侧基甲壳效应和甲壳型液晶高分子

侧链液晶高分子体系里,液晶基元可以通过尾接或腰接的方式与主链相连.一般认为,在液晶基元与主链间插入一段长度合适的＂柔性间隔基＂可有效实现主、侧链间的动力学去偶合,从而有利于侧基液晶基元之间的有序排列.作为一类特殊的腰接型侧链液晶高分子,甲壳型液晶高分子中体积较大的侧基（如棒状液晶基元）通过非常短的间隔基或仅通过一个碳-碳键直接横挂至主链上,这导致了强烈的甲壳效应,使得主链被迫伸展.因此,可从与＂柔性间隔基＂完全不同的角度出发,充分利用主链和侧基间的偶合作用,设计甲壳型液晶高分子.本文综述了腰接型侧链液晶高分子中的侧基甲壳效应、甲壳型液晶高分子中由主链与侧基相互作用所导致的特殊构象以及液晶相结构.研究表明,侧基甲壳效应在调控甲壳型液晶高分子的形状、尺寸以及螺旋结构等方面有重要作用.甲壳型液晶高分子可作为刚-柔嵌段共聚物的刚性链段,也可作为主/侧链结合型液晶高分子的主链部分参与到多层次分级超分子有序结构的构筑之中.     

偶氮苯为探针的液晶聚合物聚集形态研究

利用紫外-可见光谱,对比研究了尾挂侧链液晶聚合物和腰挂侧链液晶聚合物在结晶相和液晶相转变过程中的液晶基元取向情况.研究表明,石英基材表面倾向于诱导偶氮液晶基元垂直于基材排列;观察到了在液晶态尾挂侧链液晶聚合物和腰挂侧链液晶聚合物的不同取向行为.在室温下重新结晶数天后,腰挂液晶聚合物的紫外可见光谱缓慢回复.     

手征性侧链液晶高分子取向结构的研究

用偏光显微镜,红外二色性和Ｘ 射线衍射研究了一种手征性侧链液晶高分子的相态织构和弛豫行为．偏光显微镜观察这种侧链液晶高分子冻结取向液晶态薄膜时,可观察到与剪切方向垂直的明暗相间的条带织构．红外二向色性的结果表明,取向态中侧链上的介晶基元倾向于与剪切方向垂直排列．取向和非取向膜的Ｘ射线衍射揭示了该侧链液晶高分子具有反铁电性液晶的两套反相螺旋结构．取向薄膜在液晶态的弛豫行为表明,取向作用能促进侧链高分子近晶相层状结构的生长,而且介晶基元的取向在弛豫过程中能保持下来．     

具有不同柱状结构的苯并菲盘状液晶化合物的合成及自组装

合成了3种含有不同长度烷基链的苯并菲盘状液晶化合物; 通过1H NMR 和 MALDI-TOF MS对其结构进行了表征; 利用差示扫描量热法(DSC)、热台偏光显微镜(POM)和小角X射线散射实验(SAXS)对3种液晶化合物的自组装行为进行了研究. 结果表明, 烷基链的长度对苯并菲盘状液晶化合物自组装结构的影响显著. 柔性链为辛基的苯并菲盘状液晶化合物自组装成六方柱状液晶相; 柔性链为十二烷基的化合物自组装成倾斜柱状液晶相; 而柔性链为十六烷基的化合物则未形成液晶相.     

聚甲基丙烯酸胆甾醇酯共聚物的合成、结构与性能研究 Ⅳ.PMACE的相态转变及光学性质

Finkelmann和等人对侧链胆甾型高分子液晶的研究表明,将具有液晶功能的低分子基团,经过一个软段连接到柔性高分子主链上的梳型高分子在一定的温度下可以形成液晶态,调节侧链高分子液晶的分子结构、软段长度,可以改变其相态转变温度及微区形态。前已报导具有不同侧链结构的聚甲基丙烯酸胆甾醇酯共聚物的合成、相态转变及光学性质,本文通过对聚甲基丙烯酸胆甾醇乙烯酯共聚物(PMACE)的液晶态及结晶态的微细结构及相态转变与胆甾侧链含量关系的研究,给出了液晶态的形成条件及结构特征。     

甲壳素——一类新的液晶性多糖

"将甲壳素的结构与纤维素进行了比较, 并根据结构和链刚性指出其形成液晶态的可能性。简要介绍了制备液晶性甲壳素衍生物所必须的一些主要的化学修饰途径。叙述了15 种甲壳素衍生物的溶致液晶行为以及结构因素对它们液晶临界行为的影响。介绍了甲壳素衍生物形成的主要液晶态织构, 如指纹状织构、交替偏振场织构、条带织构和滴状织构, 以及甲壳素衍生物? 二氯乙酸溶液的热致相转变。综述了甲壳素的成纤性和液晶纺丝。     

