Chain Folding in Liquid-Crystalline Main-Chain Polymers with a Smectic Phase

Abstract

Thermotropic main-chain liquid-crystalline polymers (LCPs) composed of azobenzene or azoxybenzene mesogens and flexible spacers with and without a phenyl side group have been characterized by gel permeation chromatography, differential scanning calorimetry, and X-ray diffraction. The polymers exhibit smectic phases in the well-accessible temperature range from room temperature up to 160 °C. The morphology of thin films on a solid substrate was studied by X-ray reflectometry and scanning force microscopy (SFM). The smectic layers are mainly oriented parallel to the film surface. On the basis of X-ray reflectometry and SFM investigations, it is concluded that, at least in thin films, the polymer main chains are not extended like in the common model for main-chain LCPs, but almost regularly folded.

Monodomain Liquid Crystal Main Chain Elastomers by Photocrosslinking

“…For nematic main chain elastomers, shape changes in a typical range of 100-150% are obtained, and the thermoplastic elastomers presented by Ahir et al exhibited reversible length changes of up to 500%. [12] The smaller spontaneous extension found for our system is almost certainly related to its pronounced smectic order, which further enhances the known strong backfolding tendency of the polymalonate chains [23,24] and leads to a smaller anisotropy of the polymer backbones in the liquid crystalline phase. Nevertheless, the distinct reversible thermoactuation of % 40%, combined with the possibility of photocrosslinking (and thus easy patterning), makes our material a promising candidate for the investigation of new LCE-microactuator geometries.…”

“…(2) MC-LC polymers show a strong tendency towards structures in which the polymer chains are tightly folded and form so-called ''hairpins''. In our specific polyesters, this effect of backfolding is especially pronounced [23,24] with the phenylmalonate groups promoting the kinks. Stretching of the sample will then lead to a drifting of the hairpin defect along the polymer chain, which only slightly changes the network's entropy, and thus leads to a softening of the mechanical response.…”

The double melting behavior of a liquid crystalline polyimide derived from PMDA and 1,3-bis[4-(4′-aminophenoxyl) cumyl] benzene

“…This was reported in some thermotropic liquid crystalline polymers. 32 The heating curves for the sample crystallized at 305°C for 12 h revealed that the small energy change was associated with this transition. The ⌬H was about 2.0 J ⅐ g Ϫ1 after 12 h crystallization, and the corresponding ⌬S was only 3.36 ϫ 10 Ϫ3 J ⅐ g Ϫ1 ⅐ K Ϫ1 .…”

Liquid Crystal Elastomers: Materials and Applications

“…From the chemical point of view, they can be made by covalently linking the mesogenic groups to form a slightly crosslinked rubbery polymer network structure [3,5,8,10,[154][155][156] or by dispersing a low-molar-mass liquid crystal in a phase-separated network structure [7,40,[157][158][159][160][161][162]. These two systems possess very different structures locally.…”