Toughness Improvement of Carbene Bioadhesives via In Situ Polyester Extension

Carbene-based adhesives suffer from weak cohesive strength due to molar mass limits to ensure transparency. A feasible approach to improve cohesion relies on polymer chain extension utilizing light-activated ring-opening polymerization of lactones. Key material properties such as yield strength, elongation, and toughness evaluate if the structure-property relationships support chain extension as a viable strategy within a bioadhesive design intent. Rapid polymerization and gelation (< 1 h) occurred under ambient temperatures with δ-valerolactone and ε-caprolactone monomers, carbene-based adhesive CaproGlu as the ROP initiator, and selected organocatalysts. A dilution of up to 40 mol% δ-valerolactone monomer shows non-inferior yield strength and toughness as neat CaproGlu for both lap shear and peel tests, implying that ROP enhances the cohesive strength of the formulation. One-component (1C) formulations found irradiated iodonium salts catalyze in situ formation of polyesters from δ-valerolactone, with a timed delay before gelation.