Visualization of Polymer Chain Scission during Melt Processing Using a Mechanochromic Probe

Abstract

We thoroughly investigated polymer chain scission occurring through thermal and mechanical degradation during kneading via complex viscosity, torque, shear stress, and feeding rate measurements. We visualized polystyrene chain scission using a diarylacetonitrile derivative (DAAN− triOMe/triOMe) that can react with mechanoradicals to generate the corresponding fluorescent DAAN−triOMe/triOMe radicals. We kneaded polystyrene containing 5 wt % DAAN−triOMe/triOMe at various screw speeds and kneading temperatures using a twin-screw kneader. The results reveal that changes in complex viscosity and fluorescence intensity are correlated, indicating polystyrene chain scission and free radical generation. Mechanochromic behavior was also associated with heat-induced polymer deformation. Furthermore, the complex viscosity decreased with increasing speed and temperature. The analyses of torque, shear stress, and feeding rate revealed intricate relationships between speed, temperature, and polymer chain scission. This study highlights the effectiveness of DAAN−triOMe/triOMe in visualizing polymer chain scission using color change during both at-line and offline observations.