Mechanophore Integration in Crosslinked Step‐ and Chain‐Polymerized Polymers and the Resulting Material Properties

ABSTRACT A facile synthesis, preparation, and integration of a diacrylate‐functionalized mechanophore is presented to demonstrate that a single, identical mechanophore is readily incorporated into polymer networks of various origins as a tool for identifying differences and similarities in the mechanical behavior of these networks. This work investigates polymer mechanical properties during and following stimulation of mechanofluorophore‐incorporated step and chain growth crosslinked polymers. This is achieved with an acrylate‐functionalized benzoxazole mechanofluorophore polymerized via a nucleophile‐mediated thiol‐Michael polymerization (step growth) or a photoinitiated radical acrylate homopolymerization (chain growth). These systems were tuned to have similar storage moduli by incorporating a monofunctional acrylate as a chain extender and crosslink density diluent in the chain growth network. Uniaxial tensile tests indicate that mechanophore incorporation in both systems results in an increase in the percent strain at break compared to control materials without the benzoxazole mechanophore but otherwise maintained monomer composition. Integration of the mechanofluorophore was also implemented in dynamic networks formed from step and chain growth polymerizations where the presence of disulfide bonds facilitated thermally activated bond rearrangement for stress relaxation. The presence of the mechanofluorophore in these networks did not inhibit the dynamic nature of the networks as evidenced by comparable stress‐relaxation traces.