Application of the dynamic rotational isomeric states model to poly(ethylene oxide) and comparison with nuclear magnetic relaxation data

Abstract

The dynamic rotational isomeric states (RIS) model recently developed for investigating local chain dynamics is further improved and applied to poly(ethy1ene oxide) (PEO). In general, a set of eigenvalues AI, j = 1 to Y *, characterizes the dynamic behavior of a given segment of N motional bonds, with v isomeric states available to each bond. The eigenvalues may be identified as the frequencies of the individual modes contributing to local chain relaxation. To calculate orientational autocorrelations, time correlations, and/or power spectra, Ais are combined with the weighting factors k, which are determined by the equilibrium statistics of the chain and the specific property investigated. The rates of transitions between isomeric states are assumed to be inversely proportional to solvent viscosity, leading to a linear dependence between viscosity and correlation times. Predictions of the theory are in satisfactory agreement with the isotropic correlation times and spin-lattice relaxation times from *3C and 'H NMR experiments for PEO in a variety of solvents. An activation energy of about one barrier height is theoretically calculated, in agreement with previous experimental studies.