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Oxidation of the surface of syndiotactic 1,2-polybutadiene (PBD) films with aqueous KMnO4/K2CO3 at room temperature produced PBD-ox, containing a range of oxidized functionality. When heated against water, the surface of PBD-ox became more hydrophobic, a result contrary to what would be expected if enthalpic forces dominated the reconstruction. Initially, the hydrophilicity of the surface varied reversibly as a function of temperature, reflecting reversible changes in the relative concentrations of hydrophilic and hydrophobic groups at the interface. Eventually, however, the surface remained hydrophilic against water, independent of temperature. The temperature dependence of this phenomenon suggests the importance of entropy in determining the state of minimum interfacial free energy in this system. This entropic effect is attributable to rubber elasticity arising from crystallinity in the polymer, and its loss is associated with a change in the amount and type of crystallinity.

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The photolytic addition of thiols or thiolacetic acid to olefinic groups at the surfaces of syndiotadic 1,2-polybutadiene (PBD) provided polymer surfaces bearing sulfide or thioacetate groups. Ethanolysis cleaved these thioacetate groups t o give the corresponding thiols. The product surfaces have been characterized by attenuated total reflectance infrared (ATR-IR) spectroscopy, X-ray photoelectron spectroscopy (XPS), and contact angles of water. Evaporated films of copper and of gold adhered to surfaces of sulfur-functionalized polymers but not to the unfmctionalized polymers in tape-peel tests. Quantitative adhesion experiments were performed using a 180" peel test with these surface-modified derivatives of PBD (and with the unmodified polymer) heated under pressure against copper foil substrates, and the limiting values of peel strength in these systems were related to the identity of the interfacial functionality in an understandable way. The rate in growth of adhesion was not limited by thermal reconstruction of the polymer surface. Mechanical studies of modified and unmodified samples of PBD indicated that the observed differences in adhesion are not due to changes in the bulk properties of the polymer.

Linear low-density polyethylene (LLDPE), polypropylene (PP), polystyrene (PS), and polyethylene-coethacrylic acid (PE-EAA, 17.5% acid content) films were treated with an aqueous solution of fibronectin. Advancing contact angles of water ( a ) were used to monitor the change in the surface wettability of these films. With the exception of PE-EAA, all of the samples showed an increase in their wettability by water, indicating that the protein had adsorbed to the polymer surface. The stability of these proteinmodified films against a buffered aqueous solution and against air under ambient conditions was monitored over time. The surface wettability of these protein-modified polymers, with the exception of PS, remained unchanged after heating against the buffer solution. In air, however, a increased over a period of 2 months. In addition, the effect of organic solvent extraction on the surface stability of these protein-modified films was investigated. Unmodified samples of LLDPE, PS, and PP were subjected to soxhlet extraction to remove impurities and low-molecular-weight oligomers prior to film preparation and subsequent treatment with fibronectin. These samples were left in air under ambient conditions for 2 months. There was no difference in the magnitude of the change in a for the protein-modified, extracted LLDPE film compared to the protein-modified, nonextracted polymer film. A slight decrease in the rate of thermal reconstruction was observed for the proteinmodified extracted PS film compared to the proteinmodified nonextracted sample, and a slight increase in the rate of thermal reconstruction was observed for the proteinmodified extracted PP film compared to the proteinmodified nonextracted sample