Blocked isocyanate‐terminated prepolymers in a delayed‐cure durable‐press finish for wool. Influence of isocyanate and blocking group structure on reactivity

Abstract

Abstract A series of prepolymers containing terminal blocked isocyanate groups was prepared by reaction of isocyanate‐terminated prepolymers [derived from a poly(propylene oxide) diol (MW = 2000) or a triol (MW = 3000) and different diisocyanates] with various blocking agents. Their curing rates with a polyepoxide crosslinking agent were measured to assess their suitability for a delayed‐cure durable‐press treatment for wool. The curing rates varied over a wide range, but commonly used blocking groups such as phenols, caprolactam, β‐diketones, and alcohols were not sufficiently reactive for the intended application, although others, e.g., oximes and certain blocking agents containing a basic center such as N,N‐diethylhydroxylamine, hydroxypyridines, and hydroxyquinolines, had the required reactivity. Blocking by 1,3‐dipolar cycloaddition of nitrones was examined, but the reactivities were too low. Prepolymers containing blocked aromatic isocyanates were more reactive than those containing blocked aliphatic isocyanates. Difunctional butanone oxime‐blocked pre‐polymers cured slightly more slowly than analogous trifunctional prepolymers.