Influence of Grafting Density on Ultrasound-Induced Backbone and Arm Scission of Graft Copolymers

The influence of grafting density on polymer conformations and ultrasonic degradation of polynorbornene-g-polystyrene (PS) or poly(methyl acrylate) (PMA) graft copolymers was explored. Multi-angle light scattering analysis, atomic force microscopy imaging, and molecular dynamics simulations supported that graft copolymers exhibited increased backbone and arm extension and increased arm-arm interactions at higher grafting density. In regard to backbone scission, faster scission rates were observed at higher grafting density, which was further supported by the generation of master curves that account for the rate enhancement due to the polymer being in an extended conformation. The grafting density also influenced arm scission rates, with PS and PMA arms exhibiting opposite trends. Specifically, arm scission was faster for PS at higher grafting density and faster for PMA at lower grafting density, which was attributed to differences in arm extension and arm-arm interactions between the two arm types.