Monomers thermotropic transitions

Main Chain LC Polymers. New thermotropic copolyesters with either random or ordered mesogenic sequences have been reported with a wide range of mesophase behaviors. Recent developments in this field have included the use of naphthalene, stilbene and related structures in addition to the traditional phenylene groups to produce the required rigid main chain, and these are described in chapters by Jin, Jackson and Morris, and Skovby et al. Efforts have been undertaken to control transition temperatures and solubility through the use of either substituents or changes in the monomer sequence distribution. Successful application of these efforts have led to the commercialization of several thermotropic aromatic copolyesters (23.24). 

We already have reported on the replacement of the terephthalic acid with kinked diphenylether dicarboxylic acids (4). 3,4 - and 4,4 -Dicarboxydiphenylether (3,4 -0 and 4,4 -0) were synthesized and all-aromatic polyesters were prepared represented by structure 1. These polyesters were thermotropic with melt transitions decreasing to about 200°C with increasing replacement of the terephthalic acid with the kinked monomers. The polymers generally were thermally stable without measurable weight loss until well over 400°C. We wish here to supplement our previous studies with rheological measurements and fiber spinning of the polymers, including some measurements of fiber properties. 

The more obvious choice for a model compound corresponds to exactly one repeat unit of the polymer. The a-ethoxy-m-(4-n-alkoxy-4 -cyanobiphenyl)s exhibit nematic mesophases at n=4-9 and SmA mesophases at n = 8-ll, and therefore match the thermotropic behavior of the polymer better than the vinyl ether monomer. However the SmA mesophase is enantiotropic only at n = 11, and the nematic mesophase is monotropic at all of these spacer lengths. Compounds which take into account only the mesogen and spacer are also good, if not better, models of the polymers. In contrast to the ethyl ethers, all of the SmA and most of the nematic mesophases are enantiotropic, which means that the melting temperature mimics the relative temperature of the glass transition of the polymer backbone better. However, the nematic mesophase still appears at n = 6 -11, and the SmA mesophase doen t appear at n = 5-7, 10, 11. 

In contrast to the poly(enamine-ketones) prepared by Imai e al. the methyl substituted poly(enamine ketones), J 2, prepared from the condensation of diamines and bis-acetylacetylarenes, were found to be hydrolytically stable and thermally stable from 257 to 340 C, When a linear and rigid aromatic bis(1,3-diketone) was condensed with alkaline dieamines with ten or more carbons or with rigid aromatic diamines, thermotropic liquid crystalline materials were obtained. The monomers and polymers have much higher solubilities and lower transition temperatures as compared with liquid crystals containing only aromatic hydrocarbon rings of similar structures. 

The main aim of this paper is to increase the understanding of the mechanism of phase formation and relaxational transitions in two representative thermotropic LC copolyesters, namely, ternary copolyester (CPE-1) containing 10 mol % p-hydroxybenzoic acid (HBA), 45 mol % phenylhydroquinone (PHQ), and 45 mol% terephthalic acid (TPA), as well as copolyester (CPE-2) composed of monomer units of 4-hydro-xybenzoic acid (HBA) and 6-hydroxy-2-naphthoic acid (HNA) (Schematics 1). 

The detailed analysis of the structure, temperature behavior and phase as weUl as relaxational transitions of two representatives of thermotropic LC copolyesters with a statistical sequence of monomers in chains shows the strong dependence of their phase composition on the chemical stmcture of monomeric units. One of the most important factors appears to be the geometrical dimensions of the monomeric groups, from which the chain of copolymer is constructed jfrom, and the presence (or absence) of relatively large side substituents. 

Novel aromatic-aliphatic biobased polyesters showing thermotropic behavior in the melt have been presented, incorporating different biobased monomers such as 2,5-furandicarbo)ylic acid (2,5-FDCA), suberic acid (SuA), and vanillic acid (VA) in thermotropic L.C. polymers (TLCPs). The chemical structures, molecular weights, phase transitions, thermal behavior, and mechanical performance of the synthesized polymers are studied using polarization optical microscopy, WAXD, DSC, TGA, DMTA, SS NMR spectroscopy, rheology, and tensile tests. These materials show a low temperature transition from the crystalline to the nematic phase, and stable nematic phases up to 300 °C and higher. ... 

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