Synthesis and characterization of polyimide/modified mCOC composites

Two types of monomers, 4,4′‐(hexafluoroisopropylidene) diphthalic anhydride and 4,4′‐oxydianiline, were employed to synthesize poly(amic acid) (PAA) as a precursor of polyimide (PI). Through the addition of modified metallocene cyclic olefin copolymer (mCOC), PAA/mCOC composites were formed. PI/mCOC composites were obtained through a blade coating and multistep thermal curing process. The structure of the prepared PI/mCOC composites was characterized through Fourier transform infrared spectrometry. The results showed that the copolymerization of PAA and modified mCOC improved thethermal stability and hydrophobic and electrical properties of the PI/mCOC composites. The formation of a network structure between PI and modified mCOC considerably reduced the mobility of PI molecules, thereby improving the glass transition temperature and thermal properties of the composite. The thermal and hydrophobic properties were improved by increasing the mCOC grafting ratio. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 44144.     

Structure and properties of novel PMDA/ODA/PABZ polyimide fibers

A series of random copolyamic acid were synthesized from various ratios of two diamines 4, 4′‐oxydianiline (ODA) and 2‐(4‐aminophenyl)‐5‐aminobenzimidazole (PABZ) by polycondensation with pyromellitic dianhydride (PMDA) in N‐methyl‐2‐pyrrolidone (NMP). Their inherent viscosities were in the range of 1.89–2.91 dl/g. The polyamic acid (PAA) solution drops were spun into fibers by the wet spinning process. The polyimide (PI) fibers were obtained from PAA fibers after drawn and treated in heating tube. The fibers were characterized by fourier transform infrared (FTIR), wide X‐ray diffraction (WAXD), scanning electron microscope (SEM), thermal gravimetry analysis (TGA), dynamic mechanical analysis (DMA), and tensile testing. WAXD showed these PI fibers were basically amorphous. The tensile strength and initial modulus of the PI fiber reached 1.53 and 220.5 GPa when diamine ratio of PABZ/ODA was 7/3, which were almost three times and 30 times over that of the PMDA/ODA PI fibers. TGA showed that the PI fibers were thermally stable with 10% weight losses recorded in the range of 492–564°C under nitrogen atmosphere, and their glass transition temperature (T_g) were found to be 410–440°C by DMA with increasing PABZ content from 30 to 70%. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers     

The retarding effects and structural evolution of a bio-based high-performance polyimide during thermal imidization

The thermal imidization evolution of a bio-based high-performance polyimide, namely adenine-containing polyimide (API), was investigated by thermogravimetric analysis (TGA), in situ Fourier transform infrared spectroscopy (in situ FTIR), and wide-angle X-ray diffraction (WAXD), in contrast to an adenine-free 4,4′-oxydiphthalic anhydride (ODPA)/4,4′-oxydianiline (ODA) PI. The influence derived from adenine was focused. At precursor stage of API (polyamic acid, PAA), the H-bonding interaction of PAA–PAA type as well as the especial interaction between the secondary amine of adenine and solvent (dimethylacetamide, DMAc) was discovered. Structural evolution of API was traced by in situ FTIR and multistage WAXD from PAA stage to PI stage. Compared with OPI, the retarding effects were found in the process of thermal imidization of API, partly due to the formation of H-bonding derived from the extra secondary amine of adenine moieties, which complicated the H-bonding form in API. Finally, a hypothesis of evolution of thermal imidization process about API molecule was proposed in contrast with adenine-free ODPA ODA PI. Compared with the consistency of both API and ODPA ODA PI in PAA stage, API possessed a more delicate thermal imidization process. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 46953.     

Synthesis and characterization of polyimide/hexagonal boron nitride composite

Polyimide (PI)/hexagonal boron nitride (h‐BN) composites were produced via the thermal imidization procedure from solution mixtures of a polyamicacid, which is prepared from 3,3′,4,4′‐benzophenonetetracarboxylic dianhydride and 3,3′‐diaminodiphenyl sulfone (DADPS) in N‐methyl‐2‐pyrrolidone (NMP), and alkoxysilane functionalized h‐BN. The structure, thermostability, thermal behavior, and surface properties of the resulting materials were characterized by means of Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), scanning electron microscopy (SEM). The thermal characteristics of PI/h‐BN films were better than the pure PIs. The physical and mechanical properties of the films were evaluated by various techniques such as contact angle, chemical resistance, and tensile tests. The flame retardancy of the composite materials was also examined by the limiting oxygen index (LOI). The experiments showed that the LOI values of PIs increased from 32 to 43 for the materials containing hexagonal boron nitride. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Polyimide nanohybrid films with electrochemically functionalized graphene

