Imide linkage

Polyamide Imides. Polyamide imides (PAIs) are formed from the condensation of trimellitic anhydride and aromatic diamines (33). The polymer is called amide—imide because the polymer chain comprises amide linkages alternating with imide linkages, with the general chemical stmcture ... 

Polyamide-imides may also be produced by reacting a diacid chloride with an excess of diamine to produce a low molecular mass polyamide with amine end groups. This may then be chain extended by reaction with pyromellitic dianhydride to produce imide linkages. Alternatively the dianhydride, diamine and diacid chloride may be reacted all together. 

Polymerization is assumed to occur only through the imide linkages—crucial to the formation of a star-branched nylon 6 species. If an imide-containing species (such as N-acetylcaprolactam) is added to the reaction, the slow step of the reaction is by-passed, allowing polymerization to take place very rapidly. This should also be the case for a tri-imide for generating star nylon species. 

A star-branched nylon 6 may be created by using a "star initiator "--a species with three or more imide linkages as activated sites. It was initially assumed that reaction would take place only at the imide sites and that cross-linking would not occur, although the bis-caprolactam species is known as a crosslinking agent. (9-... 

The thermal polymerization of /3-carboxymethyl caprolactam results in a novel polyimide which has been identified as a poly(2,6-dioxo-l, 4-piperidinediyl)trimethylene. The formation of this structure is explained by a mechanism that consists in an initial isomerization of the caprolactam derivative to 3-(3-aminopropyl)glutaranhydride or its linear dimer and subsequent polymerization by condensation involving the terminal amino group and the anhydride moiety. Suggested reaction schemes and corresponding kinetic equations are based upon the premise that the extent of polymerization is represented by the concentration of imide linkages. Results of rate studies carried out at 210°-290°C. support the proposed mechanism. 

The concentrations of polymer molecules, c, (chains) and imide linkages, I, are given by the relationships... 

Independent of any mechanism that may be considered, the concentration of imide linkages is given by the relationship... 

Plants. In soya beans and maize, the major metabolite is 2-chloro-4-fluoro-5-(4-hydroxy-1, 2-cyclohexane-dicarboximido) phenoxyacetic acid formed by reduction of the tetrahydrophthaloyl double bond and hydroxylation other metabolic pathways include cleavage of the ester, and cleavage of the imide linkage... 

Potentiometric titration of simple proline derivatives and of poly-O-acetyl-hydroxyproline in acetic anhydride also demonstrate protonation of the imide linkages with about 0.35 mole proton boiuid per mole imide bond (Steinberg et ah, 1960o). 

The extent of reaction (i.e. conversion of lactam into imide linkages) is expressed by... 

Other types of isocyanate-based polymer foams, such as polyiso-cyanurate foams modified by oxazolidone, carbodiimide or imide linkages, have outstanding properties in flame retardance and fire endurance without the addition of any flame retardants... 

Imide-Modified Isocyanurate Foams. The imide linkage is a thermally stable linkage, and therefore, imide-modified isocyanurate foams have higher thermal stability and flame retardance than urethane-modified isocyanurate foams. R. Grieve (114) prepared such foams in a one-shot process by reacting a polycarboxylic acid anhydride with an organic polyisocyanate in the presence of a catalytic amount of a monomeric homocyclic polyepoxide and a tertiary amine. 

The research team of S.R. Rajski demonstrated that o-carboalkoxy triarylphosphines react with aryl azides to afford Staudinger ligation products bearing O-alkyl imidate linkages. In comparison, the reaction of alkyl azides with o-carbalkoxy triarylphosphines usually gives rise to amide linkages. The importance of this technique lies in its ability to couple abiotic reagents under biocompatible conditions. 

In order to overcome the problems associated with acid hydrolysis of amides of prolinol, the Evans research group has investigated the diastereoselectivity of the alkylation of imides derived from chiral 2-oxazolidones. Imide enolates are somewhat less nucleophilic than amide enolates, but they have the advantage that their diastereomeric alkylation products are easily separated and the imide linkage is cleaved with a variety of reagents under mild conditions. As shown in Scheme 64, alkylation of the chelated (Z)-enolate of the propionimide derived from (S)-valinol (135) with benzyl bromide occurred in high chemical yield and with high si-face diastereoselectivity. In addition to oxazolidones, imidazoli-diones have proved to be useful chiral auxiliaries for diastereoselective enolate alkylations. ... 

A change in conformation must, theoretically, result from the opening of imide linkages. Such changes in structure would be analogous to phenomena involved in denaturation of enzymes. The breaking of covalent imide bonds in proteinoids, however, partly (39) distinguishes the two processes. 

IR spectroscopy may be used to follow two reactions occurring in polyimides exposed to high temperatures and humidities hydrolysis of the imide linkages and hydrolysis of residual anhydride end groups. The hydrolytic susceptibilities of several polyimides were measured at 90°C/95% R.H. Polymers based on benzophenone tetracarboxylic acid dianhydride (with either oxydianiline or m-phenylene diamine) appeared to undergo rather rapid hydrolysis initially, but the reaction had essentially halted by the time the measured imide content had decreased by 5-6%. Polymers based on 3,3 ,4,4 -biphenyl tetracarboxylic acid dianhydride (with p-phenylene diamine) and pyromellitic dianhydride (with oxydianiline) showed no significant imide hydrolysis. In all the polymers, the anhydride was hydrolyzed quite readily. 

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