5-{[(4′-正戊基氧-4-联苯基基)羰基]氧}-1-戊炔的相转变与相结构

采用差示扫描量热(DSC)、一维(1D)广角X射线衍射(WAXD)、热台偏光显微镜(PLM-hotstage)等研究手段对含联苯液晶基元的侧链液晶聚炔单体5-{[(4′-正戊基氧-4-联苯基基)羰基]氧}-1-戊炔(A3EO5)的本体相转变和相结构进行了研究.DSC和1D-WAXD实验结果表明,A3EO5在升温和降温过程中均呈现四个相转变过程,形成双向性液晶.样品从各向同性态降温至室温过程中,首先形成近晶A相,随后进入层内排列具有准长程有序的近晶B相,继续降温将形成层内为正交排列的近晶E相,在此之后样品进入晶相.PLM结果指出样品在各向同性态降温过程中分别形成球状织构、角锥织构和同心圆弧织构.     

基于“多链超分子柱”的侧链液晶高分子柱状相

一些具有伸展构象的侧链液晶高分子,如甲壳型液晶高分子或树枝化高分子,可以经由分子链的平行排列而呈现柱状液晶相.一般认为,该类柱状相的基本结构单元是单根高分子链所形成的超分子柱.而以几根链组装形成的超分子柱,即"多链超分子柱",也可作为侧链液晶高分子柱状相的基本结构单元,但多年以来这一现象并未引起人们的重视.近期,我们以hemiphasmid型侧链液晶高分子为研究对象,阐明了"多链超分子柱"是侧链液晶高分子柱状相微相分离的一种重要形式.本文从hemiphasmid型侧链液晶高分子的柱状相结构分析、化学结构对"多链超分子柱"的影响、"多链超分子柱"模型的理论分析与预测、"多链超分子柱"的"柱内缠结"以及hemiphasmid型侧链液晶聚降冰片烯的功能性等若干方面,对基于"多链超分子柱"的侧链液晶高分子柱状相进行了介绍.我们认为,深入研究"多链超分子柱"性质,将拓展侧链液晶高分子的应用领域,加深对高分子物理基本问题的认识.     

基于“甲壳”效应、不同尾链长度的离子液晶高分子的相行为和相结构

考察了一系列基于"甲壳"效应的离子液晶高分子poly(2,5-bis{[6-(4-butoxy-4?-imidazolium phenyl)k-alkyl]oxy carbonyl}styrene bis(fluoroborate)salts)Pk-6-BF4(k=4,8,12,16)的相行为和相结构.热重分析结果表明,该系列聚合物的热分解温度都在320?C以上,说明其均具有优异的热稳定性能.示差扫描量热仪结果表明,P4-6-BF4和P8-6-BF4仅表现出一个玻璃化转变,随着尾链的增长,P12-6-BF4和P16-6-BF4具有一个结晶熔融峰.偏光显微镜、一维广角X衍射、二维广角X衍射结果表明,该系列聚合物均形成稳定的近晶A相结构,并且随着烷烃尾链的增长,层间距增加、近晶结构内部分子堆积形式有所改变.     

甲壳型液晶高分子的独特液晶行为*

通过ATRP合成了低分散度的甲壳型液晶高分子PBPCS. 用GPC测定了聚合物的分子量及其分布; 用热分析仪测定了聚合物的玻璃化转变温度; 用POM, WAXD, DSC, Rheometrics ARES流变仪等多种手段表征了PBPCS的独特液晶行为: 升温过程中, PBPCS在玻璃化转变温度之上存在一个各向同性相, 进一步升温进入液晶相——六方柱状向列相; 降温过程中, 液晶相消失, 重新进入各向同性相. 这种独特相转变发生的关键因素是熵的增加, 是一个熵驱动过程.     

不同结晶度的乙二醇及其水溶液玻璃化转变与焓松弛

为了考察晶体成分对无定形成分玻璃化转变和结构松弛行为的影响,利用差示扫描量热法(DSC),结合低温显微技术,研究了乙二醇(EG)及其50％水溶液在不同结晶度时的玻璃化转变和焓松弛行为.采用等温结晶方法控制骤冷的部分结晶玻璃体中的晶体份额.DSC结果表明,对于部分结晶的EG,只有单一的玻璃化转变过程,而对于50％EG,当结晶度不同时,不同程度地表现出两次玻璃化转变（无定形相Ⅰ和无定形相Ⅱ）.相Ⅰ的玻璃化转变温度和完全无定形态的含水EG的玻璃化转变温度相一致;相Ⅱ的玻璃化转变温度要比此温度约高6 ℃.低温显微观察结果印证了DSC实验结果.DSC等温退火的实验和KWW(Kohlrausch-Williams-Watts)衰变函数分析结果表明,EG无定形和50％EG中的两种无定形有不同的焓松弛行为.     

