Radical Polymerization of TFEMA and Relationship Between Surface Hydrophobicity and Molecular Weight of Poly-TFEMA

Abstract

Conventional free radical polymerization of 2,2,2-trifluoroethyl methacrylate (TFEMA) with 2,2′-Azobisisobutyronitrile (AIBN) as initiator has been investigated. With isoamyl acetate as solvent, the effects of polymerization conditions, such as reaction temperature and concentrations of AIBN, on both the yield and number average molecular weight (Mn) of polymers were investigated in detail. For bulk polymerization of TFEMA, the molecular weight was as high as 1,471,000 with the monomer conversion up to 90% when the reaction temperature was 60°C and AIBN was 0.5 wt% to monomer. Interestingly, the experiment results showed that the water contact angles of the poly-TFEMA films increased from 98 ± 1° to 118 ± 1° when the Mn of poly-TFEMA increased from 95,000 to 1,471,000. Surface analysis techniques, including contact angle measurement, atomic force microscopy (AFM), scanning electron microscope (SEM) and X-ray photoelectron spectroscopy (XPS), were used to characterize the surface hydrophilicity, roughness, surface morphology and chemical composition of the polymer films. The results demonstrated that the degree of the roughness of the film surface increased with an increase of polymer molecular weight while the surfaces chemical compositions had almost no significant variation. The changing of the water contact angle with the Mn of the poly-TFEMA is likely due to the roughness of the film surface which depended on the Mn of the poly-TFEMA.