Preparation of hyperbranched polymers by atom transfer radical polymerization

A cheap acrylic AB* monomer, 2-(2-chloroacetyloxy)-isopropyl acrylate (CAIPA), was prepared from 2-hydroxyisopropyl acrylate with chloroacetyl chloride in the presence of triethylamine. The self-condensing vinyl polymerization by atom transfer radical polymerization (ATRP), a "living"/controlled radical polymerization, has yielded hyperbranched polymers. All the polymerization products were characterized by proton nuclear magnetic resonance spectroscopy (H-1 NMR). CAIPA exhibited distinctive polymerization behavior that is similar to a classical step-growth polymerization in the relationship of molecular weight to polymerization time, especially during the initial stage of the polymerization. However, a significant amount of monomer remained present throughout the polymerization, which is consistent with typical chain polymerization. Also, if a much longer polymerization time was used, the polymer became gel. As a result of the unequal reactivity of group A* and B*, the polymerization is different from an ideal self-condensing vinyl polymerization: the branch structures of polymers prepared depend dramatically on the ratio of 2,2'-bipyridyl to CAIPA. Hyper-branched polymers exhibit improved solubility in organic solvent, however, they have lower thermal stability than their linear analogs. (C) 2002 John Wiley Sons, Inc.