The structure of randomly branched polymers synthesized by living radical methods

Abstract

We present a new versatile model for the description of randomly branched polymers. Hyperbranched and highly branched polymers have many potential applications including viscosity modification, drug-delivery vehicles or supports for catalysts. Because of their complex architectures, it is difficult to visualize and describe the structure of randomly branched polymers. This work aims to introduce a new tool that will address this issue, by developing a model called kinetic random branching theory (KRBT). This new theory is based on random branching theory, optimized so that it is applicable to a wider range of polymers. In order to test the robustness of our model, we have considered three classes of branched polymers synthesized by radical polymerisation using the well-established ‘Strathclyde approach’, which is known to produce polymers of very complex structure. The three classes of polymer studied are methyl methacrylate, alternating styrene-maleic anhydride and divinyl benzene-only polymers, and in each case reversible addition-fragmentation chain transfer (RAFT) was used. We find that the majority of the polymer structures studied agree well with the predictions of our model, thus implying that they are indeed randomly hyperbranched polymers. The only case where the model failed to predict the structure of the polymer for a highly branched methyl methacrylate, synthesized to high conversions, in presence of an excess of brancher. This suggests that the sample is not a hyperbranched polymer, instead the polymers structure may be dominated by loops and cross-links such as in a nano-gel. By demonstrating the robustness of our model against these typical examples, we have established a new tool for characterising the structure of complex branched structures.