ECEC/AA液晶溶液取向态织构及其自由基聚合

利用光学显微镜和小角光散射等方法研究了乙基氰乙基纤维素(ECEC)/丙烯酸(AA)取向液晶态织构。在切应力作用下ECEC/AA液晶溶液形成带状结构,其中大分子链沿切应力方向呈锯齿形取向,溶液浓度越高,取向液晶溶液中大分子链有序性越高,带状织构中的条带愈窄。通过紫外光引发聚合方式获得了保持取向液晶态中带状织构的复合物膜。     

氰乙基纤维素/二甲基乙酰胺液晶溶液的研究

本文利用Abbe折射仪,热台偏光显微镜,小角光散射等方法研究了氰乙基纤维素/二甲基乙酰胺液晶溶液的形成,形态结构和某些性质。溶液随浓度的增加,从各向同性态经过两相共存状态,转变成为单一的液晶态。该液晶是胆甾型的。溶液的双折射Δn随浓度的增加或温度的降低而增大。在无外力作用时,液晶相由许多无规分布的取向微区组成。液晶溶液受切应力后形成“条纹结构”,大分子链沿切应力方向取向,并在各条纹中排列有序。     

THE SPHERULITE-LIKE STRUCTURE OF MAIN CHAIN THERMOTROPIC AROMATIC COPOLYESTERS

A new spherulite-like structure of main chain thermotropic aromatic copolyesters formed insolution cast specimens was observed and was studied by means of polarizing microscopy, X-ray diffraction,SEM and IR spectrometry. Results indicate that the spherulite-like structure of main chain thermotropicaromatic copolyesters formed from the casting solution (phenol/Cl_2CH_2CH_2Cl_2) is not a real crystal but only ahigh oriented arrangement of the macromolecular chains as a spherulite. This resulted from the interactionbetween the needle-like crystal of phenol and the rigid mesomorphic groups of molecular chain. The parallelpacking of extended copolyester molecules along the needle-like crystal of phenol leads to the formation ofthe spherulite-like structure.     

乙基醋酸纤维素溶致性液晶的研究

乙基醋酸纤维素溶于三氟乙酸、二氯乙酸、醋酸中.在浓度大于临界浓度时,形成胆甾型液晶态.溶液随浓度的增加,从各向同性态经两相共存转变成液晶态.在加热液晶溶液时,溶液转变成各向同性态.降低温度,液晶相再生成.在形成液晶过程中,存在过冷现象.在一定的条件下,液晶相以球状的形式存在.溶液的双折射△n在两相共存与完全液晶态间相互转变时会发生较大变化.乙基醋酸纤维素大分子链的刚性随有机酸溶剂体系的酸强度的增大而增大,使临界浓度C_1~*随溶剂酸强度的增大而减小.     

Bireactive calamitic liquid crystals derived from fluorene ester linkage

New thermotropic liquid crystalline monomer esters, containing fluorene in their mesogenic core with luminescent properties, were synthesized and characterized. The monomers studied exhibited a broad mesomorphic range and a nematic phase was identified by differential scanning calorimetry and polarized optical microscopy. Absorption and photoluminescence spectra studied in solution indicated that these compounds possess good optical stability. Linearly polarized light emission was observed in oriented thin films prepared by an in‐situ photopolymerization technique. The preparation of oriented thin films shows a preferential emission direction necessary for application in linearly polarized blue light‐emitting diodes.     

Bireactive calamitic liquid crystals derived from fluorene ester linkage

New thermotropic liquid crystalline monomer esters, containing fluorene in their mesogenic core with luminescent properties, were synthesized and characterized. The monomers studied exhibited a broad mesomorphic range and a nematic phase was identified by differential scanning calorimetry and polarized optical microscopy. Absorption and photoluminescence spectra studied in solution indicated that these compounds possess good optical stability. Linearly polarized light emission was observed in oriented thin films prepared by an in-situ photopolymerization technique. The preparation of oriented thin films shows a preferential emission direction necessary for application in linearly polarized blue light-emitting diodes.     

Aging of poly(2-methoxy-5-(2'-ethylhexyloxy)-1,4-phenylenevinylene)/toluene solutions and subsequent effects on luminescence behavior of cast films

Morphological effects in luminescence properties of a representative semiconducting polymer, poly(2-methoxy-5-(2'-ethylhexyloxy)-1,4-phenylenevinylene) (MEH-PPV), has recently attracted much attention. Previous studies indicated that short-term heat treatment of solution-cast MEH-PPV films may result in the formation of mesomorphic order that is responsible for the "red" emission around 640 nm, in contrast to the single-chromophore "yellow" emission near 590 nm from the disordered matrix. On the basis of microscopic and spectroscopic evidence for films cast from freshly prepared and aged solutions, here we show that prolonged storage of MEHyellowPPV solutions at room temperature or lower may result in retardation of the thermally induced mesophase formation in the subsequently cast films. According to small-angle neutron scattering and differential scanning calorimetric observations over aged MEH-PPV/toluene solutions, we propose that the suppressed transformation into mesomorphic order is due to further development of nanocrystalline aggregates that serve as physical cross-links among MEH-PPV chains in the solution state upon long-term storage. These solvent-induced nanocrystalline aggregates, however, do not exhibit new spectroscopic features beyond the suppression of "red" emission at 640 nm from the mesomorphic phase.     

