Methanol vapor sorption isotherms for methyl acrylate (MA) and styrene plasma polymer thin films are measured and compared with those for conventionally polymerized analogs. Isotherms are collected for the series of thin films between 30 and 75 degreesC using a quartz crystal microbalance. Rubbery poly(methyl acrylate) (PMA) and plasticized poly(styrene) (PS) conscribe to the classical Flory-Huggins-type sorption mechanism, whereas the sorption isotherms of the plasma polymer analogs have a distinct Langmuir-type sorption component. Plasma polymers are analyzed using the dual mode sorption model commonly applied to conventional glassy polymers. The heat of sorption of the 'glassy' ppMA films (-56 kJ/mol) is far above that measured for PMA (-20 kJ/mol) and much closer to that measured for glassy poly(methyl methacrylate) (PMMA) (-48 kJ/mol). The work shows that both the plasticization effect of sorbed penetrants and relaxation phenomena associated with slow cooling are suppressed in the plasma polymer materials when compared to the conventional polymer analogs. (C) 2004 Elsevier Ltd. All rights reserved.