Temperature‐induced morphological evolution in polymer blends produced by cryogenic mechanical alloying

Novel nanoscale morphologies are achieved in blends of poly(methyl methacrylate) (PMMA) and either polyisoprene (PI) or poly(ethylene-alt-propylene) (PEP) produced by high-energy mechanical alloying at cryogenic temperatures. Since the blends are prepared as solid powders, they must be post-processed in the melt to be of practical relevance. In this study, we employ scanning transmission X-ray microscopy (STXM), transmission electron microscopy (TEM) and light microscopy (LM) to investigate the stability of nanostructural features and the dynamics of phase coarsening at elevated temperatures (above the glass transition temperature of milled PMMA). Substantial coarsening is observed in PEP/PMMA blends at relatively short times, indicating that the two polymers are highly immiscible and mobile at the conditions examined. The nanostructure evident in PI/PMMA blends is, however, more robust and undergoes less evolution due to milling-induced PI crosslinking. Instead of forming discrete dispersions in a PMMA matrix, the PI molecules organize into a fine network morphology upon annealing in the melt.