聚芳醚酮与液晶聚酯多嵌段共聚物的合成表征

近年来,以热塑性聚合物为基体,热致液晶聚合物(TLCP)作为增强剂的高分子原位复合材料由于其具有优异的机械性能和优良的成型加工性能,已引起各国工作者的普遍关注和极大兴趣．然而由于自聚集和相分离作用的影响,大部分液晶聚合物与通常的热塑性聚合物基体基本不相容或弱相容,这对于提高原位复合材料的力学性能不利．     

STUDY ON THE BLENDS OF NYLON 66 AND LIQUID CRYSTALLINE POLYESTERS

Blends of polyamide (Nylon 66) with two different kinds of liquid crystalline polyesters were studied in all the composition range. Homogeneous samples were obtained by coprccipitation from 2 wt%. solution of blends. The thermal properties, crystallinity and morphology of these blends were studied by using DSC, polarizing microscopy, and scanning electron microscopy. The phase transition and morphology of the blends are markedly-influenced by the composition of liquid crystalline polyesters. The mechanical behaviour of PHB/HNA-Nylon 66 blend was improved. although polyamidc (Nylon 66)with the liquid crystalline polyesters were incompatible, but a rather strong interaction between the polymers did exist.     

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.     

The synthesis and thermal properties of polyepichlorohydrin side-chain liquid crystal polymers

The synthesis and characterization of a new series of side-chain liquid crystal polyepichlorohydrin (PECH) polymers are described. The structures and thermal properties of the synthesized polymers were investigated using IR, NMR, polarized optical microscopy and differential scanning calorimetry. A substantial increase of the glass transition temperature with the degree of substitution of side-chain groups was observed. Polymers with a degree of substitution of side groups, of at least 60%, exhibited thermotropic liquid crystalline behaviour. The polymers present thermal liquid crystalline behaviour and form Schlieren and thread texture upon cooling from the isotropic phase, after annealing for 120 min at different temperatures. In addition, the thermal decomposition of PECHOPhPhCN was studied by thermogravimetry under both nitrogen and air environments. The temperature of the maximum decomposition rate was about 340 °C. Weight loss decreased considerably after 350 °C and was approximately 98% at 700 °C. Chemical modification of functional polymers offers a simple method for obtaining liquid crystalline polymers whose transition temperature can be tailored by varying the amount of substitution, however complete substitution cannot be achieved.     

Calorimetric study of blends of poly(butylene terephthalate) and a liquid crystalline polyester

The thermal properties of solution-prepared blends of poly(butylene terephthalate) (PBT) and liquid crystalline poly(biphenyl-4,4′-ylene sebacate) (PB8) have been studied by differential scanning calorimetry (DSC). The smectic-to-isotropic (s → i) transition of the mesomorphic component is observed at temperatures slightly increasing with the PB8 content, in the 270–280°C range; on cooling, the mesophase formation (i → s transition) takes place at temperatures that decrease markedly with decreasing PB8 content. The temperatures of the crystal-to-smectic and smectic-to-crystal transitions of PB8 are almost invariant with blend composition. The melting and crystallization temperatures of the PBT phase decrease on increasing the content of the liquid crystalline component. These results, together with those of isothermal calorimetry of both the crystallization of the PBT component and the mesophase formation of the PB8 component of the blends, indicate that the two polymers are not immiscible in the isotropic state. In this latter state, however, the two polyesters undergo transesterification, which can be followed through changes in the DSC scans. The effect of the thermal history on the properties of the blends has been studied with particular attention. Both the dynamic and the isothermal calorimetric measurements provide evidence of an increase of the degree of crystallinity of PBT on addition of the liquid crystalline component up to about 35–50% by weight.     

