Lead aromatic imides

The double bond of maleimides in very reactive towards electron-rich dienes, to give a normal Diels-Alder cycloaddition. Thus BMIs were used to obtain linear polyimides by reaction with several kind of dienes [46-51]. However the dienes are often difficult to prepare [51] and functionalized dienes have been used. Furan terminated oligomers react with BMIs at 70 °C leading to an oxygen-containing cycloadduct [52-57] which can react with acetic anhydride to give an aromatic imide (Fig. 13) [58-59]. 

The most general method for the preparation of high temperature polyimides is based on the reaction between an aromatic diamine and an aromatic dianhydride or tetracarboxylic acid. This proceeds via the formation of the intermediate polyamic acid which in further heating undergoes a ring closure condensation reaction leading to imide formation. The reaction is as follows... 

The cathodic reduction of aromatic carboxamides and imides in acid solution at lead or mercury cathodes generally leads to amines and isoindolines, respectively 7,9 These reactions are of great preparative interest but their mechanism have not been examined. Cpe of isonicotinic amide and 2-thiazolecarboxaldehyde in acid solution gives the corresponding aldehydes in good yields 139>141)... 

Monotrifluoroacetylated diaminopyrazole was first reacted with the free Kemp s triacid to produce the imide, followed by N-Boc protection and amide-coupling with a m-substituted aniline derivative. Final Boc-deprotection occurred on the chromatography column leading directly to the new receptor modules. The recognition site X was chosen to be ethyl as a neutral reference, acetyl for polar side-chains, nitro for electron-rich aromatic residues and carboxylate for basic amino acids (Figure 2.4.4). 

The synthesis of siloxane-polyimide elastoplastics requires an approach slightly different from that used in preparing the thermoplastic materials because of differences in reactivity between the aliphatic-anhydride-terminated siloxane oligomers and the aromatic dianhydrides. A one-pot condensation of the anhydride-terminated siloxane oligomers, BPADA, and the diamine in o-dichlorobenzene solution in the presence of 2-hydroxypyridine as catalyst leads to a siloxane-deficient polyimide. To circumvent this deficiency, a two-step synthetic scheme was used in which the anhydride-terminated siloxane oligomers were first capped with an excess of the diamine. The aromatic dianhydride was then added to the resulting amic acid oligomeric mixture and warmed to complete imidization (Scheme IV). 

Poly(imide)s as a class of polymer exhibit a range of properties, such as high Tg, excellent thermal stability, high chemical resistance, low dielectric constant and ease of fabrication, which have lead to important uses in the semiconductor and advance composite industries. In addition, the high aromatic content of many of these polymers and consequent high stability to ionizing radiation, leads to usage of poly(imide) films and composites in the nuclear and aerospace industries. 

Other special aliphatic imide forming compounds claimed in patents, like 2-oxazolidone [85] or epsilon-caprolactame, lead to polymers having aliphatic chains. These chains are responsible for the lower Tg of the cured films in comparison with the polymers having aromatic diamines. No commercial polyfes-ter-imide) wire enamel in western Europe contains them. 

Table 23 demonstrates the mesogenicity of polymers containing biphenylene-S j -tetracarboxylic imide. A comparison of series 9 and 10 in the table shows that replacement of pyromellitic dianhydride with BPTA in a copolymer with two moles of m-aminophenol and an aromatic diacid does not lead to mesogenic polymers. The assignment of an MI score of 4 compared to 2 for pyromellitic anhydride does however raise the MI as far as the borderline condition of MI=9.5 when 2,6-naphthalene dicarboxylic acid is the co-monomer. 

With the growing demand for coextruded products, barrier plastics have shown significant growth in the last several years. Historically, the high barrier resins market has been dominated by three leading materials — vinylidene chloride (VDC) copolymers, ethylene vinyl alcohol (EVOH) copolymers, and nitrile resins. Since 1985, however, there has been a lot of interest worldwide in the development of moderate to intermediate barrier resins, as apparent from the introduction of a number of such resins, notably, aromatic nylon MXD-6 from Mitsubishi Gas Chemical Company, amorphous nylons SELAR PA by Du Pont and NovamidX21 by Mitsubishi Chemical Industries, polyacrylic-imide copolymer EXL (introduced earlier as XHTA) by Rohm and Haas and copolyester B010 by Mitsui/Owens-Illinois. 

Trimerization of nitriles, isocyanates, isothiocyanates, imidates, and carbodiimides all lead to symmetrical 2,4,6-trisubstituted 1,3,5-triazines (see Section 6.12.9.5). The use of lanthanide trifluoromethanesulfonate and ammonia as cocatalysts is claimed as a big improvement. The trisaminal of 2,4,6-triformyl-l,3,5-triazine is also useful for further derivatization to unusual structures (see Section 6.12.7.1). Treatment of a 1 1 pyridine/conc. ammonia solution of an aromatic aldehyde with excess Fremy s salt is another development. Separation of the amide coproduct was claimed to be easy. The synthesis fails with aliphatic aldehydes (see Section 6.12.9.5.4). Aminolysis of 2,4,6-triaryl-1,3,5-oxadiazinium salts gives symmetrical 1,3,5-triazines but the reactions are limited in that electron-withdrawing groups in the aromatic rings lead to instability and difficulty in separation of products (see Section 6.12.10.4). 

This group also found that the isomunchnones derived from these diazo imides react with aromatic aldehydes with excellent diastereofacial- and exoselectivity. Thus 4-nitrobenzaldehyde reacts with the isomunchnone derived from 476 to give adduct 477 (Fig. 4.148). Hydrolysis leads to a,p-hydroxy acid 478 in optically pure form. 

El-Gendi et al. (2010) studied the PV properties of block ether aromatic copoly-imide series membranes where the ether soft block acted both as a selective and a permeable block. The PV results showed that rubbery copolyimides can lead to promising asymmetric membranes for liquid-liquid separations (water-EtOH). 

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