Block Copolymer Monolayers at Surfaces
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ABSTRACT Monolayers on surfaces have become a topic of considerable interest over the last few years. This has arisen from the need to functionalize a surface so that its properties are different than the properties of the bulk material. This research has involved functionalizing copper surfaces to enhance adhesion to epoxy. We have accomplished this using block copolymers made by RingOpening Metathesis Polymerization (ROMP). In this paper we discuss the synthesis and characterization of these block copolymers and their segregated monolayer conformation at copper surfaces, including NMR, GPC, SANS, neutron reflectivity, and TOF-SIMS. We also discuss a comparison of block copolymers to SAMS for surface functionalization. INTRODUCTION It is often desired to alter the surface of a material so that the surface properties are different than the bulk properties. For example, a metal may need to be bound to an organic resin, but the metal may inherently have poor adhesion characteristics. It becomes necessary to alter the surface of the metal so that it binds stronger to the resin being applied. Another example is the inherent corrosion that occurs on many metal surfaces. Therefor the surface must be altered to prevent moisture and oxygen from reaching the metal. Our work has focused on functionalizing these types of surfaces to promote adhesion and prevent corrosion. Our specific goal was to promote the adhesion of epoxy to copper surfaces. Our approach involves using functionalized block copolymers to accomplish these goals. Block copolymers consist of two linear homopolymers covalently bound together. We have functionalized one block with chemical groups that bind to copper, and the other block with groups the react with the epoxy resins. This will hopefully promote adherence of the block copolymer to the surface, with one block preferentially at the surface and the other preferentially away from the surface (scheme 1). The chemical groups used for copper surfaces are imidazoles and benzotriazoles, and those for reacting with B block epoxy resins are secondary amines. The block copolymers were synthesized using Ring-Opening Metathesis Polymerization (ROMP) employing a Schrock-type initiator'. This technique was used because of its ability A block to perform living polymerizations, and its tolerance of a wide variety of24chemical functionalities on monomers . In this paper Scheme 1. Structure of diblock copolymer at an we discuss important improvements on amine functionalized monomer synthesis, inorganic surface and aspects of the polymerization kinetics of these monomers. We also discuss the synthesis and characterization of block copolymers from these monomers, including NMR, GPC (where possible), and SANS. We then discuss the formation of monolayers of these block copolymers at the desired surfaces, and characterization of the surfaces using neutron reflectivity and time-of-flight SIMS. Finally, we will discuss the pros and cons of this approach as compared to self-assembled monolayers. RESULTS AN
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