Polymer and Materials
Wiley InterScience Backfile Collection 1832-2000
Chemistry and Pharmacology
Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
In the previous investigation it was found that 3,5-diethyl-4,4'-diisocyanatodiphenylmethane (DEMDI) exhibits a marked asymmetry in the reaction with isoamyl alcohol. Since DEMDI is potentially rather cheap, and since the unsymmetrical nature of the diisocyanate is quite advantageous in certain urethane formulations, the reactions of this diisocyanate with a series of model compounds were investigated. The model compounds were chosen so as to represent the important classes of functional groups commonly reacted with diisocyanates in the preparation of polyurethanes. The compounds used were isoamyl alcohol, 2-octanol, water, 2,6-diethylaniline, 1-n-butyl-3-phenylurea, and 1-(4-n-butylphenyl)-3-(methylphenyl)-urea. The reactions were conducted in dry diglyme solvent. The extent of reaction of the isocyanate groups was followed by reaction with excess di-n-butylamine and back-titration with hydrochloric acid. Tetramethyl-1,3-butanediamine and dibutyltin dilaurate were used as catalysts in some runs. The results show that DEMDI has a desirably high asymmetry of reaction with alcohols or water at low temperatures. Catalysis with dibutyl dilaurate markedly increases this asymmetry. An increase in temperature generally decreases the asymmetry of DEMDI reactions, so that elevated temperatures should be avoided in prepolymer formation. The dibutyltin dilaurate is a more effective catalyst than the diamine for all of the reactions studied. The diamines are very poor catalysts for urea reactions, whereas the tin compound is quite effective.
Type of Medium: