Two approaches to the description of solvent effects upon some NMR properties observed on highly concentrated polymer systems

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Abstract
Two approaches are proposed to calculate the nonzero average dipolar spin coupling strength observed on highly concentrated polymer solutions. One is based on the current particle path picture. The model of polymerized solids of Edwards and Kerr is used to predict the approximate dependence of the nonzero average dipolar spin coupling upon entanglements and cross links. The other approach is based on the effect of the probability distribution of monomer unit pairs. The lattice treatment of solvent polymer mixtures proposed by Guggenheim is used to predict the dependence of the dipolar coupling strength upon the temperature and the solvent concentration. This dependence is compared with recent experimental results obtained from high resolution proton spectra of polyisobutylene chains. It is shown to be in good agreement with the observed dependence. Accordingly, the free energy of mixing of the solvent–monomer unit is considered as available from proton high resolution spectra of highly concentrated polymer solutions. The two approaches are supposed to hold only when polymer chains are completely mixed with each other.