Coagent-induced transformations of polypropylene microstructure: Evolution of bimodal architectures and cross-linked nano-particles

Polypropylene is transformed by simultaneous, radical-mediated chain scission and cross-linking to generate branched architectures. While macroradical fragmentation reduces the molar mass of the dominant chain population, cross-linking by triallyl trimesate (TAM) activation yields a minority population of hyper-branched chains that is less susceptible to molecular weight loss. This disparity in chain reactivity leads to bimodal molecular weight and branching distributions. Furthermore, a precipitation polymerization of TAM can proceed concurrently with PP branching to produce a low yield of cross-linked, TAM-rich nano-particles. The mechanisms through which unimodal composition and molecular weight distributions evolve toward a bimodal condition are discussed, along with the factors that lead to particle formation.