Isoselective 4-Methylpentene Polymerization by Pyridylamido Hafnium Catalysts

The stereospecific polymerization of 1-alkenes is a continuing issue for metal catalysis. We have initially reported isoselective 4-methylpentene polymerizations by nonconventional pyridylamido hafnium catalysts with different bridgehead substituents (L(R1R2)Hf(Me)2, L...

Stereospecific polymerization of conjugated dienes using neodymium alkylborohydride complexes

Two neodymium alkylborohydride complexes that differ with respect to the number of hydrides on the boron center were synthesized and characterized.

Substituent Effects of Phenyl Group on Silylene Bridge in Stereospecific Polymerization of Propylene with C1-Symmetric Ansa-Silylene(fluorenyl)(amido) Dimethyl Titanium Complexes

A C1-symmetric (methylphenyl)silylene-bridged (fluorenyl)(naphthylamido) titanium complex (1) and (diphenyl)silylene-bridged (fluorenyl)(naphthylamido) titanium complex (2) were synthesized and characterized by 1H NMR, element analysis, and X-ray crystal analysis. The coordination mode of the fluorenyl ligand to the titanium metal is an η3 manner in each complex. These complexes were applied for propylene polymerization using dried modified methyaluminoxane (dMMAO) as a cocatalyst under different propylene pressures in a semi batch-type method. The catalytic activity was strongly dependent on the structure of the complex and the propylene pressure, where complex 1 exhibited the highest activity (600 kg mol−1·h−1) under a propylene pressure of 8.0 atm to produce high molecular weight polypropylene. The polypropylenes obtained were syndiotactic-rich with an rr value of 0.50, indicating that the silylene bridge was not efficient for the isospecificity of a constrained geometry catalyst (CGC). The mechanical properties of the resulting polymers depended on their microstructure.

IL 50° ANNIVERSARIO DEL NOBEL A GIULIO NATTA

On March 11, 1954 Giulio Natta synthetized isotactic polypropylene. It was the first synthesis, in laboratory, of a polymer having a sterically ordered structure, similar to those found in some natural polymers like, for instance, natural rubber and cellulose. This meaningful aspect was emphasized by Prof. Fredga of the Swedish Academy in his speech at the customary ceremony of Nobel Prize on December 10, 1963, when he stated “Natta has broken the monopoly of nature”. With the polypropylene synthesis Natta discovered the “stereospecific polymerization” defined by Toblosky (Princeton University) and by Flory, one of the most eminent scientist in the macromolecular chemistry and future Nobel laureate in Chemistry (1974), a “revolution” in the macromolecular field. Natta was recognized as the “father” of stereospecific polymerization. The Journal of Polymer Science, vol. 51 (1961), dedicated to Natta, reports “Seldom a scientific contribution aroused such a deep and fundamental interest and was followed by such a rapid technical development as the series of publications by Professor Natta and his coworkers on the stereospecific polymerization. Yet Professor Natta has succeeded in maintaining undisputed leadership in this field of polymer chemistry and continues to surprise his colleagues with new and unexpected results”. The revolution brought by Natta in the field of macromolecular chemistry involved the entire scientific and industrial world specialized in that area. Soon after 1954-55 a lot of universities and industrial laboratories around the world started to work on activities concerning the novel stereospecific polymerization. The results of these studies are reported in about a thousand scientific publications and some hundreds of patents issued from the Milan Polytechnic Institute of Industrial Chemistry between 1955 and 1977 (concentrated in 1955-57). The importance of polypropylene from the commercial point of view is evident from the fact that the world production of various types of polypropylene now stands at about 60 million tons/year. It is estimated that the related global economic value approaches the second place over all synthetic products, after polyethylene, together with ammonia, and before other products such as urea, polymers of styrene and vinyl chloride, nylons, etc. For their part 1,4-cis polybutadiene and copolymers based on ethylene and propylene occupy respectively the second and the third place in terms of worldwide production and market value among synthetic elastomers, after styrene-butadiene rubbers (SBR). More information concerning the personality and the scientific and didactic activities of Giulio Natta and his relations with the scientific and industrial world are reported on the internet site www.giulionatta.it containing the “Giulio Natta Archive” (more than 40.000 pages).