Immobilization of a hyperbranched polyester via grafting-to and electron beam irradiation

Stable thin films of an aromatic-aliphatic hyperbranched polyester with hydroxyl groups were fabricated on silicon substrates using electron beam irradiation and grafting-to approach. We present a detailed study on the influence of the dose, dose rate. and temperature on the film properties and degradation behavior of the polyester immobilized by electron beam irradiation. A patterned polyester film was prepared on the substrate using a masking technique. In the second part of this work, we report on a method for the strong binding of the hyperbranched polyester onto the surface of an "activated" silicon substrate without using any coupling agent. The results are compared with the grafting-to of the hydroxyl-terminated polyester using thin PGMA anchoring layers (Reichelt et al. Macromol. Symp. 2007. 254, 240-247). The optimal conditions and mechanism of the anchoring procedures were investigated. The surface and film properties of all immobilized polymer films were characterized by atomic force microscopy (AFM). X-ray photoelectron spectroscopy (XPS), electrokinetic measurements, contact-angle measurements by drop-shape analysis, spectroscopic and imaging ellipsometry, and infrared spectroscopy. It is shown that all immobilization methods can be optimized in such a way that the polymer surface properties remain unchanged compared to those of nongrafted polyesters.