Isomeric effects on thermal rearranged polymers: Synthesis, characterization, and gas separation study

Abstract

A new o-hydroxydiamine monomer, 3,3'-diamino-4,4'-dihydroxybiphenyl (i-HAB), has been synthesized with good yield and purity. This monomer has been polymerized with 6FDA, using two synthetic methods, to give o-hydroxypolyimides (POHIs) with good film-forming ability. The conversion from these polyimides to polybenzoxazoles (TR-PBOs) has been carried out at high temperature in solid state. It has been found that the thermal rearrangement produced a considerable increase in FFV. Their gas transport properties have been compared with the analogous polymers obtained from the commercial monomer, 3,3-dihydroxybenzidine (HAB). The TR-PBOs improved the gas permeability of their precursors polyimides. Isomerism seems not to play a main role in the POHIs separation properties but it is important in TR-PBOs. Finally, it can be concluded from this study that TR-PBOs formed from the monomer i-HAB showed excellent gas separation productivity.