Effect of Monomer Concentration on Propene Polymerization with the rac-[Ethylenebis(1-indenyl)]zirconium Dichloride/Methylaluminoxane Catalyst

Abstract

The structural details of isotactic polypropene (iPP) produced with the moderately isospecific racemic-ethylenebis( 1-indeny1)zirconium dichloriddmethylaluminoxane (rac-(EBI)ZrClzflMAO) catalyst are strongly dependent on monomer concentration. Polymerizing propene at 50 "C in toluene, at propene concentrations in the experimentally measurable range 0.4-11 mol&, rF-(EBI)ZrC12/MAO shows activities in the range 2-350 kgpp/(mmolzr * h) and yields polypropenes with M. , 's from 8800 to 36 600, percent mmmm pentads ranging from 54 to 86%, and corresponding melting temperatures from 86 to 136 "C. Two types of regioirregular (secondary) placements in an isotactic sequence of primary propene insertions are observed in iPP synthesized in liquid monomer, erythro (E, ca. 0.4%) and threo (T, ca. 0.2%). These secondary units are gradually converted into 1,3 propene units as the monomer concentration is lowered.In "starved-catalyst" conditions, that is, as [MI -0, ruc-(EBI)ZrClz/MAO produces atactic propene oligomers (M, = 1080, mmmm = 9.1%). These effects are the most probable cause for the discordance of literature data on metallocene-catalyzed propene polymerization. Three chain transfer mechanisms have been detected: P-hydrogen transfer to the metal and /3-hydrogen transfer to the monomer, both occurring after a primary insertion, and P-hydrogen transfer to the monomer after a secondary insertion with the exclusive formation of a cis-2-butenyl end group.

Isospecific Propylene Polymerization Behavior of Lewis Base Functionalized Unbridged Zirconocences under Bulk Conditions

“…Namely, the insertion rate of propylene is so high in the bulk polymerization that the difference in the Lewis basicity or the steric effect between NMe 2 and OMe groups might not be significant in controlling isospecificity. 22,34 The similar [mmmm] methyl pentad values of H-insol portions for the NMe 2 -functionalized zirconocenes and the OMe-derivatives also support that once the C 2 -symmetric-like cation-anion pairs form, the isospecific propagation rapidly proceeds.…”

Propylene Polymerization Using ansa‐Zirconocenes with Water/Pentafluorophenol‐Modified Methylaluminoxane

“…[3] The other is the epimerization of the growing chain end, followed by b-hydride elimination (Scheme 1) reported by Brintzinger and Busico, independently. [30][31][32][33][34][35][36] Table 1. Propylene polymerization using C 2 -symmetric ansa-zirconocenes with MMAOs.…”

Stereospecific Olefin Polymerization Catalyzed by Metallocene Complexes

“…On the other hand, the selectivity in propylene insertion into Zr-CH 2 CH 3 is excellent [59]. Experimental studies show that the face selectivity during polymerization is complete, and that stereoerrors observed in polypropylene are not due to misinsertion but rather to chain-end epimerization [60,61,62].…”