Impact of Domain Rearrangement on Mechanochemical Activation in Triblock Elastomers

Triblock elastomers are an attractive platform for polymer mechanochemistry, in which the forces that arise during chain stretching are used to drive molecular-scale chemical transformations. Previous experiments have suggested that mechanochemical activation occurs only after the yield point in triblock elastomers with high glassy block content, but the specific rearrangement of the block copolymer structures that is required to allow activation is not entirely clear. Here, we address this problem by synthesizing a spiropyran-containing triblock copolymer (PMMA-b-PnBA-SP-b-PnBA-PMMA) which self-assembles into well-ordered morphologies. We conduct simultaneous optical and tensile measurements and correlate the activation of the spiropyran mechanophore with the rearrangement of the PMMA domains observed by transmission electron microscopy and small-angle x-ray scattering. We find that, in samples with high PMMA content, mechanochemical activation occurs only after breakup and alignment of the PMMA domains. This result provides insight into the interplay between plastic deformation of the glassy domains and chain stretching in the triblock copolymer, and how changes to the self-assembled nanostructure can be used to affect mechanochemical activation.