Isocyanate-terminated Prepolymer Research Articles

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

AbstractA 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.

Optimizing the properties of isocyanate-terminated polyurethane prepolymers by statistically designed experiments

The properties of isocyanate-terminated polyurethane prepolymers were optimized through the use of statistically designed experiments. A simple 2 × 2 factorial with centerpoint statistical design was used to determine the effect the diol-to-triol ratio and per cent free isocyanate had on the viscosity of the prepolymer. Combinations of a 1000 or 2000 molecular weight diol with either a 1500 or 4100 molecular weight triol showed that a reasonable range of viscosity could be maintained only with the 4100 molecular weight triol. A nine-point design was then utilized to predict the best levels of free isocyanate and polyol ratio that would yield cured urethane polymers with the highest tensile strengths, moduli, and elongations. With this design, second-order equations were computed that predict the mechanical responses of urethane polymers based on the free isocyanate and polyol ratio used in its formulation.

Block polymers from isocyanate‐terminated intermediates. III. Preparation and properties of cured diene–urea block polymers

AbstractIsoprene–urea and butadiene–urea block polymers have been prepared by reaction of isocyanate‐terminated prepolymers with diamines and diisocyanates. It was found that the per cent of blocked urea in these copolymers is dependent on the isocyanate–diamine stoichiometry. Stress–strain data were obtained on sulfur‐cured copolymers. Stress levels at any given extension were directly dependent on the urea content, however, ultimate strength was maximized at about 35 wt‐% urea. Slight variations in urea structure produced rather dramatic changes in the modulus of these cured elastomers. Diamine–diisocyanate stoichiometry did not affect the physical properties of these cured copolymers at equal or excessive diamine concentrations. However, at excess diisocyanate levels, elastomeric properties deteriorated rapidly. Finally, stress–strain properties were affected by polymerization solvent. Copolymers prepared in hexane gave higher values of stress at low strains than corresponding elastomers prepared in toluene. These latter results are explained in terms of the nonaqueous emulsion in which the urea blocks form.

The Reaction of Aliphatic Isocyanates with Some Compounds Which Contain an Active-Hydrogen

Abstract A study has been made of the kinetics and mechanism of the reactions of aliphatic isocyanates with several active-hydrogen compounds. The effect of hydrogen chloride on the reaction of aliphatic isocyanates with alcohols, water, ureas, and urethanes has been investigated. The significance of these results to the application of aliphatic isocyanate-terminated prepolymers to wool is discussed.

Approach to the characterization of isocyanate-terminated prepolymers

Approach to the characterization of isocyanate-terminated prepolymers