Poly liquid crystalline polymers

Poly(phenyleneethynylene)s, 482 optically active, 516-517 synthesis of, 496-500, 502 Poly(m-phenylene isophthalamide), 136 synthesis of, 185-186 Poly(l,4-phenylene terephthalate) liquid crystalline polymers, 51 Poly(para-phenylene)s, 472. See also Poly (p -pheny lene)... 

In order to make polymers behave as liquid crystals it is necessary to introduce some structural rigidity. A typical polymer which has the required rigidity is poly(phenylenetetraphthalamide) (10.7). This material belongs to a class of polymer known as the aramids. Other liquid crystalline polymers are the thermotropic polyesters derived from /7-hydroxybenzoic acid, p, p -biphenol and terephthalic acid (10.8). 

Jackson, Jr, W. J. and Morris, J. C., Poly esters of 4,4 -biphenyl dicarboxylic acid and aliphatic glycols for high-performance plastics, in Liquid Crystalline Polymers, ACS Symposium Series, Vol. 453, American Chemical Society, Washington, DC, 1990, pp. 16-32. 

Fig. 7. Comparison of experimental phase boundary concentrations between the isotropic and biphasic regions for various liquid-crystalline polymer solutions with the scaled particle theory for wormlike hard spherocylinders. ( ) schizophyllan water [65] (A) poly y-benzyl L-glutamate) (PBLG)-dimethylformamide (DMF) [66-69] (A) PBLG-m-cresoI [70] ( ) PBLG-dioxane [71] (O) PBLG-methylene chloride [71] (o) po y(n-hexyl isocyanate) (PHICH°Iuene at 10,25,30,40 °C [64] (O) PHIC-dichloromethane (DCM) at 20 °C [64] (5) a po y(yne)-platinum polymer (PYPt)-tuchIoroethane (TCE) [33] ( ) (hydroxypropyl)-cellulose (HPC)-water [34] ( ) HPC-dimethylacetamide (DMAc) [34] (N) (acetoxypropyl) cellulose (APC)-dibutylphthalate (DBP) [35] ( ) cellulose triacetate (CTA)-trifluoroacetic acid [72]...

Recently, experimental data of S for various liquid-crystalline polymer solutions have become available. Figure 12 illustrates the concentration dependence of S for three polymer liquid crystal systems (a) PBLG-DMF [92,93], (b) PHIC-toluene [94], and (c) poly(yne)-platinum polymer (PYPt)-trichloro-ethane (TCE) [33]. For systems (a) and (c), with the alignment made by... 

The zero-shear viscosity r 0 has been measured for isotropic solutions of various liquid-crystalline polymers over wide ranges of polymer concentration and molecular weight [70,128,132-139]. This quantity is convenient for studying the stiff-chain dynamics in concentrated solution, because its measurement is relatively easy and it is less sensitive to the molecular weight distribution (see below). Here we deal with four stiff-chain polymers well characterized molecu-larly schizophyllan (a triple-helical polysaccharide), xanthan (double-helical ionic polysaccharide), PBLG, and poly (p-phenylene terephthalamide) (PPTA Kevlar). The wormlike chain parameters of these polymers are listed in Tables... 

Scheme 10 Liquid crystalline polymer poly(I7) and its precursors...

Felix, A.M. Site-specific poly(ethylene glycol)ylation of peptides, in "Poly(ethylene glycol) Chemistry and Biological Applications" (J.M. Harris and S. Zalipsky, Eds.) ACS symposium Series 680, 218-238 (1997). American Chemical Society, Washington DC. Gallot, B. "Comb-like and block liquid crystalline polymers for biological applications". Prog. Polym. Sci. 21(6), 1035-1088 (1996). 

Regioselective dialkylation of naphthalene is another reaction of considerable interest as 2,6-dialkylnaphthalenes can be oxidised to naphthalene-2,6-dicarboxylic acid, which is used in the synthesis of the commercially valuable polymer, poly(ethylene naphthalenedicarboxylate) (PEN).22 PEN has properties that are generally superior to those of polyethylene terephthalate) (PET) and has become the polymer of choice for a variety of applications such as in films, industrial fibres, packaging, liquid crystalline polymers, coatings, inks and adhesives. However, the high cost of naphthalenedicarboxylic acid has been a major hindrance to widespread application. 

