Early Detection of Mechanical Damage in Plastics Using Diarylacetonitrile Fluorescent Probes

Abstract

The development of polymeric materials capable of reporting mechanically induced chain-scission events before macroscopic fracture and pronounced stress whitening is of considerable interest for improving the safety, reliability, and lifetime of plastic components. Herein, diarylacetonitrile (DAAN), physically dispersed within commodity polymers, is demonstrated to function as an effective fluorescent probe for detecting mechanically induced polymer-chain scission without requiring covalently incorporated mechanochromic probes or specifically engineered polymer architectures. Using poly(vinyl acetate) (PVAc) as a model system, a pronounced fluorescence response is observed upon deformation, while electron paramagnetic resonance (EPR) measurements confirm the generation of radical species. Probe activation occurs above a critical strain threshold associated with the onset of strain hardening and precedes macroscopic failure and pronounced stress whitening, providing an early optical indication of molecular damage relative to these macroscopic events. The response intensity increases with deformation and crosshead rate, while microcrack formation and stress whitening likely contribute to signal amplification. The activated species gradually decay over time through radical recombination or dimerization, oxygen-mediated trapping, and hydrogen-atom abstraction, although partial signal recovery is achieved through subsequent deformation. Extension of the approach to poly(methyl methacrylate) (PMMA) and polystyrene (PS) supports the applicability of the sensing strategy to different polymer matrices, whereas no detectable activation is observed in low-density polyethylene (LDPE) under the investigated conditions. Overall, these findings establish DAAN as a simple, noncovalent, and versatile platform for detecting chain-scission-associated mechanoradical formation in several commodity polymers.