Graphite was functionalized electrochemically in a potassium fluoride solution and used to prepare polyimide (PI)/graphene nanohybrid films. The as‐made electrochemically fluorinated graphene (EFG) was used to prepare nanohybrid films with colorless PI, which was synthesized from 4,4′‐(hexafluoroisopropylidene) diphthalic anhydride and bis(trifluoromethyl) benzidine by in situ polymerization. The surface functionalization of graphite was characterized by powder XRD, TEM with energy dispersive X‐ray spectroscopy elemental mapping, X‐ray photoelectron spectroscopy, Raman spectroscopy, and TGA. The microstructure of the films was characterized by Fourier transform IR spectroscopy, XRD and SEM. The film properties were measured using a universal testing machine, TGA, dynamic mechanical analysis, four‐point probe, UV–visible spectroscopy and water contact angle analysis. EFG improved the tensile strength and modulus of the nanohybrid films by 20% and 50%, respectively. The glass transition temperature and electrical conductivity of the nanohybrid films were 12 °C and nine orders of magnitude higher than those of the neat PI film, respectively. The nanohybrid film maintained 80% optical transmittance even after the addition of 0.1 wt% EFG. © 2019 Society of Chemical Industry     

Enhanced mechanical and thermal properties of polyimide/organically modified montmorillonite hybrid film based on stable poly(amic acid) ammonium salt

In this study, polyimide/organically modified montmorillonite (PI/OMMT) hybrid film was prepared by in situ polymerization from the stable poly(amic acid) ammonium salt/OMMT (PAAS/OMMT) precursor hybrid. PAAS was obtained by incorporating calculated triethylamine into terpolymer poly(amic acid) (PAA), which was synthesized by pyromellitic dianhydride (PMDA), 4,4′‐oxydianiline and p‐phenylenediamine in dimethylacetamide (DMAc). OMMT as a type of layered clays was prepared through surface treatment of montmorillonite (MMT) with 1‐hexadecylamine. Mechanical property measurements of PI/OMMT hybrid film indicated that the addition of 5 wt% of OMMT increased the Young's modulus of PI film up to 11.24 GPa, which is 58% higher than the pristine PI film from PAAS. Besides, the tensile strength increased to 168.36 MPa, which was higher than that of PI film derived from PAA (164.3 MPa) and PI film derived from PAAS (145.2 MPa). Moreover, the thermal stabilities of PI/OMMT hybrid film with appropriate OMMT content were also better than those of original PI films. POLYM. COMPOS., 34:2076–2081, 2013. © 2013 Society of Plastics Engineers     

Preparation of highly uniform self‐standing submicrometer polyimide films and an investigation of their antibulging capabilities

Aiming for X‐ray astronomy applications, we prepared large‐area submicrometer polyimide (PI) films [diameter (Φ) = 8 cm] with great thickness uniformity via the spin‐coating technique by using a PI precursor, poly(amic acid) (PAA) derived from 3,3′,4,4′‐biphenyltetracarboxylic dianhydride, and p‐phenylenediamine as the starting materials. The effects of the spinning speed, apparent viscosity of the PAA solution (η), and spinning time on the PI film thickness and its uniformity, as characterized by the measurement of the film thickness every 0.5 cm along the diameter direction, were investigated. By optimizing the spin‐coating conditions, we prepared final submicrometer PI films with average thicknesses in the range of 200–850 nm and with film thickness fluctuations of less than 1.3%. The pressure bulge test results indicate that at a thickness of 805 nm and an inside test aperture diameter of 2.64 cm, the prepared PI films reached a final burst pressure of 20.2 KPa; this suggested excellent mechanical performances in the self‐standing submicrometer PI film. This study makes a contribution by providing a typical example and opening the way for the preparation of robust self‐standing submicrometer PI films with great thickness uniformities for X‐ray astronomy applications. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2014 , 131, 39977.     

