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Effect of solvent and plasticizers on the rheology and morphology of a thermotropic liquid crystalline polymer with low temperature transitions

Publication Date
DOI: 10.1016/s0032-3861(96)00541-1
  • Liquid Crystal
  • Plasticizer
  • Crystallization


Abstract The effect of solvent and of small molecule plasticizers on the rheology and morphology of a main chain thermotropic liquid crystalline polymer with low melting transition has been studied. Of the two plasticizers used, diphenylisophthalate (DPIP) has a melting temperature ( T m) in the same range as that of the polymer, while diphenylterephthalate (DPTP) has a much higher T m of 198°C. Incipient crystallization occurs in the starting samples when solvent cast, whereas the melt-pressed initial samples were amorphous. The influence of the crystallinity of the starting material and the concentration of the plasticizers on the time-dependence of the rheological parameters, η ∗, G′ and G″ are discussed. Differential scanning calorimetry, X-ray diffraction and optical microscopy were used in parallel to rationalize the rheological behaviour in terms of the crystallinity and the morphology of the samples. It is shown that the relative molecular conformations of the polymer and the plasticizer molecules can affect the morphology and hence the rheological behaviour of the composite. The twisted conformation of the DPIP can disrupt the ordering of the chains whereas the ‘rodlike’ shape of the DPTP molecule can facilitate intercalation with the polymer chains, leading to enhanced ordering of the polymer. Although the rheological characteristics of the TLCP were affected by the plasticizers, the glass transition temperature was not.

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