Impact of Reversible Deactivation Radical Copolymerizations (RDRPs) on Gelation, Phase Separation, and Mechanical Properties of Polymer Networks

Polymer networks are widely used in engineering and biomedical applications because they can sustain large deformations. However, their mechanical properties, particularly at large strains, remain challenging to design within their molecular architecture through conventional synthetic methods, as these offer limited control over the kinetics and thermodynamics of gelation and, in turn, the connectivity of the polymers. In this work, we leverage recent advances in Reversible Deactivation Radical Copolymerizations (RDRPs) to tune the kinetics and thermodynamics of gelation and explore their impact on the molecular architecture and mechanical properties of polymer networks. We demonstrate that RDRPs lead to delayed gelation, phase separation, and softer and more extensible networks relative to conventional free radical copolymerizations. The reversible deactivation of the radical chain ends slows the kinetics of gelation, segregates the network precursors or clusters into cross-linker-rich and cross-linker-poor phases, and narrows the distribution of chain lengths within the polymers. This impact of the kinetics of gelation on the molecular architecture affects the load distribution among the constituent polymers and the interplay between the small- and large-strain mechanical properties. Overall, this work paves the way for rationally using polymer chemistry to design advanced polymer networks for emerging and more stringent applications.