Synthesis of Bottlebrush Polymers via Transfer-To and Grafting-Through Approaches Using a RAFT Chain Transfer Agent with a ROMP-Active Z-Group
A novel dithiocarbamate chain transfer agent (CTA1) with a directly polymerizable Z-group was synthesized for use in reversible addition_fragmentation chain transfer polymerization (RAFT). This CTA effectively mediated RAFT polymerization of styrenic and acrylic monomers with dispersities (_) < 1.08. Utilizing the polymerizable Z-group on the _-chain end that is inherited from the RAFT process, bottlebrush polymers were synthesized via ring-opening metathesis polymerization (ROMP) in a grafting-through process. The effect of a number of parameters on the grafting process was studied, and optimized conditions yielded bottlebrush polymers of controllable molecular weights, narrow molecular weight distributions, and high conversions (>90%). Bottlebrush polymers made by a transfer-to strategy were also synthesized from CTA1. In this case, ROMP was first carried out to produce poly(CTA1) (PCTA1), then RAFT was performed from the PCTA1 backbone. This technique allows for the preparation of high molecular weight bottlebrush polymers without radical coupling between bottlebrush polymers. Lastly, regardless of the synthetic method, all bottlebrush polymers produced using CTA1 are composed of polymeric side chains that are attached to the bottlebrush backbone through a labile dithiocarbamate linkage that can be cleaved in the presence of nucleophiles such as amines. The unique combination of these capabilities allows for the study of bottlebrush polymer formation by both transfer-to and grafting-through strategies using a single agent.