Titanium silane polymerization

A similar dichotomy was observed in the titanium catalyzed polymerization of primary silanes coupled to the hydrogenation of norbornene (20). At low catalyst concentration (ca. 0.004H), essentially complete conversion of norbornene to an equimolar mixture of norbornane and bis-phenylsilyl- (and/or 1,2-diphenyl-disilyl)norbornane was observed. Under these conditions no evidence for reduction of titanium was obtained. At higher catalyst concentrations (> 0.02M) rapid reduction of the dimethyltitanocene to J, and 2 occurs and the catalytic reaction produces mainly polysilane (DPn ca. 10) and norbornane in ca. 80 per cent yields, and silylated norbornanes in about 20 per cent yield. 

The chemistry of titanium is of considerable importance, primarily because of its roles as a catalyst in various chemical reactions (e.g., silane polymerization... 

Divalent titanium has been implicated as a catalyst in several reactions, including silane polymerization (1) and hydrosilation (2). Considerable theoretical effort has therefore been expended recently in analyzing the role of divalent titanium as a catalyst in the hydrosilation and bis-silylation reactions. 

The chemistry of titanium is of considerable importance, primarily because of its roles as a catalyst in various chemical reactions (e.g silane polymerization (1), hydrosilation (2), and Ziegler-Natta (3) polymerization), as materials and materials precursors, and as the basis for electronic and magnetic devices. In the past several years, the interest in titanium chemistry in this group has focused on its fundamental molecular and electronic structure in a variety of chemical environments, on its function as a catalyst in the hydrosilation and bis-silylation reactions, and on the nature of the structure, bonding, and mechanism of formation of metallocarbohedrenes. 

Dehydrogenative Coupling. Transition-metal catalyzed polymerization of silanes appears to hold promise as a viable route to polysilanes. A number of transition-metal complexes have been investigated, with titanium and zirconium complexes being the most promising (105—108). Only primary silanes are active toward polymerization, and molecular weights are rather low. The dehydrogenative polymerization is depicted in reaction 11, where Cp = cyclopentadienyl ... 

PREPARATIVE TECHNIQUES Ziegler-Natta polymerization with titanium halide/ aluminum cdkyl catalyst and, optionally, ether, ester, or silane activator. Catalyst may be deposited on a magnesium chloride support. Slurry and gas phase processes are used. Catcdyst systems based on metallocenes are under development. Typical comonomers are ethylene and 1-butene. 

Proteins are also deposited on any solid substrate which has come into contact with the suspension holding the cells. Many studies have shown that a film of polymeric material builds up on all surfaces, such as glass or polymer, which have held the cell dispersion. These slimy films may have an effect on the cell adhesion to that surface. For example, when fibronectin was coated onto polished metal surfaces of titanium and cobalt alloys, the cell adhesion increased by a factor of 2.6. In this manner, the adhesion molecules act like the silane coupling agents used to coat glass fibers in Section 16.10. 

---