Segmental Dynamics in net -poly(methyl methacrylate)- co -poly(n-butyl acrylate) Copolymer Networks

Abstract

Dynamic mechanical spectroscopy and differential scanning calorimetry investigations of segmental dynamics are reported for net-poly(methyl methacrylate)-co-poly(n-butyl acrylate) copolymer networks. Three characteristic temperatures, namely, Vogel (T∞), glass transition (T g ), and crossover (T c ), were used to define cooperativity range and a new reduced temperature parameter (Solidness, S). The results showed that broadness of the α -dispersion (glass transition) and cooperativity length scale at the glass transition temperature decreased with increasing butyl acrylate content and T g -scaled temperature dependence of the relaxation time (fragility). However, the cooperativity range (T c –T∞), decreased with increasing fragility index. Furthermore, the solidness at T g (S(T g )) was nearly independent of chemical structure of the samples. Finally, a correlation was found between two measures of cooperativity length scale in the glass transition region, namely, average volume of cooperatively rearranging regions, V CRR , and the number of basic units in an act of rearrangement in the glass transition region, Z(T g ), determined from two completely independent experimental techniques.