Synthesis Of Liquid Crystalline Polymers Research Articles

Synthesis of liquid crystalline polymers from polyethylene terephthalate and 4‐acetoxybenzoic acid: A kinetic study

AbstractLiquid crystalline polymers (LCPs) have been synthesized from polyethylene terephthalate (PET) and 4‐acetoxybenzoic acid (OB) through melt step‐growth polymerization. The presence of liquid crystalline texture is first examined using optical polarizing microscopy. The thermal durability of the developed systems is studied through thermogravimetric analysis. The kinetics of the polymerization processes is analyzed. The effectiveness of three catalysts commonly used in polyesterification is investigated. The effect of reaction temperature is also examined. The progress of polycondensation reactions over time takes a nonlinear behavior of slight sigmoidal shape, irrespective of whether or not the reaction is catalyzed. Simple second and third order equations, along with a nonlinear model, are used to determine the kinetic parameters characterizing these reactions. The rate of reaction is enhanced when the reaction temperature is increased. Overall, second‐order kinetics well describes the polymerization reactions when the data set is divided into two regions. Antimony trioxide induces a more visible enhancement to the rate of reaction, compared to zinc acetate and sodium acetate. The presence of a catalyst generally increases the reaction activation energy. This indicates that entropy factors outweigh the increase in activation energy and drive the catalyzed reactions to completion. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

Highly birefringent liquid-crystalline polymers for photonic applications: synthesis of liquid-crystalline polymers with side-chain azo-tolane mesogens and their holographic properties

We have synthesized highly birefringent liquid-crystalline polymers (LCPs) containing an azobenzene group directly connected to a tolane moiety (P3ATm), in which the alkyl spacer length (CH2)m was varied as m = 6, 9 and 12. All LCPs showed a nematic phase in a broad temperature range (>170 °C). The homogeneously aligned LCP films showed a high value of birefringence (about 0.4) and a large change in the birefringence could be induced by photoinduced alignment change. Grating formation of LCPs has been explored in a glassy state. The diffraction efficiency (η) showed a maximum when an order–disorder change was completed in the bright areas of the interference patterns. Studies on the effects of light intensity on the grating formation suggested that the diffraction efficiency was high (η = 20%) even though the alignment change of the azo-tolane moieties was small. Furthermore, the behavior of the grating formation was found to be dependent on the alkyl spacer length of P3ATm.

Synthesis of block copolymers consisting of liquid crystalline and amorphous segments by living/controlled radical polymerization

Living polymerization is most often observed in systems where the growing species are ions. In such systems the chain ends do not react to each other due to elestrostactic repulsion, but only to monomers allowing, this way, the control in structure of the formed polymer. Free radicals, which are the growing species in the radical polymerization, easely undergo combination and prevent a living radical polymerization. Thus, a great challenge to polymer science was in meeting a system that offered to the radical polymerization a radical stabillization alike in ionic polymerizations. At the same time, the radicals should undergo rapid propagation and should not be able to initiate new chains, in a controlled reaction. Some succesfull techniques of living/controlled radical polymerization, such as stable free radical polymerization (SFRP), mediated by nitroxide, INIFERTER and atom transfer polymerization (ATRP) will be overviewed here, as well as their application to the synthesis of liquid crystalline polymers.

Synthesis of Liquid Crystalline Polymers with X- and T-Like Mesogenic Fragments Via Diels-Alder Reaction

Abstract Main chain polymers with a mesogen which contains the residue of muconic acid as the central unit were synthesized. Polymers with a T-like mesogen were obtained by thermal addition of N-substituted maleiaides. As a result of reaction with fumaroyl chloride and subsequent reaction with phenols or amines, polymers with X-like mesogen were obtained.

Crystal and Molecular Structures of Diethyl 6-[4-(4′-Nitrophenylazo)phenoxy]-hexylmalonate and its 2′-Nitrophenyl Isomer

Abstract The crystal and molecular structures of diethyl 6-[4-(4′-nitrophenylazo)phenoxy]hexylmalonate (1) as a comonomer in the synthesis of liquid-crystalline polymers and its 2′-nitrophenyl isomer (2) have been determined by X-ray analysis. Both compounds crystallize in space group P1 with two molecules per unit cell and the following lattice parameters. 1: a = 7.995(2), b = 10.699(2), c = 15.021(4) A, a = 95.04(2), β = 96.54(2), γ = 94.72(3)°. 2: a = 8.912(2), b = 9.664(2), c = 16.064(4) A, α = 98.68(2), β = 97.54(1), γ = 105.11(1)°. The structures were solved by direct methods and refined to R (wR) values of 0.082 (0.068) and 0.071 (0.076), respectively. The molecules have an optimum stretched shape excepted one of their two ethoxycarbonyl groups which is perpendicularly oriented to the molecular long axis. The molecular packing in the crystal can be described in terms of a sheet structure in which the sheets are penetrated by the laterally branched ethoxycarbonyl groups of neighboring sheets.

Liquid crystalline polymers by cationic polymerization

AbstractThe synthesis of liquid crystalline polymers and oligomers containing calamitic and disc‐like mesogens by cationic polymerization and oligomerization is reviewed. Examples from ring‐opening, carbocationic, and radical‐cation polymerizations and oligomerizations are discussed.

Synthesis and phase behaviour of liquid crystalline polymers from chloroacrylates and methacrylates

Influence de la structure de chaine sur le type de phase et relation entre la masse moleculaire et les temperatures de transition

A novel method for the synthesis of liquid crystalline polymers. Preparation by the interaction of poly(acryloyl chloride) with mesogenic compounds

AbstractA new method for the synthesis of thermotropic liquid crystalline polymers, which is comprised of the interaction of reactive polymers with mesogenic compounds, was investigated. This method is illustrated by the interaction of poly(acryloyl chloride) with p‐hydroxybenzylidene‐p‐butylaniline or p‐aminobiphenyl on the preparation of poly(p‐acryloyloxybenzylidene‐p‐butylaniline and poly(N‐p‐biphenylacrylamide)), respectively. These polymers were subjected to characterization studies which included optical microscopy, x‐ray diffraction analysis, and differential scanning calorimetry. It was established that both polymers in the melt exhibit smectic mesomorphism.