Liquid crystalline polymers and elastomers

The results of experiments and theory correlate increasingly well in the investigation of liquid crystalline polymers. Current work focuses on rheology and the behavior of blends of thermotropic LC polymers, due to reemerging economic interest in these materials. Research on liquid crystalline elastomers concentrates on potential applications such as artificial muscles and lasing.     

Dichroic dyes,and liquid crystalline side chain polymers

Functional guest molecules incorporated into LC-side-chain polymers lead to polymeric materials which combine the physical and optical anisotropic properties of liquid crystals with the special functions of the guest components. This contribution focused on dichroic dyes, but the results are transferable to other guest moieties. The covalent fixation of the dye to the polymer backbone affords several advantages. Liquid crystalline materials with high dye concentrations were obtained opening the way to the preparation of highly ordered, optical uniaxial films with adjustable thickness and optical density. Thin well aligned LC-polymer films can in principle be used as an active medium for reversible optical information storage and mixtures of dye-containing copolymers in low molar mass liquid crystals can be used in displays. Current developments in the area of ferroelectric chiral smectic-C side-chain polymers will further enhance interest in this area.     

New stimuli-responsive polymers derived from morpholine and pyrrolidine

The preparation of three new ionizable monomers: N-ethyl morpholine metacrylate (EMM), N-ethyl morpholine methacrylamide (EMA) and N-ethyl pyrrolidine metacrylamide (EPA) and their respective homopolymers poly-EMM, poly-EMA and poly-EPA prepared by radical polymerization in solution, is described. The systems have been characterized by NMR and FTIR spectroscopic techniques, determined their glass transition temperatures by DSC and their respective pKs. Moreover, crosslinked samples were prepared by bulk polymerization using N,N-methylene bisacrylamide (BAam) and the trifunctional 1,3,5-triacryloylhexa-hydro-1,3,5-triazine (135-T) as crosslinkers. The studies of swelling kinetics were carried out in different pH buffer solutions (2, 7.4 and 10) in a thermostatic bath at 37 °C showing hydration degrees that go from 2,600% to about 200% depending on the pH and on the crosslinker used. The systems seem to be suitable for the preparation of smart hydrogels for drug delivery and Tissue Engineering.     

板料弯曲回弹影响因素的有限元模拟研究

通过静态力学、动态力学实验方法,研究了热致性液晶聚合物(LCP)的种类对环氧树脂共混物在不同温度下的拉伸强度和应力-应变曲线的影响,通过TEM观察了共混物的相形态结构.结果表明,反应型液晶聚合物(LCPU)比其它种类的液晶聚合物对环氧树脂的改性效果更好;在不同温度下,其拉伸强度和应力～应变行为均比其它材料优越;固化物的动态力学结果表明:反应型的液晶聚合物键入了固化网络,出现新的松弛,TEM结果表明,反应型的液晶聚合物在基体材料中形成大小在nm数量级的液晶聚集微区,没有反应基团的液晶聚合物PHBHT在10%的加入量下,与环氧的共混物结构也有液晶聚集微区产生,但是聚集区大小在微米量级.     

Chiral melamine derivatives: design, synthesis, and application to mass spectrometry-based chiral analysis

A novel class of chiral melamine derivatives has been designed and synthesized. The ability of these compounds to perform chiral recognition toward 19 natural chiral alpha-amino acids has been investigated by electrospray ionization tandem mass spectrometry for the first time. The enantioselectivities of these new chiral selectors are encouraging. To elucidate some mechanism and regularity in the chiral recognition process using chiral melamine derivatives as chiral selectors, the effect of different noncovalent interactions caused by various chiral or achiral moieties in melamine derivatives on the chiral recognition in the gas phase has been studied at the same time. The result shows that electrostatic, hydrogen bond, pi-pi stacking, and steric interaction between selector and analyte play important roles in the association and enantioselective recognition of amino acids with the chiral melamine derivatives as chiral selectors. Enantiodiscrimination for analytes with different structures and properties could be improved by modifying substituents in melamine derivatives on purpose.     

