Abstract: | Crystallizable runs of ethene in ethene-propene copolymers can be identified in 13C CPMAS NMR spectra as a resonance at 33 ppm. In the absence of spin diffusion, the variation in intensity of this resonance with a 1H spin lock will reflect the intrinsic TH1ρ. 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 TH1ρ observed via the 13C 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 TH1ρ 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. © 1994 John Wiley & Sons, Inc. |