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Propylene Polymerization with rac ‐SiMe 2 (2‐Me‐4‐PhInd) 2 ZrMe 2 /MAO: Polymer Characterization and Kinetic Models
Author(s) -
Lahelin Mika,
Kokko Esa,
Lehmus Petri,
Pitkänen Päivi,
Löfgren Barbro,
Seppälä Jukka
Publication year - 2003
Publication title -
macromolecular chemistry and physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.57
H-Index - 112
eISSN - 1521-3935
pISSN - 1022-1352
DOI - 10.1002/macp.200390106
Subject(s) - chemistry , monomer , methylaluminoxane , chain transfer , polymer chemistry , polymerization , activation energy , molar mass , catalysis , polymer , hydrogen , metallocene , organic chemistry , radical polymerization
Poly(propylene)s were prepared with metallocene catalyst rac ‐SiMe 2 (2‐Me‐4‐PhInd) 2 ZrMe 2 /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 13 C NMR spectroscopy revealed isobutyl and allyl end‐groups. Chain transfer to aluminium and β ‐CH 3 elimination were concluded to be the dominating chain‐termination mechanisms. The importance of β ‐CH 3 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 ‐CH 3 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.