Isocyanates aminimides

The preparation and properties of these tertiary aminimides, as weU as suggested uses as adhesives (qv), antistatic agents (qv), photographic products, surface coatings, and pharmaceuticals, have been reviewed (76). Thermolysis of aminimides causes N—N bond mpture foUowed by a Curtius rearrangement of the transient nitrene (17) intermediate to the corresponding isocyanate ... 

Acyl aminimides have proved useful as surface-active and antimicrobial agents and as an intermediate for isocyanate preparation (50). 

Dialkylamino isocyanates are known transient intermediates and, in the absence of other reagents, have been shown to dimerize. When the cyclic aminimide (c) was heated at 130°C under vacuum (0.3 mm) for 3 h, (d) was obtained in 89% yield. At higher temperature (d) was formed but rearranged to (e) as depicted in scheme 146. 

The chemistry of aminimides has been reviewed elsewhere (Ref. 204, 205) and the chemistry of dimethyl amino isocyanate, prepared in the form of dimer (d) through a phosphoramide synthesis, studied (206). 

The photolysis of aminimides produces acylnitrenes, which have usually been trapped in intermolecular reactions.151,159 Again, isocyanates often accompany the reactions. The thermolysis of 2,4,6-triphenylpyridine N-acylimines at 170-250°C affords isocyanates in good yields.160... 

Urethane group containing-coatings can also be obtained from other types of compounds capable of generating Isocyanates. These are aminimides, especially those based on methacrylic acid (189-191) ... 

Aminimides decompose on heating to yield isocyanate groups as follows ... 

Copolymerization studies demonstrated that aminimide, 1,1-dimethyl-l-(2-hydroxypropyl)amine methacrylimide (DHA) copolymerizes readily with 4-vinylpyridine (4VP) and N-vinylpyr-rolidone (NVP). These copolymers could he thermolyzed in solution to give soluble poly(4-vinylpyridine-co-isopropenyl isocyanate) and poly(N-vinylpyrrolidone-co-isopropenyl isocyanate) materials. The reactivity ratios of each monomer pair were determined, and the Alfrey-Price Q and e values for DHA were calculated for DHA (Mt)-4VP (M2), r, = 0.41, r = 0.77, Q = 0.68, and e = 0.58 and for DHA (Mt)-NVP (Mg), r2 = 0.15, r2 = 0.35, Q = 0.14, and e = 0.58. The DHA-4VP copolymers quaternized readily to give a new family of water-soluble polyelectrolyte materials. The various copolymers were examined as adhesion promoters for rubber-tire cord composites. 

The IR spectra of the copolymers had strong absorption bands at 1710 cm"1 (pyrrolidone unit) and 1580 cm"1 (aminimide carbonyl). When films of the copolymers were heated (150°-200°C), the band at 1580 cm-1 vanished and a new strong band appeared at 2250 cm"1 which was indicative of the described aminimide-isocyanate rearrangement. Again, the NMR spectra had poor resolution but the broad bands indicated DHA and NVP moieties. 

Allyl isocyanate n-Butyl isocyanate t-Butyl isocyanate 3-Chloro-4-methyl phenyl isocyanate 2-Chlorophenyl isocyanate Cyclohexyl isocyanate 2,3-Dichlorophenyl isocyanate 2,4-Dichlorophenyl isocyanate 2,5-bichlorophenyl isocyanate 2,6-Dichlorophenyl isocyanate 3,4-Dichlorophenyl isocyanate Ethyl isocyanate Hexyl isocyanate Isobutyl isocyanate Isopropyl isocyanate Methacrylonitrile Methoxymethyl isocyanate n-Propyl isocyanate m-Tolyl isocyanate o-Tolyl isocyanate p-Tolyl isocyanate intermediate, aminimides 1,1-Dimethylhydrazine intermediate, ampicillin Acetamide... 

The Ashland Chemical Company markets a commercial chemical class called aminimides which act as isocyanate precursors, eliminating the problem of by-product phenol from the use of phenol-blocked isocyanates (see Fig. 8.10). 

The blocked isocyanate function of aminimides also allows their use as polyurethane adhesives. Thus bis(aminimides) crosslink with polyester or polyether diols to yield a range of elastomers dependent upon the structure of the bis(aminimide) and the co-reactant chosen. For example, bis(aminimides) mixed with polyhydroxyl components can provide stable, single-package prepolymer compositions which yield polyurethanes on heating without the problem of isocyanate moisture sensitivity which can plague polyurethane applications. 

The trimerization of isocyanates to form isocyanurate rings is particularly important in producing iire-resistant rigid foams, and a large volume of work has appeared on this topic. Much of it has been done by Kresta and co-workers, who have discussed the general mechanism, the co-catalytic effect of urethane groups, and the use of cyclic sulphonium zwitterions and aminimides as catalysts. Model systems have been used for these studies, but attention has also been paid to the kinetics and mechanism of commercial polyisocyanurate systems. ... 

A, A -Dialkylamino isocyanates 153, generated from l,l-dimethyl-4-t-butyl-1,2,4-triazolidine-3,5-dione-l,2-aminimide 152, react with aliphatic isothiocyanates to give the [3+2] cycloadducts 154 resulting from addition across the C=N bond of the isothiocyanate... 

Sodium methoxide Isocyanates from carboxylic acid esters via aminimides... 

Conunercially available blocked isocyanates have included Hylene MP from duPont (XXI) " which is phenol-blocked MDI Mon-dur S (XXII), a phenol-blocked TDI adduct Mondur SH (XXIII), a cresol-blocked TDI tiimer and Experimental E-320 blocked isocyanate (XXIV), a ketoxime-blocked tetraisocyanate, all from Mobay and Isonate 123P (XXV)" which is -caprolactam-blocked PAPI from the Upjohn Company. The Ashland Chemical Company has marketed a conuner-cial chemical class called aminimides which act as isocyanate precursors, eliminating the problem of by-product phenol from the use of phenol-blocked isocyanates.Their chemistry relevant to this use, is as follows ... 

These isocyanate groups can be cured according to the reactions mentioned above, giving polyurethane resins. Aminimides can also be copolymerized with other vinyl monomers and urethane copolymers can thus be obtained. 

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