Ethylene/propylene copolymerization over three conventional C₂‐symmetric metallocene catalysts: Correlation between catalyst configuration and copolymer microstructure

Abstract

This work reports on a correlation between catalyst configuration and copolymer microstructure for ethylene/propylene (E/P) copolymerization using three conventional C 2 -symmetric metallocene catalysts, namely, rac-Et(Ind) 2 ZrCl 2 (EBI), rac-Me 2 Si(2-Me-4-Ph-Ind) 2 ZrCl 2 (SiPh), and rac-CH 2 (3-tBu-Ind) 2 ZrCl 2 (MBu), with MAO as a common cocatalyst. Copolymerization reactions were conducted in toluene at three different temperatures with varied E/P ratios. Some typically obtained copolymers were characterized in detail using 13 C-NMR spectroscopy, by which triad distribution data were elaborated in a statistical method to determine the reactivity ratios (r E and r P ) of the comonomers, which were also obtained by Fineman-Rose estimation. The production of alternating-like copolymers from EBI is attributed to the rapid interconversion between two conformation states of the active site, one of which favors the incorporation of propylene but the other one does not. Both SiPh and MBu are structurally more rigid and of larger dihedral angles than EBI; however, SiPh which owns open active site conformation tend to produce random copolymers at all studied temperatures, and for MBu, sterically hindered catalyst, block-like copolymers were obtained.

Backbone rearrangement during olefin capture as the rate limiting step in molecular olefin polymerization catalysis and its effect on comonomer affinity

“…Catalysts 4c‐Zr and 4d‐Zr show BBRA/BBRA competition in the temperature range of −50 to 0 °C, but crossover to BBRA/INS competition at higher temperatures. Predictions for 4d‐Zr are in nice agreement with experiment which implied a switch in rate limiting step around 60 °C. In the BBRA/INS regime, incorporation decreases fast with increasing temperature (twofold over only 50 K for 4c‐Zr ).…”

“…The authors explained this observation with solution‐enthalpy of gaseous ethene in the solvent. Lu et al report r e and r c for ethene/propene copolymerization using Me 2 Si(2‐Me‐4‐Ph‐Ind) 2 ZrCl 2 ( 4d‐Zr ) at 40, 60, and 80 °C . From 40 to 60 °C, S = 12–18 cal mol −1 K −1 can be estimated and from 60 to 80 °C, S = 2–5 cal mol −1 K −1 ; r c appears to be more temperature dependent than r e in their data.…”

The Influence of Ziegler-Natta and Metallocene Catalysts on Polyolefin Structure, Properties, and Processing Ability

“…This provided organometallic and polymer chemists with a potent co-catalyst able to activate group 4 metallocenes (and a large number of other transition metal complexes, too) towards the polymerization of virtually any 1-olefins, as well as several cyclic olefins [ 65 ]. Over the past 30 years, these homogenous SSCs have dominated the literature due to a greater understanding of the mechanism of polymerization of ethylene leading to opportunities for designing and developing improved classes of catalysts [ 64 , 150 , 151 , 152 , 153 , 154 , 155 , 156 , 157 , 158 , 159 , 160 , 161 , 162 , 163 , 164 , 165 , 166 , 167 , 168 , 169 , 170 , 171 , 172 , 173 , 174 , 175 , 176 , 177 , 178 ]. However, the activity of Cp 2 -MtX 2 /MAO catalysts was moderate with propylene and, more importantly, did not produce stereo-regular polymers [ 65 ].…”

Methyl branching in polyethylene from homopolymerization of ethylene with N‐arylcyano‐β‐diketiminate methallyl nickel‐B(C6F5)3

“…The aforementioned kind of polymer can be produced via ethylene–propylene copolymerization with metallocene catalysts, and to some extent with nickel catalysts based on α‐di‐imines. An adequate control of the ethylene pressure and the reaction temperature is also necessary .…”