Structural studies of laterally attached liquid crystalline polymers

Abstract

Structural studies of a series of laterally attached side chain liquid crystalline polysiloxanes have been made by X-ray diffraction. All but one exhibit a nematic phase with S_C-like short range ordering. The diffraction has been interpreted in terms of a model in which the mesogenic units form a ‘jacket’ around the polymer backbone. The backbone conformation has been studied by small angle X-ray scattering from oriented samples of mesomorphic solutions and by infrared dichroism measurements on oriented samples of the polymers. In both cases the results were consistent with the mesogens being oriented parallel to the backbone which is consistent with the ‘mesogen jacket’ model.     

Structural studies of laterally attached liquid crystalline polymers

Structural studies of a series of laterally attached side chain liquid crystalline polysiloxanes have been made by X-ray diffraction. All but one exhibit a nematic phase with S_C-like short range ordering. The diffraction has been interpreted in terms of a model in which the mesogenic units form a 'jacket' around the polymer backbone. The backbone conformation has been studied by small angle X-ray scattering from oriented samples of mesomorphic solutions and by infrared dichroism measurements on oriented samples of the polymers. In both cases the results were consistent with the mesogens being oriented parallel to the backbone which is consistent with the 'mesogen jacket' model.     

Synthesis and mesomorphic properties of some aryl β-D-C-glycosides

The synthesis of some aryl β-D-C-glycosides bearing long alkoxy chains (grafted on the carbohydrate moiety through the intermediate of an aromatic core) is described. Their mesomorphic properties (studied by microscopic observations under polarized light, DSC and X-ray diffraction) are presented.     

Synthesis and mesomorphic behaviour of comb-like polymers based on lipopeptides with two hydrophobic chains

Polymerizable lipopeptides with two hydrophobic chains were synthesized and transformed into comb-like polymers by radical polymerization. The structure of dry polymerizable lipopeptides and comb-like polymers and of their aqueous solutions was determined by X-ray diffraction. Comb-like polymers exhibit both thermotropic and lyotropic properties. Three types of mesomorphic structure were resolved: smectic B, smectic A and cylindrical hexagonal. The domains of stability of the mesophases and the values of their structural parameters were established.     

Structure and phase transitions in poly[bis-(2,2,3,3-tetrafluoropropoxy) phosphazene]

The structure and phase transitions in poly[bis-(2,2,3,3-tetrafluoropropoxy)phosphazene] have been studied by differential scanning calorimetry (DSC) and x-ray diffraction. Two crystalline phases and one mesomorphic phase are found, denoted I, II, and III, respectively. These phases convert reversibly one into the other on heating and cooling. The Phase I–Phase II transition occurs in a temperature range from 5 to 30°C whereas the Phase II mesophase (Phase III) transition proceeds above 80°C. Heats of transitions are measured to be about 29.0 J/g and 3.6 J/g, respectively. Crystalline Phase I is characterized by a monoclinic unit cell with the parameters: α = 24.4 Å, b = 9.96 Å, c = 4.96 Å, γ = 123°. The axes of both chains, traversing the unit cell, are directed along the “c” axis, the main chains having cis-trans conformation. Phase I is the common crystalline structure for the main chain and side chains. The structure of Phase II is controlled mainly by packing of the side chains. Transition of Phase II into mesomorphic Phase III is accompanied with distortion of packing of the side chains. Only regular packing of the main chains of macromolecules in the plane perpendicular to their axes exists in Phase III. Mesomorphic phase III is stable up to the degradation temperature of the polymer. A significant effect of stress on the Phase II–III transition in oriented samples was found.     

MORPHOLOGY OF A THERMOTROPIC AROMATIC POLYESTER

The crystalline morphology of a thermotropic aromatic polyester has been studied by microscopy techniques. Spherulites with ringed structure under polarizing micioscope were observed for solution cast specimens, They were composed of radially growing crystalline lamellae of thickness around 100. It was found that the molecules were packed in the thickness direction. Banded texture was observed in randomly packed domains for melt cast specimens. The bands have the same width and internal structure as those usually observed in oriented specimens of these polymers obtained by shearing their mesomorphic melt.     

