Extending the fused-sphere SAFT-gamma Mie force field parameterization approach to poly(vinyl butyral) copolymers

CC Walker and J Genzer and EE Santiso, JOURNAL OF CHEMICAL PHYSICS, 152, 044903 (2020).

DOI: 10.1063/1.5126213

SAFT-gamma Mie, a molecular group-contribution equation of state with foundations in the statistical associating fluid theory framework, is a promising means for developing accurate and transferable coarse-grained force fields for complex polymer systems. We recently presented a new approach for incorporating bonded potentials derived from all-atom molecular dynamics simulations into fused-sphere SAFT-gamma Mie homopolymer chains by means of a shape factor parameter, which allows for bond distances less than the tangent-sphere value required in conventional SAFT-gamma Mie force fields. In this study, we explore the application of the fused-sphere SAFT-gamma Mie approach to copolymers. In particular, we demonstrate its capabilities at modeling poly(vinyl alcohol-co-vinyl butyral) (PVB), an important commercial copolymer widely used as an interlayer in laminated safety glass applications. We found that shape factors determined from poly(vinyl alcohol) and poly(vinyl butyral) homopolymers do not in general correctly reproduce random copolymer densities when standard SAFT-gamma Mie mixing rules are applied. However, shape factors optimized to reproduce the density of a random copolymer of intermediate composition resulted in a model that accurately represents density across a wide range of chemical compositions. Our PVB model reproduced copolymer glass transition temperature in agreement with experimental data, but heat capacity was underpredicted. Finally, we demonstrate that atomistic details may be inserted into equilibrated fused-sphere SAFT-gamma Mie copolymer melts through a geometric reverse-mapping algorithm.

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