Free volume effects on the melt viscosity of low molecular weight poly(methyl methacrylate)

The zero-shear melt viscosity η 0 has been obtained for a series of low molecular weight PMMA fractions ( M ≲ 5000). The strong sensitivity of η 0 to M observed for these fractions is attributed to a depression of viscosity by an M n-dependent free volume effect. The Rouse model modified with a friction coefficient depending on M n is shown to describe the data adequately. The necessary free volume parameters were determined from the temperature dependence of viscosity for each fraction through fits to the WLF equation. The influence of the free volume associated with chain ends through the end-group composition is also discussed.