Thermal phase behavior of homologous liquid crystalline side group polyesters in dependence on the polymethylene main chain spacer length

Abstract

SUMMARY With the aim to investigate the influence of a systematic variation of the length of flexible nonmesogenic main chain segments on the mesomorphic properties a series of new liquid crystalline polyesters with 4-(4-nitrobenzyloxy)biphenyl moieties as mesogenic side groups was prepared. The mesomorphic and dynamic behavior were investigated by means of differential scanning calorimetry (DSC), X-ray measurements, polarization microscopy and dielectric spectroscopy. All polyesters exhibit nematic and different smectic phases. Some of the homologues show "re-entrant" nematic phases. The clearing point decreases at first with increasing main chain spacer length and passes through a minimum. From the results it was possible to propose packing models of the smectic phases with low order.

Square Patterns and their Dynamics in Electroconvection

“…The experiments were done in the nematic phase of a "swallow-tailed" compound, p-(nitrobenzyloxy)-biphenyl [13]. The phase sequence is as follows: I -110 0 C -N -94 0 CSm C -75 0 C -Sm F -(66.5 0 C -Sm X) -69 0 C -Cr.…”

Periodically Spaced Side-Chain Liquid Crystalline Polymers

“…The choice of different nonmesogenic comonomers permitted the variation of backbone properties, such as rigidity, hydrophilicity, and crystallization propensities . Thereafter, several other studies examined structural variants of PS–SCLCPs wherein different types of mesogenic moieties were incorporated, like bisazobenzene, , azobenzene with terminal cyano, nitro, or alkoxy substituents, , and biphenyl-based dipolar mesogens . These studies revealed an intricated interplay of two effects as a function of the length of the backbone segment straddling adjacent pendant mesogensinitially, when the density of mesogens is high, smectic/nematic mesophases are seen; at intermediate spacer segment lengths, the LC behavior is often lost; and at even longer spacer segment lengths, a nematic/smectic mesophase is recovered.…”

“…29 Thereafter, several other studies examined structural variants of PS−SCLCPs wherein different types of mesogenic moieties were incorporated, like bisazobenzene, 30,31 azobenzene with terminal cyano, nitro, or alkoxy substituents, 32,33 and biphenyl-based dipolar mesogens. 34 These studies revealed an intricated interplay of two effects as a function of the length of the backbone segment straddling adjacent pendant mesogensinitially, when the density of mesogens is high, smectic/nematic mesophases are seen; at intermediate spacer segment lengths, the LC behavior is often lost; and at even longer spacer segment lengths, a nematic/smectic mesophase is recovered. The loss of LC property at intermediate backbone spacer lengths was attributed to mesogen dilution effect, while incompatibility between the pendant mesogenic unit and the backbone segment was suggested as a possible reason for the recovery of mesomorphic behavior at higher spacer segment lengths.…”