Temperature dependent light transmission-light scattering switching of (homeotropic liquid crystalline polymer network/liquid crystals/chiral dopant) composite film

A (photo-polymerizable liquid crystal (LC) monomer/LCs/chiral dopant/photoinitiator) mixture with a smectic A (SmA)-chiral nematic (N*) phase transition was sandwiched between two ITO glass substrates which were not subjected to any surface orientation treatment. When an electric field-induced homeotropically oriented SmA phase of the mixture was irradiated with UV light, an oriented liquid crystalline polymer (LCP) network was formed upon photo-polymerization of the LC monomer. Then, a (homeotropically oriented LCP network/LCs/chiral dopant) composite with a SmA-N* phase transition was prepared. A focal-conic texture appeared in the heat-induced N* phase of the composite upon heating from the transparent state of the homeotropically oriented SmA phase; the focal-conic texture exhibited strong light scattering. Upon cooling the composite to the SmA phase, this phase was again homeotropically oriented due to the strong intermolecular interaction between the LC molecules and the homeotropically oriented LCP network. Thus, the transparent state of the SmA phase and the light scattering state of the N* phase occurred reversibly upon cooling and heating, accompanied by the thermal SmA-N* phase transition.     

Temperature dependent light transmission-light scattering switching of (homeotropic liquid crystalline polymer network/liquid crystals/chiral dopant) composite film

A (photo-polymerizable liquid crystal (LC) monomer/LCs/chiral dopant/photoinitiator) mixture with a smectic A (SmA)-chiral nematic (N*) phase transition was sandwiched between two ITO glass substrates which were not subjected to any surface orientation treatment. When an electric field-induced homeotropically oriented SmA phase of the mixture was irradiated with UV light, an oriented liquid crystalline polymer (LCP) network was formed upon photo-polymerization of the LC monomer. Then, a (homeotropically oriented LCP network/LCs/chiral dopant) composite with a SmA-N* phase transition was prepared. A focal-conic texture appeared in the heat-induced N* phase of the composite upon heating from the transparent state of the homeotropically oriented SmA phase; the focal-conic texture exhibited strong light scattering. Upon cooling the composite to the SmA phase, this phase was again homeotropically oriented due to the strong intermolecular interaction between the LC molecules and the homeotropically oriented LCP network. Thus, the transparent state of the SmA phase and the light scattering state of the N* phase occurred reversibly upon cooling and heating, accompanied by the thermal SmA-N* phase transition.     

半刚性乙酰氧丙基纤维素的制备与液晶相转变的影响研究

以羟丙基纤维素为原料,通过酯化反应合成了分子量较高的乙酰氧丙基纤维素,并用ＦＴ－ＩＲ表征了化学结构。以ＤＳＣ,Ｘ－ｒａｙ衍射ＰＬＭ和ＳＡＬＳ手段研究了产物的热致液晶相转变及其影响因素和溶致液晶性。实验表明,产物的乙酰基含量受合成温度和反应时间影响,其热致液晶的相转变温度和温域随乙酰基含量变化。     

Phase transition properties of vanadium oxide films deposited by polymer-assisted deposition

Vanadium dioxide (VO₂) films were synthesized on mica substrates by a polymer-assisted deposition method, followed by rapid annealing with different annealing temperatures. The crystalline structure and morphology of the films were investigated by XRD and FE-SEM, and their phase transition properties were studied by in situ FT-IR. The results indicated that the annealing temperature affected the crystalline structure and morphology of the films remarkably, which then resulted in varied phase transition properties. In particular, the films annealed at higher temperature showed more polycrystalline structure, increased particle size and reduced phase transition intensity. But the films exhibited the similar hysteresis temperature width with increasing annealing temperature.     

高于玻璃化温度Tg退火对无规聚甲基丙烯酸甲酯液-液转变的影响

液 -液转变是在非晶态高聚物中 ,高于玻璃化温度 Tg 的转变 ,是“固定流体”到真正液态的整链运动 ,是流动的开始 [1,2 ] .液 -液转变对于高分子材料挤出、压延、热可回复凝胶的形成、多相聚合物体系的混合、增塑剂和加工助剂在聚合物中的扩散等诸多问题的理解和解决有重要的指导意义[3] .目前研究的重点主要集中于聚合物本身的物性参数对液 -液转变的影响 ,而有关退火对其影响鲜有报道[4 ,5] .通常认为 ,非晶态高聚物在 Tg 温度以上处于热力学平衡态 ,因此在此温度下退火不会对其结构和性能产生影响 .但近来也有文献报道 ,非晶态高聚物在…     

