Dynamics of an amorphous polymer by an improved NMR approach based on the simultaneous analysis of 1H and 13C relaxation times

A new approach to extract quantitative dynamic information from NMR relaxation data of amorphous polymers is presented, consisting of the simultaneous fitting of 1H and 13C T1 vs temperature curves obtained at different frequencies by means of unified motional models. The reliability of the dynamic parameters obtained by this approach is substantially increased with respect to the single curve analysis because of the possibility of both investigating motions over a wide frequency range and combining relaxation times carrying either global (1H nuclei) or local (13C nuclei) dynamic information. Experimental data were obtained for an amorphous ethylenepropylene random copolymer over a wide temperature range above its glass-transition: 1H spin-lattice relaxation times were measured by wide-line techniques at four Larmor frequencies, while high-resolution MAS techniques were used to get 13C spin-lattice relaxation times at a single frequency. The experimental data were analyzed in terms of segmental main-chain motion, rotation of the methyl groups about their ternary symmetry axes, and librations of C-H bonds, described by suitable models. The results showed good agreement between experimental and calculated data and allowed a detailed characterization of the motions investigated to be obtained.