Process for the preparation of an aqueous polymer dispersion

A process, comprising

• free radical polymerizing ethylenically unsaturated monomers in the presence of at least one free radical initiator and at least one RAFT compound in an aqueous polymerization medium to obtain an aqueous polymer dispersion,
• wherein
• (A) ≧1 and ≦80% by weight of at least one ethylenically unsaturated monomer A having a solubility of ≧200 g per 1000 g of deionized water at 20° C. and 1 atm (absolute), and
• (B) ≧20 and ≦99% by weight of at least one ethylenically unsaturated monomer B having a solubility of ≦100 g per 1000 g of deionized water at 20 ° C. and 1 atm (absolute)
• are polymerized in the polymerizing and A and B sum to 100% by weight, which is a total amount of monomers, wherein
• (C) ≧0.1 and ≦5% by weight, based on the total amount of monomers, of at least one RAFT compound and
• (D) ≧0.01 and ≦5% by weight of at least one free radical initiator, based on the total amount of monomers,
• are present during said free radical polymerizing, wherein first only
• ≧73.3% by weight of a total amount of the at least one RAFT compound, the total amount of the at least one monomer A,
• ≦5% by weight of a total amount of the at least one free radical initiator, and
• no monomer B
• are present in the aqueous polymerization medium before said free radical polymerizing is carried out, and, after said free radical polymerizing has commenced, the process further comprises adding any remaining residual amount of the at least one RAFT compound, the total amount of the at least one monomer B and of the at least one free radical initiator under polymerization conditions and polymerizing the added monomers.