A dielectric relaxation study of the gamma-relaxation in tetramethylbisphenol A polycarbonate plasticized by tris(2-ethylhexyl) phosphate

Dielectric relaxation spectroscopy (DR) was employed to study the dynamics of glassy tetramethylbisphenol A polycarbonate (TMBPA-PC) containing variou s amounts of tris(2-ethylhexyl) phosphate (TOP) added as diluent molecules. The present data confirm that the gamma-relaxation dynamics, at constant f requency, shift to lower temperatures with increasing TOP content, an effec t observed for the first time by dynamic mechanical measurements. This beha vior of the gamma-relaxation in TMBPA-PC plasticized by TOP is to be contra sted with that in bisphenol A polycarbonate (BPA-PC) plasticized by TOP. In the latter case, the gamma-relaxation dynamics, at constant frequency, shi ft to higher temperatures with addition of TOP. These opposite trends of th e gamma-relaxation dynamics in two similar polycarbonates are surprising. H owever, the results can be rationalized by the coupling model.