STUDIES ON THERMOTROPIC LIQUID CRYSTALLINE COPOLYESTERS——POLY (ARYLENE TEREPHTHALATE-CO-BUTYLENE TEREPHTHALATE)

A series of copolyesters based on bis(4-hydroxybutyl) terephthalate, terephthaloyl chloride andvarious aromatic diols (i.e. hydroquinone, chlorohydroquinone, bromohydroquinone or dihydroxybi-phenyl) was prepared. ~1H-NMR studies revealed that the monomer units had microstructures closeto random distribution in the chains. The copolymers showed composition-dependent liquid crystal-line properties as verified by visual observation of stir opalescence, polarizing microscope, DSC andX-ray diffration. The copolyesters with aromatic diol contents over a certain extent (for chloro-hydroquinone m≥0.33) were thermotropic with wide liquid crystalline temperature ranges. Theintroduction of chlorohydroquinone into the copolyesters could gradually destroy the crystallinityof the polymers but retain the liquid crystalline characteristics.     

一种基于联苯二甲酸为介晶基元的含磷液晶共聚酯的合成与表征

以联苯二甲酸二甲酯、二甘醇和9,10-二氢-9-氧杂-10磷酰杂菲-对苯二酚二羟乙基醚(DOPO-HQ-HE)为单体,通过无规共聚合成了一种新型含磷液晶共聚酯(PDEBP).用1H-NMR对共聚酯的结构进行了表征,用TGA、DSC和POM对其热性能及液晶行为进行了研究.结果表明,阻燃单体DOPO-HQ-HE的引入不会降低共聚酯的热稳定性,含7.5 mol％ DOPO-HQ-HE的共聚酯PDEBP7.5在700℃的氮气氛中的残余物(Wt700R)可达31.9 wt％,并且具有很好的阻燃性.DOPO-HQ-HE含量的增加对共聚酯的结晶性有较大的破坏,5 mol％ DOPO-HQ-HE的共聚酯PDEBP5的清亮点温度为154.2℃,焓变为4.64 J/g,而PDEBP7.5在POM测试中在升温及降温过程中均难观察到液晶相的双折射现象.     

Thermal Properties and Crystallinity of Thermotropic Liquid Crystalline Copolyesters Prepared from Poly(ethylene terephtalate) (PET) and Rigid Aromatic Units

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 50 mol% 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.     

Block copolyesters of poly(pentamethylene p,p′‐bibenzoate) and poly(tetramethylene adipate)

Hydroxy‐terminated poly(pentamethylene p,p′‐bibenzoate) oligomers with different molecular weights were prepared. The poly(pentamethylene p,p′‐bibenzoate) oligomers showed rather high crystallinity, and some of them exhibited a monotropic smectic phase. Block copolyesters with hard segments of poly(pentamethylene p,p′‐bibenzoate) and soft segments of poly(tetramethylene adipate) were prepared by coupling the poly(pentamethylene p,p′‐bibenzoate) oligomer and a poly(tetramethylene adipate)glycol with methylene‐4,4′‐diphenylene diisocyanate in solution. The block copolyesters were characterized by IR, ¹H NMR, differential scanning calorimetry, a polarized microscope, and X‐ray diffraction. The thermal transitions of the block copolyesters were dependent on the composition and the molecular weight of the poly(pentamethylene p,p′‐bibenzoate) oligomer used. The hard segments in the block copolyesters showed no liquid crystallinity and exhibited rather low crystallinity or were even amorphous. The molecular weight of the poly(pentamethylene p,p′‐bibenzoate) oligomer used influences the glass‐transition temperature and crystalline properties of the soft segments in the block copolyesters significantly. The effect on the glass‐transition temperature of the soft segments is described as the difference in miscibility between the hard and soft segments. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 2626–2636, 2002     

Synthesis and characterization of potentially biodegradable thermotropic polyesters based on p-hydroxybenzoic acid and glycolic acid

