Melt viscosity characteristics of methacrylate–styrene copolymers



The activation energies of flow EA of methacrylate–styrene copolymers containing n-butyl, n-hexyl, n-heptyl, n-octyl, n-decyl, n-dodecyl, n-tridecyl, n-octadecyl, and cyclohexyl methacrylate have been investigated as a function of molecular weight, composition, and methacrylate monomer. Below a critical pendent group molar volume per chain unit (120 ± 10 ml Le Bas units), EA was found to increase with molar volume; and above this value, a decrease in EA was observed, reflecting a decrease in copolymer density. Copolymers with pendent group molar volumes per average chain unit of between 96 and 140 ml (Le Bas units) were found to exhibit sufficiently high EA values to render them suitable for use in thermoplastic and photothermoplastic devices with superior development and erasure rates, at temperatures which enabled the attainment of the development and erasure viscosities with a low expenditure of heat energy. Methacrylate–styrene copolymers with long-chain ester methacrylates (viz., n-decyl and n-dodecyl methacrylate) were found to exhibit critical molecular weights Mc below 3000; and Mc was found to decrease with increasing methacrylate tail length and methacrylate concentration. These Mc values correspond to critical chain lengths Zc below 45. Similar Zc values have been previously reported for acrylonitrile–methyl methacrylate copolymers30 and ethylene–propylene copolymers.28