 and (b) PI-7; Figure S7: TGA curves of PI-3 and PI- PAA-6, and (b) PI-6; Figure S6: FT-IR spectra of (a) PAA-7 and (b) PI-7; Figure S7: TGA curves of PI-3 and PI- Table S1: Thermal diffusivity and thermal conductivity values of the PI-3 and PI-3/Al O composite films; 2 3 3/Al2O3 composite films; Figure S8: Stress–strain curves of PI-3 and PI-3/Al2O3 composite films; Table S1: 3/Al2O3 composite films; Figure S8: Stress–strain curves of PI-3 and PI-3/Al2O3 composite films; Table S1: Table S2: Thermal diffusivity and thermal conductivity values of the PI-4 and PI-4/Al O composite films; 2 3 Thermal diffusivity and thermal conductivity values of the PI-3 and PI-3/Al2O3 composite films; Table S2: T Thermal diffusivity and thermal conducti able S3: Thermal diffusivity and thermal conductivity vity values of t values he PI-3 and PI-3/Al of the PI-5 and PI-5/Al 2O3 composite O composite films; Ta films. ble S2: 2 3 Thermal diffusivity and thermal conductivity values of the PI-4 and PI-4/Al2O3 composite films; Table S3: Thermal diffusivity and thermal conductivity values of the PI-4 and PI-4/Al2O3 composite films; Table S3: Thermal diffusivity and thermal conductivity values of the PI-5 and PI-5/Al2O3 composite films. Thermal diffusivity and thermal conductivity values of the PI-5 and PI-5/Al2O3 composite films. Appl. Sci. 2019, 9, 548 9 of 11 Author Contributions: Conceptualization, J.-Y.C., S.P., and C.-M.C.; methodology, J.-Y.C.; formal analysis, J.-Y.C., K.-N.N., and S.-W.J.; investigation, D.-M.K., I.-H.S., and H.-J.P.; writing—original draft preparation, J.-Y.C. and C.-M.C.; writing—review and editing, C.-M.C.; supervision, C.-M.C. Conflicts of Interest: The authors declare no conflict of interest. References 1. Gutfleisch, O.; Willard, M.A.; Bruck, E.; Chen, C.H.; Sankar, S.G.; Liu, J.P. Magnetic materials and devices for the 21st century: Stronger, lighter, and more energy efficient. Adv. Mater. 2011, 23, 821–842. [CrossRef] [PubMed] 2. Jayaprakash, N.; Das, S.K.; Archer, L.A. The rechargeable aluminum-ion battery. Chem. Commun. 2011, 47, 12610–12612. [CrossRef] [PubMed] 3. Gain, A.K.; Fouzder, T.; Chan, Y.C.; Sharif, A.; Wong, N.B.; Yung, W.K.C. The influence of addition of al nano-particles on the microstructure and shear strength of eutectic Sn–Ag–Cu solder on Au/Ni metallized Cu pads. J. Alloys Comp. 2010, 506, 216–223. [CrossRef] 4. Li, T.-L.; Hsu, S.L.-C. Enhanced thermal conductivity of polyimide films via a hybrid of micro-and nano-sized boron nitride. J. Phys. Chem. B 2010, 114, 6825–6829. [CrossRef] [PubMed] 5. Wang, M.; Jiao, Z.; Chen, Y.; Hou, X.; Fu, L.; Wu, Y.; Li, S.; Jiang, N.; Yu, J. Enhanced thermal conductivity of poly(vinylidene fluoride)/boron nitride nanosheet composites at low filler content. Compos. Part A Appl. Sci. Manuf. 2018, 109, 321–329. [CrossRef] 6. Han, Z.; Fina, A. Thermal conductivity of carbon nanotubes and their polymer nanocomposites: A review. Prog. Polym. Sci. 2011, 36, 914–944. [CrossRef] 7. Huang, X.; Jiang, P.; Tanaka, T. A review of dielectric polymer composites with high thermal conductivity. IEEE Trans. Dielectr. Electr. Insul. 2011, 27, 8–16. [CrossRef] 8. Fang, H.; Zhang, X.; Zhao, Y.; Bai, S.