The synthesis of novel thermotropic liquid crystalline copolyesters derived from aliphatic hydroxy acid (glycolic acid, GA) and aromatic hydroxy acid (p-hydroxybenzoic acid, PHBA) via a melt-copolycondensation process in the presence of various catalysts was explored. The following three possible routes were checked: PHBA and GA in different feed ratios with or without a catalyst; PHBA and GA in different feed ratios with or without a catalyst in the presence of acetic anhydride as a condensation agent; and different PHBA derivatives were used to examine the reactivity of aromatic hydroxy acid. The copolycondensability, chemical structure, liquid crystallinity, textures and morphology, phase transition behaviors and thermal stability, and solubility were investigated by FTIR, NMR, DSC, TGA, and polarized-light microscope. It has been found that only the 60–70 mol % PHBA-containing copolyesters could exhibit a nematic liquid crystallinity. The as-prepared polymers were brittle due to relatively lower molecular weights. © 1994 John Wiley & Sons, Inc.     

Synthesis and characterization of fully aromatic thermotropic liquid‐crystalline copolyesters containing m‐hydroxybenzoic acid units

A series of fully aromatic copolyesters based on p‐acetoxybenzoic acid (p‐ABA), hydroquinone diacetate (HQDA), terephthalic acid (TPA), and m‐acetoxybenzoic acid (m‐ABA) were prepared by a modified melt‐polycondensation reaction. The copolyesters were characterized by DSC, thermogravimetric analysis, ¹H NMR, polarized optical microscopy, X‐ray diffraction, and intrinsic viscosity measurements. The copolyesters exhibited nematic liquid‐crystalline phases in a broad temperature range of about 150 °C, when the content of linear (p‐ABA, HQDA, and TPA) units was over 67 mol %. DSC analysis of the anisotropic copolyesters revealed broad endotherms associated with the nematic phases, and the melting or flow temperatures were found to be in the processable region. The flow temperatures and crystal‐to‐nematic and nematic‐to‐isotropic transitions depend on the type of linear monomer units, and these transitions increased as the content of the p‐ABA units increased, as compared to the HQDA/TPA units. When the content of the p‐ABA units increased, as compared to other linear units (HQDA and TPA), the intrinsic viscosity and degree of crystallinity of the copolyesters also increased, implying a higher reactivity for p‐ABA in the p‐ABA/HQDA/TPA/m‐ABA polymer system. The aromatic region in the ¹H NMR spectra of the copolyesters containing equal molar compositions of p‐ABA, HQDA, and TPA units were sensitive to the sequence distribution of aromatic rings. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 3263–3277, 2001     

Effect of Polycondensation Reaction Conditions on the Properties of Thermotropic Liquid‐Crystalline Copolyester

In this study a range of wholly aromatic copolyesters based on kink m‐acetoxybenzoic acid (m‐ABA) monomer (33 mol%) and equimolar‐linear p‐acetoxybenzoic acid (p‐ABA), hydroquinone diacetate (HQDA) and terephthalic acid (TPA) monomers (67 mol%) have been synthesized by melt polycondensation reaction process at 280°C and 260°C 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 280°C in 5 h. 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 (160°C and 165°C) in the nematic mesophase. The T_g values are increased with an increasing polycondensation reaction time and temperature and they were observed between 93–126°C. Fibers prepared by a hand‐spinning technique from the polymer melt exhibit well‐developed fibrillar structure parallel to the fiber axis.     

Sequence distribution in polyethylene/tetramethylene terephthalate copolyesters by 13C-NMR

¹³C-NMR gives sequence information in copolyesters synthesized from ethylene glycol (EG), 1,4-butane diol (BD), and methyl terephthalate (TP). The EG-TP-EG and BD-TP-BD blocks are distinguishable from the unsymmetrical diester sequence EG-TP-BD. The carbonyl and aromatic quaternary carbons of terephthalate have different chemical shifts but identical relaxation times and nuclear Overhauser enhancements in the three different triad sequences. Peak areas indicate random copolymerization of the three copolyesters studied.     

