Browsing by Author "Altinok H."

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Effect of polycondensation reaction conditions on the properties of thermotropic liquid-crystalline copolyester
(2008-08-01) Yikici M.; Yerlikaya Z.; Aksoy S.; Altinok H.
In this study a range of wholly aromatic copolyesters based on kink m-acetoxybenzoic acid (m-ABA) monomer (33mol%) and equimolar-linear p-acetoxybenzoic acid (p-ABA), hydroquinone diacetate (HQDA) and terephthalic acid (TPA) monomers (67mol%) have been synthesized by melt polycondensation reaction process at 280C and 260C for different time intervals. Characterization of copolyesters were performed by solution viscosity measurement, wide-angle X-ray diffraction (WAXD), differential scanning calorimetry (DSC), hot-stage polarized light microscopy, proton-nuclear magnetic resonance analysis (1H-NMR). According to the results obtained, copolyesters showed thermotropic liquid crystalline behavior in an appropriate temperature range. The copolyesters were prepared in high yields. It was observed that the intrinsic viscosities of the copolyesters are increased regularly with increasing polymerization time and temperature. All the copolyesters were soluble in a trifluoroacetic acid/dichloromethane (30:70 v/v) except the copolyesters which were synthesized at 280C in 5h. According to the WAXD results; the degree of crystallinity of copolyesters were found to be between 5-15%. DSC and hot stage polarized light microscopy results showed that all the copolyesters are melt processable and a significant molecular interaction exist in a very broad temperature range (160C and 165C) in the nematic mesophase. The Tg values are increased with an increasing polycondensation reaction time and temperature and they were observed between 93-126C. Fibers prepared by a hand-spinning technique from the polymer melt exhibit well-developed fibrillar structure parallel to the fiber axis.
Thermal and morphological properties of thermotropic liquid-crystalline copolyesters containing poly(ethylene terephthalate), 4-hydroxyphenylacetic acid and main-chain rigid aromatic units
(2010-06-01) Babacan V.; Aksoy S.; Yerlikaya Z.; Altinok H.
Thermotropic liquid-crystalline polymers (TLCPs) have aroused considerable interest due to their attractive properties as highperformance materials. Significant research attention has been devoted to investigating the relationship among monomer structures, syntheses and end-use properties of TLCPs. The study reported here concerns the preparation, characterization and melt spinning of novel copolyesters containing two different flexible units together with two different aromatic units in the polymer chains. A range of copolyesters based on p-hydroxybenzoic acid (p-HBA), m-hydroxybenzoic acid, p-hydroxyphenylacetic acid and poly(ethylene terephthalate) were synthesized. The liquid crystallinity, thermal properties and degrees of crystallinity of these copolyesters were investigated using hot-stage polarized light microscopy, differential scanning calorimetry, thermogravimetry and wide-angle X-ray diffraction. Copolyester fibres were characterized using scanning electron microscopy. The copolyesters were melt-processable, thermally stable and could be processed above their melting temperatures without degradation. The degree of crystal structure was found to depend upon the content of p-HBA. The fibres prepared showed that polymer chains had a well-developed fibrillar structure. Novel TLCPs containing flexible units in the main chain were synthesized and characterized. Copolyesters containing p-HBA units ranging from 55 to 70 mol% exhibited phase-separated liquid-crystalline morphology, appropriate melting temperatures and high thermal stability for melt processing. © 2010 Society of Chemical Industry.
Thermal properties and crystallinity of thermotropic liquid crystalline copolyesters prepared from poly(ethylene terephtalate) (PET) and rigid aromatic units
(2007-04-01) Tan A.; Altinok H.; Yerlikaya Z.; Aksoy S.
A series of copolyesters were synthesized by melt-polycondensation reaction of poly(ethylene terephtalate) (PET) with various proportions of equimolar compositions of p-acetoxybenzoic acid (p-ABA), hydroquinone diacetate (HQDA) and terephtalic acid (TPA). Viscosity, liquid crystallinity, thermal properties, degree of crystallinity and thermal stabilitiy of these copolyesters were investigated by Ubbelohde viscometer, hot-stage polarized light microscopy (PLM), differential scanning calorimetry (DSC), wide-angle X-ray diffraction (WAXD) and thermogravimetric analysis (TGA), respectively. On the basis of viscosity measurement, it was observed that intrinsic viscosity values of the copolyesters are increased regularly with increasing amounts of aromatic units (p-ABA, HQDA and TPA) in the polymer chain. Thermotropic liquid crystalline behavior was observed in the copolyesters containing over 50mol% of rigid p-ABA/HQDA/TPA aromatic units. DSC analysis of the anisotropic copolyesters revealed broad and weak endotherms associated with the nematic phases, and the melting temperatures were found to be in the processable region. As the mol% of PET in the polymer chain increased, the specific enthalpies of fusion and the degree of crystallinity of the copolyesters were also increased regularly.