Poly , thermotropic liquid crystalline

Poly(epichlorohydrin) (PECH) and poly(2,6 - dimethyl-1,4-phenylene oxide) (PPO) containing pendant mesogenic units separated form the main chain through spacers of zero to ten methylene units were synthesized and characterized in order to test the "spacer concept." Both polymers were modified by phase transfer catalyzed esterifications of the chloromethyl groups (PECH) or the bromobenzyl groups (brominated PPO) with potassium co -(4-oxybiphenyl) alkanoates and potassium u-(4-methoxy-4-oxybiphenyl)-alk.an oates. While PPO required ten methylene units as a spacer and 4,4 -methoxybiphenyl as mesogen to present thermotropic liquid crystalline mesomorphism,... 

Block copolymers with PS and a polymethacrylate block carrying a liquid crystalline group, PS-b-poly 6-[4-(cyanophenylazo)phenoxy]hexyl methacrylate, were successfully prepared in quantitative yields and with relatively narrow molecular weight distributions (Scheme 5) [18]. The thermotropic liquid crystalline behavior of the copolymers was studied by differential scanning calorimetry. 

Thermotropic liquid crystalline (LC) phases or mesophases are usually formed by rod-like (calamitic) or disk-like (discotic) molecules. Spheroidal dendrimers are therefore incapable of forming mesophases unless they are flexible, because this would allow them to deform and subsequently line up in a common orientation. However, poly(ethyleneimine) dendrimers were reported to exhibit lyotropic liquid crystalline properties as early as 1988 [123],... 

Jackson and co-workers reported in 1976 [21,22] (on work carried out in 1971) that poly-p-oxybenzoyl-modified poly(ethylene terephthalate) was found to exhibit thermotropic liquid crystalline characteristics. A variety of thermotropic liquid crystalline polyarylates have since been described, and some of these also contain flexible spacer units [23-30]. 

The potential for novel phase behaviour in rod-coil block copolymers is illustrated by the recent work of Thomas and co-workers on poly(hexyl iso-cyanate)(PHIC)-PS rod-coil diblock copolymers (Chen etal. 1996). PHIC, which adopts a helical conformation in the solid state, has a long persistence length (50-60 A) (Bur and Fetters 1976) and can form lyotropic liquid crystal phases in solution (Aharoni 1980). The polymer studied by Thomas and co-workers has a short PS block attached to a long PHIC block. A number of morphologies were reported—wavy lamellar, zigzag and arrowhead structures—where the rod block is tilted with respect to the layers, and there are different alternations of tilt between domains (Chen et al. 1996) (Fig. 2.37). These structures are analogous to tilted smectic thermotropic liquid crystalline phases (Chen et al. 1996). 

An effort to combine the thermotropic liquid-crystalline properties of selected cellulose derivatives with the ion-conductive characteristics of poly(ethylene oxide) (PEO) has currently been pursued [234,235]. TPEO-CELL shown in Scheme 7 is a representative sample. 

Low polarisation ratios (<2 1) for absorption had also been found for amorphous PPV (1) deposited from solution by spin-coating on rubbed poly(tetrafluoroethylene) [PTFE]. It is evident that this could be improved on by making use of the high order parameter and self-organising properties of the nematic phase of liquid crystalline electroluminescent polymers such as those (16, 28 and 78-82) shown in Table 6.16. - 2 ° This was then found subsequently to be the case using thermotropic liquid crystalline polyfluorenes, such as 28 and 80 shown in Table 6.6 and segmented PPV derivatives, such as 81. The nematic phase exhibits the lowest viscosity of... 

Materials and Processing. Copolyesters of poly(ethylene terephtha-late) (PET) and para-oxybenzoic acid (FOB) were supplied by the Tennessee Eastman Corporation. Past work Indicates the copolyesters form thermotropic liquid crystalline phases at compositions containing more than 30 mole% POB (26,27,28). The composition of the copolyester studied here contains 60 mole% POB. Quiescent liquid crystalline films were made by compression molding the copolyester at 210, 230, 255, and 285 C, and followed by a quench Into Ice water, ambient air, or cooled In the press with the power off. Film thicknesses ranged between 0.05-0.15 mm. Another sa(q>le of the 40/60 PET/POB copolyester was melted at 270 °C In a Mettler hot stage, manually sheared between glass slides, and then ambient air cooled. 

A multistep reaction pathway leads to polymers 43 and 44 with phosphatidylcholine moieties in the main chain and long alkyl groups in the side chain [122]. These polymers exhibit thermotropic liquid-crystalline behavior. Polyamides 45 were obtained by interfacial polycondensation they are insoluble in any normal solvent [123]. Poly-MPC capped with cholesteryl moieties at one or both polymer ends was prepared by the radical polymerization of MFC initiated with 4,4 -azobis[(3-cholesteryl)-4-cyanopentanoate] in the presence of a chain transfer agent [124]. The self-organization of these polymers was analyzed with fluorescence and NMR measurements. 

We are now studying both the lyotropic and thermotropic liquid crystalline properties of poly(enamine-ketones). Also in progress is the synthesis of poly(enamine-ketones) derived from diaminoarenes, polymers containing all ring systems. We hope to obtain rod-like polymers with both lyotropic and thermotropic liquid crystalline properties that permit their processing into useful end products. 

