Process for the production of prepolymers containing isocyanate groups, prepolymers produced by this process and their use

A process for the production of a prepolymer containing free tertiary isocyanate groups and having an average molecular weight of about 1000 to 3000 and an NCO content of about 4 to 12% by weight which comprises reacting at an NCO/OH equivalent ratio of 1.6:1 to 2:1

• (a) an organic diisocyanate having a molecular weight of 168 to 320 and containing an isocyanate group attached to a primary carbon atom and an isocyanate group attached to a tertiary aliphatic or cycloaliphatic carbon atom, optionally in admixture with up to 25 equivalent percent, based on component (a) as a whole, of a diisocyanate containing aliphatically and/or cycloaliphatically bound isocyanate groups and having a molecular weight of 168 to 300 which does not contain any isocyanate groups attached to a tertiary carbon atom with
• (b) a polyol component comprising at least one polyester polyol having a molecular weight of 800 to about 12,000 and a hydroxyl functionality of 2 to 6, optionally in admixture with at least one low molecular weight, polyhydric aliphatic alcohol having a molecular weight of 62 to 799, said polyol component having an average hydroxyl functionality of 2.1 to 3.