Anisotropic hydrolysis susceptibility in deformed polydimethylsiloxanes

Environmental factors such as humidity have potential to drive chemical degradation of polymer networks in ways that compound with mechanical stressors. Using two levels of quantum chemical theory, we identify a possible electronic driver for strain-induced chemical susceptibility in deformed polydimethylsiloxane (PDMS) chains. High throughput sampling with a validated semiempirical density functional tight binding (DFTB) model is used to explore the complicated interplay between hydrolytic chain scissioning reactions, mechanical deformations of the backbone, water attack vector, and chain mobility. We show that sustaining tension through concerted strains of the backbone over at least a few monomer units is necessary to significantly increase hydrolysis susceptibility. A reactive order parameter is developed that describes chain scission probabilities as a complicated function of the backbone degrees of freedom. The trends identified suggest simple physical descriptions for the synergistic coupling of local mechanical deformation and chemistry in silicones.