Decoupling Mechanical Performance and Macrophase Morphology in Compatibilized Polymer Blends

Abstract Recycled plastics suffer from inferior performance due to sorting errors, which limits their commercial adoption. Macromolecular compatibilizers have long been proposed to alleviate embrittlement from imperfect sorting, but compatibilizer cost and varying efficacy limit commercial adoption despite the plethora of compatibilizers reported. In this work, we present a modular C–H activation and click chemistry approach to systematically probe the influence of architectural details of graft copolymers on their efficacy to improve the ductility of polyethylene (HDPE) with dispersed polystyrene (PS) as a model plastic waste. For these compatibilized blends, mechanical performance does not correlate with the size of the dispersed PS phase; moreover, the same compatibilizer can increase or decrease the ductility of identical composition of HDPE/PS blends, where only the molar masses of the matrix and dispersed phase are changed. This sensitivity to ductility is hypothesized to be associated with selection of the dispersed PS and its molar mass dependence of the ductile-to-brittle transition. Increasing the molar mass of the PS grafts of the graft copolymer tends to improve the compatibilization and mechanical performance more effectively than increasing the number of grafts. The sensitivity of compatibilizer performance to the plastic recyclate molar masses demonstrates the value in examining potential compatibilizers against a broad swath of model recyclate to confirm general efficacy.