Poly(methyl methacrylate) (PMMA) monolayers with different molecular weights at the air/water interface were investigated at three different temperatures. The monolayer characteristics of PMMA were studied in terms of surface pressure-area per molecule (pi-A) isotherm and isobaric relaxation experiments. The results show that the pi-A isotherms of PMMA converge at 40 degrees C regardless of molecular weight. The collapse pressure of PMMA monolayers decreases as the temperature is elevated. It was shown the area relaxation process of PMMA could be described by a model considering the nucleation and growth mechanisms. The simulation parameters of area relaxation of PMMA with different molecular weights at 8 mN/m are very similar, indicating similar mechanisms. (C) 2010 Wiley Periodicals, Inc. J Appl Polym Sci 120: 2615-2620, 2011