Polymer tacticity is an important structural attribute of polystyrene, influencing diverse physical properties such as crystallinity and thermal stability. The local dynamics of a polymer, i.e., the set of librational motions and conformational transitions which occur on the order of picoseconds in monomeric subunits and short backbone regions, are tacticity-dependent and responsible in part for variation in these physical properties. In this study, the local dynamics of isotactic polystyrene (iPS) in semi-dilute solution are investigated using a twofold approach of NMR spin-lattice relaxation experiments and molecular dynamics (MD) simulations. Relaxation of the coupled carbon-13 and proton spins in a methylene group in iPS is characterized by multiple carbon-13 inversion recovery style experiments. Additionally, spectral densities determined from relaxation curve fitting procedures are used to calculate Cartesian correlation times for the reorientation of multiple perpendicular vectors aligned relative to the methylene group. These experimental values are directly compared to values calculated by MD simulations of iPS. Using the GROMACS suite, correlation times are calculated from the P<sub>2</sub>(t) autocorrelation functions of the appropriate vectors. Comparison of local dynamics data from experiment and simulation offers insight into theoretical models concerning the role of tacticity in localized polymer motion.

Characterization of the local dynamics of isotactic polystyrene in semi-dilute solution by NMR spin-lattice relaxation experiments and molecular dynamics simulations

255th National Meeting (2018)

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