Stereospecific Ziegler−Natta Model Catalysts Produced by Electron Beam-Induced Deposition of TiCl₄:  Deposition Kinetics, Film Structure, and Surface Structure

A multilayer film of TiClx, 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 TiClx took place by dissociation of TiCl4 adsorbed at the substrate surface by electronsboth 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 TiClx film selectively produced isotactic polypropylene. The absence of atactic polypropylene was due to the lack of TiClx sites with the basal plane structure, caused by the deposition method involving high-energy electrons and low substrate temperature.