Novel process to prepare polyisocyanates blocked with 3,5-dimethylpyrazol
摘要
<p>Method for blocking organic polyisocyanate (I) with 3,5-dimethyl pyrazole (A) comprises preparing, in situ, 80-99.5 mol% of free isocyanate group of (I) by reacting acetylacetone and hydrazine hydrate in the presence of organic solution of (A) and blocking remaining free isocyanate group with solid (A), where the concentration of free isocyanate groups (calculated as a NCO; molecular weight is 42) amounts to less than 1 wt.%. Independent claims are also included for: (1) dimethyl pyrazole blocked polyisocyanate obtained by the method; and (2) a substrate coated with a coating obtained form the blocked polyisocyanate.</p>