Dielectric relaxation studies on a three component fully aromatic copolyester

The family of aromatic copolyesters based on the hydroxybenzoic acid (HBA) unit has been studied extensively by a number of groups. In particular the copolyesters of HBA and 2,6‐hydroxynaphthoic acid (HNA) have received much of attention due to their superior physical properties. This paper, however, describes some detailed dielectric studies on a related fully aromatic copolyester, poly(p‐oxybenzoate‐co‐p‐phenylene isophthalate), known simply as HIQ. This polymer is of particular interest because it can be solvent cast in an amorphous form, with no apparent crystallinity or frozen liquid crystalline texture and subsequently annealed, to increase the amount of crystalline and frozen liquid crystalline material. Dielectric measurements were therefore made on tape and film samples with differing morphologies produced by different processing histories. Measurements were made from 1 Hz to 10 kHz over the temperature range ?100 °C to 150 °C. A low temperature γ relaxation is observed which appears to be similar in nature to that which is observed in copolymers of HBA and HNA. An intermediate temperature β process is seen in isotropic samples which has a much higher activation energy than that found in HBA/HNA polyesters for example. The intensity of this process, which is not seen in mechanical measurements on highly oriented samples, increases on annealing and it is therefore suggested that the process is the glass transition of the liquid crystalline phase, though why the process is not seen in mechanical measurements on oriented samples is unclear. Copyright © 2001 John Wiley & Sons, Ltd.     

Sequentially ordered,thermotropic aromatic copolyesters: Synthesis and comparison of their properties with random copolyesters

Synthetic methods of aromatic copolyesters having ordered comonomer sequence are described. In order to obtain a regular sequence copolyester, one first has to prepare a dimeric or trimeric compound with a predesigned sequence via a multistep route and then polycondense it with another difunctional compound. Low reaction temperature is required to avoid the occurrence of undesired interchange reactions that would lead to randomization of the comonomer sequence. Sequentially ordered copolyesters exhibit significant differences in thermal transitions, crystalline properties, and occasionally even in liquid crystallinity when compared with the properties of the corresponding random copolyesters. According to the preliminary results randomization in comonomer sequence of sequentially regular aromatic copolyesters above their melting points is rather rapid.     

Poly(ethylene terephthalate) copolyesters derived from (2S,3S)‐2,3‐dimethoxy‐1,4‐butanediol

Novel poly(ethylene terephthalate) (PET) copolyesters, abbreviated PEDMBT, containing optically active (2S,3S)‐2,3‐dimethoxy‐1,4‐butanediol (DMBD) as the second comonomer were investigated. Copolymers with ethylene glycol to DMBD ratios between 95/5 and 50/50 as well as the two parent homopolymers, PET and PDMBT, were prepared by a two‐step melt polycondensation. The resulting copolymers were found to approximately have the composition of the polymerization reaction feed and a random microstructure. Polymer intrinsic viscosities varied from 0.4 to 0.6 dL g^?1 with weight‐average molecular weights ranging from 16,000 to 44,000. PEDMBT copolyesters were distinguished in being much more soluble than PET and showing an increasing affinity for water with the content in dimethoxy groups. According to the asymmetric constitution of DMBD, they displayed optical activity in solution. Both melting and glass‐transition temperatures of the copolyesters were observed to steadily decrease with the content in DMBD. PEDMBTs were found to be crystalline for contents in DMBD up to 30 mol %. Both powder and fiber X‐ray diffraction revealed that the same crystalline structure is shared by PET and the crystalline copolyesters. The homopolyester PDMBT resulted in becoming a polymer with a crystallinity comparable to PET but with a significantly different crystalline structure. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 3250–3262, 2001     

含二羟基二苯酮的系列热致液晶共聚酯的合成和表征──Ⅲ．含4，4＇－二羟基二苯砜结构的共聚酯

含二羟基二苯酮的系列热致液晶共聚酯的合成和表征──Ⅲ．含４，４＇－二羟基二苯砜结构的共聚酯董德文，池振国，倪玉山，丁孟贤（中国科学院长春应用化学研究所长春１３００２２）陈玉（东北师范大学分析测试中心长春１３００２４）关键词４，４＇－二羟基二苯酮，热致...     

