Drinfeld's construction allows one to define the quantum affine algebra U_q(g^) starting from the usual quantum group U_q(g). The affine algebras are Hopf, but very importantly, their coproduct does not extend the usual coproduct on U_q(g). In this talk, we will use a new kind of shuffle algebra (in a certain sense orthogonal to the usual construction by Feigin-Odesskii and Enriquez) in order to construct a topological coproduct on U_q(g^) that does indeed extend the one on U_q(g). The only catch: g itself needs to have a unitary R-matrix that we use as an input in our construction, so the case we are able to treat is when g = sl_n^ and U_q(g^) is the quantum toroidal algebra of sl_n.