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

Mechanochemical reactions in functional polymers occur when mechanical forces cause labile bonds, e.g., in mechanophores, to break. While it is known that these reactions require a critical amount of force, the structure of the polymer network strongly affects the efficiency of force transduction. Experimentally it is challenging to track the force transmission along the polymer backbone. Despite the availability of quantum mechanochemical tools, the information on force transmission from the bulk to a local scale is still limited. Here we introduce a multiscale mechanochemical model that establishes a connection between bulk deformation and mechanophore activation. This is achieved by combining the quantum mechanical (QM) COnstrained Geometries simulate External Force (COGEF) method with cost-efficient molecular mechanical (MM) simulations. Based on a new parameterization of the well-known Spiropyran-Merocyanine (SP-MC) isomerization under stretching forces, we simulate mechanophore activation inside a realistic poly(methyl methacrylate) (PMMA) network at different strain rates and loading modes. The results are discussed in terms of stress-strain behavior of the system, influence of temperature and mechanochemical activity. The developed multiscale simulation model paves the way for further investigations on more complex mechanophore-doped polymer networks, subjected to external load.