A comparative study of the thermotropic mesomorphic tendencies and rheological characteristics of three cellulose derivates: Ethylene and propylene oxide ethers and an acetate butyrate ester

Samples of cellulose acetate butyrate (CAB) hydroxypropyl cellulose (HPC) and ethyl cellulose (EC) are contrasted with commercial (atactic) polystyrene (PS) and isotactic polypropylene (PP) in studies of (i) differential scanning calorimetry, (ii) quiescent polarized light microscopy (iii) optical retardation variation following an imposed stress field. It is concluced that HPC and EC are thermotropic liquid crystals, while CAB behaves in a manner similar to a vitrifying isotropic melt such as PS. Studies of the shear viscosity and dynamic viscosity indicate HPC and EC exhibit yield values while CAB shows a zero shear viscosity and Vinogradov-Malkin reduced viscosity curve identical to PS. The normal stress and extrudate swell behavior of CAB are also similar to PS. The HPC and EC exhibit substantially reduced extrudate swell. Measurement of the principal normal stress difference behavior of the HPC melt is troubled by the existence of yield values.     

纤维素及其衍生物液晶研究近况

就纤维素及其衍生物溶性液晶和热致性液晶的液晶性及其影响因素,和流变性能等方面的研究作了较为详尽的综述。     

EVIDENCE FOR THERMOTROPIC LIQUID CRYSTALLINITY OF A FUSIBLE POLYDIACETYLENE

The thermotropic liquid crystalline behavior of a fusible polydiacetylene has beenstudied by using polarizing optical microscopy and wide angle X-ray diffraction. It wasfound that the typical threaded texture can exhibit in the melt and the banded texture canbe observed when applied a gentle shear to the melt. The results indicate that thispolydiacetylene is really a thermotropic liquid crystalline polymer.     

CRYSTALLIZATION BEHAVIOR OF A THERMOTROPIC LIQUID CRYSTAL COPOLYESTER

A thermotropic liquid crystal copolyester resin based on p-hydroxybenzoic acid, 2, 6-naphthoic acid, hydroxyquinone and PET was synthesized by melt condensation and studied. The results based on DSC and X-ray diffraction indicated that there were a rapid and a slow crystallization processes for the copolyester at certain conditions. A critical temperature was suggested, below which the slow crystallization could hardly happen. Above the critical temperature the extent of the slow crystallization process depended not only on annealing temperature but also on the annealing time. A fine crystal structure with high melting point and narrow diffraction peak was formed under favorable conditions.     

纤维素芳族酯热致液晶对PET结晶成核作用的研究

用自制的热致液晶性纤维素芳族酯(CAE)作聚对苯二甲酸乙二醇酯(PET)的成核剂,研究了PET/CAE体系(CAE含量≤1%)在110～200℃温度范围内的等温结晶动力学特性.结果表明,CAE能显著加快PET结晶速率(Z),Z随结晶温度和CAE含量变化均有极大值Z_max(T_C)和Z_max(W_CAE),Z_max(T_C)对应的温度T_max随CAE含量增加而降低,CAE促进PET结晶的作用机理与普通成核剂不同.     

The molten phase conductance and the thermotropic phase transition in lead(II), zinc(II) and cadmium(II) 10-hydroxyoctadecanoates

The electrical conductances and heats of phase changes in lead(II), zinc(II) and cadmium(II) 10-hydroxyoctadecanoates are measured. The soaps are prepared by metathesis in alcohol solution from 10-hydroxyoctadecanoic acid which in turn is prepared from the oxidation of cis-9-octadecenoic (oleic) acid with concentrated sulphuric acid.The Arrhenius plot for lead(II) 10-hydroxyoctadecanoate shows a maximum, a behaviour that had earlier been interpreted to be due to complex formation. A similar plot for zinc(II) 10-hydroxyoctadecanoate is linear while that for cadmium(II) 10-hydroxyoctadecanoate presents a discontinuity which is interpreted, with the aid of the differential scanning calorimetric (DSC) spectra and optical examination, to be suggestive of the formation of an intermediate phase between the solid and the liquid phases. The low conductances of the soaps in comparison with the literature data on some metal caboxylates indicate the existence of extensive intermolecular hydrogen bonding in the molten phase. Both lead(II) and zinc(II) 10-hydroxyoctadecanoates melt directly from the solid to the liquid phase while their cadmium(II) counterpart passes through the gel-like phase before melting into the liquid. The mesophase of cadmium(II) 10-hydroxyoctadecanoate is transformed to the liquid phase with a relatively low enthalpy change and the behaviour is associated with the cylindrical micekkar structures of the liquid phase that have their formative stage from the gel-like mesophase.     

