STUDY ON LIQUID CRYSTAL POLYMERS WITH TWO-DIMENSIONAL MESOGENIC UNITS

A series of liquid crystalline polymers with two-dimensional mesogenic units were synthesized by solution polycondensation at low temperature. All the polymers were liquid crystalline. The melting temperature T_m (except that with substituent of methoxy) and the clearing temperature T_i of the polymers change regularly with varying of the length of the alkyl substituent groups.     

Synthesis,liquid crystalline and luminescent properties of trimeric phenylenevinylene with end-groups of(R)-(+)-2-methylbutyric acid ester

The trimeric phenylenevinylene with the symmetrical chiral end-groups(ChTPV) was synthesized.The liquid crystalline and luminescent properties of the ChTPV have been studied by differential scanning calorimetry(DSC),polarized optical microscopy (POM),absorption and photoluminescence spectra.The results indicated that the ChTPV exhibits mesophase over a wide temperature range and a typical optical texture of smectic phase.In contrast with the spectra of the solution,that of the film showed blue-shift in m...     

SYNTHESIS AND CHARACTERIZATION OF PALLADIUM COORDINATING IMINE SIDE CHAIN LIQUID CRYSTALLINE POLYSILOXANES

New thermotropic chloro-bridged dinuclear palladium coordinating imine side chain liquid crystalline polysiloxanes have been synthesized. Their mesomorphic properties have been investigated by DSC, X-ray diffraction and polarizing microscopy. The polymeric complexes show nematicdiscotic (Nd) mesophase. It is found that the temperature range of liquid crystalline state of chloro- bridged polymeric complexes is much wider than that of acetato- bridged ones and imine side chain polysiloxane. This indicates that the disc-like chloro-bridged palladium complexing units play a role as mesogen in mesophase.     

SYNTHESIS AND MESOGENIC PROPERTY OF Pd-COORDINATING AZO-TYPE SIDE CHAIN LIQUID CRYSTALLINE POLYSILOXANE

A novel palladium-coordinating Azo-type liquid crystalline polysiloxane (Pd-AZLCP) has been synthesized by chelation reaction of polymeric ligand, Azo-type liquid crystalline polysiloxane(AZLCP), with palladium dichloride and potassium chloride in the presence of tetrahydrofuran (THF) as reaction medium instead of dioxane/water system, which has been used since Cope first reported the synthesis of palladium-azobenzene in 1965 . The mesogenic behaviors examined by DSC, temperature-variable X-ray diffraction and polarizing microscopy indicate that the incorporation of Pd ions into the liquid crystal polymer can play a positive effect on the mesogenic property of the parent polymeric ligand. It is exhibited that the isotropization temperature T_i is increased and the mesophase range ΔT has been widened, too.     

STATISTICS OF A NOVEL CLASS OF LIQUID CRYSTAL POLYMERS

A novel class of the liquid crystal polymers with mesogens laterally attached to flexible main chain backbones has been synthesized recently by us. While the flexible backbones tend to take configuration of maximum entropy the mesogenic side groups tend to orientate because of the anisotropie soft dispersion forces. A mean field theory is presented to describe the competition between these two trends which makes it possible for this class of polymers to show anisotropic (liquid crystal) phase within certain temperature range where the polymer main chains and the side chain mesogens will take approximately parallel arrangement, which is different from the normal side chain liquid crystal polymers. The temperature range of the liquid crystal phase, its ordering and phase transition all depend on the flexibility of the backbone, the strengthof the anisotropic forces of the side groups and the hinge elasticity. The results show that the liquid crystalisotropic phase transition is of the first order. The phase diagram, i. e. the dependence of the transition temperature on the structure of the polymers is also given.     

