Structure-Rheology-Domain Texture Relationships in Thermotropic Liquid-Crystalline Polymers

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ABSTRACT CTS-9320351 University of Akron P.I.: Chang D. Han It is proposed to investigate structure-rheology-domain texture relationships in thermotropic liquid-crystalline polymers (TLCPs). For the investigation, a homologous series of aromatic homopolyester, poly (phenylsulfonyl)-p-phenylene bis(4-oxybenzoate) with methylene units (CH2)n as flexible spacers (PSHQ), will be synthesized via solution polymerization. On the basis of the preliminary study performed by the principal investigator who used decamethylene (CH2)10 as flexible spacers, PSHQ can be used as a model compound to study structure-rheology-domain texture relationships in TLCP because, owing to its relatively low clearing temperature, PSHQ allows one to control the initial condition (i.e., initial domain texture) by first heating to an isotropic state and then cooling slowly down to an anisotropic state. In the synthesis of PSHQ the number of methylene units (i.e., n=7-16) will be varied, in order to investigate the effect of flexible spacer, especially the so-called 'odd-even' effect, on the resulting rheological behavior and domain texture in the specimen. The major thrust of the proposed research project is to enhance our understanding as to how the domain texture of TLCP, which depends on both thermal and shear histories, influences its rheological behavior, which in turn is affected by the orientational order of the polymer. Therefore we propose to conduct, with emphasis on the 'odd-even' effect, the following investigations: (1) A rheo-optical study will be conducted to understand the relationship between the rheological behavior and the flow-induced textures of PSHQ; (2) The domain size and its distribution in PSHQ specimen will be determined, via image analysis, under well-controlled annealing conditions; (3) The orientational order parameter of PSHQ specimens will be determined, via solid-state nuclear magnetic resonance spectroscopy, as a function of temperature; (4) The persistence length of PSHQ will be determined using dynamic light scattering; (5) An expression for the excluded volume (intermolecular) potential will be developed for PSHQ; and (6) The rheological behavior of PSHQ will be predicted by numerically solving the Doi Kinetic equation, by using the expression for the excluded volume potentia, which is to be developed in the proposed study.