Crystallization and melting behavior of liquid crystalline copolyesters based on poly(ethylene terephthalate)

✍ Scribed by Yongjian Liu; Yi Jin; Linsen Dai; Haishan Bu; Robert R. Luise

• Publisher: John Wiley and Sons
• Year: 1999
• Tongue: English
• Weight: 224 KB
• Volume: 37
• Category: Article
• ISSN: 0887-624X
• DOI: 10.1002/(sici)1099-0518(19990201)37:3<369::aid-pola15>3.0.co;2-q

✦ Synopsis

A series of copolyesters were prepared by the incorporation of p-hydroxybenzoic acid (HBA), hydroquinone (HQ), and terephthalic acid (TA) into poly(ethylene terephthalate) (PET). On the basis of viscosity measurements, high molar mass copolyesters were obtained in the syntheses, and 1 H-NMR analyses indicated the total insertion of comonomers. They exhibit nematic phase above melting temperature, as observed by polarized light microscope (PLM). Their crystallization and melting behaviors were also studied by differential scanning calorimetry (DSC) and wide angle X-ray diffraction (WAXD). It was found that these copolyesters are more crystalline than copolyesters prepared from PET and HBA. Introduction of HQ/TA disrupts longer rigid-rod sequences formed by HBA, and thus enhances molecular motion and increases crystallization rate and crystallinity. Isothermal crystallization at solid phase polymerization conditions (up to 24 h at 200°C) resulted in increased copolymer randomness (by NMR) and higher melting point, the latter attributed to structural annealing.