Investigation of pendant group and chain segment motions in P(MMA/BA) copolymers by thermally stimulated depolarization current

Poly(methyl methacrylate/butyl acrylate) [P(MMA/BA)] copolymers (M-eta similar to 2 x 10(5)) with different mass percentages of MMA were synthesized by the method of solution polymerization. Thermally stimulated depolarization current (TSDC) technique was used to investigate the effect of copolymerization on pendant group and chain segment motions. Three TSDC peaks were observed over the temperature range from 310 to 400 K. The highest temperature, rho peak originates from the detrapping of trapped charge carriers. The lower temperature, alpha peak corresponds to the glass transition. The activation energy of the alpha relaxation decreases from 1.2 eV for PMMA to 0.98 eV for MMA(75)/BA(25). In the fitting process, another peak, beta ', is separated on the low temperature side. The apparent energy barrier of the beta ' for PMMA is 0.80 eV. The beta ' relaxation is thought to correspond to the motion of pendant groups including intra-and inter-molecular interactions. All three peaks move to lower temperatures with an increase in BA component, and the activation energy for the alpha and beta ' relaxations also decreases with the increase of BA component in copolymers, indicating that the flexible side groups of BA have an effect of plasticization on the glass transition and motion of pendent groups. The temperatures of the alpha and beta ' peaks of P(MMA/BA) copolymers follow the Fox equation. Fitting results gives the alpha peak at 238 K and beta ' peak at 225 K for polybutyl acrylate (PBA).