Using coarse-grained models to examine structure-property relationships of diblock-arm star polymers

Abstract

Molecular dynamics simulations were used to verify that diblock-arm star polymers (SPs) can be accurately described using coarse-grained models. Each arm of the SPs examined consist of an inner polyethylene block and an outer polyethylene oxide block. A sixteen-arm SP with arm chemistry -CH224-CH2OCH26-H was mapped to a MARTINI coarse-grained representation and compared to results from atomistic simulations of an identical chemistry and architecture. Results for radius of gyration, radial distribution functions, and occupied volumes all show agreement with the atomistic model and reproduce general trends with respect to temperature. Additional measurements of interfacial area and anisotropy reveal that our model does not demonstrate crystallization of the polyethylene blocks at low temperatures as observed in the atomistic model which can be ascribed to the reduction in degrees of freedom that follow from coarse-graining. Calculated values for relaxation times agree with the general trends from the atomistic simulations. Nineteen additional coarse-grained star polymers were examined in order to investigate structure-property relationships that arise by varying arm number and arm length. The ability to model these chemical species at this resolution will allow for simulations of polymeric nanocarriers in more complex environments including at increased concentrations and near surfaces. This work demonstrates an important first step in work that will enable improved design of these polymeric nanoparticles for drug delivery applications.