Carbon-13 NMR investigation of local dynamics in bulk polymers at temperatures well above the glass transition temperature. 1. Poly(vinyl methyl ether)

Local dynamics of isotactic and syndiotactic polypropylene in solution

“…The fit was achieved by treating simultaneously the 25 and 50 MHz T 1 data assuming for the motional model a time scale separation between the fast librations and the segmental motions, as was systematically observed in previously studied polymer chains. 9,[15][16][17] The parameters 2 / 1 and a are kept constant over the whole temperature range while 1 is assumed to vary according to Arrhenius' law 1 ϭA exp(E a /k B T). For a given microstructure, common values of the activation energies E a and prefactors A are adopted for both methylene and methine carbons.…”

“…The detailed analysis of relaxation data determined in a number of polymer systems, 9,[15][16][17][18][19][20][21][22] either in solution or in bulk at temperatures well above the glass transition temperature, has shown that the local motions observed by 13 C spinlattice relaxation can be satisfyingly described in terms of damped diffusion of bond orientation along the chain sequence, which represents the segmental motions, and independent fast bond librations. 9 The corresponding orientation autocorrelation function is written as…”

“…6,7 This function was later found adequate to describe the fluorescence anisotropy decay of anthracene labeled polybutadiene chains dispersed in a polybutadiene matrix, 8 a further test of the pertinence of this function to represent the reorientational dynamics process of a bond subject to restrictions from chain connectivity. The application of this functional form in the interpretation of 13 C NMR relaxation data 9 required the adjunction of an additional faster decorrelation process modeling the fast librational motions, hence leading to the so-called DLM model. The application of this phenomenological approach to the interpretation of NMR relaxation data on a wide variety of polymers ͑in solution or in melts well above the glass transition͒ has been generally quite successful.…”

“…The application of this phenomenological approach to the interpretation of NMR relaxation data on a wide variety of polymers ͑in solution or in melts well above the glass transition͒ has been generally quite successful. 9 Molecular dynamics simulations are nowadays more and more integrated in a multidisciplinary effort aimed at linking the local dynamics of polymers with their chemical structure. In this field, simulations have provided much insight about the nature of conformational transitions, 3,4 about the limitations of the Kramers theory when describing single bond rotation, 5 about the validity of Langevin dynamics for macromolecules in solution 5 or about many jumps features like geometrical aspects or the size of the moving polymer segment.…”

“…We report a series of new 13 C NMR relaxation experiments which probe the methine/methylene bond reorientational dynamics within specific microstructures and we interpret these NMR data with the DLM motional model. 9 In parallel, we analyze a series of molecular dynamics experiments performed at three temperatures on isotactic ͑iPP͒ and syndiotactic ͑sPP͒ oligomers in an explicit solvent.…”