One of the more interesting applications of Reversible Addition-Fragmentation Chain Transfer (RAFT) chemistry is the ability to functionalise vinyl polymerisation reactions with specified chain end functional groups. Recent research by Rimmer et al. using a branching RAFT agent combined with high concentrations of radical initiators form highly branched stimuli-responsive soluble polymer particles. These are semi-soluble materials that, when a stimuli responsive monomer is used, have some remarkable biological applications. This talk reviews the known reaction conditions and variables that influence the resultant polymer properties. A 15-25 branch to 1 monomer ratio produces high molecular weight materials (Mn commonly above 500,000 g mol-1) with bimodal size distributions (due to there being a dispersity both in polymer mass and branching). The low molar mass chains are highly branched with Mark-Houwink alpha values &lt; 0.5 indicating they act as hard spheres in solution. The higher molar mass chains are relatively less branched, with greater solution viscosities, but still possess many functionalizable chain ends. The lower molar mass component can be isolated or removed via ultrafiltration to produce unimodal low dispersity materials that can be tailored for a range of biomedical interactions. Work using these polymers compared to linear analogues has shown that linear architectures are often unsuitable for biological binding – as attaching a ligand along the polymer chain reduces the binding affinity of the ligand. Functionalising the chain end however leaves the binding site ready to attachment – and the stimuli-responsive properties of the highly branched polymer increase its biological affinity. These materials have a broad thermal response and partially desolvate upon binding – the macromolecular reconfiguration increasing the binding strength of the chain end ligand. These properties are unique to this highly-branched polymer architecture. We propose several applications unique to the highly branched structure that is distinct from comparative crosslinked or hyper-branched analgoues.

Highly branched, self-condensing vinyl polymerisation via reversible addition-fragmentation chain transfer with a comparatively high initiator loading: Review of material properties

2019 Fall National Meeting

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