A series of block and random copolyimide films were synthesized from various molar ratios of two diamines, rigid 2-(4-aminophenyl)-5-aminobenzimidazole (APBI) and flexible 4,4′-oxydianiline (ODA) by polycondensation with dianhydride 3,3′,4,4′-biphenyltetracarboxylic dianhydride. The contents of APBI ranged from 10 to 60 mol % in copolyimides. The copolyimide films obtained by thermal imidization of poly(amic acid) solutions, were characterized by TMA, DMA, TGA, DSC, wide-angle X-ray diffraction, FTIR, tensile testing, water uptake (WU), and dielectric constant measurements. Rigid heterocyclic diamine APBI with interchain hydrogen bonding capability, led to low coefficient of thermal expansion (CTE), high T_g, high thermal stability and better mechanical properties. Increasing the APBI mol % caused a gradual decrease in the CTE and increase in T_g, thermal stability and tensile strength properties of the copolyimides films. Moreover, significantly enhanced thermal and mechanical properties of the block copolyimides were also found as compared to random copolyimides. The block copolyimide with APBI content of 60 mol %, achieved excellent properties, that is, a low CTE (4.7 ppm/K), a high T_g at 377°C, 5% weight loss at 562°C and a tensile strength at 198 MPa. This can be interpreted because of comparatively higher degree of molecular orientation in block copolyimides. These copolyimides also exhibited better dielectric constant and WU. This combination of properties makes them attractive candidates for base film materials in future microelectronics. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

A series of copolyimides were prepared by incorporating pyromellitic dianhydride (PMDA) into the homopolyimide derived from 5,4′-diamino-2-phenyl benzimidazole (DAPBI) and 3,3′,4,4′-biphenyl tetracarboxylic dianhydride (s-BPDA), with the purpose of enhancing backbone rigidity of the homopolyimide. A systematic change in thermal, mechanical and optical properties was observed by changing the ratios of PMDA and s-BPDA components. Glass transition temperatures were in the range of 404–425°C, depending on the pyromellitimide content. Mechanical properties were significantly enhanced: Tensile modulus and strength ranged from 5.8 to 8.5 GPa and 249 to 263 MPa, respectively, and much higher than that of the homopolyimide (s-BPDA/DAPBI). Wide-angle X-ray diffractions showed that the copolymer films were amorphous, although locally ordered regions were observed with long periodicity larger than that of the homopolyimide. The properties enhancement was attributed to the increased overall rigidity of the polymer backbones and enhanced molecular in-plane orientation. Possible structure–property relationships were also discussed. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 1653–1658, 2013

BACKGROUND: Recently, much work has focused on the efficient dispersion of carbon nanotubes (CNTs) throughout a polymer matrix for mechanical and/or electrical matrices. However, CNTs used as enhancement inclusions in a high-performance polymer matrix, especially in poly(aryl ether ketone) (PAEK), have rarely been reported. Therefore, multi-walled carbon nanotube (MWNT)-modified PAEK nanocomposites were synthesized by in situ polymerization of monomers of interest in the presence of pre-treated MWNTs.

RESULTS: This process enabled a uniform dispersion of MWNT bundles in the polymer matrix. The resultant MWNT/PAEK nanocomposite films were optically transparent with significant mechanical enhancement at a very low MWNT loading (0.5 wt%).

CONCLUSION: These MWNT/polymer nanocomposites are potentially useful in a variety of aerospace and terrestrial applications, due to the combination of excellent properties of MWNTs with PAEK. Copyright © 2009 Society of Chemical Industry

BACKGROUND: Recently, much work has focused on the efficient dispersion of carbon nanotubes (CNTs) throughout a polymer matrix for mechanical and/or electrical enhancement. However, there are still only few reports about gradient distribution of CNTs in polymer matrices. In the work reported here, CNTs embedded in a polymer film with a gradient distribution were successfully obtained and studied.

RESULTS: For composite films with gradient distributions of CNTs, the upper surface behaves as an intrinsic insulator, while the lower one behaves as a semiconductor, or even as a conductor. It is also found that with an increase of 1 wt% CNTs, the resistance of the bottom surface decreases by 2–3 orders of magnitude, as compared with pure polyarylene ether nitrile; furthermore, when the proportion of CNTs increases up to 5 wt%, the resistance of the bottom surface shows only very little change. As a result, sufficient matrix conductivity of the bottom surface could be achieved at a lower filler concentration with CNTs in a gradient distribution. Meanwhile, the thermal stability, glass transition temperature and tensile properties of the matrix are maintained.

CONCLUSION: There is considerable interest in such gradient composite films, which could be applied in the electrical engineering, electronics and aerospace fields, for their excellent mechanical properties, thermal stability and novel electrical properties. Copyright © 2008 Society of Chemical Industry