| abstract |
The invention relates to copolymers containing carboxyl groups with an acid number of 20 to 150 mg KOH/g and an average molecular weight of 2000 to 8000, obtained preferably by reacting copolymers containing hydroxyl groups with carboxylic acid anhydrides. The invention also concerns a process for producing them and their use in coating materials. The copolymers can be obtained by radical solution polymerization, at temperatures of 130 to 200°C, preferably 150 to 180°C, of 5 to 25 wt.% of vinyl ester, 10 to 50 wt.% of vinyl aromat, 10 to 40 wt.% of hydroxyalkylester α,β-unsaturated carboxylic acids and 0 to 40 wt.% of monomers containing carboxyl groups and/or other monomers. The other monomers are added to the vinyl ester, in a monomer addition time which is identical for all monomers, as follows: 1) the quantity of hydroxyalkyl ester added per unit time is constant; 2) 15 to 30 wt.% of the total quantity of vinyl aromat is added during the first third of the monomer addition time, 25 to 40 wt.% is added during the second third and 35 to 60 wt.% is added during the final third. |