Mechanochromic Polyolefin Elastomers

The optical detection of mechanical strain and stress in polymers is a powerful and convenient approach for studying deformation processes in these materials and identifying damage prior to failure in crucial components. We show here that mechanochromic behavior can be introduced via a straightforward one-step process that involves the modification of a commercial polyolefin elastomer (POE) grafted with reactive anhydride groups with small amounts (<0.8 wt %) of mechanochromic cross-linkers (Loop or sPDI). These motifs contain excimer-forming perylene diimides (PDIs) and react with POE to afford mechanochromic polyolefin elastomers (POE-Loop or POE-sPDI). The Loop motif contains two excimer-forming PDI moieties that can form folded structures in which the two PDIs within the Loop motif interact with each other, i.e. intra-Loop, while sPDI contains one PDI that can only form interactions with PDIs of other sPDI probes. Upon mechanical deformation of POE-Loop and POE-sPDI, the dye aggregates disassemble and the ratio of monomer-to-excimer emission intensity increases. The data suggest that dye interactions between probes, i.e. inter-Loop or inter-sPDI, dominate the optical characteristics of both polymers.