Thermodynamic behavior of poly(3-alkyl thiophene) blends: Equilibrium cocrystal formation and phase segregation

The equilibrium cocrystal formation of poly(3-alkyl thiophene) (P3AT) blends has been studied by isothermal cocrystallization in a differential scanning calorimeter (DSC-7). The equilibrium melting points (T(m)0) of the cocrystals are measured using the Hoffman-Weeks extrapolation procedure. The equilibrium phase diagrams are of three different types: (a) concave upward, (b) linear, and (c) linear with phase separation at higher content of lower melting component. The phase diagram nature depends on the regioregularity difference and also on the difference in the number of carbon atoms in the pendent alkyl group of the components. The origin of biphasic nature of type "c" phase diagram has been explored from the glass transition temperature (Tg) measurement using a dynamic mechanical analyzer. The biphasic compositions show two glass transition temperatures (Tg) as well as two beta transition temperatures (T beta). The T(g)s of phase-separated regions correspond to almost the component values but the T(beta)s correspond to that of a lower (T beta) component value, and the other is higher than that of the higher (T beta) component value. Possible reasons are discussed from the interchain lamella thickness in the P3AT blends and molecular modeling using molecular mechanics program.     

MICRO-PHASE SAEPARATION IN EPOXY RESIN WATERBORNE PARTICLES DURING CURING PROCESS

Sub-micron sized phenolic epoxy resin waterborne particles were prepared by phase inversion emulsification. Micro-phase separation occurred during the curing process at high temperature. The as-prepared samples possessed one glass transition temperature （Tg） and two exothermal processes during DSC heating scannings. After being thermally treated above the exothermal peak temperature, they possessed two glass transition temperatures with the disappearance of exothermal peaks, whilst a core/shell structure was formed. This was likely related with the outward diffusion of reactive oligomers to the outer layer of particles.     

Side chain disorder and phase transitions in alkyl-substituted, conjugated oligomers. Relation to side-chain melting in P3ATs

Certain 4,4'-alkyl substituted 2,2'-bithiazole and bithiazole-thiophene oligomers display an endothermic transition in their DSC trace below their respective melting points. Variable-temperature FTIR, MAS-1H NMR, UV-vis spectra, and XRD all indicate that the thermal transition is due to a crystal-crystal phase transition that we have labeled alpha --> beta. FTIR shows a stepwise increase in the concentration of gauche defects at the alpha --> beta transition temperature, but MAS NMR spectra show little increase in the side chain motion until the mp is reached. UV-vis spectra demonstrate that the conjugated main chains remain essentially planar through the alpha --> beta transition, and significant deviations from planarity occur only at higher temperatures, but well below the mp. The close similarity of this behavior to the phase transitions in long chain n-paraffins and the "side-chain melting" phenomenon in poly(3-alkylthiophenes), P3ATs, suggests that the latter may actually be more accurately described as a crystal-crystal phase transition of the crystalline fraction, driven by side chain disorder.     

Poly(methyl methacrylate-co-ethyl acrylate) latex particles with poly(ethylene glycol) grafts: structure and film formation

Water-based copolymer dispersions were prepared using methyl methacrylate (MMA), ethyl acrylate (EA) (MMA/EA = 1:2), and a series of nonionic polymerizable surfactants, i.e., "surfmers" based on poly(ethylene glycol)-(meth)acrylates. The latexes were compared with the behavior of a conventionally stabilized (nonionic nonylphenol ethoxylate, NP100 with 84 ethylene oxide units) dispersion with the same MMA-EA composition (PMMAEA). A number of techniques were employed in order to characterize structure, dynamics, and film formation properties: solution/solid-state NMR, dynamic/static light scattering (DLS/SLS), differential scanning calorimetry (DSC), tensile/shear mode dynamic mechanical thermal analysis (DMTA), and atomic force microscopy (AFM). The surfmers were found to be miscible with the MMA-EA copolymer at room temperature, with 46-85 mol % of the reacted surfmer detected at the particle surfaces, and the remaining part buried in the particle bulk. In contrast, the NP100 surfactant formed a separate interphase between the copolymer particles with no mixing detected at room temperature or at 90 degrees C. For a 4.0% dry weight concentration, NP100 phase separated and further crystallized at room temperature over a period of several months. Composition fluctuations related to a limited blockiness on a length scale above approximately 2 nm were detected for PMMAEA particles, whereas the surfmer particles were found to be homogeneous also below this limit. On a particle-particle level, the dispersions tended to form colloidal crystals unless hindered by a broadened particle size distribution or, in the case of PMMAEA, by the action of NP100. Finally, a surface roughness (Rq) master plot was constructed for data above the glass transition temperature (Tg) from Tg + 11 degrees C to Tg + 57 degrees C and compared with the complex shear modulus over 11 frequency decades. Shift factors from the 2 methods obeyed the same Williams-Landel-Ferry (WLF) temperature dependence, thus connecting the long-time surface flattening process to the rheological behavior of the copolymer.     

