Metallocene Catalysts for

In the early 1990s, solution processes acquired new importance because of their shorter residence times and abiUty to accommodate metallocene catalysts. Many heterogeneous multicenter Ziegler catalysts produce superior LLDPE resins with a better branching uniformity if the catalyst residence time in a reactor is short. Solution processes usually operate at residence times of around 5—10 min or less and are ideal for this catalyst behavior. Solution processes, both in heavy solvents and in the polymer melt, are inherently suitable to accommodate soluble metallocene catalysts (52). For this reason, these processes were the first to employ metallocene catalysts for LLDPE and VLDPE manufacture. 

In attempts to understand more fully the mechanism of Ziegler-Natta polymerisations chemists came to develop what have become known as metallocene catalysts for polymerisation. In due course it was found possible to... 

The goal of precise synthesis of supported mononuclear and polynuclear metal complexes can be traced to the early work of Yermakov [1], Ballard [2], and others. Their work stimulated the hvely field referred to as surface organometalhc chemistry [3-6]. The success and importance of precise synthesis of supported molecular catalysts are illustrated by the apphcation of supported metallocene catalysts for industrial alkene polymerization [7j. 

Eisch s work promoted investigation into the preparation of cationic metallocene complexes of Group 4 metals. Several preparative routes to cationic group 4 metallocene complexes are illustrated in Scheme II. Catalytic activities of some selected cationic metallocene complexes for the polymerization of a-olefins are summarized in Tables 5 and 6. The catalyst systems based on these cationic complexes are just as active as M AO-activated metallocene catalysts for the polymerization of a-olefins. 

Deffieux A, Cramail H, Radharkrishnen K, Pedeutour JN (2001) Reactivity of metallocene catalysts for olefin polymerization influence of activator nature and structure. Macromol Rapid Commun 22 1095-1123... 

Chien JCW, Llinas GH, Rausch MD, Lin YG, Winter HH, Atwood JL, Bott SG (1992) Metallocene catalysts for olefin polymerizations. XXIV. Stereoblock propylene polymerization catalyzed by rac-anri -ethylidene(l-T 5-tetramethylcyclopentadienyl)(l-r 5-indenyl) dimethyltitanium A two-state propagation. J Polym Sci A 30 2601-2617... 

Insite Not a process, but a range of constrained-geometry metallocene catalysts for polymerizing olefins. Developed by Dow Chemical. 

Brookhart and coworkers [1] have recently developed Ni(II) and Pd(II) bis-imine based catalysts of the type (ArN=C(R)-C(R)=NAr)M-CH3+ (la of Figure 1) that are promising alternatives to both Ziegler-Natta systems and metallocene catalysts for olefin polymerization. Traditionally, such late metal catalysts are found to produce dimers or extremely low molecular weight oligomers due to the favorability of the P-elimination chain termination process [2],... 

Figure 10.5. The first homogeneous metallocene catalyst for ethene polymerisation...

A unique immobilization strategy was developed by Alt, who synthesized metallocenes with alkene functionalities and employed these functionalized metallocene catalysts for polymerization. During the polymerization process, the metallocene catalysts are consumed as a co-monomer, leading to the generation of polymer-supported metallocene catalysts. 

Sudhakar, P. and Sundararajan, G. (2005) Tuning the reactivity of N, O.O.O-non-metallocene catalysts for a-olefin polymerization issues related to ligand symmetry and derivatization. Macromol. Rapid Commun., 26, 1854. 

Fig. 6 Typical metallocene catalysts for olefin polymerization containing a C2-symmetric ligand (left) and a Cs-symmetric ligand (right)...

Compare the electronic structure of group 4 and group 3 metallocene catalysts for olefin polymerisation. 

Conjugated dienes have been polymerised using supported half-sandwich metallocene catalysts. For instance, catalysts derived by supporting CpTiCl3 on alumina-silica gels, containing—0-Ti(Cp)Cl2 species, displayed activity in isoprene polymerisation without the addition of any other activator. Depending on the alumina-silica gel composition, the kind of polymerisation medium and the temperature, these catalysts exhibited various activities and selectivities polyisoprenes with a predominant 3,4 structure and mixed 1,2/ trans-1,4 structure were obtained [118,119],... 

Kaminsky, W., Highly Active Metallocene Catalysts for Olefin Polymerisation , J. Chem. Soc., Dalton Trans., 1998, 1413-1418 (1998). 

Further evidence for the existence of cationic centers is given by the activation of metallocene catalysts for olefin polymerization by the use of anionic counterions such as tetraphenylborate (CeFIs B-, carborane (C2B9H12), or fluorinated borate. The use of (CgF5)4B counterions by Hlatky et al. (83), Sishta et al. (84), and Zambelli et al. (85) leads to highly active metallocene catalysts, which are formed by the reaction of a dealkylated zirconocene with dimethylaniliniumtetra(/us,-perfluorophenyl)borate ... 

Kaminsky, W., Metallocene catalysts for olefin polymerization, in Science and Technology in Catalysis 1998 (V. Dragutan and R. Streck, Eds.), p. 3. Elsevier, Amsterdam, 1999. 

Another combination catalyst that includes a Lewis acid component is Cp2MCl2/2n-BuLi/B(C6F5)3.60-61 Interest in such systems came about as a consequence of the successful use of well-characterized homogeneous cationic and cation-like Group 4 and actinide metallocene catalysts for olefin polymerization.62 63... 

The polymerization tests with ethylene and 1-olefines as well as with dienes showed a good ability of the metallocene catalyst for copolymerization. Interesting results from practical and theoretical point of view could be gained in the copolymerization of ethylene and 1,5-hexadiene. During polymerization first a complexation of one of the double bonds of 1,5-hexadiene takes place at the vacant coordination side of the transition metal. After insertion into the polymer chain the complexation of the second double bond occurs followed by intramolecular cyclisation of the 5-membered ring. Analysis of the 13C-NMR spectra reveals an incorporation of 4.2 mole% 1,5-hexadiene and a predominance of trans rings caused by the diastereoselectivity of the cyclisation step. 

Insite Not a process, but a range of constrained-geometry metallocene catalysts for polymerizing olefins. Olefin block copolymers made using these catalysts have the trade name Infuse. Developed by J.C. Stevens at the Dow Chemical Company, for which he received several medals. 

He is currently supervising a group of 15 students and scientists in the field of pyrolysis of plastic waste in a fluidized bed process and a group in the field of metal-locene/methylaluminoxane chemistry. His past experience includes the development of pilot plants for the feedstock recycling of plastic wastes and scrap tires, and discovering highly active metallocene catalysts for the polymerization of olefins. He has published more than 300 papers and books and holds 20 patents. He has organized several international symposia in the field of pyrolysis and olefin polymerization. 

Resconi, L. Giannini, U. Dall Occo, T. MAO-free Metallocene Catalysts for Ethylene (Co)Polymerization. In Metallocene-based Polyolefins Preparation, Properties and Technology, Scheirs, J., Kaminsky, W., Eds. Wiley Chichester, 2000 Vol. 1, 69. 

Resconi, L. Fritze, C. Metallocene Catalysts for Propylene Polymerization. In Polypropylene Handbook, 2nd ed. Pasquini, N., Ed. Hanser Munich, 2005, p 107. 

---