Sulfone‐Containing polymers as high barrier materials

Abstract Three types of sulfone‐containing polymers, poly(carbonate‐sulfone)s, poly(ester‐sulfone)s, and poly(urethane‐sulfone)s, were characterized as high barrier materials. They were made by condensing sulfone‐containing diol, 1,3‐bis(3‐hydroxypropylsulfonyl)propane (Diol‐333), or 1,4‐bis(3‐hydroxypropylsulfonyl)butane (Diol‐343), with diphenyl carbonate, diphenyl esters, and diisocyanates, respectively. The incorporation of polar sulfone groups into polymer backbones increases the glass transition temperature of polymers in all cases; however, the increment is different with different functional linkages. The increments in polycarbonates and polyesters are higher than that in polyurethanes. This is because the interactions between carbonate or ester groups are much weaker than the interactions between sulfone groups, whereas the hydrogen bonding between urethane groups is comparable with the polar interaction between sulfone groups. The polymers were coated on 50‐μm‐thick Kapton films by solution casting and their permeabilities toward carbon dioxide were measured at 25°C using the ASTM D1434 volumetric method. The sulfone‐containing polymers have carbon dioxide permeability coefficients at least 50 times smaller than the corresponding polymers without sulfone groups. The carbon dioxide barrier properties of sulfone‐containing polymers are comparable with ethylene/vinyl alcohol copolymers (EVAL), which are commercial high barrier polymers. An isomer effect on polymer permeability was observed in the aromatic‐aliphatic poly(ester‐sulfone) series. The permeability coefficients of the aromatic‐aliphatic poly(ester‐sulfone)s decrease from terephthalate to isophthalate to phthalate, corresponding to the increase of chain flexibility above the T g . These results support the hypothesis that high chain flexibility in the rubbery state and a glass transition temperature above room temperature are two key factors that promote low permeability. © 1994 John Wiley & Sons, Inc.