Structural effect of monomer type on properties of copolyimides and copolyimide-silica hybrid materials

Abstract

In this work, the effect of two different diamine monomers, containing phosphine oxide, on thermal, mechanical and morphological properties of copolyimides and their hybrid materials was investigated. Gas separation properties of the synthesized copolyimides were also analysed. Two different diamine monomers with phosphine oxide were bis(3-aminophenyl) phenylphosphine oxide (BAPPO) and bis(3-aminophenoxy-4-phenyl) phenylphosphine oxide (m-BAPPO). In the synthesis of copolyimides 3,3?-diamino-diphenyl sulfone (DDS) was also used as the diamine, as well as 2,2?-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride (6FDA). Copolyimide films were prepared by thermal imidization. Hybrid materials containing 5 % SiO2 were synthesised further by sol-gel technique. The Fourier-transform infrared spectroscopy (FTIR), Nuclear magnetic resonance spectroscopy (NMR) confirmed the expected structure. Dynamic mechanical analysis (DMA) demonstrated that m-BAPPO based copolyimides had lower glass transition temperatures (Tg) than BAPPO based copolyimides. m-BAPPO containing copolyimide without silica shifted the thermal decomposition temperature to a higher value. The moduli and strength values of BAPPO diamine containing copolyimide and its hybrid were higher than those of m-BAPPO containing materials. The contact angle measurements showed the hydrophobicity. Scanning electron microscope (SEM) analysis exhibited the silica particles dispersion in the copolyimides. These copolyimides may be used in the coating industry. The CO2 permeability and the permselectivity were the highest among the other values in this study, when m-BAPPO containing copolyimide in the absence of silica was used. The gas permeabilities obtained from this work were in this decreasing order: PCO2 > PO2 > PN2.