Epoxy reactions with isocyanate

Regioselective C-2 amination of 2,3-epoxy alcohols can be realized by intramolecular oxirane ring opening of the carbamates prepared by the reaction of the epoxy alcohols with isocyanates." -" In some cases, however, acyl transfer is a serious side reaction (Scheme 59)." ... 

Reaction with isocyanates also provides a route to carbamates, which serve as masked amines (eq 8) or as diamines for epoxy resin curing. Carbamates of o-NBA possess moderate antitumor activity. ... 

Curing an epoxy resin by reaction with an isocyanate... 

Reports of allergic sensitivity to MDA are confounded by mixed exposures to chemicals such as epoxy resins and isocyanates, which make it difficult to relate specific cause with effect. MDA does appear to cause an intense yellow staining reaction involving the skin (especially fingers and palms), nails, and occasionally hair in exposed workers. The staining should serve as a marker for potential systemic exposure. 

Chemical reaction depends on the presence of reactive substrates and on the probability of their encounters. Thus, the possibilities of reactions can be numerous. The literature describes reactions of OH groups on the surface of kaolin with isocyanates, vulcanization of nitrile rubber by ZnO, reactions of carboxyl groups on the filler surface with amines and epoxy groups, reactions of carboxyl groups with diols," and many others.The presence of a reactant on the surface of a material particle increases the probability of chemical reaction. Other factors include statistical probabilities, surface barriers which affect contact, dilution factors, molecular mobility, and viscosity changes in the system. These are discussed in other sections of this book. 

Eschenmoser a,p-epoxy ketone cleavage (2,419-422 3,293). In the synthesis of a prostanoid, Corey and Sachdev encountered a case where the Eschenmoser cleavage reaction with p-toluenesulfonylhydrazine gave a very complex mixture from which none of the desired acetylenic aldehyde could be isolated. They then found that cleavage could be effected with 2,4-dinitrobenzenesulfonyl-hydrazine in CH2CI2 or THF at 0-25°. Pyridine, sodium carbonate, or sodium bicarbonate can be used as catalysts. The yield can sometimes be improved by addition of ethyl isocyanate to scavenge the sulfinic acid formed in the fragmentation. This modified procedure was shown to be effective in five cases. 

Chemical reactions with alkyd resins can take place via their hydroxyl or carboxyl groups as well as via the double bonds of the unsaturated fatty acids. Isocyanates, epoxy resins, or colophony, for example, may be reacted with the hydroxyl groups. The carboxyl groups can be reacted with polyamidoamines (reaction products formed from dimerized linoleic acid and ethylenediamine) to form thixotropic resins, or can react with hydroxy-functional silicone precondensates. The double bonds of the unsaturated fatty acids permit copolymerization with vinyl compounds [e.g., styrene or (meth)acrylic acid derivatives]. 

Bayer introduced the Blendur resins (EPIC) based on the catalyzed reaction of an epoxy resin with an isocyanate. 

A series of patents issued to Asahi Chemical Industry Co., deal with the modification of hexamethylenediamine by reaction with (meth)acrylic-, glycidyl ether-, hydroxyl-, amino-, amido-, or carboxy-substituted vinyl compounds, isocyanate, and amino acid compounds (Table IV). These modified amine curing agents are active at low temperatures and, in some cases, on wet substrates. Amine-substituted resole phenolics have also been described as useful epoxy curing agents." " Preparation of these curing agents is via condensation of the phenol, formaldehyde, and polyamine (Eq. 8). 

Vinyl acetal polymers can be formulated with other thermoplastic polymers and with a variety of multifunctional cross-linkers. Examples of polymers that are at least partially compatible with PVF or PVB resins include some types of polyurethanes, some types of celluloses, epoxies, isocyanates, phenolics, silicones, unsaturated polyesters, and melamine- and urea-formaldehyde polymers (19-21). Although vinyl acetal polymers are thermoplastic, hydroxyl groups permit cross-linking reactions with a variety of thermosetting resins, for example. 

The applications of this technique have been reviewed [68]. In addition to chemical reactions associated with thermal and oxidative decomposition, DSC can also be used to monitor the curing of thermosets (see Section 10.3). Examples are the polymerisation of unsaturated polyester resins, poly-addition of epoxy resins with curing agents, and isocyanates with polyols. 

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