Azoxy polymers

The melting temperature is, of course, dependent on the sample history and molecular weight, so polymer samples within such a series must be heat treated in the same manner and be of sufficiently high molecular weights for comparisons to be possible. For the latter, studies on both the OTO triad and on an azoxy polymer show that polymer transition temperatures level off at fairly low molecular weights, as... 

Structurally similar polymers with azo links, Polymers 9 and 10, formed no meso-phases when the rigid aromatic unit contained terminal carbonyl groups, but these formed nematic mesophases when the ester link was reversed The transition temperatures of the azo and azoxy polymers with the same spacer were quite close to each other. Substitution of methyl groups on the phenylene rings of these polymers reduced melting temperatures without adversely affecting nematic mesophase stability... 

The effect of reversing ester groups, which has already been briefly discussed, should be mentioned again here. In the case of the azo and azoxy polymers made from carboxy-terminated flexible spacers, polymers with stable mesophases were formed. In contrast, polymers made from oxy terminated spacers had no mesophase. While this behavior is an extreme case, when comparisons are possible it seems that polymers made with the carboxy-terminated spacers almost always have wider ranges... 

The effect of substituents on the thermal properties of a series of aromatic azoxy polymers is shown in Table 3, Polymers 10-12, in which it is seen that the introduction of methyl groups into the mesogenic units resulted in a depression in both the melting point and the clearing temperature of the polymer. As can be seen from these data, the substitution position in the mesogenic unit is also important, but it will be necessary to have much more experimental results before the positional effect may be evaluated systematically. 

One of the most surprising observations was that the X-ray diffraction pattern of the azoxy polymers showed crystalline-like d-spacings in the liquid crystalline melt while in the isotropic region the polymers showed the expected amorphous halo. A possible explanation of such a highly ordered mesophase was the retention of much of the order of the solid in the molten state. A highly structured mesophase occurs in the smectic E state where directional and layered order are maintained in the melt... 

Finally, polymer 594 has been used as an arene-catalyst to activate nickel from nickel(II) chloride and lithium, in order to perform hydrogenation of different organic substrates such as afkenes, afkynes, carbonyl compounds and their imines, alkyl and aryl halides (chlorides, bromides and iodides), aromatic and heteroaromatic compounds as well as nitrogen-containing systems such as hydrazines, azoxy compounds or Af-amino oxides, giving comparable results to those obtained in the corresponding reaction in solution . 

The order and mobility of a labeled flexible alkyl spacer in the linear thermotropic polymeric nematic liquid crystal poly(2,2 -dimethyl-4,4 -dioxyazoxybenzenedodecanedioyl-dj0) (poly[oxy(3-methyl-1,4-phenylene)azoxy 2-methyl-1,4-phenylene)oxy(1,12-dioxo-1,12-dodecanediyl-d2oll) is explored with deuterium NMR. The quadrupol splittings of the spacer methylene segments in the nematic melt of the polymer are reported as a function of the temperature and are contrasted with observations on model compounds solubilized in a nematic solvent. 

Iimura, K., Koide, N., Ohta, R. and Takeda, M. Synthesis of thermotropic liquid crystalline polymers, 1, azoxy and azo-type polyesters. Makromol. Chemie 182, 2563 (1981)... 

Nitro compounds are easily reduced, catalytically or chemically, to amino compounds. Incomplete reduction can lead to a hydroxylamino derivative or to binuclear azo, azoxy, and hydrazo compouds, e.g., 789 790, 791. Examples include reduction of 3-nitropyridines using aqueous sodium hydrosulfite at room temperature <2005JME5104> and of 2-nitropyridine by transfer hydrogenation in the presence of 10% Pd/G and recyclable polymer-supported formate, prepared from aminomethylpolystyrene resin and ammonium formate <2005SC223>. A nitro group can be reduced in the presence of an A-oxidc group, e.g., 784 782. 

Another type of unsaturated mesogenic structure, which is based on a structure in between an azo- and vinylene-type, is that in which a Schiff base unit links two phenylene groups. This unit is similar in geometry to the three previous mesogenic units, the azo, azoxy and stilbene groups The only reported example of this structure, however, was Polymer 8 with a decamethylene spacer, and it was quite similar in properties to the polymers just discussed. It also possessed a smectic phase, and the mesogenic unit had terminal carboxy groups. 

Esnault, R, Gahand, D., Vohno, E, and Blumstein, R. B., The anisotropy of magnetic suscepti-bihty of para-azoxy-anisole and of related nematic polymer model compounds. Mol. Cryst. Liq. Cryst., 157, 409-426 (1988). 

In gas chromatography, thermotropic hquid crystals belonging to such groups of chemical compounds as Schiff s base, azo- and azoxy-compounds, esters, derivatives of biphenyls and terphenyls, organic complexes with transition metals, and organic polymers are used. Siloxane polymers of liquid-crystaUine properties are stable within the wide range of temperatures from 50°C to 300°C. 

In addition to the esterifrcation mentioned above, other reactions are also possible and could result in perturbation of the regularity of the chain. It is well known that aromatic azoxy derivatives undergo Wallach rearrangement on irradiation with visible light and under the effect of other factors, turning into the hydroxyazo derivatives [18], which are frequently incorporated in the chain of LC polymers [6]. 

The focus of studies of the processes of ordering of linear LC polymers with mesogenic groups in the main chains of the macromolecules has up to now been concentrated on the study of their orientational behaviw undo the effect of a magnetic field. Blumstein et al. were able to obtain the x-ray fiber pattran of the nematic azoxy derivative of the polyester... 

The critical magnetic field strength should naturally be directly correlated with the elastic characteristics of the polymer liquid crystal. Preliminary results of the first experiments on the measurement of the elasticity constants /STjj and Ky of nematic solutions of polyester azoxy derivative XV of different molecular weight in p-azoxyanisole [49] show that an increase in X33 is observed with an increase in the molecular weight of the polymer and an increase in the concentration of the polymeric component in the solution, while the ratio X33/X11 remains unchanged. It is possible to hypothesize that the increase in the length of the polym chain in the case of a linear LC polymer will be accompanied by an increase in the modulus of elasticity, which is on the whole in agreement widi the theoretical predictions made in [50] relative to polymer liquid crystals. 

The initial step in the metabolism of TNT by nearly every organism seems to be reduction (8-13, 18, 19, 27, 32, 51, 52, 59, 63, 64, 74, 87, 96, 97). Most often nitrotoluenes are biotransformed to aromatic amines (31, 40) through a series of reduction steps as described by Yamashima et al. (99). The para nitro group of TNT is usually reduced preferentially to the ortho group. A second series of reductions predominantly leads to the formation of 2,4-diaminonitrotoluene (2,4-DAT). Reduction of the third nitro group usually only occurs under anaerobic conditions (55). Under aerobic conditions, hydroxylamino metabolites are sufficiently long lived to lead to the formation of azoxy compounds or polymers which are products of condensation of hydroxylamino and nitroso dinitrotoluenes (56). 

---