Chromic acid solutions were used to oxidize the surface of branched (low density) polyethylene(PE). Poly(methyl methacrylate) (PMMA) and PE samples were prepared by hot pressing PE and PMMA sheets between with glass plates (high surface energy substrate) or Teflon sheets (low surface energy substrate) to give surfaces that are modified to be either hydrophilic or hydrophobic in nature. The hot pressing temperature is 76°C for PE and 120°C for PMMA. One can obtain better adhesion of a water based paint when the PMMA surface is made more hydrophylic and one can obtain better adhesion of a solvent based paint when the PMMA surface is made more hydrophobic.