Graft Copolymers for Blend Compatibilization: Mathematical Modeling of the Grafting Process

The grafting of PE onto PS through a Friedel‐Crafts reaction, which results in a mixture of PE‐g‐PS copolymer, unmodified PE, and modified PS, is investigated. The copolymer may be suitable for compatibilization of immiscible mixtures in the household plastic waste stream, where PE and PS are majority components. Since the compatibilization effect depends on the composition and block lengths in the copolymer, a model is presented for predicting the complete molecular weight distribution of the homopolymers and the chemical composition distribution of the graft copolymer. The model has potential for application in an optimization tool for the compatibilization process, as it is able to account for the opposing effects of competing reactions that characterize the graft reaction. The operating conditions that favor grafting of PE on PS through a Friedel‐Crafts reaction also promote an undesired side reaction, the degradation of PS. This results in nontrivial molecular‐weight and chemical‐composition distributions. A mathematical model is presented that is capable of predicting both in good agreement with available experimental data.