含二羟基二苯酮的系列热致液晶共聚酯的合成和表征──Ⅲ．含4，4＇－二羟基二苯砜结构的共聚酯

hermotropic liquid crystalline copolyesters were synthsized from his(4-hydroxyphenyl) methanone (BHP), tereplithalic acid (TPA), p-hydroxybenzoic acid (PHB) and dihydroxydiphenyl sulfone(DPS). The properties of the copolyesters were characterized by polarized microscope with a hot stage, wide angle X-ray diffraction and differential scanning calorimetry. The results show that the copolyesters containing the BHP exhibit nematic liquid crystallinity.     

Synthesis of high‐molecular‐weight aliphatic–aromatic copolyesters from poly(ethylene‐co‐1,6‐hexene terephthalate) and poly(L‐lactic acid) by chain extension

A series of aliphatic–aromatic multiblock copolyesters consisting of poly(ethylene‐co‐1,6‐hexene terephthalate) (PEHT) and poly(L ‐lactic acid) (PLLA) were synthesized successfully by chain‐extension reaction of dihydroxyl terminated PEHT‐OH prepolymer and dihydroxyl terminated PLLA‐OH prepolymer using toluene‐2,4‐diisoyanate as a chain extender. PEHT‐OH prepolymers were prepared by two step reactions using dimethyl terephthalate, ethylene glycol, and 1,6‐hexanediol as raw materials. PLLA‐OH prepolymers were prepared by direct polycondensation of L ‐lactic acid in the presence of 1,4‐butanediol. The chemical structures, the molecular weights and the thermal properties of PEHT‐OH, PLLA‐OH prepolymers, and PEHT‐PLLA copolymers were characterized by FTIR, ¹H NMR, GPC, TG, and DSC. This synthetic method has been proved to be very efficient for the synthesis of high‐molecular‐weight copolyesters (say, higher than M_w = 3 × 10⁵ g/mol). Only one glass transition temperature was found in the DSC curves of PEHT‐PLLA copolymers, indicating that the PLLA and PEHT segments had good miscibility. TG curves showed that all the copolyesters had good thermal stabilities. The resulting novel aromatic–aliphatic copolyesters are expected to find a potential application in the area of biodegradable polymer materials. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 5898–5907, 2009     

Biodegradable liquid crystalline aromatic/aliphatic copolyesters. Part I: Synthesis, characterization, and hydrolytic degradation of poly(butylene succinate-co-butylene terephthaloyldioxy dibenzoates)

To increase the thermal and mechanical properties of the aliphatic polyester poly(butylene succinate) (PBS), a series of potentially biodegradable liquid crystalline aromatic/aliphatic random copolyesters were prepared by melt polycondensation of new mesogenic monomers dimethyl 4,4′-(terephthaloyldioxy) dibenzoate (MTB), dimethyl succinate, and 1,4-butanediol. The synthesized copolyesters were characterized by means of proton nuclear magnetic resonance spectroscopy (¹H NMR), gel permeation chromatography (GPC), viscosity measurements, differential scanning calorimetry (DSC), thermogravimetry (TG), X-ray diffraction (XRD), polarizing light microscopy (PLM) and mechanical property measurements. The MTB content was varied so that the effects of the mesogen content on the thermal and mechanical properties, degradable behaviours and mesophase were examined. It was found that introducing the rigid rod mesogens could increase the thermal stability and the mechanical properties, while it reduced the melting temperature (T_m), the crystallization temperature (T_c), the degree of relative crystallinity (X_c) and the hydrolytic degradation rate. Only the homopolyester poly(butylenes terephthaloyldioxy dibenzoates) was able to show the schlieren texture characteristic of nematics.     

