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synopsisThe poly(buty1 methacrylate) studied is a polymer with a normal molecular weight distribution and a relatively low molecular weight close to M,, the critical molecular weight from the viscosity-molecular weight relation. The polymer was subjected to uniaxial extension and shear over a temperature range which included T,. It was found that in the region of T, an increase in applied stress is accompanied by a decrease both in the temperature shift factor u T and in the activation energy for relaxation and rupture of polymer melts. Close attention is given to the long-term durability of the polymer. As is expected in the temperature range below T,, its dependence on the stress is exponential, whereas at temperatures above T,. a power law fits the data. In the latter case a log-log plot of the long-term durability versus stress can be represented by two intersecting straight lines which can be replotted as a generalized straight line if the long-term durability values are normalized by the viscosity. MATERIALS AND METHODSPoly(buty1 methacrylate) (PBMA) was prepared by free-radical polymerization in a 10% solution of monomer in isopropyl alcohol. The polymer was reprecipitated before use. Its viscosity-average molecular weight IE was 'Dedicated to Professor F. R. Schwarzl on his 60th birthday.

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