SYNTHESIS AND-CHARACTERIZATION OF THE SOLUBLE, HIGH MOLECULAR WEIGHT AND LADDERLIKE POLYHYDROSILSESQUIOXANE AND ITS COPOLYMERS

The high molecular ladderlike polyhydrosilsesquioxane (LPHSQ) and its copolymer, ladderlike random copolymethylhydrosilsesquioxane (LR-PMHSQ) and ladderlike block copolymethylsilsesqui-oxane(LB-PMHSQ) have been synthesized by a preaminolysis reaction of the corresponding trichlorosilane with 1 ,4-phenylene diamine(PDA) then by hydrolysis and polycondensation reactions The thermographs of these polymers measured by DSC method indicate that these macromolecular backbones are very rigid as seen from the DSC curves which are almost horizontal from room temperature until 350 ~C without noticeable glass transition. The content of Si—H group in the polymers can be regulated by changing the composition of the two copolymerized monomers. So the ladderlike polymers including its copolymers can be the useful precursors for the functional polymers, especially such as fishbone-like liquid crystalline polymers.     

Liquid crystal character controlled by complementary discotic molecules mixtures: Columnar stacking type and mesophase temperature range

In this work, the mesophase properties were tuned via mixing two discotic molecules with structural complementarity. Compared with the liquid crystalline hexakis(n-hexyloxy)triphenylene(H6TP)materials(columnar hexagonal phase from 53 8C to 91 8C), mesophase types as well as phase transition temperatures varied with the introduction of crystalline hexaazatriphenylene derivative(PBH)molecules. The introduction of less than 33% amount of PBH disrupted the columnar hexagonal phase formed by H6 TP remarkably, followed by the decreased clearing temperatures of liquid crystals. As the PBH amount was further increased, the destroyed columnar hexagonal phase was turned into the columnar rectangular phase, in which H6 TP and PBH molecules together formed the columnar mesophase. The formation of new mesophase contributed to the enlarged mesophase temperature(from44 8C to 144 8C). We speculated that the alkyl chains interaction induced by the PBH component competed with the strong p–p stacking between H6 TP molecules, thus altering the liquid crystalline properties including mesophase types and phase transition temperatures.     

SYNTHESIS AND CHARACTERIZATION OF COMB-LIKE POLYMERS BEARING HETEROCYCLIC AZO GROUP AND MESOGENIC GROUP

The synthesis and characterization of a series of novel comb-like polymethacrylates bearingheterocyclic azo group and mesogenic group are described. The thermal properties of the polymers such asthermal stability and phase transition behavior were investigated by thermogravimetric analysis, differentialthermal analysis and polarizing optical microscopy techniques. The experimental results show that all thesynthesized polymers do not exhibit liquid crystallinity except the homopolymer of the mesogenic monomerMAPB2 and the glass transition temperatures of the polymers increase with increasing content of azo moietyin polymers linearly.     

STUDY ON LIQUID CRYSTALLINITY OF POLY(N-VINYLCARBAZOLE)

The liquid crystallinity of poly(N-vinylcarbazole) was studied by using powder X-ray diffraction, polarized opticalmicroscopy, and differential scanning calorimetry. The results show that the lower molecular weight fractions of this polymerdo not form a liquid crystalline phase, while the samples of sufficiently high molecular weight do form a mesophase attemperatures above the glass transition. The lowest value of the degree of polymerization for PVK to form a stable liquidcrystalline phase was found to be in the range of 150 to 200, significantly higher than the value of 50 for most conventionalside chain liquid crystaline polymers.     

STUDIES ON THE KINETICS OF PHASE TRANSITIONS OF A MAIN CHAIN THERMOTROPIC POLYESTER

The kinetics of phase transitions including a transition between mesophases were studied for a main-chain thermotropic polyester by means of DSC and depolarizing transmittance techniques. The isothermal process of these transitions was found to be described by the Avrami equation to high conversions. The Avrami exponents n are about 2,4, 5.3 and 2.2 for liquid crystallization, transition between mesophases and crystallization from mesophase respectively. The liquid crystallization from isotropic liquid phase occurs at very low undercoolings with high transformation rate. This behavior is explained as the results of the smaller value of the surface free energy for mesophase than that for crystallites which is evidenced by the very weak temperature dependence of liquid crystallization rate.     

