Secondary processes of poly(methyl methacrylate) and their activation energies as determined by shear and tensile creep compliance measurements

Abstract

AbstractThe results of measurement of the shear and tensile creep compliance of poly(methyl methacrylate) between −150 and 75°C. are presented. The master curves show the creep behavior from essentially elastic response to the onset of the α‐process. The logarithmic retardation spectra and shear loss compliance reveal two molecular processes, one process being partially obscured by the α‐process and therefore not as well defined as the other. These processes manifest themselves as breaks in an Arrhenius plot of the shift factors at about −35 and +25°C. The activation energies in the −35 to 25°C. and 25 to 80°C. ranges are 17.8 kcal./mole and 42.2 kcal./mole, respectively. The former temperature range and activation energy corresponds to the well‐known ß‐process in poly(methyl methacrylate), the latter to a process which is apparently detectable using various long‐time experimental techniques but whose molecular interpretation is at present obscure. The activation energy in the −150 to −35°C. range is about 8.7 kcal./mole.