Interpenetrating polymer networks (IPN's) of poly(alky1 methacrylates) and poly-(alkyl acrylates) have been synthesized in latex form. Dynamic mechanical spectroscopy studies on these materials revealed extraordinarily broad glass transition regions, illustrating the semicompatible nature of these materials. In a true synergistic effect, the value of tan 6 remains high and nearly constant over a broad temperature range for select compositions, emphasizing their potential value in noise and vibration damping applications. Compositionally identical latex IPN pain were prepared by slow and rapid addition of monomer. The mechanical behavior of the resulting materials was similar and can be explained in terms of the core-shell model. A 50/50 isomeric homologous series of compositions was examined. After taking into account the relative difference between the glass transition temperatures of the methacrylic/acrylic pair, no substantial change in compatibility was noted throughout the series. Because the acrylic monomer I1 is roughly equally solvated by both the previously formed methacrylic polymer I and the nascent acrylic polymer 11, extensive polymer I/polymer I1 mixing is encouraged, and sharp phase separation discouraged in these materials.