Correlation between Gas Diffusion Coefficient and Positron Annihilation Lifetime in Polymers with Rigid Polymer Chains

Diffusion coefficients D of CO 2 and CH 4 and lifetimes of orthopositronium (o-Ps) τ 3 were measured at temperatures from 308 to 473 K for polyimides, a polybenzoxazole, and poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) with high glass transition temperatures T g 's above 488 K. The plots of log( D / T ) and τ 3 for these polymers at 308 K were below the correlation line observed for polymers with relatively low T g 's at temperatures from T g − 90 K to T g + 70 K and interpreted by the free volume theory for diffusion. The lower D values for these high- T g polymers were attributed to the restricted local motion of their polymer chains. With increasing temperature, the plots for PPO and a polyimide became close to the correlation line.