Cyanobiphenyl ethers

The nematic LC is the original eutectic mixture of 35% (weight %) 4 (m-octyl oxy)-4-cyanobiphenyl (80CB) and 65% 4/-(n-pentyl)-4-cyanobiphenyl (5CB). The sample is doped with perylene and 2% (mol %) of NIAC, which is acrylate monomer containing the easily reduced l,4 5,8-naphthalenediimide moiety (see Scheme 3). Finally, 0.5% (mol %) of benzoin methyl ether (BME) is added to photoinitiate polymerization of the NIAC. 

Methyl-2-cyanobiphenyl (5.59 g) was brominated using benzoyl peroxide as an initiator. The product was recrystallized from ether to yield 4.7 g of 4 -bromomethyl-2-cyanobiphenyl, melting point 114.5-120.0°C. 

By using this method, 4-methyl-2 -cyanobiphenyl, an important intermediate for the synthesis of the antihypertensive drug Losartan, can be easily prepared.132 2-(t>-Chlorophenyl)-oxazoline reacts with excess of arylmagnesium halide without catalysis, as it was shown by Meyers for 2-(o-methoxyphenyl)-oxazolines.133 Cobalt(ll) salts catalyze the coupling of Grignard reagents with a-chloroazines at —40°C in ether (Scheme 47).134 135... 

Biphenyl mesogens with R=CN [(4 -cyanobiphenyl-4-yl-)oxy-] or R=OCH3 [(4 -methoxybiphenyl-4-yl)-oxy-] were attached to norborn-2-ene moieties, and separated by different spacer lengths and carboxylic acid ester, ether or imido-groups as anchoring moieties, as shown in Fig. 4. 

A solution of 20 g. (0.12 mole) of o-aminobiphenyl in hydrochloric acid is diazotized in the usual manner [Org. Syntheses Coll. Vol. 1, 170 (1941)], and the solution of the diazonium salt is added to a solution of cuprous cyanide prepared from 35 g. of copper sulfate [Org. Syntheses Coll. Vol. 1, 514 (1941)]. When evolution of nitrogen ceases, the mixture is warmed for 30 minutes on a water bath and then made alkaline with sodium hydroxide. The mixture is steam-distilled, and the distillate is agitated with stannous chloride solution. SuflBcient sodium hydroxide is added to precipitate the tin, and the mixture is extracted with ether. The ethereal solution is dried and distilled to give 11.0 g. (50%) of o-cyanobiphenyl boiling at 174°/13 mm., m.p. 37°. 

Fig. 8. The dependence of the nematic-isotropic transition temperature, T i, on the total number of atoms, n, in the spacer for the cyanobiphenyl dimers linked via ether (O) [18], alkyl ( ) [16] and carbonate groups ( ) [16, 53]...

Table 6. Thermotropic behavior of 4-n-alkoxy-4 -cyanobiphenyls [228], poly n-[(4 -(4"-cyanophenyl)phen-oxy)alkyl]vinyl etherjs (DP =17-32, pdi = 1.09-1.21) [122-127,212,213], n-[(4 -(4"-cyanophenyl)phen-oxy)alkyl]vinyl ethers [122-127] and a-ethoxy-t0-(4-n-alkoxy-4 -cyanobiphenyl)s [122-127].

The more obvious choice for a model compound corresponds to exactly one repeat unit of the polymer. The a-ethoxy-m-(4-n-alkoxy-4 -cyanobiphenyl)s exhibit nematic mesophases at n=4-9 and SmA mesophases at n = 8-ll, and therefore match the thermotropic behavior of the polymer better than the vinyl ether monomer. However the SmA mesophase is enantiotropic only at n = 11, and the nematic mesophase is monotropic at all of these spacer lengths. Compounds which take into account only the mesogen and spacer are also good, if not better, models of the polymers. In contrast to the ethyl ethers, all of the SmA and most of the nematic mesophases are enantiotropic, which means that the melting temperature mimics the relative temperature of the glass transition of the polymer backbone better. However, the nematic mesophase still appears at n = 6 -11, and the SmA mesophase doen t appear at n = 5-7, 10, 11. 

Nevertheless, the polyfvinyl ether)s and all of these model compounds demonstrate that liquid crystals based on cyanobiphenyl me-sogens tend to form nematic and SmA mesophases. 

FIGURE 7.6 Effect of the linking group on the odd-even character of the PM-type spacer. The transition entropy, 45ni/R, oscillates with the numher of methylene units (n) of the spacer. The upper three curves represent the dimer, and the lower two are for the monomer LCs. The filled symbols indicate the carbonate-type dimer, a ,ester-type dimer, a,< -bis[(4,4 -cyanobiphenyl)carbonyloxy]alkane (CB-n triangles), and the ether-type monomer LC, 4 -n-aUcoxy-4-cyanobiphenyl (nOCB squares). 

Novel diamine monomers such as l,3-bis[3 -trifluoromethyl-4 (4 -aminobenzoxy)benzyl]benzene (TABB) [104], 4,4-bis[3 -trifluoromethyl-4 (4-amino benzoxy)benzyl]biphenyl (TABBP) [104], 2,6-bis(3 -trifluoromethyl-p-aminobiphenyl ether)pyridine (TABP) [105], 2,5-bis(3 -trifluoromethyl-p-aminobiphenyl ether)thiophene (TABT) [105], 4,4 -bis(aminophenoxy)-3,3 -trifluoromethyl terphenyl (ATFT) [106], 2,2 -bis(4 -cyanobiphenyl-4-yloxy)-4,4 -diaminobiphenyl (CBO) [107], PFMB [108], 4,4-bis(p-aminophenoxymethyl)- -cyclohexene (CHEDA) [109], 2,2-bis(4 -aminophenoxy)-4,4,6,6-bis[spiro(2 ,2 -dioxy-l ,l -biphenylyl)] cyclotriphosphazene (geminal diamine, GDA) [110] were synthesized to prepare PEIs. 

The most flexible, the benzyl ether linkage (OCH2), is here associated with the lowest Tg and values and fails to provide a mesophase when n = 4. Only the cyanobiphenyls are non-crystalline at both spacer lengths considered, while all four benzyl ethers and cyanobenzoate esters exhibit crystalline phases. 

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