Effect of Isomerism on Molecular Packing and Gas Transport Properties of Poly(benzoxazole-co-imide)s

A facile approach to synthesize poly(benzoxazole-co-imide)s without thermal rearrangement at high temperature is proposed. Poly(benzoxazole-co-imide)s with improved mechanical and solution-processable properties were prepared through polycondensation of 4,4'-(hexafluoroisopropylidene) diphthalic anhydride (6FDA) with three synthesized novel benzoxazole-containing diamines and a commercial diamine. These poly(benzoxazole-co-imide)s had high tensile strengths of 110.3122.0 MPa and good elongation at break of 11.926.3%, good thermal stability and high glass transition temperatures (T(g)s) of up 306 degrees C. The effect of chain isomerism on molecular packing and physical and gas transport properties of the poly(benzoxazole-co-imide)s was investigated. The para-connecting isomers exhibited higher molecular weights (M(w)s), better mechanical properties, higher T(g)s, higher chain packing order and better overall performance for CO2/CH4 and CO2/N-2 separations as compared to the corresponding meta-connecting ones. This study guides molecular architecture to improve particular membrane separation performance by introducing either para- or meta-connections into polymeric main chains.