Swelling‐induced Mechanochromism in Multinetwork Polymers

Abstract

We report a novel and versatile approach to achieving swelling-induced mechanochemistry using a multinetwork (MN) strategy that enables polymer networks to repeatedly swell with monomers and solvents. The isotropic expansion of the first network (FN) provides sufficient force to drive the mechanochemical scission of a radical-based mechanophore, difluorenylsuccinonitrile (DFSN). Although prompt recombination generally occurs in such highly mobile environments, the resulting pink radicals are kinetically stabilized in the gels, probably due to limited diffusion in the extended polymer chains. Moreover, the DFSN embedded in the isotropically strained chain exhibits increased thermal reactivity, which can be reasonably explained by an entropic contribution of the FN to the dissociation. The utility of the MN polymers is demonstrated not only in terms of swelling-force-induced network modification, but also in the context of tunable reactivity of the dissociative unit through proper design of the hierarchical network architecture.

Multiscale Mechanochemical Modeling of Spiropyran–Merocyanine Isomerization in Linear PMMA Polymers

“…Mechanophores are molecular subunits of polymers that are capable of converting mechanical stress into chemical energy, e.g. , via the rupture of a covalent bond. − Due to this effect, mechanophores are at the heart of many functional polymers, enabling mechanochemical reactions in a complex environment. − Some mechanophores show significant changes in their UV/vis absorption or fluorescence spectra upon isomerization, leading to mechanochromism. − Experimentally, mechanophores can be activated using a plethora of methods, e.g. , single-molecule force spectroscopy, , ultrasonication, , ball milling, , tensile stretching, and compression. , In each of these techniques, mechanical stress is propagated differently throughout the polymer, , eventually leading to mechanophore activation …”

Multiscale Mechanochemical Modeling of Spiropyran-Merocyanine Isomerization in Linear PMMA Polymers

“…[4][5][6][7][8][9] Some mechanophores show significant changes in their UV/Vis absorption or fluorescence spectra upon isomerization, leading to mechanochromism. [10][11][12][13][14][15][16] Experimentally, mechanophores can be activated using a plethora of method, e.g., single molecule force spectroscopy, 17,18 ultrasonication, 19,20 ball milling, 21,22 as well as tensile stretching 23 and compression. 10,24 In each of these techniques, mechanical stress is propagated differently throughout the polymer, 25,26 eventually leading to mechanophore activation.…”