| abstract |
The invention relates to a method for producing an impact modifier which is an isocyanate-terminated polymer, the isocyanate groups of which are partially or completely blocked by reaction with a blocking agent, comprising the steps of A) adding to a mixture that comprises a) two or more polyols comprising a1) polytetramethylene ether glycol and a2) at least one hydroxy-terminated polybutadiene, wherein the total proportion of polytetramethylene ether glycol and hydroxy-terminated polybutadiene is at least 95 wt.-%, relative to the total weight of polyols, and b) at least one acyclic aliphatic or cycloaliphatic polyisocyanate, and c) at least one blocking agent selected from the group consisting of phenols, 2-benzoxazolinones and pyrazoles, e) at least one catalyst K1, and then B) adding at least one catalyst K2 while forming the partially or completely blocked isocyanate-terminated polymer. The invention also relates to the impact modifiers obtained according to said method, to the use thereof and to epoxy resin formulations containing said impact modifiers. |