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    Molecular Imaging and Analysis of Branching Topology in Polyacrylates by Atomic Force Microscopy

    Year: 2011

    Journal: Macromolecules, 2011, 44 (15), 5928–5936, 20131009

    Authors: Sherryl Y. Yu-Su, Frank C. Sun, Sergei S. Sheiko, Dominik Konkolewicz, Hyung-il Lee, Krzysztof Matyjaszewski

    Organizations: Department of Chemistry, The University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599-3290, United States; Center for Macromolecular Engineering, Department of Chemistry, Carnegie Mellon University, 4400 Fifth Avenue, Pittsburgh, Pennsylvania 15213, United States

    Molecular imaging by AFM provides direct and quantitative information about branching topology including length and distribution of branches, not accessible by other methods. In this paper, we report the analysis of branching in linear acrylate-based macromolecules synthesized via free radical polymerization (FRP) and atom transfer radical polymerization (ATRP). The branched structures are formed from chain transfer reactions, specifically transfer to polymer. Quantitative analysis showed that both methods produced branched species, with FRP having degree of branching of 0.035 ± 0.003% and ATRP having a degree of branching of 0.025 ± 0.002%, when measured per backbone repeat unit. The observed lower branching density in ATRP compared to FRP is consistent with a recent 13C NMR study, which also found that controlled radical methods, such as ATRP give lower degrees of branching than FRP. The absolute fraction of long chain branches measured by AFM is significantly lower than the total amount of branches evaluated by measurement of fraction of quaternary carbons using 13C NMR, indicating a predominant intramolecular chain transfer.