Abstract
AbstractA new silolene‐bridged compound, racemic (1,4‐butanediyl) silylene‐bis (1‐η5‐in‐denyl) dichlorozirconium (1) was synthesized by reacting ZrCl4 with C4H8Si (IndLi)2 in THF. 1 was reacted with trialkylaluminum and then with triphenylcarbenium tetrakis (penta‐fluorophenyl) borate (2) to produce in situ the zirconocenium ion (1+). This “constraint geometry” catalyst is exceedingly stereoselective for propylene polymerization at low temperature (Tp = −55°C), producing refluxing n‐heptane insoluble isotactic poly(propylene) (i‐PP) with a yield of 99.4%, Tm = 164.3°C, δHf = 20.22 cal/g and M̄w = 350 000. It has catalytic activities of 107−108 g PP/(mol Zr · [C3H6] · h) in propylene polymerization at the Tp ranging from −55°C to 70°C, and 108 polymer/(mol Zr · [monomer] · h) in ethylene polymerization. The stereospecificity of 1+ decreases gradually as Tp approaches 20°C. At higher temperatures the catalytic species rapidly loses stereochemical control. Under all experimental conditions 1+ is more stereospecific than the analogous cation derived from rac‐dimethylsilylenebis (1‐η5‐indenyl)dichlorozirconium (4). The variations of polymerization activities in ethylene and in propylene for Tp from −55°C to +70°C indicates a Michaelis Mention kinetics. The zirconocenium‐propylene π‐complex has a larger insertion rate constant but lower thermal stability than the corresponding ethylene π‐complex. This catalyst copolymerizes ethylene and propylene with reactivity ratios of comparable magnitude rE ˜ 4rp. Furthermore, rE.rp ˜ 0.5 indicating random copolymer formation. Both 1 and 4 activated with methylaluminoxane (MAO) exhibit much slower polymerization rates, and, under certain conditions, a lower stereo‐selectivity than the corresponding 1+ or 4+ system. © 1994 John Wiley & Sons, Inc.
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
More From: Journal of Polymer Science Part A: Polymer Chemistry
Disclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.