observed in the first heating cycles to melting of crystalline polymer. Such first heating cycle endotherms that disappear in subsequent heating cycles have been observed by others. Various mechanisms have been proposed to explain this phenomenon including liquid-liquid transition, loss of a volatile constituent (e.g., solvent) from the sample, and a change in physical contact between sample and sample pan due to liquid flow.18'19 We tentatively ascribe the 56 °C phenomenon in the DSC curve to the polymer glass transition. This assignment is not made with great certainty since Tt is accompanied by a change in slope of the DSC curve whereas the DSC curve for the naphthyl polymer has what appears to be an endotherm at 56 °C. The 56 °C phenomenon is so weak that it may not be possible to distinguish an endotherm from a change in slope.ABSTRACT: Polyesters prepared from chlorohydroquinone diacetate and hexahydroterephthalic acid (1,4-cyclohexanedicarboxylic acid) were extruded from liquid crystalline melts directly into highly oriented fibers with initial moduli as high as 450 g/denier or 57.5 GPa. Heat-treatment in a relaxed state to near the melting point resulted in a 5-to 6-fold increase in tenacity-up to 20 g/denier (2.5 GPa). These polyesters were characterized by X-ray, NMR, IR, DSC, TGA, and optical microscopic methods. Polyesters based on cisand trans-hexahydroterephthalic acid were prepared by both melt and low-temperature solution methods. Solution-prepared cis polymer, in which the cis configuration was confirmed by high-resolution NMR, was found to fornj an isotropic melt at 250 °C that converted to a liquid crystalline melt on heating at 310 °C due to cis-trans isomerization (NMR). The latter indicates the more extended trans form is required for melt anisotropy. All melt-prepared polymers were found by NMR to exist in the trans configuration and formed anisotropic melts and high-strength fibers on spinning and heat treatment.
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