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

In this work, the effects of two different diamine monomers con­taining phosphine oxide on the thermal, mechanical and morphological pro­perties of copolyimides and their hybrid materials were investigated. The gas separation properties of the synthesized copolyimides were also analyzed. The two different diamine monomers containing phosphine oxide were bis(3-ami­nophenyl]phenylphosphine oxide (BAPPO) and bis[4-(3-aminophenoxy)phe­nyl)­phenylphosphine oxide ( m -BAPPO). In the synthesis of the copolyimides, 3,3′-diaminodiphenyl sulfone (3,3′-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. Furthermore, hybrid mat­erials containing 5 % SiO 2  were synthesized by the sol–gel technique. Fourier-transform infrared spectroscopy (FTIR) and  nuclear magnetic resonance  spec­tros­copy (NMR) confirmed the expected structures. Dynamic mechanical anal­ysis (DMA) demonstrated that the  m -BAPPO-based copolyimides had lower glass transition temperatures ( T g ) than the BAPPO-based ones. The thermal decom­position temperature of the  m -BAPPO-containing copolyimide without silica was shifted to a higher value. The moduli and strength values of the BAPPO diamine-containing copolyimide and its hybrid were higher than those of the  m -BAPPO-containing materials. Contact angle measurements showed their hydrophobicity. Scanning electron microscope (SEM) analysis showed the dis­persion of the silica particles in the copolyimides. These copolyimides may be used in the coating industry. The CO 2  permeability and the perm­selectivity were the highest, among the other values found in this study, when the  m -BAPPO-containing copolyimide in the absence of silica was used. The  gas permeabilities obtained from this work were in the decreasing order:  P CO 2 > P O 2  >  P N 2 .