Synthesis and properties of fluorene‐based polyimide adhesives

Five kinds of fluorene‐based polyimides (PIs) based on 4,4′‐oxydiphthalicanhydride (ODPA), 9,9′‐bis(4‐aminophenyl)fluorene (BAFL), and 3,4′‐diaminodiphenyl ether (3,4′‐ODA) were synthesized through two‐step method. The partially or fully imidized PI films were cast from poly(amic acid) (PAA) solution and were imidized by far‐infrared radiation at various temperatures. The degree of imidization was characterized by FT‐IR and TGA. The fully imidized PI films were characterized by DMTA, TGA, and tensile tests. The partially imidized PI films were adhered to stainless steel plates for preparing the single lap joints. Lap shear strength (LSS) at room temperature was measured to compare the adhesive strength of single lap joint. Fractured surfaces were analyzed using scanning electron microscopy (SEM). The effects of fluorene content on thermal, tensile, and adhesion properties of PIs were elaborately studied. The results showed that PI films exhibited high glass transition temperature (T_g), good thermalplasticity, and thermal stability. The LSS of PIs increased abruptly with the incorporation of fluorene groups. The LSS of PI‐50/50 was the highest, which was 22.3 MPa. The LSS of PI‐50/50 was also measured at high temperature to investigate the thermal resistance of fluorene‐based PI adhesive. POLYM. ENG. SCI., 2011. © 2011 Society of Plastics Engineers.     

Preparation and properties of polyimide/silica hybrid composites based on polymer‐modified colloidal silica

A new type of polyimide/silica (PI/SiO₂) hybrid composite films was prepared by blending polymer‐modified colloidal silica with the semiflexible polyimide. Polyimide was solution‐imidized at higher temperature than the glass transition temperature (T_g) using 3,3′,4,4′‐biphenyltetracarboxylic dianhydride (BPDA) and 4,4′‐diaminodiphenyl ether (ODA). The morphological observation on the prepared hybrid films by scanning electron microscopy (SEM) pointed to the existence of miscible organic–inorganic phase, which resulted in improved mechanical properties compared with pure PI. The incorporation of the silica structures in the PI matrix also increased both T_g and thermal stability of the resulting films. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 2053–2061, 2006     

Preparation and properties of APPSSQ‐like/polyimide hybrid composites

Hydrolysis and condensation proceeded to generate 3‐aminopropyl polysilsesquioxane‐like (APPSSQ‐like) particles from 3‐aminopropyl triethoxysilane. An APPSSQ‐like particle includes two domains: crosslinking Si? O? Si networks inside and 3‐aminopropyl groups outside the particle. The APPSSQ‐like/polyimide (APPSSQ‐like/PI) hybrid composites were prepared from a solution of poly(amic acid) (PAA, polyimide precursor) and APPSSQ‐like particles using N,N‐dimethylacetamide as a solvent. Scanning electron microscopy (SEM) showed that the APPSSQ particle sizes were about 100 nm, and there was no obvious phase separation between the APPSSQ‐like particles and the PI matrix in the fracture surfaces of the hybrid films. Owing to the highly crosslinked Si? O? Si networks inside the APPSSQ‐like particles, the APPSSQ‐like/PI hybrid composites possessed desired properties such as improved thermal resistance and reduced coefficients of thermal expansion (CTE). The presence of covalent bonds between the APPSSQ‐like particles and the PI molecules improved the compatibility between these two components. Thus, the tensile strength increased with the APPSSQ‐like content, and the elongation at break also slightly increased with the APPSSQ‐like content. The initial tensile and storage moduli of the APPSSQ‐like/PI hybrid composites increased with the APPSSQ‐like content, which indicates that the mechanical properties of these hybrid composites were enhanced by the incorporation of the APPSSQ‐like content in the PI matrix. Furthermore, the glass transition temperatures of these composites increased with the APPSSQ‐like content because the adhesion between the APPSSQ‐like particles and the PI molecules restricts the PI chains' mobility. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 2865–2874, 2003     

Effect of organosilica isomers on the interfacial interaction in polyimide/aromatic organosilica hybrids

