Synthesis of single chain polymer nanoparticle networks by reinitiating RAFT polymerization

Hydrogel materials, which are polymer networks comprised mostly of water, hold significant promise for biomedical applications due to their compatibility with biological systems. Conventional hydrogel materials are often brittle and weak, but most applications in biomedical systems require materials to be strong and tough. The topology of a polymer network dictates its mechanical properties. An important strategy for designing tougher hydrogels is the release of stored length, such as from the unfolding of polyprotein cross-linkers. Inspired by the success of the strategy, we report progress towards a fully synthetic design using single chain nanoparticles (SCNPs) into a hydrogel. SCNPs, which have been widely studied for their protein mimetic functions, have shown to store and release stored length under mechanical force or in response to a stimulus in solution. We hypothesize that SCNPs can be incorporated into a polymer network to provide a strengthening mechanism due upon unfolding. Our strategy is to prepare SCNPs through reversible addition-fragmentation chain-transfer (RAFT) polymerization using bifunctional chain-transfer agents, and reinitiating polymerization to synthesize networks from the chain ends. We report on successful synthesis of bifunctional chain-transfer agents, synthesis of macromolecular chain-transfer agents (macro-CTA), reinitation of RAFT polymerization to elongate polymer chains, and synthesis of polymer networks through reinitiating RAFT polymerization. In the future, following this methodology SCNP macro-CTA will be synthesized and incorporated into a hydrogel network material via the reinitiation of RAFT polymerization.