INFLUENCE OF THE CHEMICAL NATURE OF CROSS-LINKS ON THE LOCAL DYNAMICS OF BULK POLY(ETHYLENE OXIDE) NETWORKS AS STUDIED BY C-13 NMR AT TEMPERATURES WELL ABOVE THE GLASS-TRANSITION TEMPERATURE

Carbon-13 spin-lattice relaxation time measurements have been performed on cyclosiloxane cross-linked poly(ethylene oxide)s (PEO) in bulk at temperatures well above the glass-transition temperature. The introduction of cyclosiloxane cross-links does not induce a strong modification of the local dynamics of PEO segments, in contrast to results observed in urethane cross-linked PEOs. Moreover, in these networks, the local chain dynamics are satisfactorily described by considering a damped bond orientation diffusion process and a fast libration of limited extent of the internuclear CH vectors about their rest position. The amplitude of the libration, which is expected to reflect the steric hindrance at the considered site, does not depend on the carbon considered and the chemical nature and density of cross-links.