Hexane-1,6-diyl diisocyanate

In the same study, it was shown that catalysis of hexane-1,6-diyl diisocyanate is carried out by acids having a pKa > 6, whereas stronger acids (pKa < 5) were less efficient catalysts. These results are compatible with the mechanism of general base catalysis with electrophilic addition of H20 postulated in Fig. 11.11. Hydration of isocyanate, thus, produces a carbamic acid, which spontaneously decomposes to the primary amine with loss of C02. 

Both k and b depend on the chosen activator. For X 1, that is, at the initial stage of polymerization, the value of k can be easily evaluated. Namely, Macosko et al have found that Malkin s model was in very good agreement with their data for both neat CL polymerization and its copolymerization with 16wt.% of OH-terminated poly(propylene oxide) (PPG) end-capped with hexane-1,6-diyl diisocyanate (HDI). 

For example, toluene-2,4-diyl diisocyanate (TDI), p-phenylene diisocyanate (PDI), and 4,4 -methylenehis(phenyl isocyanate) (MDI), which are large-scale raw materials for the manufacture of polyurethane foams [248], can be isolated as spectroscopically pure materials from their corresponding methyl carbamate esters in yields of 70-79%. Toluene-2,4-diyl diisocyanate can also be isolated in good yield from its methyl carbamate ester when the reaction is performed in toluene (65% isolated yield) or hexanes (41% isolated yield). Chlorinated solvents, however, are not suitable media for this reaction. As expected, BCI3 is converted to trialkyl borate (identifiable by GC-MS after the reaction), consistent with Scheme 4.4. 

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