the present invention relates to a process for preparing a polymer latex that includes comprising polymerizing one or more ethylenically unsaturated aromatic monomers and one or more conjugated diene monomers in the presence of a hydroperoxide chain transfer agent and sulfur - containing chain transfer agent , wherein the sulfur - containing chain transfer agent is added after the hydroperoxide chain transfer agent . it further relates to the polymer latex thus obtained , to a composition comprising the polymer latex and to the use of the polymer latex or polymer latex composition in a carpet backing , paper coating , or fiber fabric pre - impregnation process .