Synthesis and mesomorphic behaviour of comb-like polymers based on lipopeptides with two hydrophobic chains

Abstract

Polymerizable lipopeptides with two hydrophobic chains were synthesized and transformed into comb-like polymers by radical polymerization. The structure of dry polymerizable lipopeptides and comb-like polymers and of their aqueous solutions was determined by X-ray diffraction. Comb-like polymers exhibit both thermotropic and lyotropic properties. Three types of mesomorphic structure were resolved: smectic B, smectic A and cylindrical hexagonal. The domains of stability of the mesophases and the values of their structural parameters were established.     

Reversible strain-induced order in the amorphous phase of a low-density ethylene/butene copolymer

This article deals with the characterization of the structural changes induced by uniaxial extension in the amorphous phase of an ethylene/butene copolymer. Volume change measurements indicate a reversible densification relevant to a strain-induced organization in the amorphous phase. The dynamic mechanical behavior shows an improvement of the β relaxation that reveals an important immobilization of the amorphous chains. The vibrational behavior investigated by means of Raman spectroscopy suggests that the strained amorphous chains are structurally analogous to the mesomorphic interfacial component. A discussion is made about the mechanism of the transformation of the amorphous phase into a mesomorphic structure compared to the more common strain-induced crystallization phenomenon. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35: 2151–2159, 1997     

Synthesis and mesomorphic properties of some bisegmented compounds derived from 4,4'-disubstituted biphenyl

New unsymmetrical disubstituted biphenyls have been synthesized. Two different chains (one hydrocarbon and the other fluorinated) are linked through an acetamide bond to 4-methoxy-4'-hydroxybiphenyl. Their mesomorphic properties have been characterized by light microscopy and by differential thermal analysis showing the peculiar contribution of the hydrocarbon chain and the fluorinated tail. The enhancement of the hydrocarbon moiety from one to twelve methylene groups leads to a decrease of the clearing temperatures; furthermore the enantiotropic behaviour is changed to monotropic. The variation of the fluorinated moiety generates strong effects on the transition temperatures. These mesomorphic properties are compared to those of their monocatenar perfluorinated analogues incorporating a connector of the ester or monosubstituted amide type.     

Polymerization of Bisacrylic Monomers within a Liquid-Crystalline Smectic B Solvent

A smectic B (S,) solvent may provide a very highly ordered, and possibly oriented, host medium for polymerization processes. Photochemical polymerizations of two bisacrylic monomers were therefore carried out in a S_B medium. The process conditions were chosen on the basis of a preliminary study of the monomer-solvent binary system carried out by differential scanning calorimetry (D.S.C.), optical microscopy and X-ray diffraction. The polymerization was then studied by D.S.C. at different reaction times. These measurements showed clearly that there is a point along the reaction path at which the growing polymer chains start segregating from the solvent and the mesomorphic bulk no longer acts as a reaction solvent but only as a reservoir for the ponomer. The polymer chains from that point keep growing only upon or between the faces of the S_B layers. Electron microscopy observations showed that the morphology of the final polymer is affected by this interlayer process.     

P(NIPAM-co-NVP)共聚物分子链水溶液中的可逆聚集研究

用溶液聚合方法合成了线型聚(N-异丙基丙烯酰胺-co-N-乙烯基吡咯烷酮)共聚物,通过弹性光散射(elastic light scattering,ELS)、荧光光谱与动态光散射研究了共聚物水溶液分子链可逆聚集的温度和时间依赖性.研究表明,升温时,ELS强度增加,分子链聚集;降温时,ELS强度降低,聚集的分子链解离.荧...     

THE OBSERVATION OF INTERNAL MOTION OF LINEAR POLYSTYRENE CHAINS IN CYCLOHEXANE AROUND 0 TEMPERATURE

A high molecular weight (M_w=1.85×10~7) polystyrene (PS) with narrow distribution was prepared by high vacuum anionic polymerization in tetrahydrofuran.By use of dynamic light scattering,the dynamics of PS chains in cyclohexane was studied around theθtemperature.For the first time,we have observed the internal motion of polymer chains in solutions below theθtemperature by using dynamic light scattering at smaller angles (even qR_g<1).     

Formation of hexagonal columnar phases by heterocyclic pyrimidine derivatives

The synthesis, characterization, and mesomorphic properties of a new type of heteronuclear compounds derived from pyrimidine as core group are reported. These compounds were prepared by condensation reactions of appropriate acetophenones and benzonitriles in the presence of trifluoromethanesulphonic anhydride. They were characterized by 1 H and 13 C NMR spectroscopy and elemental analysis, and their phase transitions characterized and studied by thermal analysis and polarizating microscopy. These compounds exhibit hexagonal columnar (Col h ) phases, as expected for disk-like molecules; the formation of columnar phases was found to be dependent on the numbers of alkoxy side chains attached. For those compounds having the same numbers of flexible side chains attached, the one with a preferred unsymmetric structure exhibited better mesomorphic properties. The observed improved mesomorphic behaviour of these compounds over other similar all-carbon heterocyclic compounds is attributed to the greater polarization of nitrogen atoms in the core ring.