Controlled Radical Polymerizations as a Tool to Tailor the Architecture and Fracture Properties of Polymer Networks

Soft materials find widespread use as elastomers and hydrogels because they can sustain large reversible deformations. These materials are constituted of polymer networks that rely on molecular friction to dissipate strain energy in the vicinity of cracks, and have an inherent trade-off between mechanical properties like stiffness and toughness. A strategy to circumvent this trade-off is to interpenetrate a stiff and highly crosslinked sacrificial network into a soft and extensible matrix, leading to a family of materials referred to as multiple-networks that dissipate a notable amount of energy by chain scission. Here, we investigated the role of sacrificial network architecture (i.e., homogeneity) on energy dissipation and fracture toughness of multiple-networks. The key result is that more homogeneous sacrificial networks, as enabled by controlled radical copolymerizations like RAFT, afford tougher multiple-networks than analogues synthesized by free radical copolymerization. Such control over the sacrificial network architecture and fracture properties of multiple-networks is essential for attaining stiffness and toughness in conditions where molecular friction is negligible like high temperatures or high water concentrations.