Thermal induced structural rearrangement of cardo-copolybenzoxazole membranes for enhanced gas transport properties

We have successfully designed amendable polybenzoxazole materials with enhanced gas transport properties via incorporation of cardo moiety into thermally rearrangeable polymer chains. A series of cardo-copoly(hydroxyimide) have been synthesized by polycondensation of dianhydride with various molar ratios of two different ortho-functional diamine sources: 3,3′-dihydroxybenzidine (non-cardo) and 9,9-bis(3-amino-4-hydroxyphenyl)fluorene (cardo). The effect of cardo-containing diamine composition in the range of 5–50 mol% on the structural and gas transport properties of the copolybenzoxazole membranes have been systematically investigated in the present work. It is found that the incorporation of cardo group has increased the gas permeability significantly. Thermally rearranged copolybenzoxazole membrane with the addition of 10 mol% of cardo moiety has shown the largest enhancement in gas permeability. An increment of 3 times in CO2 permeability has been achieved as compared to the CO2 permeability in the non-cardo counterparts. The excellent features of the cardo-copolybenzoxazole shows a promising approach for the future cavity engineering in the field of high performance materials.