Year: 2026
Type: preprint
Abstract: Force-adaptive polymer networks, whose mechanical response evolves under load, offer a route to structural materials that combine high stiffness and strength with efficient energy dissipation.[1,2] Most existing force-adaptive systems achieve this through mechanochemical reactions that generate reactive intermediates and thereby stiffen or rearrange the network,[3-5] a strategy that is intrinsically limited by diffusion, reaction kinetics, and the irreversible consumption of the reactive species. Here we pursue a fundamentally different strategy, in which a force-triggered transformation regulates the topological freedom of a slide-ring crosslink[6,7] rather than driving a chemical reaction. We integrate a mechanophore directly into the stopper of a rotaxane crosslinker, in which a cyclobutane formed by the [2+2] photodimerization of two cinnamate units[8,9] acts as the bulky stopper that confines a 24-crown-8 macrocycle on a dibenzylammonium axle.[10,11] Under load, retro-[2+2] cycloreversion reduces the steric dimension of the stopper and thereby expands the sliding space accessible to the macrocycle, so that a single covalent event gates a large slidingdissipation channel rather than dissipating energy directly. We incorporated this crosslinker into a segmented polyurethane and evaluated it against an orthogonal three-member sample set (R, C1, C2) of identical crosslinker content that decouples whether the stopper can open from whether the macrocycle can slide. The optimal composition, R3, reaches a toughness of about 215 MJ m-3 and a tensile strength of about 38 MPa—up to 9.4 and 5.6 times the toughness and strength of the openbut-cannot-slide control (C1), and far exceeding the constitutively sliding control (C2). Smallstrain dynamic mechanical analysis confirms that the mechanophore is silent at low strain, whereas gradient cyclic loading reveals a force-activation fingerprint: the dissipation ratio of R3 rises from below both controls at 100% strain to above them at high strain, crossing over near 300–400%. Infrared spectroscopy detects the regenerated cinnamate C=C band only after stretching and only in the cyclobutane-bearing samples,[8,9] and an annealing-reload test shows that the extra dissipation of R3 is largely recoverable with the smallest permanent damage of the three, consistent with a reversible sliding channel that shields the matrix.[12,13] These results establish a general design principle in which the structural precision of a mechanochemical transformation programs the evolution of topological freedom during deformation.
Source: ChemRxiv
Authors: Chenjuan Yu, Yuping Wang
Institution: Zhejiang University
Language: English
Subfield: Polymers and Plastics
Field: Materials Science
Domain: Physical Sciences
Open Access status: green
OpenAlex ID: W7213332028