Thermotropic properties

Polymer IX illustrates that it is possible to include a limited proportion, for example 20 moles %, of amide linking groups into this type of copolymer without destroying the thermotropic property. In this case the melting point of the copolymer containing 60 moles % of 2,6-oxynaphthoyl units and 20 moles % each of p-oxybenzoyl and p-iminobenzoyl units is only 277 °C 43>, similar to that just noted for the copolymer with ester instead of amide groups. 

Fig. 3 Hekates with flexible spacers. Compounds 1, 2 Thermotropic properties as a function of spacer length. Compounds 3, 4 LC properties with unchanging spacer length and variable peripheral chains. Compounds 5, 6 Nematogens claimed to form biaxial nematic phases. Cr crystal, g glass, N nematic, N cholesteric, SmX unidentified smectic phase, Colh columnar hexagonal phase. All temperature are given in °C...

Fig. 5 Shape-persistent Hekates based on oligo(phenyleneethynylene) scaffolds. Compounds 14 and 15 form columnar mesophases. For stars 16 (R = H or fullerene, R = C10H2i) thermotropic properties have not been published...

Table 2 Thermotropic properties of Hekates based on oligobenzoate scaffolds...

Once bearing some substituents, the decrease of polarity of the sucrose derivatives makes them soluble in less-polar solvents, such as acetone or tert-butanol, in which some lipases are able to catalyze esterifications. Unlike proteases, which necessitate most often the use of an activated acyl donor (such as vinyl or trifluoroethyl esters), lipases are active with simple esters and even the parent carboxylic acids in the presence of a water scavenger. The selectivity of the lipase-catalyzed second esterification is specific for OH-6 allowing the synthesis of mixed T,6 -diesters.123,124 For some lipases, a chain-length dependence on the regiochemistry was observed.125 Selectively substituted monoesters were thus prepared and studied for their solution and thermotropic behavior.126,127 Combinations of enzyme-mediated and purely chemical esterifications led to a series of specifically substituted sucrose fatty acid diesters with variations in the chain length, the level of saturation, and the position on the sugar backbone. This allowed the impact of structural variations on thermotropic properties to be demonstrated (compare Section III.l).128... 

The interactions of TDZ (6) with model membranes composed of different phospholipids were also studied by the same group [78]. Calorimetric studies demonstrated that TDZ (6) altered the thermotropic properties of negatively charged DMPC membranes to a larger extent than of zwitterionic phospholipids (PC and PE). The character of the drug-induced changes of the transition parameters of all studied lipids indicated that TDZ (6), similarly to other phenothiazine derivatives, was likely to be localized close to the po-lar/apolar interface of the bilayers. Experiments in which fluorescent probe 1,6-diphenyl-1,3,5-hexatriene (DPH) was employed revealed that TDZ (6) reduced the mobility of lipid molecules in a concentration-dependent manner and thus decreased membrane fluidity. The influence of TDZ (6) on isolated... 

The influence of substituent size, polarity, and location on the thermotropic properties of synthetic phosphatidylcholines has been studied by Menger et al. [18], The effect of increasing membrane curvature on the phase transition has been investigated by DSC and FTIR [19]. In addition, a data bank, LIPIDAT, on lipid phase transition temperatures and enthalpy changes is available [20, 21],... 

Recently much effort has been made to induce liquid crystallinity in polyimides. Kricheldorf et al., Chen et al., and Sato et al. have suggested that an aromatic im-ide ring may be an excellent mesogen through their studies on thermotropic liquid-crystalline polyimide-esters [41-54] and polyimide-carbonates [55, 56]. Some thermotropic properties of aromatic polyether-imides have also been reported by Asanuma et al. [57]. 

Suwalsky, M., Rivera, C., Sotomayor, C.P., Jemiola-Rzeminska, M., Strzalka, K. (2008). Monomethylarsonate (MMAv) exerts stronger effects than arsenate on the structure and thermotropic properties of phospholipids bilayers. Biophys. Chem. 132 1-8. 

