Dynamic mechanical and gas transport properties of blends and random copolymers of bisphenol‐A polycarbonate and tetramethyl bisphenol‐A polycarbonate

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Abstract
Dynamic mechanical and gas transport properties for homogeneous homopolymer blends and random copolymers of bisphenol‐A and tetramethyl bisphenol‐A polycarbonates (PC‐TMPC) were determined. The gas transport measurements were performed at 35°C for the gases He, H2, O2, Ar, N2, CH4, and CO2. The results show that the copolymers have lower permeability, apparent diffusion, and solubility coefficients than the blends. Permeability coefficients for blends follow a semilogarithmic ideal mixing rule while copolymers exhibit negative deviations from this. Specific volume measurements show that the free volume available for gas transport is slightly larger in copolymers than in blends of the same composition. These apparently contradictory results may relate to the differences in local mode chain motions observed for the copolymer and blend series. The γ relaxation processes in PC and TMPC seem to operate independently in the blends (no intermolecular coupling) while there is clear evidence for intramolecular coupling in the copolymers. © 1992 John Wiley & Sons, Inc.