Small‐angle neutron scattering of a model crystallizable polymer: Crystallization and size‐mismatch effects

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Abstract
Small‐angle neutron scattering (SANS) experiments have been conducted on mixtures of nearly monodisperse hydrogenated polybutadiene (HPB) and its deuterated counterpart (DPB) in molten and semicrystalline states. A direct comparison of scattering patterns from molten and quench‐crystallized samples shows unambiguously that chain conformation is unchanged by crystallization over large and intermediate size scales. The HPB's are shown to have slightly larger coil dimensions than linear polyethylenes of the same molecular weight. The scattering law for mixtures of different chain lengths was also investigated. Mismatched mixtures of monodisperse components give rise to scattering with an angle dependence well described by the Debye function for a Gaussian chain, even in the 50/50 composition range. This permits evaluation of SANS parameters [apparent radius gyration (Rg)e and apparent degree of polymerization Ne] by analysis of the full scattering curve, removing the restrictions that the Guinier condition (qRg < 1) be satisfied. The values of (Rg)e and Ne obtained from experiment are in good agreement with predictions of the scattering law for ideal mixtures.