Characteristic Features of α and β Relaxations of Poly(diethyl fumarate) as the Poly(substituted methylene)

Abstract

Recently the β relaxation draws attention because it may act as a precursor of the α relaxation and potentially influences a wide range of properties. In many cases, the weak intensity of the β relaxation limits the experimental investigation. Herein, the β relaxation of poly(diethyl fumarate) (PDEF) using differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), and dielectric spectroscopy is investigated. Originating from the absence of methylene spacer in the main chain, polyfumarates possess an intense β relaxation. Unlike common vinyl polymers, PDEF shows two distinct steps in DSC measurement corresponding to α and β relaxations. Interestingly, the relative intensities of α and β relaxations depend on the thermal history. The β relaxation of PDEF obtained by dielectric spectroscopy at high temperature is similar to that of poly(methyl methacrylate) (PMMA). However, the β relaxation of PDEF follows the VFT equation rather than the Arrhenius equation at low temperatures. The analysis of PDEF/PMMA blend suggests the local orientation of PDEF chain plays a vital role in the intense β relaxation.