-L. Dense graphene foam and hexagonal boron nitride filled PDMS composites with high thermal conductivity and breakdown strength. Compos. Sci. Technol. 2017, 152, 243–253. [CrossRef] 9. He, X.; Huang, Y.; Liu, Y.; Zheng, X.; Kormakov, S.; Sun, J.; Zhuang, J.; Gao, X.; Wu, D.J. Improved thermal conductivity of polydimethylsiloxane/short carbon fiber composites prepared by spatial confining forced network assembly. J. Mater. Sci. 2018, 53, 14299–14310. [CrossRef] 10. Kim, Y.; Hwang, S.; So, J.I.; Kim, C.L.; Kim, M.; Shim, S.E. Treatment of atmospheric-pressure radio frequency plasma on boron nitride for improving thermal conductivity of polydimethylsiloxane composites. Macromol. Res. 2018, 26, 864–867. [CrossRef] 11. Feng, L.; Iroh, J.O. Polyimide-b-polysiloxane copolymers: Synthesis and properties. J. Inorg. Organomet Polym. Mater. 2013, 23, 477–488. [CrossRef] 12. Barry, A.; Beck, H. Inorganic Polymers; Academic Press: New York, NY, USA, 1962. 13. Valentini, L.; Bittolo Bon, S.; Pugno, N.M. Severe graphene nanoplatelets aggregation as building block for the preparation of negative temperature coefficient and healable silicone rubber composites. Compos. Sci. Tech. 2016, 134, 125–131. [CrossRef] 14. Clarson, S.J. Silicones and silicone-modified materials: A concise overview. ChemInform 2004, 35, 1–10. [CrossRef] 15. Yao, Y.; Chen, Z.; Lu, G.; Boroyevich, D.; Ngo, K.D.T. Characterization of encapsulants for high-voltage high-temperature power electronic packaging. IEEE Trans. Compon. Packag. Manuf. Technol. 2012, 2, 539–547. [CrossRef] 16. Scofield, J.D.; Merrett, J.N.; Richmond, J.; Agarwal, A.; Leslie, S. Performance and Reliability Characteristics of 1200 V, 100 A, 200 C Half-Bridge SIC MOSFET-JBS Diode Power Modules. In Proceedings of the International Conference on High Temperature Electronics, International Microelectronics & Packaging Society, Albuquerque, NM, USA, 11–13 May 2010; pp. 000289–000296. 17. Yao, Y.; Lu, G.-Q.; Boroyevich, D.; Ngo, K.D.T. Effect of Al O fibers on the high-temperature stability of 2 3 silicone elastomer. Polymer 2014, 55, 4232–4240. [CrossRef] 18. Nakanishi, F. Photoreaction of amphiphilic diolefins in monolayers formed on an air-water interface. J. Polym. Sci. Part C Polym. Lett. 1988, 26, 159–163. [CrossRef] Appl. Sci. 2019, 9, 548 10 of 11 19. Liaw, D.-J.; Liaw, B.-Y.; Li, L.-J.; Sillion, B.; Mercier, R.; Thiria, R.; Sekiguchi, H. Synthesis and characterization 0 0 of new soluble polyimides from 3,3 ,4,4 -benzhydrol tetracarboxylic dianhydride and various diamines. Chem. Mater. 1998, 10, 734–739. [CrossRef] 20. Mathews, A.S.; Kim, I.; Ha, C.S. Fully aliphatic polyimides from adamantane-based diamines for enhanced thermal stability, solubility, transparency, and low dielectric constant. J. Appl. Polym. Sci. 2006, 102, 3316–3326. [CrossRef] 21. Wachsman, E.D.; Frank, C.W. Effect of cure history on the morphology of polyimide: Fluorescence spectroscopy as a method for determining the degree of cure. Polymer 1988, 29, 1191–1197. [CrossRef] 22. Ngo, I.-L.; Jeon, S.; Byon, C. Thermal conductivity of transparent and flexible polymers containing fillers: A literature review. Int. J. Heat Mass Transf. 2016, 98, 219–226. [CrossRef] 23. Kato, R.; Maesono, A.; Tye, R.P. Thermal conductivity measurement of submicron-thick films deposited on substrates by modified ac calorimetry (laser-heating Çngstrom method). Int. J. Thermophys. 