SURFACE ENERGETICS OF FILMS OF SURFACTANT FREE POLY(METHYL METHACRYLATE-CO-BUTYL ACRYLATE) EMULSION POLYMERS

The surface energetics of poly(methyl methacrylate-co-butyl acrylate) emulsion polymer films was investigated using dynamic contact angle (DCA) analysis. From a series of Wilhelmy plate experiments using several probe liquids, the dispersive and polar components of the surface energy were determined to be 20.6 and 3.4 mJ · m-2, respectively. The surface energy was calculated from these values to be 24 mJ · m-2. It was found that addition of molecular weight modifiers (ethylene glycol dimethacrylate crosslinking agent and carbon tetrabromide chain transfer agent) during polymer synthesis had no effect on the surface tension of the polymer. The surface energy measured here was lower than expected for a poly(methyl methacrylate-co-butyl acrylate) system. This result was attributed to the exudation of oligomeric or polymeric pseudosurfactant to the surface of the films. The sulfate ion terminated pseudosurfactant is produced from the ammonium persulfate initiator used during the emulsion polymerization. The presence of these groups at the film surface was confirmed by attenuated total reflectance Fourier transform infrared spectroscopy. In addition to the measurement of the polymer surface energy, the effect of water inhibition on the polymer-water contact angles was studied. The reduction of the contact angles after water exposure times of 1 week and 1 month indicated progressive orientation of the hydrophilic functionalities toward the water phase. © 1992.