The present invention provides aqueous amphiphilic emulsion copolymer compositions comprising one or more aqueous phase copolymer, a residue of one or more hydrophilic chain transfer agent, and a residue of one or more hydrophobic chain transfer agent, as well as methods of making such copolymers in water or an aqueous liquid by copolymerizing a monomer component of from 20 to 80 wt. %, based on the weight of the monomer component, of a hydrophilic group-containing monomer and the remainder of a copolymerizable ethylenically unsaturated monomer or prepolymer in the presence of a mixed chain transfer agent component comprising a hydrophilic chain transfer agent, such as 3-mercaptopropionic acid, and a hydrophobic chain transfer agent, such as N-dodecyl mercaptan. The aqueous amphiphilic emulsion copolymers of the present invention are storage stable and exhibit excellent viscosity control even in high solids compositions, e.g. from 50 to 80 wt. % of the composition. The high solids compositions can be diluted at the point of use, thus reducing shipment costs.