Stereoregular Polymerization of Propylene

Natta first used the in-situ prepared Ziegler catalyst (TiCl4 + Et3Al), which produced polymers with low stereoselectivity324 (isotacticity index = 30 10%). 

By assuming that stereoselectivity is connected to the regular heterogeneous catalyst surface, Natta introduced violet T1CI3 and used preformed heterogeneous catalysts in further studies.234,240 These complexes may act as stereoselective catalysts and polymerize propylene to crystalline stereoregular polymers. 

Isospecific polymerization. Important features of stereoregular isospecific polymerization of propylene, and in general, terminal alkenes, are as follows 125,254,32 328 

Isotactic polymerization occurs with practically complete regioselectivity, that is, with a continuous head-to-tail addition, which is a prerequisite to stereoregularity. 

It was demonstrated by spectroscopic studies (IR, NMR) that in isotactic polymerization of propylene a so-called primary or type 1-2 insertion 

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Esteb, J. J. Chien, J. C. W. Rausch, M. D. Novel Ci symmetric zirconocenes containing substituted indenyl moieties for the stereoregular polymerization of propylene. J. Organomet. Chem. 2003, 688, 153-160. 

Figure 5.10 (a) Setup for stereoregular polymerization of propylene using TiCl3—AlEth3 catalyst in n-heptane. (b) Schematic representation of effect of stirring on polymerization for two speeds of stirring Ni and N2-... 

The next major commodity plastic worth discussing is polypropylene. Polypropylene is a thermoplastic, crystalline resin. Its production technology is based on Ziegler s discovery in 1953 of metal alkyl-transition metal halide olefin polymerization catalysts. These are heterogeneous coordination systems that produce resin by stereo specific polymerization of propylene. Stereoregular polymers characteristically have monomeric units arranged in orderly periodic steric configuration. 

A guide to the manner in which structural theory may be applied to a detailed consideration of the mechanism of a surface-catalyzed reaction is found in papers by Cossee (113), Arlman (114), and Arlman and Cossee (115) concerning the mechanism of the stereoregular heterogeneous catalyzed polymerization of propylene. Particular crystallographic sites are shown to be the active centers at which the reactants combine and ligand field theory is used to demonstrate a plausible relationship between the activation energy for the conversion of adsorbed reactants to the product and the properties of the transition metal complex which constitutes the reaction center. 

When catalysts suitable for the polymerization of propylene are applied to the polymerization of 4-methyl-l-pentene, they show a fairly high level of performance but do not prove to be entirely satisfactory with regard to the yield of the TPX per unit weight of the catalyst or the proportion of a stereoregular TPX in the resulting polymerization product (6). 

Polymerization in liquid monomer was pioneered by Rexall Drug and Chemical and Phillips Petroleum (United States). Gas-phase polymerization of propylene was pioneered by BASF, who developed the Novolen process which uses stirred-bed reactors, Eastman Chemical has utilized a unique, high temperature solution process for propylene polymerization. In the 1970s, Solvay introduced an advanced TiCl3 catalyst with high activity and stereoregularity. 

Deng, H. Winkelbach, H. Taeji, K. Kaminsky, W. Soga, K. Synthesis of high-melting, isotactic polypropene with C2- and Ci-symmetrical zirconocenes. Macromolecules 1996, 29, 6371-6376. Mise, T. Miya, S. Yamazaki, H. Excellent stereoregular isotactic polymerizations of propylene with C2-symmetric sUylene-hiidged metallocene catalysts. Chem. Lett. 1989, 1853-1856. 

Mise, T. Miya, S. Yamazaki, H. Excellent stereoregular isotactic polymerizations of propylene with C2-symmetric silylene-bridged metallocene catalysts. Chem. Lett. 1989, 1853-1856. 

Volkis, V Shmulinson, M. Averbuj, C. Lisovskii, A. Edelmann, F. T. Eisen, M. S. Pressure modulates stereoregularities in the polymerization of propylene promoted by roc-octahedral heteroallylic... 

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