Propylene Polymerization with rac‐SiMe₂(2‐Me‐4‐PhInd)₂ZrMe₂/MAO: Polymer Characterization and Kinetic Models

Abstract

Poly(propylene)s were prepared with metallocene catalyst rac‐SiMe2(2‐Me‐4‐PhInd)2ZrMe2/MAO (rac‐dimethylsilylbis(2‐methyl‐4‐phenylindenyl)dimethylzirconium/methylaluminoxane) in heptane solution at temperatures from 50 to 80 °C with varying concentrations of monomer, hydrogen, triisobutylaluminium (TIBA) and MAO. Polymer molar mass depended on the monomer, MAO, TIBA, and hydrogen concentrations and on polymerization temperature. The isotacticity was very high (mmmm > 95%), and only a slight decrease was detected at high temperatures. Regio selectivity was also high; the total amount of 2,1‐ and 3,1‐insertions was less than 0.4 mol‐%. Lowering the monomer concentration and raising the temperature increased the amount of 3,1 defects over the amount of 2,1 defects. End‐group analysis by 13C NMR spectroscopy revealed isobutyl and allyl end‐groups. Chain transfer to aluminium and β‐CH3 elimination were concluded to be the dominating chain‐termination mechanisms. The importance of β‐CH3 elimination increased with temperature. Hydrogen addition changed both the initiation and termination mechanisms as indicated by the presence of propyl, butyl and 2,3‐dimethylbutyl end‐groups. According to modeling studies, the molar mass follows a first‐order relationship with propylene and hydrogen concentrations, and a half‐order relationship with MAO concentration. Arrhenius‐type activation energy coefficients were 125 kJ · mol−1 for β‐CH3 elimination, 66 kJ · mol−1 for chain transfer to aluminium, and 53 kJ · mol−1 for chain transfer to hydrogen. A value of 45 kJ · mol−1 was used for the propagation.magnified image

Indirect Synthesis of Bis(2‐PhInd)ZrCl2 Metallocene Catalyst, Kinetic Study and Modeling of Ethylene Polymerization

“…Despite much research carried out in the field of the kinetics of olefin polymerization, in most cases, the kinetic constants are not estimated [27][28][29]. In some works, the evaluation of kinetic constants are based on polymerization time, average rate of polymerization, and final polymer characters [30][31][32], while in recent models, instantaneous reaction rates and final molecular weight of the resulting polymer have been used for estimation of kinetic parameters [26,[33][34][35][36][37][38][39].…”

Synthesis of Allyl-Terminated Syndiotactic Polypropylene: Macromonomers for the Synthesis of Branched Polyolefins

“…Only -CH 3 elimination yields an allylic end group in this primary insertion mechanism. [86][87][88][89] Although most metallocenes exhibit low selectivity for allylic end groups in polypropylene synthesis, 87 Cp* 2 MCl 2 (M ) Zr, Hf) and bridged bis-(fluorenyl)zirconocenes exhibit between 70 and 90% -CH 3 elimination to give allyl-terminated atactic polypropylene, 87 while select chiral metallocenes exhibit up to 80% -CH 3 elimination to give allyl-terminated isotactic polypropylene. 87,90,91 Subsequent polymerization steps incorporate propylene as well as allylterminated polypropylene chains, leading to the formation of LCB-PP.…”

Modeling of Slurry Polymerization of Ethylene Using a Soluble Cp2ZrCl2/MAO Catalytic System

“…In some works, estimates of kinetic constants are based on time averaged values of reaction rates and final molecular weights 12–16. In more recent models, the kinetic parameters have been estimated using instantaneous reaction rates and end of batch molecular weights 4, 7, 8, 17–32…”