NOVEL WAYS OF COVALENT ATTACHMENT OF POLY(ETHYLENE OXIDE) ONTO POLYETHYLENE - SURFACE MODIFICATION AND CHARACTERIZATION BY XPS AND CONTACT-ANGLE MEASUREMENTS

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) (PEG), 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 singl e-step direct bromination of PE, either the PE substrate was exposed t o a glow discharge plasma obtained from CHBr3 vapor or Ar plasma activ ated PE was reacted with bromoform. The Br or I functional groups were reacted with PEO solution or with PEO melt. XPS and contact angle stu dies were used to characterize the surfaces during the different stage s of the procedures. Wettability as well as surface free energies comp ared for various PEG-covered surfaces show that the higher the surface amount of PEG, the lower the contact angle (corresponding to higher s urface free energy). It has been established that a relatively small a mount of PEG proved to be sufficient to render the PE substrate hydrop hilic when it had been already hydrated. Both contact angle study and analysis of surface composition suggest that a more homogeneous surfac e could be obtained by treatment involving plasma bromination in contr ast to those produced by wet chemistry. The relative amount of ether t ype carbon, derived from XPS, has been proposed to be a general parame ter for comparison of surface energetics of various PEG-grafted surfac es irrespective of the nature of the substrate.