Viscoelastic behavior of poly(methyl methacrylate-co-methyl acrylate) random copolymer studied by dynamic mechanical analysis and nanoindentation

The viscoelastic behavior of poly(methyl methacrylate) (PMMA) homopolymer and poly(methyl methacrylate-co-methyl acrylate) random copolymers was characterized by dynamic mechanical analysis and nanoindentation. Differential scanning calorimetric results showed only one glass transition, indicating the random distribution of comonomers in the copolymers. The a relaxation temperature (T_α) and activation energy (H_α) decreased with increasing content of methyl acrylate monomers (C_MA%). The β relaxation temperature (T_β) also decreased whereas the activation energy (H_β) showed only small variations compared with H_α. Moreover, the indention displacement and creep compliance strongly depended on C_MA%. Two creep stages were found in the creep compliance curves.