Differences in tacticity were also reflected by thermal data. While the iso-tropization temperature of (-)-poly-(IV-ll) and ( )-poly-(IV-ll),synthesized using initiator 1, stayed approximately unchanged, the isotropization temperatures for the chiral liquid crystalline polymers shifted to higher values when initiators 2 or 3 were used. The difference was up to 7 °C. If the decreased glass transition temperatures (Tg) for the chiral analogues were taken into account, the temperature range of the liquid crystalline phase was broadened by up to 12 °C. This means that a certain diad must be responsible for this behavior. The authors assumed that the diad cmHT was most suitable one for the formation of stable liquid crystalline phases in poly(norbornene) main chains. 

Another important application of thermoplastic fibers such as poly ether ether ketone (PEEK), Poly etherimide(PEI), and VectranM andHS (Vectranis the trade mark of Hoechst liquid crystalline polymer) is in making thermoplastic matrix composites. Commingled yams of the reinforcement and matrix such as quartz/PEEK, glass/PEI, Vectran HS/M are used to make the composites wherein the matrix yarn fuses to form the continuous phase of the composite. 

Although the technical applications of low molar mass liquid crystals (LC) and liquid crystalline polymers (LCP) are relatively recent developments, liquid crystalline behavior has been known since 1888 when Reinitzer (1) observed that cholesteryl benzoate melted to form a turbid melt that eventually cleared at a higher temperature. The term liquid crystal was coined by Lehmann (2) to describe these materials. The first reference to a polymeric mesophase was in 1937 when Bawden and Pirie (2) observed that above a critical concentration, a solution of tobacco mosaic virus formed two phases, one of which was bireffingent. A liquid crystalline phase for a solution of a synthetic polymer, poly(7-benzyl-L-glutamate), was reported by Elliot and Ambrose (4) in 1950. 

The concept of a side chain liquid crystal polymer has been demonstrated in a number of laboratories and is well documented in the literature (J ). Most of the side chain liquid crystalline polymers reported to date contain polysiloxane, polyacrylate or polymethacrylate main chains. More recent studies on the effect of backbone flexibility now include the use of flexible poly(ethylene oxide) or more rigid poly( a-chloroacrylate) chains. 

Side-chain liquid-crystalline polymers with controlled molecular weights have been obtained by the polymerization of FM-25 with 1-22 (X = Br)/CuBr/ L-3 in the bulk at 100 °C, to examine the thermotropic transition as a function of the MWD.324 Second-order nonlinear optical materials with branched structure were prepared by the copper-catalyzed radical polymerization of FM-26 and FM-27 using hyperbranched poly[4-(chloromethyl)styrene] as a multifunctional initiator.325... 

Extensive studies on photochromic liquid-crystalline polymers have been made by Krongauz et al,2 Liquid-crystalline phases caused marked colour changes of poly(acrylates)98 and poly(siloxanes) substituted with spiropyran side chains upon UV irradiation owing to the aggregation of the photomerocyanines." In contrast, spirooxazines attached to liquid-crystalline polymer backbones displayed no aggregation and hence exhibited normal photochromism similar to that in solution. Fulgimides bound covalently to the side chains of nematic liquid-crystalline polymers also showed normal photochromism. 

There have been many papers concerning liquid-crystalline polymers having azobenzenes in their side chains (Figure 14) because of the mesogenic nature of the azo chromophore. Liquid-crystalline polymers incorporating azobenzene moieties in their main chains (30) have also been prepared.102 A family of poly(acrylates) substituted with azobenzenes having chiral alkyl groups (31) showed smectic A as well as cholesteric phases.103 The photochromic behavior... 

Kijima, M. Kinoshita, L Hattori, T. Shirakawa, H. Synthesis of a novel liquid crystalline polymer, poly(2,5-didecyloxy-l,4-phenylenebutadiynylene). J. Mater. Chem. 1998, 5(10), 2165-2166. 

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