2001, 22, 617–629. [CrossRef] 24. Kurabayashi, K.; Asheghi, M.; Touzelbaev, M.; Goodson, K.E. Measurement of the thermal conductivity anisotropy in polyimide films. J. Microelectromech. Syst. 1999, 8, 180–191. [CrossRef] 25. Irwin, P.C.; Cao, Y.; Bansal, A.; Schadler, L.S. Thermal and mechanical properties of polyimide nanocomposites. In Proceedings of the 2003 IEEE Annual Report Conference on Electrical Insulation and Dielectric Phenomena, Albuquerque, NM, USA, 19–22 October 2003; pp. 120–123. 26. Guo, Y.; Xu, G.; Yang, X.; Ruan, K.; Ma, T.; Zhang, Q.; Gu, J.; Wu, Y.; Liu, H.; Guo, Z. Significantly enhanced and precisely modeled thermal conductivity in polyimide nanocomposites with chemically modified graphene via in situ polymerization and electrospinning-hot press technology. J. Mater. Chem. C 2018, 6, 3004–3015. [CrossRef] 27. Wang, T.; Wang, M.; Fu, L.; Duan, Z.; Chen, Y.; Hou, X.; Wu, Y.; Li, S.; Guo, L.; Kang, R.; et al. Enhanced thermal conductivity of polyimide composites with boron nitride nanosheets. Sci. Rep. 2018, 8, 1557. [CrossRef] [PubMed] 28. You, L. Preparation and thermal properties of silicon-containing polyimide composite films. Chem. Eng. Trans. 2017, 59, 1051–1056. 29. Lupinski, J.H.; Moore, R.S. Polymeric Materials for Electronics Packaging and Interconnection; American Chemical Society: Washington, DC, USA, 1989; Volume 407, p. 516. 30. Mahoney, C.M.; Gardella, J.A.; Rosenfeld, J.C. Surface characterization and adhesive properties of poly (imidesiloxane) copolymers containing multiple siloxane segment lengths. Marcromolecules 2002, 35, 5256–5266. [CrossRef] 31. Homma, T.; Yamaguchi, M.; Kutsuzawa, Y.; Otsuka, N. Electrical stability of polyimide siloxane films for interlayer dielectrics in multilevel interconnections. Thin Solid Films 1999, 340, 237–241. [CrossRef] 32. Rogers, M.E.; Rodrigues, D.; Wilkes, G.L.; McGrath, J.E.; Brennan, A. Perfectly alternating segmented polyimide siloxane copolymers. In Advances in New Materials; Springer: Boston, MA, USA, 1992; pp. 47–55. 33. McGrath, J.E.; Dunson, D.L.; Mecham, S.J.; Hedrick, J.L. Synthesis and characterization of segmented polyimide-polyorganosiloxane copolymers. In Progress in Polyimide Chemistry I; Springer: Berlin/Heidelberg, Germany, 1999; pp. 61–105. 34. Zou, L.; Anthamatten, M. Synthesis and characterization of polyimide-polysiloxane segmented copolymers for fuel cell applications. J. Polym. Sci. Part A Polym. Chem. 2007, 45, 3747–3758. [CrossRef] 35. Pechar, T.W.; Kim, S.; Vaughan, B.; Marand, E.; Baranauskas, V.; Riffle, J.; Jeong, H.K.; Tsapatsis, M. Preparation and characterization of a poly(imide siloxane) and zeolite L mixed matrix membrane. J. Memb. Sci. 2006, 277, 210–218. [CrossRef] 36. Bujard, P.; Kuhnlein, G.; Ino, S.; Shiobara, T. Thermal conductivity of molding compounds for plastic packaging. IEEE Trans. Compon. Packag. Manuf. Technol. 1994, 17, 527–532. [CrossRef] 37. Droval, G.; Feller, J.-F.; Salagnac, P.; Glouannec, P. Thermal conductivity enhancement of electrically insulating syndiotactic poly(styrene) matrix for diphasic conductive polymer composites. Polym. Adv. Technol. 