Toughening Healable Supramolecular Double Polymer Networks Based on Hydrogen Bonding and Metal Coordination.

Double polymer networks (DNs) consist of two interpenetrating polymer networks and can offer properties that are not merely a sum of the parts. Here, we report an elastic DN made from two supramolecular polymers (SMPs) that consist of the same poly(n-butyl acrylate) (BA) backbone. The two polymers feature different non-covalent binding motifs, which form dynamic, reversible cross-links. The polymers were prepared by reversible addition-fragmentation chain-transfer polymerization of n-butyl acrylate and either the self-complementary hydrogen-bonding motif 2-ureido-4[1H]pyrimidinone, or the 2,6-bis(1'-methylbenzimidazolyl)pyridine ligand, which forms complexes with metal ions. The supramolecular DN made by these components combines features of the single networks, including high thermal stability and resistance to creep. The DN further exhibits excellent healability and displays a higher extensibility and a higher toughness than its constituents. The mechanical characteristics of the DN can be further enhanced by selectively pre-stretching one of the networks, which is readily possible due to the reversible formation of the supramolecular cross-links and their orthogonal stimuli-responsiveness.