Novel Ways of Covalent Attachment of Poly(ethylene oxide) onto Polyethylene: Surface Modification and Characterization by XPS and Contact Angle Measurements

Abstract

Procedures involving the surface halogenation of polyethylene (PE) by wet chemical reactions or radio frequency plasma treatments, followed by covalent bonding of poly(ethylene oxide) (PEO), have been developed. The two-step wet chemical halogenation comprised the chlorination of PE by SO2Cl2 and the transhalogenation by AlBr3 or NaI. For the single-step direct bromination of PE, either the PE substrate was exposed to a glow discharge plasma obtained from CHBr3 vapor or Ar plasma activated PE was reacted with bromoform. The Br or I functional groups were reacted with PEO solution or with PEO melt. XPS and contact angle studies were used to characterize the surfaces during the different stages of the procedures. Wettability as well as surface free energies compared for various PEO-covered surfaces show that the higher the surface amount of PEO, the lower the contact angle (corresponding to higher surface free energy). It has been established that a relatively small amount of PEO proved to be sufficient to render the PE substrate hydrophilic when it had been already hydrated. Both contact angle study and analysis of surface composition suggest that a more homogeneous surface could be obtained by treatment involving plasma bromination in contrast to those produced by wet chemistry. The relative amount of ether type carbon, derived from XPS, has been proposed to be a general parameter for comparison of surface energetics of various PEO-grafted surfaces irrespective of the nature of the substrate.