Quantity or Quality: Are Self-Healing Polymers and Elastomers Always Tougher with More Hydrogen Bonds?

Polymer materials containing dynamic bonds have many potential applications including adhesives, elastomers, and coatings with long lifetimes. Interpenetrated networks (IPNs) were studied, where one network had covalent linkers, and the other network had dynamic quadruple-hydrogen-bonded 2-ureido-4[1H]-pyrimidinone (UPy) linkers. IPNs typically have superior mechanical properties to each component network. IPNs had either nonpolar poly(ethyl acrylate) (PEA) or hydrogen-bond-rich poly(2-hydroxyethyl acrylate) (PHEA) matrixes. Although the PHEA materials have more hydrogen bonds, the self-healing, toughness, and fracture energies were poorer than the PEA systems. This suggests that strong and dynamic hydrogen bonds, even at the potential expense of total hydrogen bonds, should be chosen for applications that require toughness such as high-performance coatings, sealants, or elastomers.