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In this contribution, the X-ray diffraction (XRD) pattern of a highly oriented sample of syndiotactic polystyrene in the mesomorphic form, collected by an automatic diffractometer, is presented, thus providing quantitative and more complete information relative to the diffracted intensity. The structural changes induced by annealing procedures in mesomorphic samples are shown through the analysis of the XRD patterns: both unoriented and oriented mesomorphic samples are transformed gradually into a-form crystals. On the basis of these evidences and of preliminary comparisons between the calculated Fourier transform of simplified models and the experimental diffraction intensity, it is suggested that the local organization in triplets of transplanar chains, typical of the different modifications of the a-form, would be largely present also in the disordered chain agglomerates of the mesomorphic form. 0 1993, Huthig & Wepf Verlag, Basel CCC 0025-1

A conformational analysis for poly(methylene-1,3-cyclopentane) (PMCP) for different microstructures is presented. Independently of the microstructure of PMCP, extended conformations suitable for the disordered crystalline phase are geometrically and energetically feasible. However, strong restrictions to the conformational freedom, both of the rings and of the backbone, are required. The similarity between the experimental diffraction profiles of a PMCP sample and the Fourier transform calculations for isolated PMCP extended chains confirms that the crystalline phase of PMCP consists of parallel extended chains (configurationally and conformationally disordered) with a pseudohexagonal arrangement of the chain axes but with a nearly complete intermolecular rotational and translational disorder along the chain axes. The large increases of the entropy of melting with all the examined kinds of configurational order (cis or trans or isotactic) would be due to the related higher conformational order in the disordered crystalline phase.

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