2006, 17, 732–745. [CrossRef] 38. Shimazaki, Y.; Hojo, F.; Takezawa, Y. Preparation and characterization of thermoconductive polymer nanocomposite with branched alumina nanofiber. Appl. Phys. Lett. 2008, 92, 133309. [CrossRef] 39. Shimazaki, Y.; Hojo, F.; Takezawa, Y. Highly thermoconductive polymer nanocomposite with a nanoporous -alumina sheet. ACS Appl. Mater. Interfaces 2009, 1, 225–227. [CrossRef] Appl. Sci. 2019, 9, 548 11 of 11 40. Li, H.; Liu, G.; Liu, B.; Chen, W.; Chen, S. Dielectric properties of polyimide/Al O hybrids synthesized by 2 3 in-situ polymerization. Mater. Lett. 2007, 61, 1507–1511. [CrossRef] 41. Ha, S.Y.; Oh, B.-K.; Lee, Y.M. Preparation of poly(amideimide siloxane) from trimellitic anhydride chloride, oxylene diamine and oligo(dimethylsiloxane) diamine. Polymer 1995, 36, 3549–3553. [CrossRef] 42. Bowens, A.D. Synthesis and Characterization of Poly (Siloxane Imide) Block Copolymers and End-Functional Polyimides for Interphase Applications; Virginia Tech: Blacksburg, VA, USA, 1999. 43. Deng, X.; Luo, R.; Chen, H.; Liu, B.; Feng, Y.; Sun, Y. Synthesis and surface properties of pdms–acrylate emulsion with gemini surfactant as co-emulsifier. Colloid Polym. Sci. 2007, 285, 923–930. [CrossRef] 44. Téllez, L.; Rubio, J.; Rubio, F.; Morales, E.; Oteo, J.L. FT-IR study of the hydrolysis and polymerization of tetraethyl orthosilicate and polydimethyl siloxane in the presence of tetrabutyl orthotitanate. Spectrosc. Lett. 2004, 37, 11–31. [CrossRef] 45. Li, K.; Zeng, X.; Li, H.; Lai, X.; Xie, H. Effects of calcination temperature on the microstructure and wetting behavior of superhydrophobic polydimethylsiloxane/silica coating. Colloids Surf. A Physicochem. Eng. Asp. 2014, 445, 111–118. [CrossRef] 46. Zhang, K.; Yu, Q.; Zhu, L.; Liu, S.; Chi, Z.; Chen, X.; Zhang, Y.; Xu, J. The Preparations and Water Vapor Barrier Properties of Polyimide Films Containing Amide Moieties. Polymers 2017, 9, 677. [CrossRef] 47. Yu, H.-C.; Choi, J.-Y.; Jeong, J.-W.; Kim, B.-J.; Chung, C.-M. Simple and easy recycling of poly(Amic Acid) gels through microwave irradiation. J. Polym. Sci. Part A Polym. Chem. 2017, 55, 981–987. [CrossRef] 48. Choi, J.-Y.; Yu, H.-C.; Lee, J.; Jeon, J.; Im, J.; Jang, J.; Jin, S.-W.; Kim, K.-K.; Cho, S.; Chung, C.-M. Preparation of polyimide/graphene oxide nanocomposite and its application to nonvolatile resistive memory device. Polymers 2018, 10, 901. [CrossRef] 49. Muratov, D.S.; Kuznetsov, D.V.; Il’inykh, I.A.; Burmistrov, I.N.; Mazov, I.N. Thermal conductivity of polypropylene composites filled with silane-modified hexagonal BN. Compos. Sci. Technol. 2015, 111, 40–43. [CrossRef] 50. Cinausero, N.; Azema, N.; Cochez, M.; Ferriol, M.; Essahli, M.; Ganachaud, F.; Lopez-Cuesta, J.M. Influence of the surface modification of alumina nanoparticles on the thermal stability and fire reaction of PMMA composites. Polym. Adv. Technol. 2008, 19, 701–709. [CrossRef] 51. Chen, Y.; Iroh, J.O. Synthesis and characterization of polyimide/silica hybrid composites. Chem. Mater. 1999, 11, 1218–1222. [CrossRef] © 2019 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).

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Published: Feb 6, 2019

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