Mass and momentum transfer in polymers. I. Effects of equilibrium vapor sorption on tensile creep of an amorphous polymer

Abstract

AbstractDiffusion and tensile creep measurements were made for systems of poly(‐n‐butyl methacrylate) (PBMA) and sorbed ethanol, MEK, or benzene at 23°C. Rates of penetration of an inert spherical indenter into PBMA also were investigated and compared with the tensile creep behavior of the polymer. Creep measurements for various volume fractions of penetrant sorbed at equilibrium revealed that master curves, resulting from a time‐concentration superposition procedure, could be constructed for each penetrant. At long times, these master curves, particularly that for ethanol, show deviations from the corresponding time‐temperature superposition master curve. These deviations are interpreted in terms of probable long‐range entanglement coupling governed in part by the partially specific nature of polymer‐penetrant interactions. Parameters calculated by a free‐volume theory, describing both diffusion and tensile‐creep data, indicate that MEK is a more efficient plasticizing agent than the other penetrants and requires less local free volume for diffusion. Analysis in terms of the free volume concept was not attempted for the case of ethanol, where specific polymer‐penetrant interactions are more important.