Dynamics of Ethylene−Propylene Random Copolymers by 1H and 13C Solid-State NMR

The dynamic behavior of three completely amorphous ethylene−propylene random copolymers with slightly different structural properties was investigated by means of a multifrequency global fitting approach, presented in a previous paper. To this end, the trends of NMR 1H and 13C spin−lattice relaxation times with temperature, obtained at different frequencies, were analyzed by means of unified motional models for the segmental main-chain motion and rotation of methyl groups about their ternary symmetry axis. To evaluate the reliability of both the models and the method used with respect to the dimensionality of the data set, as well as to identify the minimal data set to be used for getting reliable dynamic information on similar systems, the fitting results obtained from the analysis of three different experimental data sets collected on the same polymer were compared. The data collected on the three polymers using the minimal data set were analyzed and the results discussed to evaluate the degree of sensitivity of the method to differences in the dynamic behavior of structurally similar systems. The results demonstrated that the method shows good sensitivity to the use of different dynamic models depending on the number and/or type of relaxation curves included in the analysis and that variations in the dynamic features of the same motions on different systems can be revealed even in the presence of polymeric systems characterized by very similar structural properties.