We report the application of hydrogen atom transfer (HAT) towards the activation of labile C-H bonds to use as radical initiators, eliminating the need for more expensive and toxic alkyl halide initiators and catalysts (CuBr, (bromo)ethylbenzene) typically required for atom transfer radical polymerization (ATRP). An excited photocatalyst, Eosin Y, is used as a hydrogen atom abstractor on the selected initiator, creating a carbon-centered radical capable of addition across a vinyl monomer as the initiating step of a radical polymerization. Controlling propagation requires a reversible HAT (RHAT) process where the chain-end hydrogen represents the lowest bond dissociation energy (BDE) in the system. Establishing an equilibrium between the H-capped polymer chain and its active radical form requires consideration of the monomer type (due to the possibility of labile C-H bonds along the backbone) and an appropriate ratio of k<sub>act</sub> compared to k<sub>deact</sub> to afford a polymerization that is both controlled and feasible. BDE of both the initiator and polymer chain end will play an important role in optimizing this equilibrium. Not only will this new method of polymerization open the door to a more cost-effective and sustainable approach to controlled radical polymerization, but it will also allow for commodity plastics and polymers, such as unfunctionalized polystyrene, to act as initiators and produce branched copolymers, effectively recycling the original polymer.

C-H activation towards the preparation and modification of polymeric materials

ACS Spring 2022

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.