Previous experiments from the Winnik group (e.g., Macromol. Rapid Commun. 1995, 16, 861) have established that several nonylphenol ethoxylate surfactants were miscible with poly(butyl methacrylate) (PBMA) latex films at 90 degrees C, and act as plasticizers to accelerate polymer diffusion rates in the films. Here we turn our attention to the question of miscibility at room temperature. Using modulated DSC, we show that a nonylphenol ethoxylate (NP-20, with 20 ethylene oxide units, EO20) has only limited (ca. 2 wt %) miscibility with high molecular weight PBMA latex films at room temperatures and that corresponding poly(ethylene glycol) (PEG) oligomers EOx (x = 10, 20) have even lower miscibility. Miscibility is detected as a decrease in the glass transition temperature of the polymer; and immiscibility, as a melting endotherm of the surfactant component. In addition, we examine the influence of the EOx oligomers on the polymer diffusion rate in PBMA latex films. Oligomers larger than EO10 retard the rate of interparticle polymer diffusion.