Imides structure

The above is an example of the Guareschi reaction. It is applicable to most dialkyl ketones and to alicyclic ketones (e.g., cyclohexanone, cyc/opentanone, etc.). The condensation product (I) is probably formed by a simple Knoe-venagel reaction of the ketone and ethyl cyanoacetate to yield ethyl a-cyano-pp dimethylacrylate (CH3)2C=C(CN)COOCjHj, followed by a Michael ad tion of a second molecule of ethyl cyanoacetate finally, the carbethoxyl groups are converted to the cyclic imide structure by the action of ammonia. 

In the narrow sense, bis-maleimide resin means the thermosetting resin eom-posed of the bis-maleimide of methylene dianiline (BMI, bis(4-maleimidophenyl)-methane) and methylene dianiline (MDA, bis(4-aminophenyl)methane) (Fig. 1). Beeause of the addition meehanism, the resin is eured without elimination, whieh is a eharacteristic of this resin. Bis-maleimide resin is used as a thermally stable matrix up to 204°C (400 F) whieh typical epoxy resins may not normally be used. However, in spite of having an imide structure, bis-maleimides are classified as being moderately thermally stable resins. The aliphatic structure of the resin is not stable for long periods above 232°C (450°F.) If a highly aromatic thermally stable thermosetting resin is necessary, acetylene end-capped aromatic imide-based oligomers should be used. 

Acidic hydrolysis of the amide group at pH 4.5 is a very slow reaction. Strong acidic conditions leads to a progressive insolubilization of the reaction product because of formation of cyclic imide structures ... 

Tractable polymers can be prepared when amino and anhydride functions are not located on the same aromatic ring, and different strategies were employed to obtain soluble polymer. AB benzhydrol imide was prepared by polycondensation of 4-(3-amino-l-hydroxymethylene) phtlialic acid monomethyl ester in NMP. The polymer soluble in NMP has been used as adhesive and coating.56 A second approach was based on an ether imide structure. AB aminophenylether phthalic acids (Fig. 5.34) were prepared by a multistep synthesis from bisphenols.155 The products are stable as hydrochloride, and the polycondensation takes place by activation with triphenylphosphite. The polymers are soluble in an aprotic polar... 

Conditions for low temperature solution polymerizations of pyromellitic dianhydride (PMDA) have been developed for a wide variety of aromatic 1,4-phenylene [54, 55] and 4,4 -biphenylene [56-58] diamine monomers in a number of aprotic solvents to give high molecular weight prepolymers referred to as polyamic acids. Since the imidized structures are insoluble, they must be processed in the form of their polyamic acids which are subsequently imidized thermally or by chemical dehydrating agents. Although this procedure is acceptable for thin film or fibers, the fabrication of thick parts is complicated by the water of imidization. 

Kaneda et al. synthesized [61] a series of high molecular weight extended chain copolyimides (XV) by the reaction of PMDA and 3,3, 4,4 -biphenyltetra-carboxylic dianhydride (PPDA) with 3,3 -dimethyl-4,4 -diaminobiphenyl. Solvents used for the one-step synthesis to the fully cyclized imide structure were phenol, p-chlorophenol, m-cresol, p-cresol and 2,4-dicholorophenol. The polycondensations were performed at 180°C for 2h with a monomer concentration of 6% by weight and p-hydroxybenzoic acid used as a catalytic accelerator. A maximum of 50 mol % of PMDA could be used before the copolymer precipitated from solution. Reconstituted copolymers as isotropic dopes (8-10% by weight) in p-chlorophenol were dry-jet wet spun between 80 and 100 °C [62]. 

A major distinction for nucleophilic reactions with ambident anions is whether they proceed with kinetic or thermodynamic control.80 N-Substituted saccharins (10) should be thermodynamically more stable because of amide character than the isomeric pseudosaccharin (3) of imidate structure. In fact 3 may be rearranged thermally to 10 in an irreversible reaction.96 The threshold for thermodynamic control appears to be lowered for electrophiles with multiple bonds, e.g., formaldehyde, reactive derivatives of carboxylic acids, but also quaternary salts of N-heterocyclic compounds.80 It will be seen that in those cases substitution indeed occurs at the nitrogen, not necessarily through thermodynamic control. 

In thermal treatment of the partially crosslinked polyamic acid ester, the conversion of the amide structures to imide structures starts at about 100°C. This conversion was investigated by means of FT-IR spectroscopy (Bruker IFS 85, reflexion measurement) on annealed films on Al-wafers, where the amide-carbonyl stretching vibrations at 1680 cm- and 1540 cm- and the corresponding imide band at 1780 cm- were quantitatively evaluated. 

In 1976 Marsmann et al. reported on the structures of doubly silylated sul-flnamides (Scheme 31) [82]. From the analysis of Si NMR and IR data the predominance of the imidic structure 114 was deduced. Some 10 years later. 

Dihydroxyimidazo[4,5-c]pyridine (3-deazaxanthine 436 R = H) and related 2-substituted derivatives (436 R = Cl) and (438) were prepared from the requisite imidazole 4-acetamide-5-carboxylic acid esters (435) and (437) by base-catalyzed cyclization to the imide structure (63JOC304l). 

Upilex Type R by UBE Ind. is produced from BPDA and ODA. It is based on a unique combination of the new monomer synthesis described in the preceding section and one step high temperature solution polymerization in a phenolic solvent [42]. High quality films and fibers can be produced from the solution because a water forming reaction is not involved [43]. The polymers produced by such a process have a completely imidized structure and provide for superior properties than polymers prepared by solid state imidization of polyamic acids. For example long term oxidative and hydrolytic stabilities and retention of electrical properties are substantially better. 

The search for a chemical understanding of the nature of the heat-inactivation phenomenon revealed that aspartoylimide residues were cleaved (16). This structure, which is formed during the polymerization reaction, is hydrolyzed most rapidly in basic solution (34, 37). Heating in buffer at neutrality causes loss of activity concomitant with hydrolysis of the imide structure. The cleavage has been monitored qualitatively by infrared analyses, and quantitatively by absorption near 200 m/i (Fig. 2), or by titration at constant pH. 

X-Ray diffraction confirms that, in the crystal, the compounds MeCON(SnMe3)Me and MeCON(SnMe3)2 have planar amide rather than imidate structures, and spectroscopic evidence suggests that this is the dominant structure also in solution in the solid, the C=0 and N-Sn bonds are cis, with a weak intramolecular O..Sn interaction, and a stronger intermolecular interaction.55... 

Interesting results are got in the work [25] in which the authorse suppose that luminescence of PCA may be attributed to the presence of compounds of keto-imide structure... 

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