High‐molar‐mass polypropene with tunable elastic properties by hafnocene/borate catalysts

Abstract

Elastic polypropene has gained growing industrial and academic interest as a thermoplastic elastomer. In this study, “rac”‐ and “meso”‐dimethylsilyl(3‐benzylindenyl)(2‐methylindenyl)hafnium dichloride complexes (Hfr and Hfm, respectively), activated with [NHMe2Ph][B(C6F5)4]/triisobutyl aluminum, were used in propene polymerization. Using these catalyst systems, we obtained polymers with high molar masses, up to 550 kg/mol, and moderate isotacticities between 34 and 52%. By varying the polymerization conditions, we could modify the polymer microstructure and molar mass. 13C NMR was used to calculate the polymer pentad sequence distributions. The crystalline parts of the polymers were analyzed with the differential scanning calorimetry successive self‐nucleation and annealing (SSA) technique. The SSA thermograms revealed that Hfr produced polypropene with a more uniform lamellar structure than Hfm. The mechanical properties were tested with dynamic mechanical analysis creep‐recovery tests. In the series, the polymers with the lowest isotacticities and therefore lowest crystallinities showed the best elastic properties. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 4743–4751, 2006

Formation and Structures of Hafnocene Complexes in MAO- and AlBui3/CPh3[B(C6F5)4]-Activated Systems

“…Significantly, the aforementioned catalysts are effectively activated by mixtures of triisobutyl aluminum and cation-generating borates (e.g., AlBu i 3 /CPh 3 [B(C 6 F 5 ) 4 ]), whereas methylalumoxane (MAO) appeared to be an unexpectedly poor activator. − Similar differences in the catalytic productivity of AlBu i 3 /CPh 3 [B(C 6 F 5 ) 4 ] – and MAO-activated systems were previously reported for some other C 1 -, C 2 -, and C s -symmetric hafnocenes. − Determining the origin of these differences is self-evidently an important task.…”

“…[1][2][3][4][5][6] Similar differences in the catalytic productivity of AlBu i 3 /CPh 3 [B(C 6 F 5 ) 4 ]and MAO-activated systems were previously reported for some other C 1 -, C 2 -, and C s -symmetric hafnocenes. [8][9][10] Determining the origin of these differences is self-evidently an important task.…”