We report the effect of organosilica precursor isomers on the interfacial interaction between polyimide and organosilica in polyimide/organosilica hybrid composite films. Poly(4,4′‐oxydianiline biphenyltetracarboxamic acid) (BPDA‐ODA PAA) was used as the polyimide precursor, while the organosilica was made using o‐substituted, m‐substituted, and p‐substituted phenyl organosilica precursor isomers. For the preparation of precursor hybrid films, BPDA‐ODA PAA and organosilica precursors were mixed and then the organosilica precursors were converted to corresponding organosilica via sol–gel process. Finally, these precursor films were converted to corresponding polyimide/organosilica hybrid films by the thermal imidization of BPDA‐ODA PAA, which results in poly(4,4′‐oxydianiline biphenyltetracarboximide) (BPDA‐ODA PI). The polyimide/organosilica hybrid films were characterized using three distinctive nuclear magnetic resonance spectroscopies (¹H NMR, ¹³C‐CPMAS‐NMR, and ²⁹Si‐MAS‐NMR), wide‐angle X‐ray diffraction (WAXD), small‐angle X‐ray scattering (SAXS), and peel strength measurement. We found that the m‐substituted phenyl organosilica shows poorer interfacial interaction with BPDA‐ODA PI than do the o‐ or p‐substituted phenyl organosilicas. It was observed, however, that the peel strength of the hybrid films against an aluminum substrate increased with increasing contents of organosilicas, regardless of the nature of the organosilica isomers. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 2507–2513, 2007     

Improving properties of superabsorbent composite induced by using alkaline protease hydrolyzed‐sericin (APh‐sericin)

A series of superabsorbent polymer composites based on sericin hydrolyzed with alkaline protease (AP) were prepared by grafting with acrylic acid (AA) and acrylamide (AM). The properties of the superabsorbent polymers (SAP) by using hydrolyzed sericin with different amount of alkaline protease (nAPh‐sericin) were compared. It was found that the polymer prepared from 5APh‐sericin (the mass ratio of AP to sericin was 5.0 mg g⁻¹) showed the highest graft percentage and water absorbency, this phenomenon may be attributed to the change of molecular weight of resulting sericin molecules. The molecular structure of the grafted polymers was proved by thermal gravimetric analysis (TGA) and Fourier transform infrared spectroscopy (FTIR) measurements. Comparing with PAA‐AM (poly AA‐co‐AM) and 0APh‐sericin/PAA‐AM polymer, 5APh‐sericin/PAA‐AM polymer had the most excellent water retention capacity and enzyme degradability. The morphological features of the polymers with different drying methods were evidenced by SEM images. The water absorbencies of 5APh‐sericin/PAA‐AM polymer prepared with freeze‐drying were 896 g g⁻¹ in deionized water, 424 g g⁻¹ in tap water, and 83 g g⁻¹ in 0.9 wt% aqueous NaCl solution. POLYM. COMPOS., 35:509–515, 2014. © 2013 Society of Plastics Engineers     

Molecular weight controlled poly(amic acid) resins end‐capped with phenylethynyl groups for manufacturing advanced polyimide films

To investigate the effect of reactive end‐capping groups on film‐forming quality and processability, a series of molecular weight‐controlled aromatic poly(amic acid) (PAA) resins functionalized with phenylethynyl end groups were prepared via the polycondensation of 3,3′,4,4′‐biphenyltetracarboxylic dianhydride (BPDA), para ‐phenylenediamine (PDA), and 4‐phenylethynyl phthalic anhydride (PEPA) served as molecular‐weight‐controlling and reactive end capping agent. The PAA resins with relatively high concentrations endow enhanced wetting/spreading ability to form PAA gel films by solution‐cast method which were thermally converted to the fully‐cured polyimide (PI) films. The mechanical and thermal properties of PI films were investigated as a function of PAA molecular weights (M_n ) and thermal‐curing parameters. Mechanical property, dimensional stability and heat resistance of the fully‐cured PI films with PAA M_n > 20 ×10³ g mol^?1 are found to be better than that of their unreactive phthalic end‐capped counterparts. The covalent incorporation of chain‐extension structures in the backbones, induced by thermal curing of phenylethynyl groups, might facilitate yielding a higher degree of polymer chain order and consequently improved resistance strength and elongation at break to tensile plastic deformation. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134 , 45168.     

Preparation and properties of T300 carbon fiber‐reinforced thermoplastic polyimide composites

In this study, a series of T300 carbon fiber‐reinforced polyimide (CFRPI) composites were prepared by laminating premolding polyimide (PI) films with unidirectional carbon fiber (CF) layers. On the basis of PI systems design, the effect of CF volume fraction, processing conditions, and PI molecular structure on the properties of CFRPI composites was studied in detail. In addition, two kinds of nano‐particles, including carbon nano‐tube (CNT) and SiO₂ were filled into the premolding PI films with different concentrations. And the effect of nano‐particles on the properties of CFRPI composites was also investigated. The surface characteristic of T300 CF was measured by X‐ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR). The properties of premolding PI film and CFRPI composites were measured by dynamic mechanical analysis (DMTA), SANS testing machine, scanning electron microscopy (SEM), and so forth. These experimental results showed that the properties of CFRPI composites were mainly affected by the premolding PI film and molding condition. The change of CF volume fraction from 55% to 65% took little effect on the mechanical properties of CFRPI composites. In addition, the incorporation of nano‐particle SiO₂ could further improve the properties of CFRPI composites, but CNT hardly improved the properties of CFRPI composites. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 646–654, 2006     

