Solid-state mechanochemical activation of anthracene–maleimide adducts: the influence of the polymer matrix†

Abstract

The repertoire of established mechanophores has been on a steady rise over the last few years, holding the promise of generating materials capable of delivering programmable, beneficial responses upon mechanical stimulation. However, investigations are usually confined to demonstrating activation within limited and seemingly arbitrary choices of polymer matrices. In contrast, the broader applicability of the mechanophore across various types of polymer materials is rarely explored. The experimental techniques generally used to achieve mechanochemical activation are also a source of discrepancy. Ultrasonication of dilute polymer solutions is a popular method that applies extreme strain rates to isolated, solvated chains. The technique is practical and convenient, but its experimental conditions are not conducive to elucidating the activity of the same mechanophore in a bulk polymer system under tensile strain. Here, we report a comparative study on the mechanochemical behaviour of anthracene–maleimide Diels–Alder adducts in a series of polymeric materials. We embed the mechanophores either in the backbone of linear polymers or as cross-links of polymer networks. We show that the solution-phase ultrasonication efficiently activates the mechanophores, regardless of the design of the linear polymer. In contrast, mechanophore activation in bulk is highly dependent on the polymer matrix, topology, and the connectivity of the mechanophore and the matrix.