Modeling the Mechanics of Polymer Chains with Deformable and Active Bonds

The force-extension relationship of single polymer chains is an essential component underlying the development of macroscopic constitutive models for elastomers. In this work, we present a model for the force-extension relationship beyond the consideration of classical entropic elasticity, by accounting for bond deformation on the chain's backbone. Parameters in this model are mostly molecular parameters for bond stretching, bending, and breaking already available in the literature, thereby limiting the parameters that need to be extracted from fitting experimental data to a minimum. In addition, an extension of the model is made to include the effects of mechanophores: molecules that react under the application of a mechanical force. This has endowed the model with the capability of predicting the mechanophore reaction as well as chain scission. The model is applied and compared to experimental data, in a range of scenarios: reproducing the measured force-extension relationship for PDMS chains, calculating the rate dependent fracture energy of PDMS films, and predicting the force-extension relationship caused by the unfolding of mechanophore domains. For the last example, it was demonstrated that this type of chain has the potential to be utilized to design elastomers with substantially enhanced strength and toughness.