一类可纺丝的全芳香热致性液晶共聚酯的合成和表征

利用Higashi芳香聚酯直接缩聚法的原理 ,采用一步混合投料直接缩聚的方法 ,以对羟基苯甲酸(PHB)、间苯二甲酸 (MPA)、4 ,4′ 二羟基二苯酮 (DHBP)和对苯二酚 (HQ)为单体原料 ,合成了全芳香共聚酯 .该合成方法反应条件温和 ,简单易控 ,产物分子量高 .用差热分析 (DSC)、热重分析 (TA)、偏光显微镜 (PLM)、广角X 射线衍射 (WAXD)等测试分析手段对共聚酯的热性能和液晶特性进行了表征 .研究结果表明 ,利用此方法合成所得的聚合物呈明显的向列型热致液晶特性 ,热稳定性高 ,并具有极易成纤的特点 ,有望成为一种可用于纺丝的全芳香热致液晶共聚酯材料     

Thermal switching characteristics based on smectic-A↔chiral nematic phase transitions of (liquid crystals/chiral dopant) composites,with and without side chain-type liquid crystalline polymer

The light switching characteristics induced by a thermal smectic A (SmA) ? chiral nematic (N*) phase transition were studied for homeotropically aligned [smectic A liquid crystal (SmA-LC)/nematic liquid crystal (N-LC)/chiral dopant] and [side chain type smectic A liquid crystalline polymer (SmA-LCP)/N-LC/chiral dopant] composites. A drastic change from a transparent SmA phase to a light-scattering N* phase occurred in both composites upon heating. In the case of the heat-induced N* phase for the (SmA-LC/N-LC/chiral dopant) composite, the N* phase exhibited weak light scattering due to formation of a scroll texture. On the other hand, in the case of the heat-induced N* phase for the (SmA-LCP/N-LC/chiral dopant) composite, the N* phase showed strong light scattering due to formation of a focalconic texture. The existence of a SmA-LCP was responsible for a higher contrast ratio between the transparent SmA phase and the light scattering N* phase for the (SmA-LCP/ N-LC/chiral dopant) composite than for the (SA-LCN/N-LC/chiral dopant) composite.     

Side chain liquid crystalline diethanolamine‐based polyesters with methoxy and/or nitroazobenzene mesogenic moieties

Side‐chain polyesters based on diethanolamine and 5‐hydroxyisophthalic acid with mesogenic methoxyazobenzene and nitroazobenzene groups were synthesized and their liquid crystalline properties were examined.

Four different types of polyesters were prepared by using various combinations of monomers differing in the mesogen group and the length of the spacer. The thermal and structural properties depend on the type of polyester as well as on the side chain length. The glass transition and isotropization temperatures increase when the methoxyazobenzene group is bound to a diol and decrease when it is bound to an isophthalic acid. Most of the polyesters are thermotropic liquid crystals and form a nematic phase on heating. Some polyesters exhibit shear induced isotropisation to nematic transition up to 25°C above the isotropization temperature.     

Phase behavior and structure development in extruded poly(ethylene terephthalate)/poly(ethylene‐2,6‐naphthalate) blend

Liquid–liquid phase separation and subsequent homogenization during annealing in an extruded poly(ethylene terephthalate) (PET)/poly(ethylene‐2,6‐naphthalate) (PEN) blend were investigated with time‐resolved light scattering and optical microscopy. In the initial stage, the domain structure was developed by demixing via spinodal decomposition. In the later stage, the blend was homogenized by transesterification between the two polyesters. The crystallization rate depended on the sequence distribution of polymer chains, which was determined by the level of transesterification rather than the composition change of separated phases. When the crystallization of PEN preceded that of PET, PEN showed a higher melting point. However, when the crystallization rate of PEN was slower than that of PET, the previously formed PET crystals suppressed the crystallization of PEN, causing the coarse crystalline structure of PEN to have a lower melting point. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 2625–2633, 2000     

Side chain liquid crystalline diethanolamine-based polyesters with methoxy and/or nitroazobenzene mesogenic moieties

Side-chain polyesters based on diethanolamine and 5-hydroxyisophthalic acid with mesogenic methoxyazobenzene and nitroazobenzene groups were synthesized and their liquid crystalline properties were examined.

Four different types of polyesters were prepared by using various combinations of monomers differing in the mesogen group and the length of the spacer. The thermal and structural properties depend on the type of polyester as well as on the side chain length. The glass transition and isotropization temperatures increase when the methoxyazobenzene group is bound to a diol and decrease when it is bound to an isophthalic acid. Most of the polyesters are thermotropic liquid crystals and form a nematic phase on heating. Some polyesters exhibit shear induced isotropisation to nematic transition up to 25°C above the isotropization temperature.     

