Liquid crystal polymers. IV. Thermotropic polyesters with flexible spacers in the main chain

Abstract

SynopsisTwo closely related series of polyesters that contain mesogenic units interconnected by flexible spacers along the main chain were prepared and characterized for their liquid crystal properties. All of these polymers showed theotropic behavior, which was examined by DSC, hot-stage microscopy on a polarizing microscope, small-angle light and wide-angle x-ray scattering methods, and visual observation of stir-opalescence of the polymer melts. The effect of the length of the flexible spacer and the nature of the substituent, which is on the central aromatic ring of the mesogenic unit, on the stability and molecular order of the mesophase for each of the polymers was investigated and the results are discussed on the basis of the thermodynamic data obtained.

Liquid Crystal Polymers. V. Thermotropic Polyesters with Either Dyad or Triad Aromatic Ester Mesogenic Units and Flexible Polymethylene Spacers in the Main Chain

“…Another interesting observation was that the polymers of Series I did not show as distinct multiple melting transitions as those of the previously reported Series III shown below. 8 The latter series of polymers, which was described in an earlier report from this laboratory, 8 Number of Methylene Groups, n The equimolar copolymers of Series I having mixed polymethylene spacers, with the compositions presented in Table I as either n = 217 or 2/10, apparently possessed a very low degree of crystallinity compared with their homopolymers, as expected. The 2/7 copolymer showed a broad and weak melting by DSC analysis, and the heat of melting, !1Hm, of this sample was much lower than those of the other polymers.…”

“…Haller and coworkers, in a study on a homologous series of aldonitrones, made a similar observation that the change in entropy, llS;, between the mesomorphic and isotropic states of the N-(p-alkoxyphenyl)-a-(p-methoxyphenyl)nitrones increased smoothly with n. 19 The increase of llS; with n indicates that, for polymer molecules with longer polymethylene spacers, the conformations of these chains and the placement of the mesogenic units were increasingiy more ordered for the mesophase relative to the isotropic phase. 19 Distinct differences were observed in the thermal behavior of the mesophases of the polymers in Series I compared to the previously investigated polymers of Series III as follows: (I) the clearing point, T;, was higher for the polymers of Series III having an odd value ofn than for those with an even value of n, while the opposite was true for the polymers of Series I, and (2) the clearing points of the polymers in Series III steadily decreased with increasing n up to 10, while in Series I, T; decreased only up to an n of 8 and then increased at n = 9 and 10. The former difference, however, may be attributable in some way to the fact that the polymethylene spacer in Series III is attached to an aromatic ring through an oxygen atom which is similar in geometrical effect to a methylene group, while the polymethylene spacer in Series I is attached through a carboxy group which imparts a considerably different spacial arrangement.…”

“…14, No. I, 1982 on the polyesters of Series 111, 8 the values of both llH; and llS; generally increased with n even though T; steadily decreased (discounting the odd-even effect). Haller and coworkers, in a study on a homologous series of aldonitrones, made a similar observation that the change in entropy, llS;, between the mesomorphic and isotropic states of the N-(p-alkoxyphenyl)-a-(p-methoxyphenyl)nitrones increased smoothly with n. 19 The increase of llS; with n indicates that, for polymer molecules with longer polymethylene spacers, the conformations of these chains and the placement of the mesogenic units were increasingiy more ordered for the mesophase relative to the isotropic phase.…”

Synthesis and Properties of Thermotropic Liquid Crystal Polymers with Main Chain Mesogenic Units

“…steric hindrance by the substituents causes an increased separation of the mesogenic units in adjacent polymer chains or (2) an interlocking by the substituent on adjacent chains decreases molecular mobility in the liquid crystal phase. 37 The former decreases Ti while the latter increases /1Si as can be seen in Tabel IV. Polar effects do not seem to exert an important role on the thermal stability of the mesophases of these polymers, in contrast to those discussed previously.…”

Thermotropic Liquid-Crystalline Copoly(ester amide) Containing a Flexible Spacer in the Main Chain

“…A thermotropic polyester obtained with 4,4' -dichloroformyl-1, 10-diphenoxydecane and hydroquinone has shown a nematic threadedSchlieren texture. 17 A copoly(ester amide), 10P20H, which contained 20 mol% of p-aminophenol, exhibited a texture similar to a threaded-Schlieren texture ( Figure 3A). On the other hand, IOP50H showed a droplet texture when measured in the descending temperature cycle from an isotropic melt ( Figure 3B).…”