Coproduct of modified Drinfeld-Cartan series for Yangians and quantum affine algebras in type A

We give explicit formulas for the coproducts of modified Drinfeld-Cartan generating series for the Yangian in type $A$ and for the quantum affine algebras in the particular type $A_2$. As an auxiliary result of the latter, we give an explicit presentation of positive prefundamental representations of the quantum affine algebra in the particular type $A_2$