Dielectric relaxation and glassy dynamics in poly(diisopropyl fumarate) and its copolymers with acrylate segments

Abstract

Dynamical behavior and glass transitions in copolymers of diisopropyl fumarate (DiPF) with 1-adamantyl acrylate (AdA) or n-butyl acrylate (nBA) are investigated by dielectric relaxation spectroscopy (DRS) to elucidate the effect of structural constraint due to the absence of a CH2 spacer on the dynamics. DRS measurements revealed that the two copolymers exhibit three dynamical processes: α-, β-, and γ-processes. The relaxation time of the β-process can be described by the Vogel-Fulcher-Tammann (VFT) law in addition to the α-process. Hence, two glass transition temperatures, Tg, can be evaluated from α- and β-processes. The AdA and nBA fraction dependence of Tgs is consistent with that obtained by dynamical mechanical analysis. The Vogel temperature of the α-process is nearly equal to that of the β-process for the PDiPF homopolymer. With the increase in the AdA fraction, the difference in the Vogel temperature between the α- and β-processes increases. This result suggested that there is an intrinsic correlation between the α- and β-processes for PDiPF, and the correlation changes with the AdA fraction. From the nBA fraction dependence of the β-process, the β-process of PDiPF can be related to the segmental motion of the main chain. Nevertheless, PDiPF exhibits a solid-like property up to the Tg, which is related to the α-process. The physical origins of other processes also were discussed.