Enhancement of Gas Selectivities of Hexafluoroisopropylidene-Based Polyimides with Poly(Methylmethacrylate) Blending

Abstract

To enhance poor gas selectivity of polyimides based oil hexafluoroisopropylidene diphthalic anhydride (6FDA), such as 6FDA-4,4'-hexafluoroisopropylidene diamine (6FDA-6FpDA) and 6FDA-6FpDA:diaminobenzoic acid (6FDA-6FpDA:DABA), membranes were fabricated from their blends with poly(methylmethacrylate) (PMMA). The resulting polyimides formed homogeneous mixtures with PMMA, regardless of the blend compositions. The miscible blends underwent phase separation upon heating due to the lower critical solution temperature phase behavior. The phase separation temperature of the 6FDA-6FpDA/PMMA blend was greater than that of the 6FDA-6FpDA:DABA/PMMA when the composition was fixed. Adding a small amount of PMMA dramatically increased the gas selectivity of the membrane. In addition, the gas selectivity of most blends was better than that of pure PMMA. The membranes showed performance advantages for the trade-off trend between gas permeability coefficient and selectivity.