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Lignin sulfonates are converted into sulfonic acid esters by blocking free phenolic hydroxyl groups on the lignin sulfonates from reaction with a suitable protective group, subjecting the blocked lignin sulfonate in aqueous solution to ion exchange to produce the free sulfonic acid thereof, exchanging the aqueous solvent into a polar organic solvent, such as isopropanol, and reacting the sulfonic acid derivative in the polar organic solvent with a saturated or unsaturated aliphatic epoxide, preferably an alkylene oxide. The resulting sulfonic acid ester adduct may be isolated and purified from the reactants using solvent extraction. Lignin sulfonic acid ester adducts are produced that are soluble in a variety of organic solvents and insoluble in water.