Stereospecific Ziegler-Natta model catalysts produced by electron beam-induced deposition of TiCl₄: Deposition kinetics, film structure, and surface structure

A multilayer film of TiCl_x, model Ziegler-Natta catalyst for stereospecific polymerization, was produced by electron beam-induced deposition of TiCl₄ on an Au substrate at 100 K. The deposition of solid-phase TiCl_x took place by dissociation of TiCl₄ adsorbed at the substrate surface by electrons-both primary and secondary. The deposition kinetics, surface composition, and structure were studied with X-ray photoelectron spectroscopy and temperature-programmed desorption. Its polymerization stereochemistry was studied by analyzing the polypropylene products with infrared spectroscopy and atomic force microscopy. The deposited film was stable at temperatures lower than 450 K and had a high concentration of chemisorbed TiCl₄ species. The film surface was composed of mostly a nonbasal plane (defective) structure. When activated by reactions with Al(C₂H₅)₃, the TiCl_x film selectively produced isotactic polypropylene. The absence of atactic polypropylene was due to the lack of TiCl_x sites with the basal plane structure, caused by the deposition method involving high-energy electrons and low substrate temperature.