Solid-State Blending of Polymers by Cryogenic Mechanical Alloying

Cryogenic mechanical alloying has been employed to blend poly(methyl methacrylate) (PMMA) with up to 25 wt% polyisoprene (PI) and poly(ethylene-alt-propylene) (PEP). Mechanical milling of the individual polymers reveals that their molecular and bulk properties depend sensitively on milling time, post-annealing and, for PMMA, temperature. Characterization of the as-milled blends by scanning transmission x-ray microscopy and transmission electron microscopy has demonstrated intimate (nanoscale) dispersions within the blends, with the degree of mixing increasing with increasing milling time. Phase domains as small as 10 nm are observed after alloying for 10 h. Post-annealing of the blends above the Tgof PMMA (which depends on milling time) induces morphological changes, which differ for blends containing PI and PEP. In blends composed of PEP, the fine dispersions gained as a result of milling are largely compromised. Conversely, PI crosslinking hinders molecular mobility so that the milling-induced nanoscale dispersions of PI in PMMA are, for the most part, retained even after long-term annealing at elevated temperatures.