Polyurethane prepolymers with low viscosity based on 2,4'-MDI

摘要

Preparation of carbonic acid ester free methylene diphenyl isocyanate (MDI)-based prepolymer (I) (having a shear viscosity of less than 100000 mPa.s at 23[deg]C) comprises reacting an isocyanate (II) with a polyether polyol mixture (III) of at least a polyether polyol (a) and optionally further polyether polyol (b) with average molecular weight greater than 2000 g/mol. Preparation of carbonic acid ester free methylene diphenyl isocyanate (MDI)-based prepolymer (I) (having a shear viscosity of less than 100000 mPa.s at 23[deg]C) comprises reacting an isocyanate (II) (which is of MDI-type having at least 95 wt.% of 2,4'-MDI) with a polyether polyol mixture (III) of at least a polyether polyol (a) (having average molecular weight (M n) of 2000-20000 g/mol and a mean hydroxyl-functionality of 3-8) and optionally further polyether polyol (b) with average molecular weight greater than 2000 g/mol, where the amount of (a) is at least 20 wt.% and the combined sum of (a) and (b) results in a total hydroxyl functionality of greater than 2 and average molecular weight (M n) of 3000-20000 g/mol. An independent claim is also included for (I) obtained by the method.