Surface-attached Polymer Networks
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Surface-attached Polymer Networks Oswald Prucker, Kristin Müller and Jürgen Rühe Institute for Microsystem Technology (IMTEK), University of Freiburg, D-79085 Freiburg, Germany ABSTRACT In this paper we present three novel routes for the preparation of surface-attached polymer networks. In one system the network is formed in situ at the surface by thermal polymerization in solution and from the surface. Another synthetic route starts with a surface that carries photoreactive groups. Onto this surface a polymer is deposited that also carries photoreactive groups and both the crosslinks of the network and the covalent bond to the surface are formed by UV illumination. The third approach start with the in situ formation of surface-attached copolymers that again carry photoreactive groups that are subsequently linked together by UV light. We present evidence for the successful synthesis of these networks and their superior adhesion on glass surfaces. INTRODUCTION The depositon of polymer networks onto solid substrates is of potential interest in many fields ranging from the protection of surfaces [1] from abrasion or corrosion to several biomedical concepts, e.g. to make implant surfaces biocompatible [2]. In all these applications a good adhesion of the network to the surface and a good long-term stability of the coatings is required. On this background it appears beneficial to covalently attach the polymers to the surface. In an attempt to address several important issues in this context we developed three different strategies to prepare such systems. EXPERIMENTAL DETAILS All solvents used for silanization and polymerization reactions were carefully dried by distillation from molten sodium using benzophenone as indicator in an atmosphere of dry argon. Monomers and crosslinkers were filtered over basic aluminum oxide to remove the stabilizer, distilled from copper-I-chloride, and kept under dry argon at –20°C. In all cases silicon wafers were used as substrates. These wafers were cleaned by extraction with various solvents prior to modification. The syntheses of the silanes carrying initiating groups and benzophenone moieties are described elsewhere [3-6]. Silanizations and polymerizations were performed under an atmosphere of dry argon. The solutions used for polymerizations were carefully degassed prior to the reaction by repeated freeze-thaw cycles to remove oxygen. Polymerizations were usually carried out at 60 or 70°C.
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RESULTS The first system described in here is based on the in situ formation of the surface-attached network by means of radical chain polymerization. A schematic sketch of the procedure is given in Figure 1. The substrate is firstly modified with a silane that carries a group capable of initiating radical chain polymerizations [3-5]. A cast is cla
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