Cooperative Segmental Motions in Ethyl Acrylate/Triethylene Glycol Dimethacrylate Copolymer Networks Studied by Dielectric Techniques

Abstract

The molecular dynamics of ethyl acrylate/triethylene glycol dimethacrylate (EA/TrEGDMA) copolymer networks on the overall composition range were investigated thoroughly by employing dielectric techniques: thermally stimulated depolarization currents (TSDC) and dielectric relaxation spectroscopy (DRS). Furthermore, di¿erential scanning calorimetry (DSC) was performed in order to investigate the thermal glass transition of these copolymers. The results show that, for low content of the TrEGDMA component, the overall dielectric behavior of the copolymers is dictated by the dynamics of PEA component, exhibiting the ¿cop relaxation process which is strongly a¿ected by the TrEGDMA moieties becoming broader and shifting to higher temperatures with increasing cross-linker (TrEGDMA) content. For the copolymer networks rich in TrEGDMA (w TE g 40 wt %), the overall dielectric behavior indicates that the dynamics of the dimethacrylate component dominates, resembling that of poly(n-alkyl methacrylates) in the sense that the temperature dependence of molecular relaxation processes presents a merging region where the local relaxation process of TrEGDMA,ßPTE, merges with the more cooperative¿cop process of the copolymers into an¿ßcop locally cooperative relaxation process. By increasing the EA content, the strength of ¿cop relaxation process enhances and simultaneously the merging region shifts to lower temperatures. The cooperative motions are signi¿cantly suppressed in the copolymers with TrEGDMA contents higher that 80 wt %. The copolymers present enhanced spatial heterogeneity the more TrEGDMA content, whereas no dynamic heterogeneity was detected.