Morphology and structure of syndiotactic polystyrene.

MOYSES, Stephane. (1997). Morphology and structure of syndiotactic polystyrene. Doctoral, Sheffield Hallam University (United Kingdom)..

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Abstract

The delta-phase of the syndiotactic polystyrene/ethylbenzene system, as formed by crystallisation from dilute solution, is shown to result in a lamellar morphology, with a monoclinic crystal lattice similar to that already reported for the complex with toluene. The temperature/concentration phase diagram for sPS/ethylbenzene gels was obtained using DSC. This shows the presence of three polymer/solvent compounds, one of which contains 0.25 solvent molecules per monomer unit. For this latter compound, the stoichiometry corresponds to that proposed by Chatani et al. for the delta-phase of sPS in toluene. Combined SAXS, FTIR, DSC and TGA measurements show that an increase in the X-ray long period between 80 and 120°C is related to solvent loss and decomplexation.There is also some temporary loss in helical order. SANS measurements on the delta-phase reveal negligible isotopic fractionation. The small increase in the in-plane radius of gyration with increasing molecular weight is interpreted as evidence of a sheetlike molecular conformation, with superfolding at higher molecular weights leading to a multiple sheet structure. On transformation to the solvent-free gamma-phase, an increase in radius of gyration results from a displacement of crystal stems out of the delta-phase sheets. Further support to these conclusions is brought by intermediate and wide angle neutron scattering. Data for delta-phase are shown to be consistent with sheetlike arrangements of crystal stems along the a direction. Adjacent stems therefore show an alternation in helicity. Simulations based on a statistical model have been used to calculate statistical parameters, such as the probability of adjacency (P[A]), for which optimum agreement is found for a value of 0.8. Radii of gyration obtained from simulations are in good agreement with experimental values. The molecular weight range studied appears to cover the change from a single sheet structure to a superfolded double sheet. The same stem statistics (with P[A] = 0.8) apply, irrespective of molecular weight. Scattering data from the gamma-phase of sPS are well reproduced by a model involving some movement of stems out of the planes of sheets.SANS measurements have been made using tilted samples in order to separate in-plane and out-of-plane radii of gyration. Comparison between the out-of-plane radius and the long spacing determined from small angle X-ray measurements shows close agreement for the lower molecular weight in both delta- and gamma-phases, while R[Z] is a factor of 2 larger for the higher molecular weight. This indicates that each molecule occupies a single lamella at the lower molecular weight and, on average, two lamellae at the higher one, in both delta- and gamma-phases. The implication is that the delta- to gamma-phase transition only involves a reorganisation of chain segments within those lamellae which originally contained the molecule.

Item Type: Thesis (Doctoral)
Additional Information: Thesis (Ph.D.)--Sheffield Hallam University (United Kingdom), 1997.
Research Institute, Centre or Group: Sheffield Hallam Doctoral Theses
Depositing User: EPrints Services
Date Deposited: 10 Apr 2018 17:21
Last Modified: 23 May 2018 11:41
URI: http://shura.shu.ac.uk/id/eprint/20096

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