Triptycene as a scaffold in metallocene catalyzed olefin polymerization.

A set of metallocene olefin polymerization catalysts bearing triptycene moieties in either position 4-5 (complexes Ty1-Ty5) or in position 5-6 (complexes Ty6-Ty8) of the basic dimethylsilyl-bridged bis(indenyl) system has been tested in propene polymerization and in ethene/1-hexene copolymerization. Comparison of the results with QSPR (quantitative structure-property relationship) predictions not parametrized for these exotic ligand variations demonstrates that trends can still be identified by extrapolation. Interestingly, Ty7, upon suitable activation, provides a highly isotactic polypropylene with an exceptional amount of 2,1 regio-errors (8%).

Cocatalyst effects in Hf-catalysed olefin polymerization: taking well-defined Al-alkyl borate salts into account.

Hafnium catalysts for olefin polymerization are often very sensitive to the nature of cocatalysts, especially if they contain "free" aluminium trialkyls. Herein, cocatalyst effects in Hf-catalysed propene polymerization are examined for four Hf catalysts belonging to the family of -symmetric (Hf-CS-Met) and -symmetric (Hf-C2-Met) metallocenes, as well as of octahedral (Hf-OOOO) and pentacoordinated (Hf-PyAm) "post-metallocenes". The performance of the recently developed {[iBu(PhNMe)Al](μ-H)}[B(CF)] (AlHAl) cocatalyst is compared with that of established systems like methylalumoxane, phenol-modified methylalumoxane and trityl borate/tri-iso-butylaluminium.

Octahedral Zirconium Salan Catalysts for Olefin Polymerization: Substituent and Solvent Effects on Structure and Dynamics.

Group 4 metal-Salan olefin polymerization catalysts typically have relatively low activity, being slowed down by a pre-equilibrium favoring a non-polymerization active resting state identified as a isomer (MM); formation of the polymerization active species (FF) requires isomerization. We now show that the chemistry is more subtle than previously realized. Salan variations bearing large, flat substituents can achieve very high activity, and we ascribe this to the stabilization of the FF isomer, which becomes in energy than MM.

A Hydrocarbon Soluble, Molecular and "Complete" Al-Cocatalyst for High Temperature Olefin Polymerization.

The dinuclear aluminum salt {[Bu(DMA)Al](-H)}[B(CF)] (; DMA = ,-dimethylaniline) is the prototype of a new class of molecular cocatalysts for catalytic olefin polymerization, its modular nature offering easy avenues for tailoring the activator to specific needs. We report here, as proof of concept, a first variant () bearing -hexadecyl-,-dimethylaniline (DMA) units, which enhances solubility in aliphatic hydrocarbons. The novel was used successfully as an activator/scavenger in ethylene/1-hexene copolymerization in a high-temperature solution process.

Short time effects of a low-frequency, high intensity magnetic field in the treatment of chronic neck and low back pain.

Introduction: Neck and back pain afflicts millions of people. Magnetotherapy has shown to have anti-inflammatory effects that could act on pain generation, but the literature lacks provide a precise therapeutic protocol.

Methods: A high-intensity electromagnetic field with a dedicated applicator was administered to 38 patients with low-back pain and 30 patients with neck pain.