Synthesis of Loop Poly(Methyl Methacrylate) Brushes via Chain-End Postpolymerization Modification

Polymer brushes are typically densely grafted assemblies of polymer chains that are tethered via one end group to a solid substrate. Anchoring linear polymer chains via both end groups to a surface results in loop-type polymer brushes. Although loop polymer brushes have been shown to be able to outperform their linear, single-chain-end tethered analogues, for example, with respect to the prevention of biofouling or reducing friction, this brush architecture has received only relatively limited attention. Loop-type polymer brushes are mostly prepared following grafting-onto approaches using alpha,omega-heterobifunctional polymers. Grafting-from strategies, so far, have been rarely explored, but could further expand the range of accessible polymer molecular weights and brush grafting densities and allow the preparation of surface-attached polymer loops from a wider scope of monomers. This manuscript reports an alternative grafting-from strategy for the preparation of loop-type poly(methyl methacrylate) (PMMA) brushes. The strategy presented here starts with the preparation of linear polymer grafts using conventional surface-initiated atom transfer radical polymerization. The free chain-ends of the linear PMMA grafts are modified with an allyl group and subsequently subjected to a metathesis reaction to induce loop closure. The formation of the loop PMMA brushes was monitored by gel permeation chromatography analysis after cleavage of the polymer from the silica nanoparticles.