GAS PERMEATION PROPERTIES OF POLYARYLATES SYNTHESIZED WITH BROMINE-SUBSTITUTED AND METHYL-SUBSTITUTED BISPHENOLS

The effect of bromine substitution on the bisphenol moiety is investig ated in terms of the physical and gas permeation characteristics of th e 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 incre ase chain rigidity; however, bromine substitution increases packing de nsity while methyl substitution reduces it. The tetrabromo substitutio n leads to high selectivities for small gases while the tetramethyl su bstitution leads to high permeabilities. In order to combine both high permeability and selectivity, both bromine and methyl substitutions w ere combined in the same polyarylate in two ways: 1) A copolymer based on TMbisA and TBrbisA and 2) a polyarylate based on dibromodimethylbi sphenol-A (DBrDMbisA). These two hybrid polymers have intermediate per meabilities and higher selectivities than either TMbisA- or TBrbisA-ba sed polyarylates. The copolymer is more selective for CO2 while the po lyarylate based on DBrDMbisA is more selective for He.