Thermal properties and crystalline structure of liquid crystalline (LC) poly(ethylene terephthalate-co-2(3)-chloro-1,4-phenylene terephthalate) [copoly(ET/ CPT)] were investigated using differential scanning calorimetry (DSC), thermogravimetry (TGA), limiting oxygen index (LOI) measurement, electron dispersive X-ray analysis (EDX), X-ray diffractometry, and infrared spectrometry (IR). The thermal transition temperatures of copoly(ET/CPT) were changed with the composition. Copoly(ET/ CPT) showed two thermal decomposition steps and the residues at 700°C and LOI values of copoly(ET/CPT) were almost proportional to its chlorine content. The activation energy of thermal decomposition of LC units was very low compared to that of poly(ethylene terephthalate)(PET) units. Crystal structure of copoly(ET/CPT) (20/80) was of triclinic system with the lattice constants of a ϭ 9.98 Å , b ϭ 8.78 Å , c ϭ 12.93 Å , ␣ ϭ 97.4°,  ϭ 96.1°, and ␥ ϭ 90.8°, which is very close to that of poly(chloro-pphenylene terephthlate) (PCPT) with the lattice constants of a ϭ 9.51 Å , b ϭ 8.61 Å , c ϭ 12.73 Å , ␣ ϭ 96.8°,  ϭ 95.4°, and ␥ ϭ 90.8°. When copoly(ET/CPT)(50/50) was annealed at 220°C in vacuum, crystallization induced sequential reordering (CISR) was not observed but the heat of fusion was slightly increased due to the increase of the trans isomer content in PET units.
ABSTRACT:Liquid crystalline properties for copoly (ethylene terephthalate/chloro-1, 4-phenylene terephthalate) have been investigated. The polymer was highly sensitive to shear stress and revealed nematic liquid crystal structure at a composition of more than 20mole% of chlorophenylene terephthalate (CPT). The liquid crystallinity increased with the increase in CPT content and inherent viscosity of the copolymer.
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