Dong Zhang

Crystallization kinetics of new copoly(ethylene terephthalate-imide)s

Crystallization kinetics of copoly(ethyleneterephthalate-imide)s (PETIs) of various imide contents were studied by the DSC technique. The results of isothermal and nonisothermal crystallization kinetics studies showed a consistent trend in that the crystallization of all copolyesterimides comprised a primary stage and secondary stage, and that the crystallization mechanism was a three-dimensional growth with athermal nucleation. The crystallization rate of PETIs first increased and then decreased as the content of imide units in the copolyesterimides increased. This indicates that the imide units in the copolymer decreased the chain-packing regularity of poly(ethylene terephthalate) (PET) and the same units also enhanced the copolymer chain rigidity. The copolyesterimide with 0.2 mol% imide unit content showed a dramatic increase of the crystallization rate, and exhibited the highest crystallization rate of all the studied compositions. Studies of isothermal and nonisothermal crystallization kinetics, showed that small amounts of imide units in the the backbone act as nucleating agents during the crystallization process of copolyesterimides.

Mesogen-jacketed Liquid Crystal Polymers With Mesogens of Aromatic Amide Structure

The synthesis and property of a new series of mesogen-jacketed liquid crystal polymers are reported. These polymers have aromatic amide structures as the mesogenic groups and are represented by poly-2,5-bis(4-methoxy- benzamido)styrene. The preliminary study on properties shows that the polymers have very high glass transition temperatures as well as very low critical concentrations for the formation of the lyotropic liquid crystal phase. The results indicate a high degree of chain rigidity. However, the liquid crystalline order of molecular organization in bulk samples disappears upon heating to the glass transition temperature as revealed by polarizing microscopy and by X-ray diffractometer. Therefore, the liquid crystalline order of these polymers forms only through solution but not through heating. This behavior is different from that of the previously studied poly-2,5-bis[(4-methoxybenzoyl)oxy]styrene and its homologs. The latter polymers are liquid crystals both lyotropically and thermotropically.

Synthesis and thermal behavior of new poly(ethylene terephthalate-imide)s

Copoly(ethylene terephthalate-imide)s (PETIs) were synthesized by the melt copolycondensation of bis(2-hydroxyethyl)terephthalate with a new imide monomer, N,N-bis[p-(2-hydroxyethoxycarbonyl)phenyl]-biphenyl-3,3,4,4-tetracarboxydi-imide (BHEI). The copolymers were characterized by intrinsic viscosity, Fourier transform infrared, 1 H NMR, differential scanning calorimetry, and thermogravimetric analysis techniques. Although their crystallinities decreased as the content of BHEI units increased, the glass-transition temperatures (T g ) increased significantly. When 5 or 10 mol % BHEI units were incorporated into poly(ethylene terephthalate), T g increased by 10 or 24 °C, respectively. The thermal stabilities of PETI copolymers were about the same as the thermal stability of PET, whereas the weight loss of PETIs decreased as the content of BHEI units increased.

Mesogen-jacketed liquid crystalline polymer with flexible dicyclopentyl terephthalate as side group

Hui-lin Tu, Dong Zhang, Xin-hua Wan, Xiao-fang Chen, Yu-xiang Liu, Hai-liang Zhang,Qi-Feng Zhou*Department of Polymer Science & Engineering, College of Chemistry, Peking University, Beijing 100871,Chinaqfzhou@pku.edu.cn(Received: April 24, 1999; revised: June 21, 1999)SUMMARY: For the first time the flexible cyclopentyl ring is used to build mesogenic units, and thus anovel mesogen-jacketed liquid crystalline polymer (MJLCP) poly(dicyclopentyl vinylterephthalate) is syn-thesized. The polymer forms a stable mesophase which changes to an isotropic phase at 267

Synthesis of novel liquid crystal compounds with aromatic amide mesogenic cores

The synthesis and properties of a new series of compounds having aromatic amide mesogenic cores are reported. Most of these new compounds are thermotropic mesogens. In consideration of the fact that aromatic amides form crystals of high melting point which is unfavourable for the formation of thermotropic liquid crystals, we make use of lateral substitution to decrease both the packing efficiency and the hydrogen bonding, so that the melting temperature of the aromatic amides is sufficiently depressed. The lateral substituent used in these new compounds is bromine. In order to investigate the influence on properties of the end groups, different alkoxy, alkyl and other groups are used at the two ends of the rod-like molecules. The two ends are either identical or different, with an electron-donating alkoxy as one end and the electron-accepting cyano group as the other. The results indicate that appropriate lateral and terminal substitution is essential for the aromatic amides to form thermotropic liquid cr...

Polymeric nematic schlieren textures with singularities of high strength

Abstract The observation of polymeric nematic schlieren textures with singularities of high strength (|S| > 1) is reported. The polymers studied are of the type with two dimensional mesogenic units. Inversion walls were also observed in the liquid crystal state of these polymers.

The synthesis and property of liquid crystalline 4-alkoxyl-4-cyano-p-terphenyls

Abstract The synthesis of some new 4-alkoxyl-4′-cyano-p-terphenyls is described. The preliminary characterization by means of polarized optical microscopy, differential scanning calorimetry and X-ray diffraction shows that all these compounds are thermotropically liquid-crystalline and can form both the nematic and smectic mesophases.

Effect of rod-like imide unit on crystallization of copoly(ethylene terephthalate-imide)

The effect of the imide unit on the isothermal and non-isothermal crystallization, kinetics crystallization of a new family of copoly(ethylene terephthalate-imides) (called copolyesterimides or PETIs) was investigated using differential scanning calorimetry. With a combined Avrami and Ozawa equation, one can describe the non-isothermal crystallization process of copolyesterimides, and the results show the same tendency as that in the isothermal crystallization process. These studies show that the processes of crystal nucleation and growth result in mainly three-dimensional growth with a thermal nucleation. In both isothermal and non-isothermal crystallization processes, the crystallization rate of PETIs, with imide content below 0.5%, is higher than that of neat PET, while PETI-3 (0.3 mol% imide) has the highest crystallization rate. This rate is significantly enhanced over PET homopolymer. It is proposed that imide units precipitate from the melt and act as nucleating agents during the crystallization process of these novel copolyesterimides.