Rowe, E. S. The effects of ethanol on the thermotropic properties of di-palmitoylphosphatidylcholine. Molecular Pharmacology 22 133-139, 1982. 

Recently Blumstein and coworkers reported on the thermotropic properties of a series of main chain copolyesters with different azoxybenzene mesogenic units and flexible spacers consisting of varying ratios of (-I-) 3-methyl adipic acid and 1,12-dodecanedioic acid. Melting temperature of the copolyesters showed minimum values for either the 50/50 compositions or the 25/75 combination of the two spacer components, depending on the nature of the mesogenic units. However, Tj tended to decrease linearly with the content of the 1,12-dodecanedioic acid unit, except in one case. They also observed that the cholesteric pitch of the copolyesters seemed to increase as the concentration of the achiral unit, dodecanedioic acid, increased. Similar observations were reported earlier by Strzelecki s group... 

Stumpe, J., Fischer, T., and Menzel, H. Langmuir-Blodgett Films of Photochromic Polyglutamates 9. Relation Between Photochemical Modification and Thermotropic Properties. Macromo/ec /es 29, 2831 (1996). 

There has been a great deal of interest in thermotropic, liquid crystalline polymers in the past twenty years or so since the discovery of useful materials based on them. Many critical factors such as structure of mesogenic units, presence and structure of flexible spacers or rigid kinks, molecular weight and its distribution, and thermal history influence thermal, physical and thermotropic properties of liquid crystalline polymers(1-13). 

Lo Celso F, Pibiri I, Triolo A et al (2007) Study on the thermotropic properties of highly fluo-rinated 1,2,4-oxadiazolylpyridinium salts tind their perspective applications as ionic liquid crystals. J Mater Chem 17 1201-1208... 

At the same time the polycarbonates 54a-f (all of them with m=3,4,5,6) were prepared and characterized by Sato and coworkers [66,67]. All syntheses were conducted by transesterification of the corresponding diols with the biscar-bonates 55 in bulk. None of the four homo PEIs (54a, m=3-6) proved to be thermotropic. In the case of the copolycarbonates only those containing more than 50 mol% of the biphenylester unit (e.g. 54d-f, m=3) were apparently thermotropic. This thermotropic property was attributed to the mesogenic character of... 

The numerous cellulose derivatives commercially available, displaying varying second order transition, molecular mass, viscosity, lyophilicity, thermotropic properties, have considerable potential. Significant advances have been made in the collection of fundamental data, but the interpretation of this information is somewhat more difficult than for synthetic polymers, mostly because of the heterogeneity of the materials, which exhibit a broad molecular mass distribution and an uneven substitution. 

Thermotropic Properties. Glycophorin can be incorporated into multilamellar liposomes by hydration of a glycophorin-lipid film prepared by rotary evaporation of a mixture of glycophorin and lipid in an azeotropic solvent (chloroform/methanol/water, 81 15 14% v/v bpt 52.6 C). VVe found that the azeotropic solvent mixture facilitated uniform dispersion of the glycophorin in the lipid (28). 

The possibility of using the thermotropic properties of macromolecular complexes of dendrimers was demonstrated by the example of oxidation of disulfides in the presence of a macromolecular complex of cobalt phthalocyanine with a polyisopropylacrylamide-based (PIPAAm-based) dendrimer characterized by temperature-dependent solubility. The oxidation rate is almost tripled by increasing the temperature from 34 to 36 °C [129]. These temperatures are close to... 

The thermotropic properties of amphotropic materials are determined by the equilibrium of the hydro- and lipophilic sections... 

Thus, symmetry of these molecules is an important factor for their thermotropic properties the higher their symmetry the more stable is the crystalline phase or the less probable is the appearance of a thermotropic mesophase. 

A discussion of the thermotropic properties of this type of compounds began in 1983 [119] with naturally occurring lipids. Again, the heterogeneity of the materials made syntheses of uniform derivatives desirable [114a]. Pure l,2-di-0-acyl-3-C)-(a-D-glu-copyranosyl)-5n-glycerols (32) were investigated in view of their thermotropic properties. The thermotropic mesophase of the members of series 32 has been denoted as... 

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