Polymer enantiotropic

Finkelmann, H., Ringsdorf, H. and Wendorff, J. H. Model considerations and examples of enantiotropic liquid crystalline polymers. Makromol. Chem. 179, 273 (1978)... 

Moraglio, G., Polizzotti, G. and Danusso, F. Enantiotropic polymorphism of transtactic poly-1,3-butadiene, Europ. Polymer J. 1, 183 (1965)... 

Most interesting are the effects of salt complexation on the mesomorphic behavior of liquid crystalline crown ethers and liquid crystalline crown ether polymers. Sodium triflate was added to poly(17) [34] and poly(25) (Scheme 14) [39]. The enantiotropic nematic and smectic phases of poly(17) were changed dramatically [40]. With increasing amounts of salt, the clearing temperatures are shifted to higher values while the melting transition increases only slightly. 

The homopolymer showed an enantiotropic nematic mesophase, whereas the diblock copolymer generated microphase-separated lamellae, in which the SCLCP block possessed a nematic-isotropization transition similar to the homopolymer (Table 17). Upon heating, the nematic microphase decreased continuously in the nematic phase from 38.5 nm to 27 nm and showed a constant value of about 26 nm after the nematic-isotropization transition. Therefore, materials in which these block copolymers are macroscopically aligned are expected to show reversible contraction in one dimension, making this polymer system an interesting candidates for an artificial muscle or actuator. 

Norbornene-based and oxa-norbornene-based monomers bearing dendritic side chains, XXX and XXXI (Fig. 19), were synthesized and polymerized via ROMP with initiator 6 [83]. Based on size exclusion chromatography data, the polymerization shows hving-like character up to DP=70. H- and C-NMR-spectroscopy revealed 35% cis and 65% tram sequences. These polymers displayed enantiotropic nematic and smectic mesophases, except for DP=5. In contrast to other classes of SCLCPs, the dependence of the DP on the transition temperatirre of the polymer was very weak. Glass transition and isotropization temperatures became independent of molecular weight above a degree of polymerization of about 10. 

A degree of polymerization of about ten was determined by end-group analysis via H-NMR. Glass transitions were found to occur below room temperature. In each case, the material was smectic at 80 The polymers exhibited a broad enantiotropic phase range. A uniaxial teflon monolayer gave well-aligned parallel samples which were used to determine the smectic tilt angle as a function of temperature. The materials were well-behaved... 

All polymers Il-m of the second class investigated show one enantiotropic mesophase which was identified as nematic (Table II). There are no significant differences in the isotropization temperatures, but the isotropization entropies increase with increasing number m of methylene groups in the alkylene segment particularly for polymers containing the 1,3-phenylene residue (meta isomers, m). 

The study by Percec, Tomazos and Willingham (15) looked at the influence of polymer backbone flexibility on the phase transition temperatures of side chain liquid crystalline polymethacrylate, polyacrylate, polymethylsiloxane and polyphosphazene containing a stilbene side chain. Upon cooling from the isotropic state, golymer IV displays a monotropic nematic mesophase between 106 and 64 C. In this study, the polymers with the more rigid backbones displayed enantiotropic liquid crystalline behavior, whereas the polymers with the flexible backbones, including the siloxane and the polyphosphazene, displayed monotropic nematic mesophases. The examples in this study demonstrated how kinetically controlled side chain crystallization influences the thermodynamically controlled mesomorphic phase through the flexibility of the polymer backbone. 

Liquid crystalline polymers containing ferrocene in their side chains have been reported.235-240 Deschenaux used free-radical synthesis to prepare thermotropic liquid crystalline polymethacrylates containing ferrocene (Scheme 2.46).235 Polarized light microscopy showed that monomer 171 and its corresponding polymer 172 exhibited enantiotropic smectic A and C phases. 

Similar polymers formed from the isomeric trimellitimide ofp-amino benzoic acid (4) do not however form an enantiotropic phase but rather a short-lived monotropic phase upon cooling from an isotropic melt [17,18]. 

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