Reactive blending of poly(ethylene 2,6-naphthalate) and Vectra A

In situ composites based on poly(ethylene 2,6-naphthalate) (PEN) and a thermotropic liquid crystal polymer (Vectra A950) were prepared by melt blending under different processing conditions. Thermal behaviour, mechanical and physical properties and morphology of the blends were investigated. The DSC analysis indicates that, as expected, Vectra enhances the crystallization process of PEN. Moreover, mechanical and thermal tests evidence the significant role of 20 wt% Vectra on increasing the material performances; tensile properties, coupled with SEM, show that strength and modulus of PEN are significantly improved when Vectra domains are long and continuous fibrils. The overall results can be attributed to the compatibilisation of the system induced by the mixing conditions that affect the extent of transreactions occurring in the melt. To deepen this aspect, the soluble and insoluble fractions in a PEN solvent were isolated and thoroughly characterized: both the fractions contain PEN/Vectra copolymers. The results underline the potentiality of the PEN/Vectra system for different high-performance applications requiring superior strength and modulus, heat stability or barrier properties.     

Microstructural effects on the dynamic rheology of a discotic mesophase pitch

The dynamic rheology and accompanying microstructure of a synthetic mesophase pitch (AR-HP) is reported. The loss modulus (G″) was found to be higher than the storage modulus (G′) at all frequencies (∼0.1 to ∼100 rad/s) and temperatures (280–305 °C) tested. The slope of the low-frequency terminal zone for G′ was found to be approximately 0.8, much lower than a value of 2 that is observed for flexible chain polymers. Cross-polarized optical microscopy with full-wave retardation plate confirmed the presence of different textures of mesophase pitch processed under different conditions. While loss moduli remained fairly unchanged, finer textures led to significantly lower storage moduli. Consistent with this trend, coarsening of the microstructure during textural relaxation led to an increase in storage moduli. Therefore, for the discotic mesophase pitch, the viscous component was found to remain unaffected by the microstructure, but the elastic modulus was dependent on the orientation of layer-planes and size of the texture.     

两种新碗形分子的合成及其纤维状晶的研究

以香兰素为原料,采用三聚法合成了2种外围脂肪族基团碳数分别为3和5的环三亚藜芦基(cyclotriveratrylene,CTV)系衍生物碗形分子--CTV-3和CTV-5,其中,用先关环后衍生化的合成路线克服了因CTV-5的外围基团太长、分子对称性不好而无法用传统方法合成的难题.产物的化学结构经1H NMR、13CNMR、质谱以及元素分析确认.在偏光显微镜下观察到纤维状晶叠加在碗形分子的向列液晶织构上.纤维状晶是从液晶态冷却时形成并装饰在原液晶织构上的一种结晶形态.通过SEM测定,观察到纤维状晶实际上是由厚度约为100-200m、宽度为2-5μm的无限长的单层片晶组成的多层片晶,而片晶则是由直径约为100nm的微纤组成的.微纤可以推断是碗形分子柱的束状聚集体.     

固态后缩聚方法合成高分子量的含磷热致性液晶共聚酯

为了获得较高分子量的具有高阻燃性的热致性液晶高分子,通过固态聚合方法合成了一种基于对羟基苯甲酸、对苯二甲酸、乙二醇和含磷菲环取代二酚的高热稳定性、较低相转变温度和宽的液晶相转变温度范围的含磷液晶共聚酯(BDQTEP),并对该含磷液晶共聚酯预聚物(pre-BDQTE)在不同固态聚合条件下获得的聚合物热性能和液晶性进行了研究.对其固态反应速率控制进行了初步的探讨,当反应温度为235℃时,固态聚合反应较为理想.在聚合的初始阶段,共聚酯特性黏数[η]、黏流温度Tf和羧基浓度[COOH]均随聚合时间而明显变化,但在6 h后变化较小,几乎不变.通过固态后缩聚,将熔融聚合获得的特性黏数[η]=0.44 dL/g的含磷液晶共聚酯BDQTE的特性黏数提高了近两倍.