Understanding Linear and Cyclic Polymer Chain Conformations and Thermodynamics in Solution

Comparing the chain conformations and thermodynamics in solutions of linear and cyclic polymers has been a topic of interest for many years. Despite this large body of work, due to challenges related to sample purity, dispersity, end-group/linker chemistry, and others, there is little consensus in the literature about the value of key properties such as the ratio of the radius of gyration between cyclic and linear polymers in solution. In recent work, small-angle neutron scattering (Hore lab, Case Western) on high-purity and low-dispersity cyclic and linear polystyrene (synthesized in Grayson lab, Tulane) has elucidated key differences in the temperature dependence of the Flory exponent in cyclic and linear polymers of identical molecular weight in deuterated cyclohexane. However, the effects of sample purity and the linker chemistry used to cyclize the ring polymers remain unclear. In this work, we apply explicit-solvent coarse-grained molecular dynamics (MD) simulations to provide the chain conformations as a function of solvent quality and linker chemistry. These MD results are then used within the framework of Polymer Reference Interaction Site Model (PRISM) theory to understand the thermodynamics of the system in terms of an effective polymer-solvent χ parameter.