Polyesters analogous to PET and PBT based on O‐benzyl ethers of xylitol and L‐arabinitol

The synthesis, characterization, and some properties of new copolyesters of poly(butylene terephthalate) (PBT) and poly(ethylene terephthalate) (PET) based on L ‐arabinitol and xylitol are described. These copolyesters were obtained by polycondensation reaction in the melt of mixtures of 1,4‐butanediol or ethylene glycol and 2,3,4‐tri‐O‐benzyl‐L ‐arabinitol or 2,3,4‐tri‐O‐benzyl‐xylitol with dimethyl terephthalate. Their weight‐average molecular weights ranged between 7000 and 55,000, with polydispersities ranging from 1.4 to 4.7. Copolymers containing 1,4‐butanediol could be analyzed by NMR, and were found to have a statistical microstructure. All these copolyesters were thermally stable, with degradation temperatures well above 300 °C. With increasing amounts of alditol in the copolyester, the melting temperature and crystallinity decreased in both series, and the glass transition temperature increased for the PBT series and decreased for the PET series. Only PBT‐derived copolyesters containing a maximum of 10% alditol units showed discrete scattering characteristic of crystalline material. No substantial differences in either structure or properties were observed between the L ‐arabinitol and xylitol copolyester series. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 5167–5179, 2008     

Synthesis, characterization and properties of high molecular weight poly(butylenes succinate) reinforced by mesogenic units

To increase the molecular weights of the synthesized liquid crystalline aromatic/aliphatic copolyesters and to avoid crosslinking, a solution polymerization of the prepolymer and chain extender hexamethylene diisocyanate was adopted. The effects of chain extension on polyester molecular weights, thermal and mechanical properties, and biodegradable behaviors were investigated respectively. The catalysis mechanism and the copolyesters morphological textures were also investigated. The synthesized copolyesters were characterized by means of Fourier transform infrared spectra (FTIR), gel permeation chromatography (GPC), viscosity measurements, differential scanning calorimetry (DSC), X-ray diffraction (XRD), polarizing light microscopy (PLM), scanning electron microscopy (SEM) and mechanical property measurements. It was found that inherent viscosities and the molecular weights of the copolyesters were remarkably increased under the action of catalyst, leading to a increase in the tensile strength. The degree of relative crystallinity, the melting temperature, and the rate of degradation decreased after chain extension.     

新型手性近晶C相液晶共聚酯的设计与合成

以对苯二甲酰氯 ,2 ,5 二 [4 ((s) 2 甲基丁氧基 )苯甲酰氧基 ]对苯二酚和乙二醇、一缩乙二醇、二缩三乙二醇、三缩四乙二醇和聚乙二醇为单体 ,采用低温溶液缩聚方法 ,合成了一系列新的手性近晶C相串型液晶共聚酯 .共聚酯通过GPC、DSC、TG、WAXD、偏光显微镜和旋光仪等方法表征 .发现所有的共聚酯加热至各自的熔点以上都能形成液晶态 ,在液晶态可以观察到近晶相的焦锥织构 ,所有的手性化合物和共聚酯都有较高的旋光性 .通过变温X 射线衍射研究结合偏光显微镜观察和旋光分析证明它们为手性近晶C相 .所有共聚酯的熔融温度 (Tm)和各向同性温度 (Ti)随共聚酯中不同柔性链段长度的增加逐渐降低 ,液晶态温度范围变宽     

SYNTHESIS AND CHARACTERIZATION OF AROMATIC LIQUID CRYSTALLINE COPOLYESTERS WITH REGULAR SEQUENCE STRUCTURE

Several novel aromatic liquid crystalline copolyesters with regular sequence structure were prepared by melt Sehotten-Baumann polycondensation via complex monomer. Polarizing microscope with hot stage, thermal analysis and X-ray diffraction were used to investigate the structure and properties of the copolyesters. The effects of structural units, such as flexible spacer, noncolinear meta-linked phenylene unit, crankshaft unit, kink with flexible bridging unit and various substituted benzene rings on melting temperature of aromatic copolyesters were studied and discussed on the basis of crystalline structure of the polymers.     

热致液晶共聚酯的熔融行为及结晶结构研究

采用ＤＳＣ及ＷＡＸＤ手段对含对羟基苯甲酸热致液晶共聚酯的相变行为及结晶结构进行了初步研究。结果表明，聚合物中存在两种同属于正交晶系的不同堆积形态结晶结构，在相变上表现为双重熔融峰。