Multi-isocyanates

Soybean oil iodo isocyanate was synthesised by reacting the pristine oil with iodo isocyanate (Scheme 4.13a) to yield a degree of triglyceride substitution of 3 [47], The same oil was treated with N-bromosuccinimide at the allylic positions of each of its fatty-acid chains, followed by reaction with silver isocyanate (AgNCO) (Scheme 4.13b) to prepare the desired multi-isocyanate in which <70 % of bromine atoms were converted into NCO groups [48]. 

Di-tert-butyl tricarbonate (BocO)2CO Recently, di-tert-butyl tricarbonate has been reported as a versatile and mild reagent for the synthesis of unusual mono- and multi-isocyanates (232) within minutes at room temperature [230, 231]. 

Due to its richness and diversity, this class of compounds, that results from the polycondensation of di- or multi-isocyanates and of di- or polyols (of di- or polyamines the case of the polyureas), is one of the hardest to place in a classification. Indeed, polyurethanes are just as much elastomers, presented in solution, possibly in emulsion or in the form of structures that are self cross-linking (through atmospheric humidity), as they are structural adhesives, where the polymer networks are obtained from two-part and one-part formulations (with hidden isocyanate functions). 

Carboxylic acids or hydroxy groups with multi-functional isocyanates. 

In another report, aspects for automating preparative chemistry are described [130]. A comprehensive description of the Ugi reaction is given in [132] and the vision of a micro multi-component reaction as automated parallel micro-channel synthesis is sketched. An interesting point is to convert aldehydes, chiral primary amines, carboxylic adds and isocyanates into corresponding a-amino acids and peptides (U-4CR). 

The [l,3]oxazino[4,3- ][l,3]oxazine 387 was obtained as the main product of a combined Asinger and Ugi multi-component reaction from MeOH, NH3, 2,2-dimethyl-3-hydroxypropanal, allyl isocyanate, and C02 in 40% yield. As shown by NMR spectroscopy and X-ray crystallography, 387 is formed as a single diastereomer <1998ACS107>. 

Kaldor [49 i, 55] demonstrated the advantages of applying solid-supported scavengers to the preparation of parallel arrays in a multi-step fashion. In these studies he examined the clean-up of multiple amine alkylation and acylation reactions using a variety of immobilized electrophilic and nucleophilic scavenger reagents including an amine, isocyanate, aldehyde and acid chloride (Tab. 2.1). 

Methanol Formaldehyde Ethylene Propylene oxide Phenol 1,4-Butanediol Tetrahydrofuran Ethylene glycol Adipic acid Isocyanates Styrene Methyl methacrylate Methyl formate Two-step, via CH4 steam reforming Three-step, via methanol Cracking of naphtha Co-product with t-butyl alcohol or styrene Co-product with acetone Reppe acetylene chemistry Multi-step Hydration of ethylene oxide Multi-step Phosgene chemistry Co-product with propylene oxide Two-step, via methacrolein Three-step, via methanol... 

The volatility of difunctional isocyanates (such as tolylene diisocyanates, hexamethylene diisocyanate, etc.) creates many environmental problems in the urethane industry. These difficulties can be overcome by preparation of NCO-terminated oligomers with low vapor pressure. One approach is the preparation of NCO-ter-minated oligomers by partial cyclotrimerization of difunctional isocyanates. Usually this is achieved by a multi-step process which includes also deactivation of the catalyst at a certain conversion. During our work on cyclotrimerization of isocyanates we found that cyclic sulfonium zwitterions are very active cyclotrimerization catalysts (2). Recently we found that cyclic sulfonium zwitterions under certain reaction conditions act as anionic initiators. This behavior of cyclic sulfonium zwitterions permits preparation of isocyanate oligomers containing isocyanurate rings by a one-step procedure, eliminating the deactivation step. 