Equilibrium phase diagram of polystyrene and 8CB

The experimental equilibrium phase diagram of a mixture of linear polystyrene of molecular weight M_w = 44,000 g/mol and 4‐cyano‐4′‐n‐octyl‐biphenyl (8CB) is established. The three transitions smectic A‐nematic, nematic‐isotropic, and isotropic‐isotropic are observed. The first two are observed both by optical microscopy and differential scanning calorimetry (DSC) while the isotropic‐isotropic transition could be seen only via optical microscopy. Two series of samples with the same compositions were independently prepared and yielded consistent results both by microscopy and DSC. Measurements of sample compositions with less than 50 weight % of 8CB were influenced by the vicinity of the glass transition temperature (T_g) of the polymer in the mixture. This quantity is also determined by DSC as a function of composition. A single T_g is observed, which decreases with composition of the LC. Other thermodynamic quantities such as the enthalpy variations of LC in the nematic‐isotropic transition and the fraction of LC contained in the droplets are also considered. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 1841–1848, 1999     

Metastability release of the form alpha of trehalose by isothermal solid state vitrification

Kinetic investigations of the polymorphic form alpha of anhydrous trehalose have been performed below its apparent melting temperature (Tm) by differential scanning calorimetry (DSC) and X-ray diffraction. The results reveal a spontaneous isothermal vitrification process which indicates that the phase alpha is in a very unusual superheating situation. This behavior has been attributed to the fact that the effective melting temperature (Tm(eff)) of the phase alpha is likely to be located far below the glass transition temperature (Tg) of this compound. The high viscosity of the liquid trehalose between Tm(eff) and Tg is thus invoked to explain the long lifetime of the phase alpha in this temperature range.     

Influence of molecular weight on the phase behaviors of comb‐like polymers with long n‐alkyl side chains based on mesogen‐jacketed liquid crystalline polymers

A series of comb‐like polymers, poly{2,5‐bis[(4‐octadecyloxyphenyl)oxycarbonyl]‐styrenes{ (P‐OC18s) with different molecular weights (M_n) and low molecular weight distributions have been successfully synthesized via atom transfer radical polymerization. The phase behaviors have been investigated by a combination of techniques including differential scanning calorimetry, polarized optical microscopy, wide‐angle X‐ray diffraction, and temperature‐variable FTIR spectroscopy. One hand, phase behaviors of the alkyl tails were strongly influenced by the mesogens of polymers, leading to the poor packing of the alkyl tails and the low melting. The other hand, the liquid crystalline phase structures of polymers were found to be strongly M_n dependent. The samples with M_n ≤ 4.6 × 10⁴ formed a smectic phase in low temperature and an isotropic phase in high temperature. The samples with M_n ≥ 5.2 × 10⁴ displayed a reentrant isotropic phase, which was separating the smectic phase and columnar nematic phase. Meantime, the experiment results showed that the glass temperature and the transition temperature from smectic phase to isotropic phase both slightly increased with the increase of M_nS; however, the transition temperature from isotropic phase to columnar phase sharply decreased with the M_nS improved. The reappearance of isotropic phase is due to the competing between the driving force of the enthalpy and the driving force of the entropy. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013     

Effects of the alkyl side-chain length on the structures of poly[oxy(N-alkylsulfonylmethyl)ethylene]s

The structures of poly[oxy(N-alkylsulfonylmethyl)ethylene]s (ASE-Ns) were examined with X-ray, IR, DSC, and polarized optical microscopy. The structures of ASE-Ns were strongly dependent on the alkyl side-chain length. ASE-2 and ASE-3, the shortest ones, were amorphous materials. ASE-4 and ASE-5 showed nematic characteristics. ASE-6–ASE-12 had smectic A structures. ASE-14 and ASE-16 could be labeled as more ordered structures higher than smectic A (probably smectic B or smectic E). The d-spacings of the first small-angle reflections were double the most extended side-chain length and linearly increased with a slope of 2.50 Å per methylene unit, regardless of the structural phases. The maintenance of the double-layered structure in all ASE-Ns may be due to the strong dipole–dipole interactions at both sides of the layers against the main chain for all amorphous, nematic, and smectic phases of ASE-Ns. The double-layered structure was maintained above the isotropic temperature, indicating that dipole–dipole interactions were not destroyed although the alkyl side chains melted during the isotropic transition. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 1868–1874, 2004