Chain segment motion, space charge and liquid-liquid transition in methyl methacrylate/butyl acrylate random copolymers

Four kinds of methyl methacrylate/butyl acrylate (MMA/BA) random copolymers with different mass fraction of 100/0, 90/10, 81/19 and 75/25 were synthesized by solution polymerization at certain temperature. Three kinds of relaxation peaks (α, ρ and τ peaks) were observed in TSDC spectra above room temperature. By varying polarization field, it has been identified that a peak is attributed to the motion of chain segment, ρ peak is originated from the release of space charge, and τ peak is corresponding to liquid-liquid transition. With the increase of BA component, three peaks all move to lower temperature, indicating that flexible side group of butyl acrylate not only has an effect of plasticization on the glass transition and the liquid-liquid transition, but also makes the trap depth shallower and the occurrence of detrapping process easier. In addition, the increase of BA component has a remarkable effect on the intensity of τ peak, showing a special polarization mechanism for the liquid-liquid transition.