A typical example of a thermotropic liquid crystalline polymers is the polyesters and the mesogen substituted polysiloxane. The aromatic amide, the super strength fiber known commercially as Kevlar belongs to the lyotropic liquid crystalline polymers. The other important lyotropic liquid crystalline polymers are poly(7-benzyl-L-glutamate), abbreviated as PBLG, cellulose derivatives, the tobacco mosaic virus, etc. 

At this point, we would like to mention again that the polymer PE-H in Table 3.14, poly-2,5-di(benzoyloxy)styrene, was first synthesized some 40 years ago as a precursor of an electron exchange polymer (Ezrin et al., 1953). In this study we were lucky to have found that this polymer is liquid crystalline at temperatures above its glass transition (Table 3.14). To our knowledge PE-H is probably the oldest thermotropic liquid crystalline polymer ever synthesized by chemists. 

A few polyacetylen s with liquid crystalline side groups have been reported. For instance, a polymer (Mw 16 x 10" ) is obtained in high yield with WCl6 from cholesteryl 4-pentynoate. The polymer shows a transition to a thermotropic liquid-crystalline phase at 89 °C and a transition to the isotropic phase at 189 °C. Other examples are poly(l,6-heptadiynes) with mesogenic side groups. Studies on their applications are under way. 

Novel organometallic poly(arylene)s with 1,3-type (cyclobutadiene)cobalt moieties 27 in the main chain are prepared by Ni(0)-mediated dehalogenative polycondensation of monomers having (cyclobutadiene)cobalt moieties [51], The polymers with of 20 kDa exhibit thermotropic liquid crystallinity. The synthesis of a variety of homometallic and heterometallic oligomers and polymers such as 28 is possible via nucleophilic aromatic substitution reactions of dichlorophenylene-Fe Cp and dihydroxyphenylene-Ru Cp complexes in DMF in the presence of K2CO3 [52]. 

A selection of monosubstituted and disub-stituted poly-(/ -phenylene-terephthalate)s is compared in Table 2. Poly(p-phenylene-terephthalate)s with methyl, methoxy, chlo-ro, or bromo substituents on either the hy-droquinone or the terephthalic acid moiety exhibit melting temperatures of 350 °C or higher. Thermotropic liquid crystalline behavior is observed in these samples, although it is in the range of thermal decomposition. A comparison of the mono- and diphenyl substituted polyesters reveals an important trend. The monosubstituted poly-(p-phenylene-terephthalate) with the phenyl substituent in the hydroquinone moiety melts at 346 °C, also forming a nematic melt up to a clearing temperature of... 

It should also be mentioned that a combination of ester and amide linkages was frequently used to prepare thermotropic LC polyesteramides. Frequently, the inexpensive p-aminophenol is incorporated. For example, the Vectra B series is a poly(naph-thoate-aminophenolterephthalate) derived from 6-hydroxy-2-naphthoic acid (HNA), p-aminophenol, and terephthalic acid [14]. It is obvious that only a limited amount of p-aminophenol can be incorporated in order to maintain thermotropic liquid crystalline behavior. The amide linkage enhances the intermolecular interactions via hydrogen bridges and improves the solid state properties of the material. 

Liu X H, Bruce DW, Manners I. 1997. Novel calamitic side chain metallomesogenic polymers with ferrocene in the backbone S5mthesis and properties of thermotropic liquid crystalline poly(ferrocenylsilanes). Chem Commun (3) 289 290. 

W. Grasser, H.-W. Schmidt, and R. Giesa. Fibers spun from poly(ethyl-ene terephthalate) blended with a thermotropic liquid crystalline copolyester with non-coplanar biphenylene units. Polymer, 42(21) 8517-8527, October 2001. 

J.D. Sudha, Synthesis and characterization of hydrogen-bonded thermotropic liquid crystalline aromatic-aliphatic poly(ester-amide)s from amido diol, J. Polym. Sci. A Polym. Chem. 38 (2000) 2469-2486. 

Gopakumar et al. [10] reported the in situ compatibilization of poly(phenylene sulfide) (PPS)/wholly aromatic thermotropic liquid crystalline polymer (TLCP) Vectra A950 blends by reactive extrusion. The authors prepared the in situ compatibilized PPS/TLCP blends in a twin-screw extruder by reactive blending of PPS and TLCP in the presence of dicarboxyl-terminated poly(phenylene sulfide) (DCTPPS). Block copolymer was formed during reactive blending, by transesterification reaction between carboxyl... 

Gopakumar, T. G., Ronrathnam, S., Lele, A., Rajan, C. R., and Fradet, A. 1999. In situ compatibilisation of poly(phenylene sulphide)/wholly aromatic thermotropic liquid crystalline polymer blends by reactive extrusion Morphology, thermal and mechanical properties. Polymer 357-364. 

PRELIMINARY THERMAL AND STRUCTURAL STUDIES OF BLENDS BASED ON A THERMOTROPIC LIQUID CRYSTALLINE COPOLYESTER AND POLY(ETHYLENE) TEREPHTHALATE... 

Jackson and Kiitifuss reported a thermotropic liquid crystalline polymer which was a copolyester of poly(ethylene) terephthalate (PET) and parahydroxybenzoic acid (PHB). In this copolyester, PET has a flexible chain conformation while PHB has a stiff, rod-like conformation and the polymer is indicated to be the liquid crystal forming component. Schematically, this copolyester... 

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