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 α,ω-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.