Thermal transition behaviors in a liquid crystalline polyesterimide

• Published in: Polymer (Guilford) Vol. 46; no. 15; pp. 5840 - 5847
• Main Authors: Chi, Zhenguo, Cheng, Dan, Pan, Xinwei, Zhang, Yi, Xu, Jiarui, Bu, Haishan
• Format: Journal Article
• Language: English
• Published: Oxford Elsevier Ltd 11-07-2005; Elsevier
• Subjects: Applied sciences; Crystallization; Exact sciences and technology; Liquid crystalline crystal; Organic polymers; Physicochemistry of polymers; Polyesterimide; Properties and characterization; Liquid crystalline crystal; Polyesterimide; Crystallization; Melting; Thermotropic state; Benzoate(hydroxy) copolymer; Esterimide copolymer; Head to head polymer; Experimental study; Phase transitions; Melt crystallization; Thermal history; Liquid crystal polymers; Kinetics; Isothermal crystallization
• ISSN: 0032-3861; 1873-2291
• DOI: 10.1016/j.polymer.2005.03.090

The crystallization and melting behaviors of the polyesterimide, derived from
N,
N′-hexane-1,6-diylbis(trimellitimides), 4,4′-dihydroxybenzophenone and
p-hydroxybenzoic acid, were investigated by using polarized light microscopy (PLM), differential scanning calorimetry (DSC) and wide-angle X-ray diffraction (WAXD). The nematic texture of the polyesterimide was observed on raising temperature to 265
°C, and the nematic phase was found to convert to isotropic melt beginning from about 300
°C, the ordered nematic micro-domains still surviving after 320
°C. Isothermal crystallization of the samples was performed at 180
°C after heating samples at various temperatures in the range of 265–360
°C, and a completed crystallization peak can appear on DSC curves up to the heating temperature of 360
°C in the presence of the nematic phase and the ordered nematic micro-domains. Non-isothermal crystallization of the samples at different cooling rate was carried out, and the melting of the resulting crystals exhibits double endotherms. It is indicated that a fast crystallization in the nematic phase forms relatively more ordered crystals, which melt at higher temperature, and a slow crystallization in the isotropic phase or in the biphasic melt produces poor crystals, which melt at lower temperature. The crystallized polyesterimide was annealed, which has a minor effect on the high-melting peak but leads to a continual shifting of the low-melting peak to higher temperature with increasing annealing temperature or annealing time. WAXD patterns indicated that the structural transform was not found during annealing process.