Physical and Gas Transport Properties of Novel Hyperbranched Polyimide – Silica Hybrid Membranes

Summary

Physical and gas transport properties of novel hyperbranched polyimide – silica hybrid membranes were investigated. Hyperbranched polyamic acid as a precursor was prepared by polycondensation of a triamine monomer, 1,3,5-tris(4-aminophenoxy)benzene (TAPOB), and a dianhydride monomer, 4,4’-(hexafluoro-isopropylidene)diphthalic anhydride (6FDA), and subsequently modified the end groups by 3-aminopropyltrimethoxysilane (APTrMOS). The hyperbranched polyimide – silica hybrid membranes were prepared using the polyamic acid, water, and tetramethoxysilane (TMOS) via a sol-gel technique. 5 % weight-loss temperature and glass transition temperature of the hyperbranched polyimide – silica hybrid membranes determined by TG-DTA measurement considerably increased with increasing silica content, indicating effective cross-linking at polymer – silica interface mediated by APTrMOS moiety. CO₂, O₂, and N₂ permeability coefficients of the hybrid membranes increased with increasing silica content. It was pointed out that the increased gas permeabilities are mainly attributed to increase in the gas solubilities. On the contrary, CH₄ permeability of the hybrid membranes decreased with increasing silica content because of decrease in the CH₄ diffusivity and, as a result, CO₂/CH₄ selectivity of the hybrid membranes remarkably increased. It was concluded that the 6FDA-TAPOB hyperbranched polyimide – silica hybrid membranes have high thermal stability and excellent gas selectivity, and are expected to apply to a high-performance gas separation membrane.