The structures of the adducts of 2-butanone oxime (1) to different diisocyanates were determined by 'H NMR spectroscopy. The reaction of diisocyanate blocking is quantitative. The different adducts of 1 to 4,4'-methylenediphenyl isocyanate (2), 2-methyl-l,4phenylene and 2-methyl-l,3-phenylene diisocyanates (8 and 10) and to the isocyanate resulting from a-hydro-w-hydroxypoly(oxytetramethy1ene) and an excess of 2, dissociate upon heating to reform the starting materials. The residual water in the NMR solvent reacts partially with the regenerated diisocyanates to give primary amines and then ureas. 10,089 (1) 2,145 (3) 1,759 (5)1,032 (7) 10,014 (2) 2,293 (4) 1,78 (6) 1,011 (8)

The preparation of blocked isocyanates and their thermal dissociation into isocyanate and blocking agent was studied by DSC and IR spectroscopy. Thermal deblocking was found to be possible only with isocyanates blocked with e-caprolactame or 2-butanone oxime, but not with b-ketoesters. With 2-butanone oximethe most convenient blocking agentthe dissociation of blocked aromatic isocyanates starts at = 80 "C and is fast at 120 "C. With blocked aliphatic isocyanates, the temperature of dissociation (Td) is higher (= 12OOC). Ether or tertiary amines have only a poor catalytic effect on the dissociation, and metal naphthenates have no apparent effect. The thermal and viscosity properties of prepolymers with terminal blocked isocyanate groups were investigated. The molecular interactions decrease in the order 1 ,Cphenylene diisocyanate (7) 4,4 '-methylenediphenylene diisocyanate > trans-1 ,4-cyclohexylene diisocyanate = 2,4-and 2,6-toluene diisocyanate.