Gas permeation properties of polyarylates synthesized with bromine‐ and methyl‐substituted bisphenols

The effect of bromine substitution on the bisphenol moiety is investigated in terms of the physical and gas permeation characteristics of the resulting polyarylates prepared with aromatic and naphthenic acids. A comparison of polyarylates based on tetrabromobisphenol‐A (TBrbisA) and tetramethylbisphenol‐A (TMbisA) shows that both substituents increase chain rigidity; however, bromine substitution increases packing density while methyl substitution reduces it. The tetrabromo substitution leads to high selectivities for small gases while the tetramethyl substitution leads to high permeabilities. In order to combine both high permeability and selectivity, both bromine and methyl substitutions were combined in the same polyarylate in two ways: (1) A copolymer based on TMbisA and TBrbisA and (2) a polyarylate based on dibromodimethylbisphenol‐A, (DBrDMbisA). These two hybrid polymers have intermediate permeabilities and higher selectivities than either TMbisA‐ or TBrbisA‐based polyarylates. The copolymer is more selective for CO2 while the polyarylate based on DBrDMbisA is more selective for He.