Local dynamics of isotactic and syndiotactic polypropylene in solution

The local dynamics of polypropylene (PP) in solution is studied by C-13 NMR relaxation and by molecular dynamics (MD) simulation via the orientational autocorrelation function (OACF) of C-H bonds. The interpretation protocol of this function proposed by Dejean de la Batie, Laupretre and Monnerie (DL M) [R. Dejean de la Batie, F. Laupretre, and L. Monnerie, Macromolecules 21 , 2045(1988)] is applied and tested on new NMR measurements of the various microstructures of polypropylene. This interpretation scheme of the OACF is supported by a detailed study employing simulated PP trajectories in an at omistic heat bath. MD simulations indicate that, quite generally, the corre lation time for segmental motions, tau(1), extracted from the DLM motional model is closely linked with the mean time between conformational jumps. Bo th experiments and simulations suggest a slightly higher mobility of meso s equences by comparison with racemic sequences. Our analysis of the microsco pic aspects of the segmental dynamics and its manifestation in motional mod els allows us to trace the microscopic origin of the larger mobility of mes o sequences. (C) 2000 American Institute of Physics. [S0021-9606(00)50321-3 ].