Preparation and properties of ternary polyimide/SiO2/polydiphenylsiloxane composite films

A series of novel ternary polyimide/SiO₂/polydiphenylsiloxane (PI/SiO₂/PDPhS) composite films were prepared through co‐hydrolysis and condensation between tetramethoxysilane, diphenyldimethoxysilane (DDS) and aminopropyltriethoxysilane‐terminated polyamic acid, using an in situ sol–gel method. The composite films exhibited good optical transparency up to 30 wt% of total content of DDS and SiO₂. SEM analysis showed that the PDPhS and SiO₂ were well dispersed in the PI matrix without macroscopic separation of the composite films. TGA analysis indicated that the introduction of SiO₂ could improve the thermal stability of the composite films. Dynamic mechanical thermal analysis showed that the composite films with low DDS content (5 wt%) had a higher glass transition temperature (T_g) than pure PI matrix. When the content of DDS was above 10 wt%, the T_g of the composite decreased slightly due to the plasticizing effect of flexible PDPhS linkages on the rigid PI chains. The composite films with high SiO₂ content exhibited higher values of storage modulus. Tensile measurements also showed that the modulus and tensile strength of the composite films increased with increasing SiO₂ content, and the composite films still retained a high elongation at break due the introduction of DDS. The density and water absorption of the composite films were also characterized. Copyright © 2006 Society of Chemical Industry     

Preparation of poly(amic acid) and polyimide derived from 3,3′,4,4′‐benzophenonetetracarboxylic dianhydride with different diamines by microwave irradiation

Polycondensation‐type poly(amic acid) (PAA) was synthesized with 3,3′,4,4′‐benzophenonetetracarboxylic dianhydride as a dianhydride monomer and 4,4′‐diaminodiphenylmethane and 4,4′‐oxydianiline as diamine monomers under microwave irradiation in dimethylformamide. Then, PAA was used to make polyimide (PI) by imidization at a low temperature. The structure and performance of the polymers were characterized with Fourier transform infrared (FTIR), proton nuclear magnetic resonance (¹H‐NMR), viscosity, X‐ray diffraction (XRD), and thermogravimetry (TG) curve analyses. The FTIR spectra of the polymers showed characteristic peaks of PI around 1779 and 1717 cm^?1. The ¹H‐NMR spectrum of PAA indicated a singlet at 6.55 ppm assigned to ? NHCO? and a singlet at 10.27 ppm assigned to carboxylic acid protons. The XRD spectrum demonstrated that the obtained PI had a low‐order aggregation structure with a d‐spacing of 0.5453 nm. The TG results revealed that the PI was thermally stable with 10% weight loss at 565°C in an N₂ atmosphere. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2008     

Development and characterization of co‐polyimide/attapulgite nanocomposites with highly enhanced thermal and mechanical properties

A series of co‐polyimide/attapulgite (co‐PI/AT) nanocomposites have been successfully fabricated from anhydride‐terminated polyimide (PI) and γ‐aminopropyltriethoxysilane (APTES)‐modified fibrous attapulgite (AT). Co‐PI was prepared from 4,4′‐diaminodiphenyl ether (ODA), 4,4′‐oxydiphthalic anhydride (ODPA), and 2,2‐bis[4‐(3,4‐dicarboxyphenoxy)phenyl]propane dianhydride (BPADA) by using the method of chemical imidization. Different amount of AT (0, 1, 3, 5, 7 wt%) were introduced into co‐PI via strong covalent interactions between terminal anhydride and amino groups. The properties of co‐PI/AT nanocomposites such as morphology, thermal stability, mechanical properties, and UV transparency were investigated to illustrate the contribution of the introduction of AT into the PI matrix. FTIR spectra and SEM images revealed that network structures between co‐PI and AT are formed, which endowed the nanocomposites with outstanding thermal and mechanical properties. The co‐PI/AT nanocomposites exhibited excellent thermal and thermo‐oxidative stabilities with the onset decomposition temperature and 10% weight loss temperature increasing to the ranges of 502–510°C and 555–562°C from 480°C to 526°C for the pristine co‐PI, respectively. The glass transition temperatures of these co‐PI/AT nanocomposites increased to the range of 231–238°C from 222°C for pure co‐PI. The co‐PI/AT nanocomposites films were found to be transparent, flexible, and tough. By incorporating 5 wt% AT into the co‐PI matrix, the tensile strength, elongation at break, and Young's modulus of the co‐PI/AT nanocomposites reached 110.7 MPa, 14.5%, and 1.2 GPa, respectively, which are 50%, 120%, and 80% increased compared with the values of pristine PI. POLYM. COMPOS., 35:86–96, 2014. © 2013 Society of Plastics Engineers     

