Effect of side chain branching on the structural and dynamic properties of polyacrylates: A combined molecular dynamics and experimental study

Abstract

Polyacrylates and polymethacrylates have found a diverse array of applications owing to their remarkable characteristic and tunability of physical and chemical properties. Systematic investigations of these polymers primarily assume homology that arises from the linear extension of the alkyl group in the alkoxycarbonyl substituent, rather than from branching of the alkyl group. Consequently, the presented atomistic molecular dynamics (MD) study is focused on the structural and dynamic properties of a series of bulk atactic poly(alkyl acrylates), which includes poly(methyl acrylate) (PMA), poly(ethyl acrylate) (PEA), poly(isopropyl acrylate) (PiPA), and poly(tert-butyl acrylate) (PtBA) at varying temperatures. For comparative purposes, poly(methyl methacrylate) (PMMA) has been included in this series as it is a polymer that has been frequently examined. The nonmonotonous trend observed in the radius of gyration and end-to-end distance of the polymer chains reflects the conflicting interplay between enhanced intrachain repulsion and reduced mutual penetration of chain pervaded volumes. The intramolecular and intermolecular radial distribution functions of pairs of branched carbon atoms were identified as being particularly sensitive to variation in substituents. The predicted local dynamics of the α- and β-relaxation processes, both computationally and experimentally, exhibit a slowdown in the following order: PEA > PiPA > PMA > PtBA > PMMA. The diffusion rate is dictated by the shape of the chain and its substituents. Similarities in dynamic properties are found between PMA and PtBA as well as between PEA and PiPA. This study has potential implications for applied polymer science including 3D printing, electrospinning, vitrimers, and other dynamic systems where flow, glass transition, and viscosity effects are relevant under thermal and pressure loads.