Synthesis and properties of novel chiral side-chain liquid crystalline polysiloxanes containing different chiral pendant groups

Two novel chiral liquid crystalline monomers, and a series of their corresponding chiral side-chain polymers (P₁–P₇) based on poly(methylhydrogeno)siloxane have been prepared. The chemical structures and liquid crystalline properties of the synthesized monomers and polymers have been investigated using various experimental techniques. Thermal analysis shows that all polymers have wide mesophase temperature ranges with a high thermal stability. With the increase of M₂ molar ratio in the polymer systems, the isotropic phase transition and glass transition temperatures of all polymers increase, and the temperature ranges of N* phase and mesophase become broad. The effect of cholesteryl mesogens on mesophase behaviors, optical properties, and molecular arrangement of LC polysiloxanes and their advanced applications have also been discussed. For homopolymer P₁, it shows a single S_A phase. With increasing the content of M₂ in the polymer systems, P₂ and P₃ reveal a S_A–N* phase transition when they are heated, and P₄–P₇ reveal a N* phase. For N* phase polymers P₄–P₇, the reflection wavelengths exhibit blue shift, suggesting that the pitch decreases with a decrease in the amount of the smectic domains induced by the M₁. The reflection wavelengths of P₄–P₇ are almost across the entire visible region when they are heated, which offer stremendous potential for various optical applications. For P₂ and P₃, the reflection wavelengths show a very steep change around the temperature of the S_A–N* phase transition, which can be used as thermally sensitive liquid crystal devices requiring fast response, such as sensors, and thermally induced tuning.     

Liquid crystalline elastomers: dynamics and relaxation of microstructure

The equilibrium mechanical response of nematic elastomers can be soft or hard depending on the relation between the imposed strains and the nematic director, in particular, if the local nematic director is able to respond by rotating. The dynamical response proves to be equally unusual. We examine the linear dynamic mechanical response of monodomain nematic elastomers under shear and the aspects of time-temperature superposition of the dynamical data across phase-transition regions. In the low-frequency region of the master curves, one finds a dramatic reduction of rubber plateau modulus and the rise in internal dissipation: in the shear geometries compatible with dynamic soft elasticity. Power-law variation of the storage modulus with frequency G' proportional, variant omega(a) agrees very well with the results of static stress relaxation, where each relaxation curve obeys the analogous power law G' proportional, variant t(-a) in the corresponding region of long times and temperatures.     

Synthesis and characterization of novel liquid crystalline polymers containing cholesteryl pendant groups

In order to investigate the chiral effect of cholesteryl pendant groups on the induction of the cholesteric phase, a new cholesteryl-containing liquid crystalline monomer was synthesized and copolymerized with an achiral comonomer in various molar ratios. The layer-like arrangement of the smectic mesophase with different monomeric compositions of copolymers was investigated using an X-ray diffraction analysis. The cholesteric liquid phase was induced by the chiral segments; the dependence of the reciprocal central reflection wavelength on the mole fraction of the chiral monomer for copolymers was investigated. This paper demonstrates the effect of chiral pendant groups on the induction of the cholesteric phase and layered molecular arrangement of side-chain liquid crystalline polymers.     

Thermal behavior and molecular simulation of liquid crystalline polymers containing a pentamethylenic spacer

The paper presents a study concerning the thermal stability and molecular simulation of some aromatic polyethers, containing a pentamethylenic spacer. The polymers were synthesised using a phase transfer catalysis technique, starting from 1,5-dichoropentane and different bisphenols: 4,4^′-dihidroxyazobenzene, 4,4^′-dihidroxydiphenyl and bisphenol A. For the investigated polymers the molecular simulation was performed prior the synthesis in order to predict the possibility of liquid crystalline behavior. Molecular simulation was also used as a complementary analysis method for a better understanding of the thermal behavior. Thermogravimetric analysis, in static air atmosphere, with a heating rate of 10 °C/min, was used. Cerius² and Hyperchem programs were used to perform the molecular simulations. All the polymers present a good thermostability with weight loss being up to 300 °C. The kinetic characteristics suggest a complex degradation mechanism, based on successive reactions. The inter-chain interaction estimated using the polar surface and the chain conformation do not significantly influence the polymer thermostabilities. A comparison between simulated and experimental values of the isotropisation temperature and temperature corresponding to 50% weight loss was performed.     

Photo-switching and nonlinear optical behaviors of center linked bent-core azobenzene liquid crystalline polymers

A new class of two series (I and II) of center linked bent-core azobenzene liquid crystalline polymers were prepared. They were prepared from two different spacer lengths (2 and 10) between polymer backbone and bent-core mesogen. The bent-core mesogen possesses photoactive linking group with variable terminal chains (7, 8, and 9). The synthesized precursors, monomers, and polymers were characterized by FT-IR, ¹H NMR, and ¹³C NMR spectroscopy. Thermal stability of polymers was examined by thermogravimetric analysis. The mesophase transition of monomers and polymers were observed through polarized optical microscopy, and confirmed by differential scanning calorimetry. Among the two series of polymers, the second series of polymers possesses liquid crystalline properties. The photo-switching properties of bent-core azo polymers were investigated using UV–Vis spectroscopy, trans to cis isomerization occurs around 35 s in chloroform and 65 s in thin film, where as reverse processes take place almost 32 h in chloroform. The photo-switching processes of polymer IIa precedes faster and also longer time thermally stable when compared with recently reported similar polymers. Negative optical nonlinear refractive index and optical limiting properties of the polymers were measured using Nd-YAG laser.     

