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Abstract
Results concerning the nature of molecular orientational order and conformation of the flexible spacer (CH2) n (n = 10 and 7) in a class of main-chain nematic polymers and corresponding dimer model compounds, are presented. The order is found to be biaxial, and the biaxiality increases with increasing both temperature and molecular mass. The conformations of even and odd spacers are found to be different and somewhat complementary. The two halves of even spacers are all trans with a significant defect localized on the central C-C bond. On the contrary, the central part of odd spacers is all trans and connected to the rest of the spacer by two C-C bonds with defects of the gauche type. These results have been obtained by analysis of NMR and magnetic susceptibility data in terms of a model in which the repeating units are assumed to exchange between two orientationally equivalent conformations, mirror images of one another. For dimer with n = 10, the results concerning the conformation of the spacer are contrasted with similar results of the literature, obtained from analysis of the same NMR data in terms of a model based on the Rotational Isomeric State (RIS) approximation. It is shown that the two models are conceptually different, and some of their consequences are discussed.