The modification of poly( vinyl alcohol) with a series of long-chain aliphatic carboxylic acids via reactive blending was studied. The method involves the reaction in the melt of polymer hydroxyl groups with carboxylic acids using a laboratory scale reactor, a medium-scale Brabender rheomixer, and a large-scale twin-screw extruder. The presence of the long aliphatic chains acted as lubricants during reactive processing. The reactivity was generally low, and increased with decreasing chain length of the acids. All modified polymers displayed lower temperature thermal transitions and improved thermal stabilities compared to the parent polymer. Thermogravimetry established that polymers incorporating short chain residues were more thermally stable than their long-chain analogs. The polymer obtained in the twin-screw extruder showed a higher degree of incorporation with improved thermal stability compared to the polymers obtained in the laboratory mixer or the rheomixer. Intermediate degree of incorporation and thermal stability was exhibited by the polymers obtained in the rheomixer.