An in situ matrix functionalization approach to structure stability enhancement in polyethylene/montmorillonite nanocomposites prepared by intercalative polymerization

This paper discusses a strategy of enhancing the structure stability of polyethylene/montmorillonite (PE/MMT) nanocomposites prepared by intercalative polymerization technique. The chemistry centers on an in situ, controlled PE matrix functionalization that is made possible by engaging a reactive comonomer in the intercalative polymerization process to intentionally anchor in the formed PE matrix ready-to-functionalize reactive groups. Thus, ethylene polymerization was conducted in the presence of p-methylstyrene (p-MS) using an OMMT (organically modified MMT)-intercalated metallocene catalyst (Et[Ind]2ZrCl2 in combination with MAO), resulting in p-MS-containing PE/OMMT nanocomposites. Subsequent functionalization of the PE matrix then facilely and selectively occurred on the benzyl group in the p-MS unit, including a free radical maleation reaction and a butyllithium-initiated metallation reaction which was followed by an anionic graft-from polymerization of methyl methacrylate (MMA), under very mild reaction conditions. The in situ-incorporated functional groups, including the pendant maleic anhydride groups and the polar poly(methyl methacrylate) (PMMA) side chains, significantly improved miscibility between the PE matrix and laminated silicate layers of MMT, leading to effective stabilization of the nanocomposite structure against processing.