SYNTHESIS AND PROPERITIES OF SHISH-KEBAB-TYPE LIQUID CRYSTALLINE POLY（p-PHENYLENE）S

Abstract The novel shish-kebab-type liquid crystalline poly（p-phenylene）s were synthesized through Suzuki coupling reaction from 2,5-bis[（4-n-alkoxyl）benzoyloxy]1,4-dibromobenzene （monomer 1） and 1,4-benzenediboronic acid bistrimethylene cyclic ester （monomer 2）. Their structure and properties were characterized by GPC, DSC, X-ray diffraction and polarizing optical microscope （POM）. It was found that the polymers turned to liquid crystalline phase above their melting point. The melting point （Tm） of the polymers decreases when the length of the alkoxy tails of the mesogenic units increases. The mesophase was identified by X-ray diffraction method. The polymers could dissolve in common organic solvents and show strong blue fluorescence. The maximum absorption bands of polymers prepared from annealed films have large red-shift due to the spontaneous orientation of the liquid crystalline side chains. The same phenomena were also observed in the fluorescence spectra.     

MICROMOLDING ON CURVED SURFACES WITH THERMOPLASTICS

Microstructures were produced on curved surfaces and micro-protrusions by using direct micromolding with fourthermoplastic polymers. This method is simpler and more convenient than micromolding with liquid prepolymer or using theμTM method. By repeated molding, crossed structures were produced with a stamp prepared only with lines. The processingvariables including the softening temperature of the polymers and heating time were discussed. The result shows that theoptimal molding temperature is preferably slightly higher than the melting temperature of the thermoplastic polymers, atwhich polymers are in the critical states of being melted. This method can be applied to many polymers except those with high softening temperatures or high rate of shrinkage upon temperature change.     

STUDY ON AB-CROSSLINKED POLYMERS Ⅰ. THE SYNTHESIS AND MECHANICAL PROPERTIES OF AB-CROSSLINKED POLYMERS BASED. ON PU/PS

The AB-crosslinked polymers (i.e. ABCP) with polystyrene as chain A and vinyl group blocked prepolymers of polyurethanes (PU) as chain B were synthesized and studied. The results of dynamic mechanical spectrometry (DMS) show that the compatibility between the components A and B can be improved greatly through chemical crosslinking during the formation of ABCPs. This effect is especially pronounced when short chain prepolymers is chosen as one of the components. It is apparent that the degree of crosslinking between the two components plays a major role in determining their compatibility. Copolymerizafion of styrene with maleic anhydride in chain A can improve the compatibility and broaden the damping temperature range. Mechanical properties of the sythesized ABCPs were also studied.     

SYNTHESIS AND CHARACTERIZATION OF LIQUID CRYSTAL POLYMERS WITH T-SHAPED TWO-DIMENSIONAL MESOGENIC UNITS

Two series of new liquid crystailine polymers with T-shaped two-dimensional mesogenicunits were synthesized by low temperature solution polycondensations of 4-substituted N-2, 5- dihydroxybenzylidene aniline monomers with different diacyl dichlorides. The polymerswere found to be nematic and shown liquid crystailine behavior. The melting temperatureT_m and the clearing temperature T_i of the polymers change regularly with varying of themonomer structures.     

MESOMORPHIC BEHAVIOR AND MULTIPLE MELTING TRANSITION OF AROMATIC POLYESTER FRACTIONS

Fractions of an aromatic polyester have been studied by DSC, polarizing microscopy, SALS and WAXS techniques. The intrinsic viscosity of the samples in tetrachloroethane is ranging from 0.197 to 0.591dl / g. All the samples exhibit enantiotropic liquid crystal behavior, and the thermal stability of mesophase decrease withlowering the molecular weight of the fractions. The glass transition temperature keeps almost constant for allthe samples, however its value for supercooled mesophase is about 20~C lower than that for amorphous phase.Multiple melting phenomenon was also found for samples crystallized from their mesophases and was similarto that observed for nonliquid crystal forming polymers.     

