LAMELLAR THICKNESS OF CRYSTALLIZABLE ETHENE RUNS IN ETHENE-PROPENE COPOLYMERS BY SOLID-STATE NMR

Crystallizable runs of ethene in ethene-propene copolymers can be identified in C-13 CPMAS NMR spectra as a resonance at 33 ppm. In the absence of spin diffusion, the variation in intensity of this resonance with a H-1 spin lock will reflect the intrinsic T1rho(H). Spin diffusion leads to a more complex relaxation decay, which reflects the local polymer morphology. Simulations of the spin diffusion process have been carried out for a simplified two-phase model for the morphology with the aim of determining whether the lamellar thickness of the crystalline and amorphous regions can be found from the T1rho(H) observed via the C-13 NMR spectrum. Calculations covering the expected range of the input parameters, namely the spin diffusion coefficients, domain lengths, and intrinsic relaxation times, show that, providing the intrinsic relaxation time in the amorphous phase is known, an accurate estimate of the crystalline and amorphous lamellar thicknesses can be made. Analysis of simulated T1rho(H) decays indicate that, in general, the time constant of the fastest decaying component can be identified with the intrinsic relaxation time of the amorphous phase. (C) 1994 John Wiley & Sons, Inc.