Azomethine polymer

The corresponding azomethine polymers (LIX) have been synthesized by the reaction of the appropriate diamine and dialdehyde [Farcas and Grigoras, 2001 Gutch et al., 2001 Morgan et al., 1987]. 

The activation energy of the acrylic comb-like polymers of smectic structure is about the same as that in nematic systems (Table 2). This is not typical for low molecular smectics which are oriented with more difficulty than nematics. The incorporation of methacrylic units increases values up to 160 kJ/mole for azomethine (polymer 2c) and 228 kJ/mole for cyandiphenyl (polymer 4b) derivatives. These data show that the activation energy depends not so much on the mesophase but primarily on the chemical structure and the mobility of polymer backbones taking part in the orientation process. 

The former mesogen was utilized in combination with polyesters which give nematic structures in the melt, with the exception of the / -terphenyl-containing polyester that shows a smectic C phase. The latter optically active mesogen was used in combination with the nematogenic azomethine polymer and with the /7-terphenyl polyester. The last polymer displays, on admixture over a significant range of composition, a twisted smectic C phase, whereas induced cholesteric structures were observed in all other cases. ... 

Similarly, Yli-Kauhaluoma and co-workers have studied the 1,3-dipolar cycloaddition of polymer-bound alkynes to azomethine imines, generated in situ from A-ami nopyridine iodides, in the synthesis of pyrazolopyridines <06JCC344>. 

Room-temperature solution polycondensation is used for the preparation of hexafluoroisopropylidene-unit-containing poly(azomethine)s. At the end of the reaction, the water liberated by the reaction is thoroughly taken off as an azeotrope by vacuum distillation to allow the reaction to go to completion. Among DMF, DMSO, HMPA, NMP, and m-cresol used as reaction solvents, m-cresol yields a polymer with higher reduced viscosity in higher yield. The reaction proceeds rapidly and is essentially completed in 30 min. 

The incorporation of fluorine atoms improves the solubility of aromatic condensation polymers without causing them to lose their high thermal stability and modifies the processability. Hexafluoroisopropylidene-unit-containing poly-(azomethine)s and copoly(azomethine)s are readily soluble in highly polar solvents such as DMAc, HMPA, and NMP, and they also dissolve completely in dichloromethane, chloroform, and THF, whereas poly(azomethine)s derived from 21 and 22 and having no fluorine atom are insoluble in these solvents.20 Accordingly, the solubility of aromatic poly(azomethine)s is remarkably improved by substituting isopropylidene units with fluorine atoms. 

The cast films ofpoly(azomethine)s are transparent but pale to deep yellow in color. The water contact angles of fluorine-containing poly(azomethine)s films from diamine (17) are 80° for terephthalaldehye (19) and 75° for isophthalalde-hyde (20) as dialdehyde component (Table 9.9).20 These low values of water contact angles are attributed to the lower fluorine content in these polymers. 

C=N bonds in acylhydrazone groups, which are formed by the condensation of hydrazides with carbonyl groups, exhibit reversibility under mild conditions. Like polyimines, polymers with acylhydrazone functionalities exhibit dynamic aspects through the reversibihty of the azomethine bond. Skene and Lehn have reported the synthesis of polyacylhydrazones and their dynamic features (Scheme 8.3) [23]. High molecular weight polyacylhydrazone 13 was prepared by the condensation of the corresponding dihydrazide and dialdehyde in the presence of an acid catalyst. When 13 was treated with aryl dialdehyde 14 or aryl dihydrazide 15 in... 

The addition to alkenes normally leads to unstable adducts that lose carbon dioxide under the reaction conditions. The intramolecular cycloaddition of the sydnone (30) takes place at room temperature, however (Equation (5)) and the cycloadduct (31) has been characterized <86HCA927>. The unstable species formed by the loss of carbon dioxide are also azomethine ylides. It is therefore possible for a second 1,3-dipolar addition to take place, as illustrated in Scheme 6 for the reaction of 3-phenylsydnone with Al-phenylmaleimide <86TL317,92JA8414>. This 2 1 addition has been used as the basis of a synthesis of polyimides. Imides of the type (32) were used as the dipolarophiles and their reaction with 3-phenylsydnone gave linear polymers <87MM726>. 

Pyrazolines have also been incorporated as modifying groups by 1,3-addition of azomethine ylides to the carbon-carbon double bond of unsaturated poly(esters) (186 Scheme 89) (68MI11100). Poly(isoxazolines) were prepared in similar fashion by reaction of an unsaturated polymer with a nitrile oxide (75MI11106). 

Melt poly condensation is also the most popular method for other thermotropic condensation polymers, including the polyazomethines where the reaction between aromatic aldehydes or ketones and primary amines with elimination of water leads to azomethine (Schiffs base) formation 48). 

Polymer-supported azomethine ylids generated from a-silylimines through a 1,2-silatropic shift, are shown to be versatile reagents suitable for the synthesis of libraries of pyrrolidine derivatives after 1,3-dipolar cycloaddition with a series of dipolarophiles. Effectively substituents R1, R2 and dipolarophiles A=B and A=B can be chosen to get the desired adduct.146... 

M.A. Marx, A.-L. Grillot, C.T. Louer, K.A. Beaver and P.A. Bartlett, Synthetic design for combinatorial chemistry. Solution and polymer-supported synthesis of polycyclic lactams by intramolecular cyclization of azomethine yhdes,... 

Fig. 21 Reaction scheme for CVD synthesis of azomethine conjugated polymer, poly.

Vapour Deposition Polymerisation. This is a little studied approach but one that offers significant potential for the fabrication of very thin films and for elaborate multilayer structures. A commercial process has been developed by the Ulvac Corporation in Japan to coat magnetic relay switches with an insulating polyimide layer. A polyamic acid is sythesised by co-deposition of two reactive monomers and is then thermally imidised. The same approach can be used for the condensation polymerisation of poly(azomethine)s, ° poly(ox-adiazoles) and poly(quinoxalines) all of which have been used in LED structures. This approach to polymer synthesis is ripe for further development. 

A convenient one-step transformation of primary and secondary amines into the corresponding unprotected guanidines using 4-benzyl-3,5-dimethyl-l/f-pyrazole-l-carboxamidine 90 and its polymer-bound variant were described <06S461>. 1,3-Dipolar cycloaddition of polymer-bound alkynes to azomethine imines generated in situ from N-aminopyridine iodides followed by aromatization of the cycloadducts gave polymer-bound pyrazolopyridines that were released from the resin as carboxylic acids with trifluoroacetic acid or as methyl esters with sodium methoxide <06JCO344>. 

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