Mechanistic Insights into the Shear Effects on Isotactic Polypropylene Crystallization Containing β-Nucleating Agent

The crystalline structures and crystallization behaviors of iPP containing β nucleation agent TMB-5(iPP/TMB-5) were investigated by synchrotron radiation wide angel X-ray diffraction(SR-WAXD), differential scanning calorimeter(DSC) and polarized light microscope(PLM). It was found that α-crystallization lagged behind β-crystallization at normal temperatures, but the discrepancy reduced with increasing temperature. TMB-5 could not induce β-iPP when the nucleation agent is wrapped up with α-crystal that crystallized at high temperatures. The polymorphic composition of iPP/TMB-5 was susceptible to the introductory moment of shear. New crystallization process of β-nucleated iPP was proposed to understand the experimental phenomena which could not be explained by those reported in the literature. It was supposed that polymer crystallization initiated from mesophase, and the formations of iPP crystals involved the organization of helical conformation ordering within mesophase. It was proposed that the iPP melt contained mesophases with stereocomplex-type ordering of right-handed and left-handed helical chains which could be disturbed by shear or TMB-5, leading to different polymorphic structures.     

SYNTHESIS AND PROPERTIES OF METAL COMPLEXES OF β-DIKETONE BASED SIDE CHAIN LIQUID CRYSTAL POLYSILOXANE

A new type of metal coordinated liquid crystalline polymers has been synthesized by complexation of metal ions with β-diketone based side chain liquid crystal polysiloxane (DKLCP). The complexation of copper ions with DKLCP greatly increases the phase transition temperature T_k from crystalline state to liquid crystalline state and T_(cl) from LC to isotropic state and makes the range of phase transition ΔT (ΔT=T_(cl)-T_k) widened. These complexes are soluble in common organic solvents. However, the incorporation of europium ions into DKLCP molecules gives rise to reduction in liquid crystallinity and crosslinking in some cases. The DKLCP coordinated with suitable amount of Eu ions can show good liquid crystallinity and fluorescent property.     

SYNTHESIS AND CHARACTERIZATION OF LIQUID CRYSTAL POLYMERS WITH T-SHAPED TWO-DIMENSIONAL MESOGENIC UNITS (Ⅱ)*

A series of liquid crystalline polymers with T-shaped two-dimensional mesogenic unitswere synthesized via low temperature solution polycondensation of 2-(4'-alkoxy-phenyl)hydroquinone with various diacyl dichlorides. The polymers were found to be nematic andshown thermotropic liquid crystalline behaviors through observations using DSC, polarizedmicroscopy and X-ray diffraction. The melting temperature T_m and the isotropizationtemperature T_i of the polymers change regularly with varying of the monomer structures.     

The Transition in the Melt of Fluorinated Ethylene-Propylene Copolymer

The subject of the transition in linear polymer melt has been of particular interest since thediscovery of liquid crystal polymers.The transitions in several polymer melts have been recog-nized in recent years.These polymers are mainly rigid chain in nature and the transitions wereassigned as mesomorphic.Recently we have found a transition in the melt of tetrafluoroethylene-hexafluoropropylene copolymer (FEP copolymer). The authors~([1]) have found that the morphology of FEP copolymer is critically dependent onthe temperature of melt near 310?20?.When the melt was held at the temperature above itsmelting temperature and below 310?,the randomly arranged lamellas morphology was obtained.When the melt was held at the temperature above 320?,the spherulitic morphology was formed.When the copolymer crystallized from the intermediate temperature range,the rodlike morphologywas usually obtained.The variation of morphology with temperature can be easily detected by Small Angle Light Scattering technique.Also the crystallization curves,measured with the Per-     

Modulating Bandgap and HOCO/LUCO Energy of Semiconducting Polymer by Copolymerization or Incorporation of Electron Withdrawing/Releasing Groups

The modulation of bandgap and HOCO/LUCO energies of conjugated polymers by copolymerization or by incorporation of electron withdrawing/releasing groups is studied.The study was conducted by band structure calculation applying density functional theory with generalized gradient approximation.The polymers and copolymers were modeled as 1D infinite system with periodical boundary condition along the molecular direction.It is concluded that the bandgap and HOCO/LUCO energies of conjugated polymers depend on both electron withdrawing/releasing effects and non-bonding interaction between a side group and the conjugated systems.