We describe the synthesis and characterization of a weakly cross-linked poly(methacrylic acid-co-ethyl acrylate) alkali-swellable emulsion (ASE), as well as an investigation of its influence on the rate of polymer diffusion in latex films. The films examined were formed from poly(vinyl acetate-co-butyl acrylate) latex particles containing a small amount of acrylic acid as a comonomer. Polymer diffusion rates were monitored by the energy transfer technique. We found that the presence of the ASE component, either in the acid form or fully neutralized by ammonia or sodium hydroxide, had very little effect on the polymer diffusion rate. However, in the presence of 2 wt % NH4-ASE, there was a small but significant increase in the polymer diffusion rate. (c) 2005 Wiley Periodicals, Inc.