Nanoparticles from Step-Growth Coordination Polymerization

Polymer nanoparticles have been studied intensely from a fundamental as well as applications oriented perspective. 1 They are prepared most often by free-radical polymerization in a nonsolvent for the polymer, usually water. In recent years, nonradical polymerization routes to aqueous polymer nanoparticle dispersions have found increased interest. 2,3 Coordination polymerizations in emulsion can offer access to nanoparticles of polymers with microstructures inaccessible by other polymerization mechanisms. A prerequisite is sufficiently waterinsensitive catalysts. To date, these catalytic nanoparticle syntheses have been restricted to chain-growth polymerizations. 3 Step-growth polymerizations are much slower, and the metal site leaves the growing chain after each addition of a repeat unit, such that a prolonged stability toward water of the metal species occurring during polymerization appears a necessity. Our interest in the latter reactions resulted from studies of conjugated polymer nanoparticles. Conjugated polymers can provide properties such as fluorescence, electroluminescene, or electrical conductivity. 4 They are key components for the development of, e.g., flexible displays, low-cost displays, or organic photovoltaics. Dispersions of conjugated polymer nanoparticles can contribute to resolve the notorious issue of processing of conjugated polymers, and they can improve control of composition of conjugated polymer blends on the nanoscale. 5