MDI offers a number of advantages. First, it is somewhat safe to use based on its much lower vapor pressure and is available in convenient forms. It is produced by the reaction of an amine and phosgene. The result is a mixture of multi-ring isocyanates. The purest form is the two-ring isomer shown in Figure 2.2. The isomer is recovered by distillation. What is left behind is the so-called polymeric MDI that... 

Bioabsorbable adhesive compounds and compositions containing a polyalk-ylene oxide backbone having branched or multi-arm structure derived from reacting with two or more isocyanate substituents were prepared by Roby [2] and used as surgical adhesives and sealants. 

Multi]de insertion reactions of isocyanates have been observed in the presence of Ni catalysts. Pyri-midinediones are obtained in low yield from reaction of diphenylacetylene with excess alkyl isocyanates in the presence of Ni(COD). Similarly, alkyl and aryl isocyanates undergo simple cyclotrimerization to form symmetrical triazinetriones in the presence of both low-valent Ni and Ti catalysts. 

The presence of the electron donor (-0-) in the vicinity of the phenolic hydroxyl activated the -OH group through induced polarization due to hydrogen bonding and therefore, increased reactivity was observed. Similarly, the polarizability of the phenolic hydroxyl groups by the tertiary amine catalyst is responsible for the multi order (1200 x) increase in the reactivity compared to the non-catalyzed reaction with isocyanate (see Table IV)... 

The above groups contain plasticizers which have several representatives of similar chemical structure. There still are plasticizers in common use or that were invented for specific purposes. These can be grouped as follows biphenyl derivatives,calcium stearate,carbon dioxide, difurans, " fluorine-containing plasticizers, " hydroxyben-zoic acid esters, " isocyanate adducts, " " malonates, " multi-ring aromatic... 

Since the EPI adhesives are emulsion based but cross-linked with isocyanate, they share characteristics with both thermosetting and thermoplastic adhesives. The adhesives are multi-phase systems comprising emulsion particles, polymer solution, cross-linker droplets and filler particles. Just as for other emulsion adhesives, the coalescence of the emulsion particles [18, 19] and the distribution of these in the glue film is important for the bond quality. The cross-linking in the adhesive film is also of great importance for the bond quality as well as for the moisture resistance and heat resistance of the adhesive. 

The group of Jensen has designed microseparators to perform Hquid-hquid extraction and to separate liquid and gas phases. Both selfiassembled microfluidic extraction systems were used in continuous multi-step syntheses of carbamates 62 from acid chlorides 61 without isolation and storage of the intermediate azides and isocyanates (Scheme 15) (2007AGI5704). 

The reaction between these three components leads to the formation of segmented copolymers characterised by the alternation of hard and soft segments. Hard segments are based on blocks formed by reaction of the di- or multi-functional isocyanate with the chain extender, while the polyol-based units form the soft segments. As a result of the thermodynamic incompatibility between hard and soft segments, PURs are characterised by a biphasic morphology (GunatiUake et al., 2011) (Fig. 6.2). 

Both processes may be carried out in one or two reaction steps, the so-called one-shot process and prepolymer method , respectively (Vermette et al., 2001). In two-step synthesis (Fig. 6.3), an isocyanate end-capped prepolymer is first synthesised through the reaction between a polyol and a diisocyanate then, adding a chain extender that reacts with the residual isocyanate functionality, the chain is extended producing a multi-block copolymer (Lamba et al., 1998 Vermette et al., 2001 ... 

Keywords a-Azido esters, isocyanates, PhaP, acetonitrile, room temperature, domino reaction, multi-component reaction, /V-carbamoyl hydantoins, Staudinger reaction... 

Another approach is based on multi-component systems [97-101]. It has been pursued, in particular, by the group of Professor Dalton. In many cases they have used a two components system formed by a polyurethane NLO oligomer with isocyanate end groups that is reacted with a cross-linking agent, triethanolamine, as example [102, 103]. In this approach, the oligomer (or prepolymer) is prepared first then a solution of the oligomer and of the cross-linker is spin-coated on the substrate (Fig. 2.25). 

---