Morphology of Organic–Inorganic Hybrid Composites in Thin Films as Multichip Packaging Material

Silica–polyimide hybrid composites were prepared via a sol–gel process and thermal imidization. Two different types of soluble precursors, poly(amic acid) (PAA) and poly(amic diethyl ester) (ES), chemically convertible to poly(p-phenylene biphenyltetracarboximide), were used as organic polymer matrix component, and tetraethoxysilane (TEOS), convertible to silica, as the inorganic component. The structure of composites prepared as thin films was investigated by means of small-angle X-ray scattering, scanning electron microscopy and atomic force microscopy. Nanometre-scale composites were successfully obtained for ≤30wt% TEOS-loaded mixtures with ES and PAA. It was considered from the microstructural investigation that the composite films based on ES were not significantly affected by the inorganic particles generated, maintaining the structure of the homopolyimide, while those based on PAA did not preserve the structure due to the nanoparticles grown in situ during the sol–gel process. © 1997 SCI.     

Preparation, Characterization and Thermal Degradation of Polyimide (4-APS/BTDA)/SiO(2) Composite Films

Polyimide/SiO(2) composite films were prepared from tetraethoxysilane (TEOS) and poly(amic acid) (PAA) based on aromatic diamine (4-aminophenyl sulfone) (4-APS) and aromatic dianhydride (3,3,4,4-benzophenonetetracarboxylic dianhydride) (BTDA) via a sol-gel process in N-methyl-2-pyrrolidinone (NMP). The prepared polyimide/SiO(2) composite films were characterized using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscope (SEM) and thermogravimetric analysis (TGA). The FTIR results confirmed the synthesis of polyimide (4-APS/BTDA) and the formation of SiO(2) particles in the polyimide matrix. Meanwhile, the SEM images showed that the SiO(2) particles were well dispersed in the polyimide matrix. Thermal stability and kinetic parameters of the degradation processes for the prepared polyimide/SiO(2) composite films were investigated using TGA in N(2) atmosphere. The activation energy of the solid-state process was calculated using Flynn-Wall-Ozawa's method without the knowledge of the reaction mechanism. The results indicated that thermal stability and the values of the calculated activation energies increased with the increase of the TEOS loading and the activation energy also varied with the percentage of weight loss for all compositions.     

Low‐κ nanocomposite films based on polyimides with grafted polyhedral oligomeric silsesquioxane

Nanocomposites of polyimides (PI) with covalently grafted polyhedral oligomeric silsesquioxane (R₇R′Si₈O₁₂ or POSS) units were prepared by thermally‐initiated free‐radical graft polymerization of methacrylcyclopentyl‐POSS (MA‐POSS) with the ozone‐pretreated poly[N,N′‐(1,4‐phenylene)‐3,3′,4,4′‐benzophenonetetra‐carboxylic amic acid] (PAA), followed by thermal imidization. The chemical composition and structure of the PI with grafted methacrylcyclopentyl‐POSS side chains (PI‐g‐PMA‐POSS copolymers) were characterized by nuclear magnetic resonance (NMR), X‐ray diffraction (XRD), and thermogravimetric analysis (TGA). The POSS molecules in each grafted PMA side chain of the amorphous PI films retained the nanoporous crystalline structure, and formed an aggregate of crystallites. The PI‐g‐PMA‐POSS nanocomposite films had both lower and tunable dielectric constants, in comparison with that of the pristine PI films. Dielectric constants (κ's) of about 3.0–2.2 were obtained. The present approach offers a convenient way for preparing low‐κ materials based on existing PI's. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci, 2006