Polymerizable living free radical initiators as a platform to synthesize functional networks.

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Hutchison, J. B.; Stark, P. F.; Hawker, C. J. and Anseth, K. S.;
Chem. Mater.
17, 4789-4797.

Photopolymerizations of multifunctional monomers afford spatial and temporal control of cross-linked network formation whereas living radical polymerizations provide a means to synthesize well-defined architectures from monovinyl monomers. By combination of these technologies in a two-stage polymerization process, a novel method is developed to synthesize functional polymer networks, and supporting results are provided for preparing controlled polymer grafts within photo-cross-linked networks. To demonstrate the concept of internal grafting, an alkoxyamine living radical initiator (for nitroxide-mediated polymerization, NMP) and a tertiary bromide initiator (for atom-transfer radical polymerization, ATRP) were functionalized with a methacrylate group and either was copolymerized with mono- and divinyl methacrylic monomers during the initial network formation step. Activation of the living radical initiators within styrene-swollen networks resulted in controlled molecular weight polystyrene grafts covalently bound to the photo-cross-linked methacrylic networks. To demonstrate the applicability of this technology for synthesizing functional networks, hydrogels with nitroxide groups were first photopolymerized, and different concentrations of acetoacetoxy, (i.e., ketoester) functionality were subsequently grafted within the loosely cross-linked networks. When the grafted networks were swollen in aqueous solutions containing Fe3+, the cations coordinated with the grafted ketoester moieties. In general, this robust technology could be applied to a wide array of monomers and functional groups to control the chemical, physical, and mechanical properties of the final grafted network for application in sensors, catalysis, separations, and combinatorial chemistry platforms.