Effect of fluorene‐bisphenol ring substitution and bridge rigidity on physical and gas permeation properties of resulting polyarylates

This study reveals gas permeability and related physical properties of aromatic polyesters prepared from fluorenone‐based bisphenols and an equimolar mixture of isophthalic and terephthalic acids. Effects of a rigid bridge group at these bisphenols were examined. Bisphenol phenyl rings were also substituted in an asymmetric substitution manner (the two positions ortho to —OH contained different groups) in dimethylfluorene bisphenol (DMFBP) and dibromodimethylfluorene bisphenol (DBrDMFBP). Polyarylates prepared using these bisphenols were studied for gas permeation with reference to the effects of bridge rigidity and asymmetric substitution by polar bromine and non‐polar methyl groups. Glass transition temperature and estimated fractional free volume were varied by incorporation of rigid 9,9′‐fluorenylidene group. An increase in gas permeability was associated with a similar or general decrease in selectivity of various gas pairs. This behaviour was attributed mainly to the rigid but flat group situated at the bridge position of the bisphenol moiety.