A paper coating slip additive obtainable by free-radical polymerization, its preparation and its use in paper coating compositions are described. The additive is formed from (a) acid monomers selected from ethylenically unsaturated C3 to C8 carboxylic acids, (b) associative monomers of the general formula H2C═CR1—COO-(EO)n—(PO)m—R2 where R1 is hydrogen or methyl, n is at least two, m is from zero to 50, EO is an ethylene oxide group, PO is a propylene oxide group and R2 is a C8-C30 alkyl group or a C8-C30 alkaryl group, and (c) nonionic copolymerizable monomers other than a) and b), wherein said additive has a weight average molecular weight of below 200 000 and wherein tert-dodecyl mercaptan is used as chain transfer agent.