The mixed monolayer behavior of stereoregular poly(methyl methacrylate) (PMMA) and poly(vinyl cinnamate) (PVCN) was investigated from the measurements of surface pressurearea per molecule (pA) isotherms at three different temperatures of 25 +/- 1, 32.5 +/- 1, and 40 +/- 1 degrees C. The miscibility and nonideality of the mixed monolayers were examined by calculating the excess area as a function of composition. Positive and negative deviations from ideality were observed. Negative deviations were observed mostly in syndiotactic PMMA (sPMMA) and PVCN blends suggesting the existence of favorable interactions. However, positive deviations in most isotactic PMMA (iPMMA) and PVCN blends indicated that the existence of unfavorable interactions. Atactic PMMA and PVCN blends demonstrated intermediate deviation behavior to sPMMA and iPMMA blends. On the basis of the results of pA isotherms, the monolayer miscibility between PMMA and PVCN was in the majority not in agreement with the studies on the same blends in the bulk state. (C) 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012