This invention refers to a novel process for the synthesis of polyethylene imine (PEI)-based pigment dispersants characterized by a “grafting from” approach, allowing the manufacture of solvent based dispersant systems. The polyethylene imine (PEI)-based pigment dispersant can be presented by the formula (I) X-(T)m-P-(T)n-H wherein P is a polyethyleneimine (PEI) back-bone; T is a residue —CO-A-O— wherein A is C2-C12 alkylene optionally substituted with C1-C6 alkyl with the proviso that each linkage between P and T is an amide bond and each linkage between X and T is an ester bond, X is a modifier or terminator residue R—CO— wherein R is a linear or branched, saturated or unsaturated alkanecarboxylic acids having from 1 to 22 carbon atoms or an unsaturated fatty acid residue or a hydroxycarboxylic residue or a polyester residue obtained from polycondensation of hydroxycarboxylic acids, or an acid terminated polyether, n, m independently are a number from 1 to 100.