Molecular Weight Dependence of Viscosity Compensation Effect for Non-Newtonian Viscous Flow in Poly(methyl methacrylate) Glass

Molecular weight dependence of viscosity compensation effect for non-Newtonian flow in polymer glasses was studied using low and high molecular weight poly(methyl methacrylate)(PMMA) glass samples: the weight-averaged molecular weight MW was 82 × 103 for the former sample, whereas MW = 3380 × 103 for the latter. The compensation effect functions obtained from steady viscous flow in the samples were slightly different, yet the functions were almost the same straight line in a range of low activation energy values of molecular rearrangement. An experimental point obtained from a PMMA melt sample at temperatures much higher than the glass transition temperature was rightly on the straight line for the glasses. This implies that the structures of low and high molecular weight glass samples flowing at low temperatures far below the glass transition temperature and high strain rates are identical with the equilibrium structure of the melt at temperatures much higher than the glass transition temperature.