Poly Azomethine s

Many approaches have been attempted to obtain soluble or fusible high-molecular-weight poly(azomethine)s, including the introduction of flexible 

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. 

Wholly aromatic poly(azomethine)s possess remarkable thermal stability, and high strength and modulus. However, owing to their limited solubility and infusibility, it is difficult to obtain poly(azomethine)s having sufficiently high molecular weight and useful processability. 

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. 

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Novel fluorine-containing aromatic poly(azomethine)s are prepared by the reaction of hexafluoroisopropylidene-unit-containing aromatic diamines, 2,2-bis[4-(4-aminophenoxy)phenyl]-l,l,l,3,3,3-hexafluoropropane (17) and 2,2-bis(4-aminophenyl)-l, 1,1,3,3,3-hexafluoropropane (18) with terephthalaldehyde (19) or isophthalaldehyde (20)20 (Scheme 11). 

None of the poly(azomethine)s show glass transition, and they are amorphous irrespective of the presence or absence of fluorine atoms20 All the poly(azomethine)s are thermooxidatively stable at temperatures as high as 400°C. Hexafluoroisopropylidene-unit-containing poly(azomethine)s are more stable to thermooxidation than those having no fluorine atom (Table 9.9). This is expected because the methyl group is more susceptible to oxidation than aromatic rings. 

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. 

Siloxane constituted from poly(azomethine)s and a six-membered poly(imide) have been synthesized from a siloxane-containing diamine with dialdehydes and 3,4,9,10-perylenetetracarboxylic dianhydride [13]. The poly(azomethine)s emit blue light, while the poly(imide) emits green light. 

Iwan A, Schab-Balcerzak E, Pociecha D, Krompiec M, Grucela M, Bilski P, et al. Characterization, liquid crystalline behavior, electrochemical and optoelectrical properties of new poly(azomethine)s and a poly(imide) with siloxane linkages. Opt Mater 2011 34 61-74. 

Aromatic copolyesters which are sufficiently rigid to form a nematic mesophase upon heating (e.g. 4 and 5) also give HSHM fibres, but major industrial exploitation awaits improved competitiveness with established fibres. Exceptionally high strength values have been reported for fibres made from thermotropic nematogenic poly(azomethine)s (e,g, 6) but these materials seem to suffer from a poor hydrolytic stability. ... 

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