Relaxation Behaviour of Poly(methacrylic acid) and Its Copolymers with 2-Hydroxyethyl Methacrylate

Abstract

A free-vibrating torsional pendulum was used to determine the temperature dependence of the storage and loss shear moduli of poly(methacrylic acid) (PMAAc), poly(2-hydroxyethyl methacrylate) (PHEMA) and their copolymers within the temperature range from −196 to 120°C. A decrease in the number of hydroxyethyl side chains per unit volume of polymer leads to a reduction of the low-temperature (γ) dispersion, which is simultaneously shifted toward lower temperatures. The intensity of the secondary (β1) dispersion increases with concentration of the carboxyl groups, while its temperature falls from 28°C for PHEMA to −20°C for PMAAc. Water causes a continuous decrease in temperature and an increase in the intensity of the secondary dispersion of PMAAc. The observed changes in molecular mobility in the glassy state are interpreted qualitatively as a consequence of changes in both steric hindrance and intermolecular interaction.