Controlled synthesis of hyperbranched polymers by slow monomer addition to a core

Continuous, slow addition of AB(2) monomer (3,5-diiodophenylacetylene) to a solution of a multi-functional core results in high molecular weight hyperbranched phenylacetylene polymers with narrow polydispersites. Control over the molecular weight (M-w = 8-90 kDa) was achieved by varying the monomer:core ratio from 17.5 to 560, At low ratios (<140, M-w = 49 kDa), monomodal molecular weight distributions were observed by SEC. A bimodal distribution was observed at higher ratios. Using an azobenzene functionalized core, in combination with SEC photodiode array detection, it was found that the core was not uniformly distributed over the entire bimodal distribution but rather predominantly found in the high molecular weight part of the distribution. The polydispersities of the hyperbranched polymers were found to decrease with increasing degree of polymerization and with increasing core functionality. Our experimental results are in good qualitative agreement with computer simulations reported by Frey et al. and the theoretical work of Muller.