Asymmetrically branched alkyl spacers in liquid‐crystalline poly(alkylene 4,4′‐terephthaloyldioxydibenzoate)s

Abstract

Poly[oxy-( 1,4-dimethyltetrarnethylene)oxycarbonyl-1,4-phenyleneoxyterephthaloyloxy-1,4phenylenecarbonyl] (1) was synthesized for the first time, and its thermal behaviour was studied by differential scanning calorimetry, thermooptical microscopy, and X-ray diffraction. The crystal to liquid-crystal and the mesophase to isotropic transition temperatures are lower by ca. 100 "C than the values reported for the unsubstituted polymer. Moreover, the formation of a threedimensional order is hindered in the case of the polymer with lateral substituents and can only be achieved by long annealing times.

Liquid Crystalline Poly(ester amide)s Based on N,N‘-Dimethyldiamines and an Aromatic Ester Triad

“…In order to synthesize amide-containing polymers having reduced melting points, the following strategies were employed: (1) hydrogen bonding was eliminated or reduced by incorporating N -methyl-substituted amide units into the polymer main chain; (2) aliphatic flexible spacer units were used to decouple the rigid-rod segments. By this approach, a series of main-chain nematic liquid crystalline poly(ester amide)s were synthesized based on terephthaloylbis(4-oxyphenylene carbonyl) units, which have been used previously to prepare many different liquid crystalline polyesters. − Several different N , N ‘-dimethylalkylenediamine monomers were used to synthesize the poly(ester amide)s.…”

Effect on TSDC relaxation spectra of substitutions in the mesogenic unit and in the flexible spacer of poly(tetramethylene terephtaloyl-bis-4-oxybenzoate)

“…Table I. Thermal, Mechanical, and Dielectric Transitions of the Polymer Liquid-Crystals Studied positions, the polymer labeled PDM4TOB does not present three-dimensional order unless long annealing processes are carried out, 13 which is not the case for the samples used in this study. This substitution results in a drastic variation of the transition temperatures, as shown in Table I.…”

“…10,[13][14][15] The intermediate products and the final polymers were characterized using elemental analysis, 1 H-NMR, 13 C-NMR, and vibrational spectroscopy, which assured the structure and the purity of the materials. The inherent viscosity of the four polymers was measured in p-chlorophenol at 45°C, and found to range between 0.29 -0.39 dL ⅐ g Ϫ1 .…”

“…The determination of the transitions and the identification of the different phases were carried out by DSC, X-ray diffraction, and optical microscopy, whose specific technical details can be found elsewhere. 10,[13][14][15] Dynamic-mechanical studies were performed on the four polymers on a TA Dynamic Mechanical Thermal Analyzer, working in the flexural bending mode. The experiments were carried out in a temperature range from 123 to 423 K at frequencies varying from 0.1 to 1 Hz using a heating rate of 5 K/min.…”

“…The series, with linear methylene spacers, have been synthesized and studied by several authors. 5,[7][8][9][10][11] We have studied the effect of symmetric or asymmetric lateral substitution in the spacer, [12][13][14][15] as well as the incorporation of polar substituents onto the aromatic units, 14 -16 in some members of this family. The presence of side groups in the spacer causes a less efficient packing of the chains, resulting in a reduction of the transition temperatures, the loss of three-dimensional ordering, and in some cases a change in the type of mesophase.…”