Polybutadiene Copolymers via Atomistic and Systematic Coarse-Grained Simulations

The systematic coarse graining of polymeric systems is a usual route in order to extend the range of spatiotemporal scales and systems accessible to molecular simulations. Here, we present a bottom-up methodology in order to obtain coarse-grained (CG) models for copolymers, derived from more than one species of monomers via detailed atomistic simulations. In the proposed scheme, each monomer type is represented as a different CG particle. The effective CG interactions are obtained via a dual-stage multi-component iterative Boltzmann inversion optimization scheme, in which the single-component terms of the CG model are obtained from homopolymer simulations, whereas the interactions between different CG-type particles (mixed terms of the CG model) are obtained from the simulation of a symmetric composition copolymer. As an example, the proposed optimization scheme is applied on polybutadiene (PB) copolymers consisting of cis-1,4, trans-1,4, and vinyl-1,2 isomers. The derived CG PB copolymer model is examined with respect to its transferability across molecular weight and copolymer composition. In addition, using the newly derived CG model, various PB copolymers across a broad range of cis-1,4, trans-1,4, and vinyl-1,2 compositions are examined. Structural and dynamical properties of PB copolymers are presented. The vinyl component is found to have a large impact on the conformational properties of PB copolymer melts because of the different packing imposed by side groups. Standard composition mixing rules are used to predict the time mapping factors for the calculation of both segmental and center-of-mass dynamics of the PB copolymer, coming from the CG model.