一种含有高分子液晶超滤膜的制备与性能

将自制的一种主链聚酯型高分子液晶添加到聚砜铸膜液中,在温度为８０℃下,制成了对牛血清白蛋白截留率大于９０％的超滤膜,研究了高分子液昌的添加对所制超滤膜性能的影响。结果表明,在相同实验条件下,含高分子液晶超滤膜的截留率相对于不含高分子液晶的超滤膜有较大提高,从６０％～７０％提高到９０％以上,考察了相关制膜参数如溶剂、高分子液晶浓度、添加剂种类、用量、聚砜的浓度、铸膜气氛温度、蒸发时间等对含高分子液晶超滤膜性能的影响。     

热致可逆变色胆甾液晶聚合物的制备和光学性能研究

合成了两种胆甾液晶单体,4-烯丙氧基苯甲酸胆甾醇酯M1和4-{4-[(4-烯丙氧基)-苯甲酰氧基]丁氧羰基}苯甲酸胆甾醇酯M2。将两种单体按一定比例与含氢聚硅氧烷(PMHS)共聚得到了一系列侧链液晶聚合物P1-P6。采用红外光谱(FT-IR)、核磁共振(1 H NMR)、差示扫描量热(DSC)、偏光显微镜(POM)和X射线等手段对单体及聚合物的结构、液晶性能和相行为进行了表征。通过分析表明单体M1、M2和聚合物为热致胆甾型液晶,聚合物在常温具有选择性反射现象,在升温—降温—再升温的过程中反射波长随温度升高发生蓝移,且聚合物具有良好的热稳定性和可逆变色性。     

三聚氯氰在活性单体及聚合物合成中的应用研究进展

本文综述了以三聚氯氰为原料，合成含烯丙基、环氧基等基团的均三嗪活性单体及以三聚氯氰的一取代物为原料合成线性聚氰酸酯和线性蜜胺的研究进展。     

Composite systems for display applications from cellulose elastomers and nematic liquid crystals

Composite systems made from cellulose derivatives solid films impregnated by a nematic liquid crystal can be used as electro-optical devices [H.V. Craighead, J. Cheng, S. Hackwood, Appl. Phys. Lett., 40 (1982) 22; M.H. Godinho, J.L. Figueirinhas, A.F. Martins, Liquid Cryst., 20(3) (1996) 373]. The electro-optical behavior of such cells depends on the nature of the cellulose derivative used, the nematic liquid crystal, the preparation conditions of the cells and of the cellulosic films, and the rugosity of the films' surface [M.H. Godinho, J.L. Figueirinhas, A.F. Martins, Liquid Cryst., 20(3) (1996) 373; M.H. Godinho, A.F. Martins, A. Almeida, J.L. Figueirinhas, 16th International Liquid Crystal Conference, Kent USA, June 24–28, 1996]. In this work we study the influence of preparation techniques, number of polymer layers (1–3 layers eac9 μm thick), thickness of the liquid crystal layer (8– μm) and ageing (9 months), upon the electro-optical response of the cells. The cells used in this work were shown to exhibit high transmission coefficients (up to 82%) in the activated state and high contrast (up to 266). They also show good temporal stability and the cells' optical behaviour is strongly dependent on the number of films' layers.     

功能侧链液晶聚丙烯酸酯及聚丙烯酰胺的合成

基于国内外最研究文献，系统论述了两种新型功能性液晶聚合物－侧链液晶聚丙烯酸酯及聚丙酰胺的合成方法，大分子链结构及其液晶相转变温度，指出这类聚合物合成方法简单，一般显示热致性向列型或近晶型液晶相，液晶相转变温度和液晶态温度范围随链结构的不同发生显著变化。     

Drug release from lipid liquid crystalline phases: relation with phase behavior

Introduction: We studied the release of propranolol hydrochloride (PHCl), a water-soluble amphiphilic drug, from monoolein (MO)/water and phytantriol/water systems. Methods: We related the dissolution profiles with phase behavior and viscosity of the different liquid crystalline phases. Diolein has been added aiming to stabilize the cubic phases and thus preventing formation of less viscous (lamellar) phases. Results: Formulations display first-order release rates and diffusion release mechanism. Some formulations (mostly MO) were close to zero-order release in the first 120 minutes. Discussion: Release mechanism can be influenced by phase changes during dissolution. Conclusions: Both MO and phytantriol show good potential to be used for propranolol hydrochloride sustained drug release.