Blocked aliphatic diisocyanates

We selected a novel approach to design a masked or blocked aliphatic diisocyanate based on the fact that 1,3-disubstituted ureas undergo facile thermal dissociation to produce an isocyanate and an amine derivative. ) In the dissociation of mono acyl and aroyl ureas an isocyanate and a carboxylic acid amide is simultaneously produced. If the urea group is part of a cyclic system both fragments are parts of the same molecule. 

Developments in aliphatic isocyanates include the synthesis of polymeric aliphatic isocyanates and masked or blocked diisocyanates for appflcafions in which volatility or reactivity ate of concern. Polymeric aliphatic isocyanates ate made by copolymerizing methacrylic acid derivatives, such as 2-isocyanatoethyl methacrylate, and styrene [100-42-5] (100). Blocked isocyanates ate prepared via the reaction of the isocyanate with an active hydrogen compound, such as S-caprolactam, phenol [108-95-2] or acetone oxime. 

TPEs associating both rigid and soft polyester blocks have also been described. They cannot be obtained by the melt polyesterification used for polyesterether TPEs, since interchange reactions would yield random—rather than block — copolyesters. The preferred method involves the reaction of OH-terminated aliphatic and aromatic-aliphatic polyesters with chain extenders such as diisocyanates and results in copoly(ester-ester-urethane)s. 

The crosslinking temperature of aliphatic poly(isocyanate)s, based on 1,6-hexane diisocyanate, which are blocked with equimolar quantities of diisopropylamine and 1,2,4-triazole is 139°C, without the addition of any catalyst. Aliphatic poly(isocyanate)s, which are bloeked with equimolar quantities of diisopropylamine and malonic acid diethyl ester have a cross-linking temperature of 130°C. °... 

Fig. 10. FT-IR absorption spectra for blocked (initial) and deblocked (final) isophorone diisocyanate. 2256 cm unblocked isocyanate carbonyl 1738 cm" = blocked isocyanal e carbonyl 1503 cm" = blocked isocyanate N-H 1446 cm" = aliphatic reference peak.

Because of its relatively low boiling point HDI is currently only supplied in the form of derivatives (trimer, allophanate, biuret, etc) (18). Polyrmeric aliphatic isocyanates are obtained by copolymerization of 2-isocyanatoethyl methacrylate and styrene (19). Hydroxyalkyl acrylates and methacrylates are used as monomers to form hydroxyl group containing polymers, which are cross-hnked with diisocyanates or blocked diisocyanates (20). The elusive parent dusocyanate, 0=C=N—N=C=0, is only stable at —75°C, and therefore it is not suitable as a monomer or comonomer in polymerization reactions (21). 

TEG, or PEG-2000. These spirocycles were used as initiators for the ring-expansion polymerization of Z-lactide in chlorobenzene at 120 °C. The resulting cyclic block co-polymers were reacted in situ with aliphatic dicarboxylic acid dichlorides (ADADs) or with hexamethylene diisocyanate (HMDI) to achieve chain extension. 

Common isocyanates used as building blocks for polyurethane adhesives include aromatic and aliphatic isocyanates. Commercial aromatic isocyanates include principally toluene diisocyanate (TDI), 4,4 -diphenylmethane diisocyanate (MDI), and polymeric MDI. 

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