Segmental Relaxation Characteristics of Cross-Linked Poly(ethylene oxide) Copolymer Networks

The segmental relaxation characteristics of UV cross-linked networks based on poly(ethylene glycol) diacrylate [PEGDA] copolymerized with either poly(ethylene glycol) methyl ether acrylate [PEGMEA] or poly(ethylene glycol) acrylate [PEGA] were investigated using dynamic mechanical analysis. The molecular weights of the PEGDA cross-linker and acrylate comonomers were selected to obtain rubbery, amorphous membrane materials with constant ethylene oxide content. The introduction of PEGMEA or PEGA in the reaction mixture was used to control cross-link density and led to the insertion of flexible oligomeric branches within the resulting networks. For both copolymer series, the introduction of acrylate comonomer led to a decrease in glass transition temperature (Tg) and a systematic reduction in cross-link density; the downward shift in Tg was much more pronounced for the PEGDA/PEGMEA copolymers. Time−temperature superposition was used to construct modulus master curves across the glass transition, and these co...