Branched Polymers Via Grubbs Catalyst

Using an olefin metathesis reaction and starting with easily synthesized monomers, Irina A. Gorodetskaya, Tae-Lim Choi, and Robert H. Grubbs at Caltech have synthesized hyperbranched polymers under mild conditions (J. Am. Chem. Soc., DOI: 10.1021/ja0759040). Hyperbranched polymers have a number of properties that make them more attractive for industrial applications than their linear analogs, including multiple end groups, better solubility, and differing viscosities. Dendrimers are an example of useful, symmetric, and monodisperse hyperbranched polymers, but their notorious reputation for labor-intensive and expensive syntheses often precludes their use. Other hyperbranched polymers demonstrate properties similar to dendrimers, but their syntheses require complicated monomers and harsh conditions. The Caltech researchers used a ruthenium catalyst (Grubbs second-generation catalyst) to initiate the acyclic diene metathesis polymerization. Monomers functionalized with two or more acrylate groups and one terminal olefin provided branched structures, which were confirmed by nuclear magnetic resonance spectroscopy and size-exclusion chromatography.