Mónica M. Marugán

Solubility of thermotropic polybibenzoates with oxyethylene spacers

SummaryThree polybibenzoates with two, three and four oxyethylene units in the spacer have been synthesized in order to analyze the influence of the length of the spacer on the stability of the mesophase and on the solubility behaviour. It was found that the thermal stability of the mesophase decreases as the length of the spacer increases, in such a manner that an amorphous polymer is obtained when four oxyethylene units are involved. On the other hand, although the value of the solubility parameter is little affected by the spacer, the solubility range is significantly widened by an increase in the number of oxyethylene units. Optimal characteristics are displayed by the polyester with three such units in the spacer.

Solubility parameters of thermotropic polybibenzoates with various spacers

Abstract Five polybibenzoates (polyesters of 4,4′-biphenyldicarboxylic acid) have been studied in order to analyse the influence of linear and branched oxyalkylene spacers on the solubility parameters of these polymers. The liquid crystalline character is lost for the polymers with branched spacers analysed in this work. The solubility parameter is almost insensitive to the explored variations in the spacer, and the studied polybibenzoates display a value of about 9.5 (cal/cm 3 ) 1 2 , 19.4 (J/cm 3 ) 1 2 , for that parameter. The components of the three-dimensional solubility parameter have been also estimated, leading to a better understanding of the solution behaviour of these polybibenzoates.

Small-angle synchrotron study of liquid crystalline poly[oxybis(trimethylene) p,p'-bibenzoate]

SummarySmall-angle synchrotron experiments have been performed in two samples of poly[oxybis(trimethylene) p,p′-bibenzoate], PDTMB. Owing to the very slow transformation of the mesophase of this polymer into the crystal, only the liquid crystalline phase is present in a PDTMB sample quenched from the melt, while about 30% crystallinity is found in the annealed specimen. The results indicate that the layer spacing peak for the mesophase is very close to a crystal diffraction. This seems to be a general fact in thermotropic polybibenzoates. Moreover, no long spacing has been detected in the quenched sample. On the contrary, the annealed specimen exhibits a long spacing centered at about 16 nm, corresponding to a rather small crystal thickness.

Viscoelastic relaxations in thermotropic polybibenzoates

Abstract The dynamic mechanical relaxations of two thermotropic polybibenzoates containing the biphenyl group in the main chain have been determined in the temperature range from −150 to 130°C, at several frequencies. The two polyesters are poly(heptamethylene p , p ′-bibenzoate) (P7MB) and poly(oxyditrimethylene p , p ′-bibenzoate) (PDTMB). These two polymers differ only in the change of the central methylene in the spacer of P7MB by an oxygen atom in PDTMB. Both polymers show three viscoelastic relaxations and the more remarkable difference is found in the relaxation occurring at higher temperature, considered as the glass transition of the mesophase. This transition appears at a temperature 26°C lower in the case of PDTMB, due to the higher flexibility introduced by the central ether group.

Phase transitions of liquid crystalline polyesters: Poly(heptane-1,7-diyl-4,4'-biphenyldicarboxylate)

Wide-angle X-ray scattering was applied to investigate the non-isothermal and isothermal phase transitions of poly(heptane-1,7-dyil-4,4′-biphenyldicarboxylate). It is suggested that the isotropic–smectic (I–S) transition is controled by a nanophase separation with a critical point Tns=151 °C. Nanophase separation is followed by a first-order S–Cr (crystal) transition. At isothermal conditions above Tns only S phase exists, whereas below it the S phase appears first and the Cr phase grows from the S by nucleation and three-dimensional crystal growth.