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Employing a Sugar-Derived Dimethacrylate to Evaluate Controlled Branch Growth during Polymerization with Multiolefinic Compounds

Pal, Sunirmal, Brooks, William L. A., Dobbins, Daniel J., Sumerlin, Brent S.
Macromolecules 2016 v.49 no.24 pp. 9396-9405
chemical structure, copolymerization, molecular weight, polyethylene glycol
Radical copolymerization of divinyl monomers in the presence of chain transfer agents leads to soluble hyperbranched polymers. In this work, hyperbranched poly(poly(ethylene glycol) methyl ether methacrylate) (PPEGMA) with degradable cross-linker branch points derived from glucarodilactone methacrylate was prepared via reversible addition–fragmentation chain transfer (RAFT) polymerization to provide insight into hyperbranch formation during copolymerizations of multiolefinic compounds. The number-average molecular weight of the polymers increased nonlinearly with monomer conversion, implying that the incorporation of the divinyl cross-linker led to chain branching and a rapid increase in molecular weight at high conversion. The degree of branching was varied by controlling the feed ratio of monomer to cross-linker to chain transfer agent. Hydrolytic degradation of the sugar-derived dilactone branch points was examined under acidic, neutral, and basic aqueous conditions. To provide fundamental insight into the growth of primary chains during RAFT polymerizations of multiolefinic compounds, the resulting hyperbranched polymers were subjected to cross-link cleavage to obtain linear polymers. The molecular weights of the resulting polymer segments were similar to the theoretical molecular weights expected for linear analogues prepared with similar ratios of monomer to RAFT agent. Not only does this approach lead to new examples of degradable polymers with complex architectures, but also to important mechanistic insights into hyperbranch formation via polymerization of multiolefinic compounds.