Synthesis and properties of polyesters of isomeric poly(oxynaphthyleneoxy-2-bromoterephthaloyl)s

A series of aromatic polyesters were prepared from 2-bromoterephthalic acid and naphthalenediol isomers. Only the polymers obtained from 1,4-, and 1,5- and 2,6-naphthalenediols were thermotropic nematogens and those from bent naphthalenediols were not liquid crystalline. Only the polyesters derived from 1,4-, 1,5-, and 2,6-naphthalenediols were semicrystalline. The melting temperatures ranged from 319 to 374°C depending on the structure of naphthalenediol moiety. The glass transition temperature, T_g, ranged from 95 to 168°C. TGA studied revealed that the polyesters have fairly good thermal stability     

一个判别液晶聚合物状态的新方法

伴随液晶相转变而产生的转变焓、转变熵可提供有关各相的结构、状态及有序度等信息.本文从动力学、热力学角度分析了液晶聚合物从各向同性熔体冷却时系统的热熵变化,建立了液晶聚合物升降温过程中的热熵图,提出了定量判断液晶聚合物从各向同性熔体冷却后所处状态的新方法.     

Mesophase behaviour in fluorocarbon-hydrocarbon polyesters

A series of liquid crystalline main chain polyesters has been synthesized in which mesogenic, linear perfluoroalkyl groups are linked to aliphatic hydrocarbon chains. The liquid crystalline phase appears to be smectic B from X-ray diffraction data. Interesting differences in the mesophase transition temperatures and enthalpies are observed along the series, as the hydrocarbon and perfluoroalkyl contents are changed. These are discussed in relation to the length of the segments. One polymer was also synthesized from biphenyl-4,4'-dicarboxyic acid for comparison with the polyesters prepared using aliphatic dicarboxylic acids.     

Novel fluorescent main-chain liquid crystalline ionomers containing Eu(III) ions

Novel nematic fluorescent main-chain liquid crystalline ionomers containing Eu(III) ions (Eu-LCI) were synthesised by the use of bis(4-(chlorocarbonyl)phenyl) decanedioate (BD), 4,4-dihydroxybiphenyl (D), 2,5-dihydroxybenzoic acid (B) and anhydrous europium chloride. The chemical structures, liquid crystalline behaviours and fluorescence properties of Eu-LCI were characterised by various experimental techniques. The introduction of small amounts of europium ions endowed the LCI with excellent luminescence properties. POM results showed that europium ions did not change the liquid crystalline texture of the LCI. Fourier transform infrared imaging showed that europium ions were evenly distributed in the matrices of ionomers. A schematic diagram of nematic fluorescent LCI was established to demonstrate the interaction and distribution of the components. Eu-LCI showed reversible mesomorphic phase transitions, wide mesophase temperature ranges and high thermal stability. The thermogravimetric analysis (TGA) results showed that decomposition temperatures (5% weight loss) were greater than 308°C in all Eu-LCI. Eu-LCI can emit red light when excited. The luminescence intensity of Eu-LCI gradually increased with increase in Eu(III) ions from 0.3 to 1.5 mol%. The temperature dependence of luminescent intensity was studied in the liquid crystalline phase, where the fluorescence intensity of Eu-LCI decreased monotonically with increase in temperature.     

Dipolar motions and phase transitions in a side‐chain polysiloxane liquid crystal. A study by thermally stimulated depolarization currents

The relaxation mechanisms present in a side‐chain liquid crystalline polymer have been studied by Thermally Stimulated Depolarization Currents (t.s.d.c.), in a wide temperature range covering the glassy state, the glass transition region, and the liquid crystalline phase. The thermal sampling procedure was used to decompose the complex relaxations into its narrowly distributed components. Three relaxation mechanisms were observed in this polymer: a relaxation below the glass transition temperature that is broad and extends from −150°C up to −110°C, the glass transition relaxation whose maximum intensity appears at ∼20°C, and a relaxation above the glass transition temperature, in the liquid crystalline phase. The attribution of these relaxations at the molecular level is discussed. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 227–235, 1999