A method has been developed that enables the simple two-step synthesis of S-I-S latex by controlled free radical (CFR) emulsion polymerization. A trithiocarbonate RAFT agent is used to prepare a controlled molecular weight polystyrene macroinitiator seed latex. In the second step, the seed is used with isoprene to prepare the S-I-S triblock latex. Although the microstructure of the center block is quite different from that prepared by anionic methods, the physical properties of the copolymer are dominated by the total PS content, its MW and its ability to rapidly phase separate. Annealed latex cast films can develop TS > 1900psi @ 600% elgn.