Three copolymers with different emulsification efficacies were used as potential interface modifiers for an immiscible blend of Linear low density polyethylene (LLDPE) and poly(vinyl)chloride (PVC). The specific interaction between blend components and the modifying copolymers was determined by measurements of interfacial tension and by inverse gas chromatographic (IGC) data, characterizing the acid-base properties of the polymers. Additional information on modifier effectiveness was obtained from blend morphology data. Acid-base pair interaction parameters, computed from IGC results, predicted the modifying potential of the two copolymers which emulsified the system, and were consistent with the morphology and interfacial tension results. IGC, however, did not distinguish between the emulsification qualities of the two good modifiers. The best of the three modifiers (P4VP-PIP) also increased the impact strength of the modified LLDPE/PVC system. The results indicate that specific (acid-base) interactions at component interfaces may represent a promising strategy for the choice of emulsifying agents for some immiscible polymer blends.