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The industrial applications of the olefin metathesis reaction are relatively recent although this reaction was observed about 50 years ago. Streck described in details the historical development of this reaction in his review in a book of the same series [1]. He gave also interesting data on the industrial processes in refs. [2] and [3]. More recently, Ivin and Mol, in their classical book on olefin metathesis, have also developped this field in a special chapter [4]. The idea of olefin disproportionation was first proposed by Robert Banks at Phillips [5], who had observed traces of pentenes and propene in the reaction mixture after passing isobutane and butenes through a bed filled with molybdenum carbonyl supported on alumina. The Ring Opening Metathesis Polymerization was found by the Natta group at Montedison [6, 7]. Many groups studied this reaction and its mechanism was proposed by Chauvin

Since the early 1980s innovations in metallocene catalyzed olefin and styrene polymerization have stimulated progress in polymer synthesis and development of new polymeric materials derived from well-known and readily available petrochemical feedstocks, such as ethylene, propylene, higher 1-olefins, cycloolefins, and styrene. Recent advances and new insights into reaction mechanisms and basic correlations between metallocene structure and polymer properties were reviewed by Brintzinger et al. [1], Kaminsky [2–4], Hamielec and Soares [5, 6], Gupta et al. [7], Reddy and Sivaram [8], Huang and Rempel [9], Tian and Huang [10], Mulhaupt [11-13], Aulbach and Kubor [14], Coates and Waymouth [15], and Albizzati et al. [16]. The state of the art in catalyst development during the mid-1990s is reflected by contributions compiled in proceedings [17, 18] of conferences held in honor of Karl Ziegler and Giulio Natta.

In 1954 G. Natta polymerized propylene in the Montecatini laboratories by means of a modified Ziegler catalyst and obtained a blend of isotactic and atactic polypropylene (PP). For this pioneering invention he and K. Ziegler received the Nobel price for chemistry in 1963.

The synthesis of block copolymers by catalyst transformation reactions was pioneered by Richards[1], who developed the transformation from anionic-to-cationic reactions to synthesize poly(styrene-block-cotetrahydrofuran). Other examples of transformation reactions include anionic-to-free radical and Ziegler Natta polymerizations. In these cases the polymerization mechanisms have been well-established and the synthesis of the copolymers has been the principal objective. We have used the synthesis of copolymers as a means to elucidate the mechanism of initiation of metathesis.

The molecular weight distribution (MWD) of polyoelfins obtained with Ziegier-Natta catalysis can range from 2 to 20 or more depending on the monomers, the process and the catalytic systems. It is rather easy to show that in most cases the broad MWD are not due to diffusion effects but to a distribution of active centers. The chemical and process factors controlling the MWD are numerous. This results in a complex patent literature with more weight on the catalyst formula and on the process.

Recent developments of commercial processes (1) for the polymerization of ethylene and propylene and which involve the use of second generation Ziegler-Natta catalysts have highlighted the need of reliable methods for the evaluation of catalyst activity. Comparative studies of catalyst activities are only useful, however, provided the factors which control these activities are understood. Such an understanding requires a fuller appreciation of the kinetic behaviour of these fascinating polymerization systems and the development of more accurate methods for the determination of active centre concentration.

Karl Ziegler who shared the Nobel Prize with Giulio Natta was a professor of chemistry at the Universities of Heidelberg and Halle before being named director of the Max Planck Institut. His interest in organometallic compounds led to the discovery of the “Ziegler catalyst” which was used to produce high density polyethylene.

Giulio Natta, who shared the Nobel Prize in chemistry with Karl Ziegler, was an Italian crystallographer who used the “Ziegler catalyst” to produce polypropylene. His wife, Rosita, coined the tacticity terms after Giulio had shown that stereoregular polymers could be produced by the polymerization of alpha substituted ethylenes.

Since its discovery a great deal of work has been done for understanding the mechanism of Ziegler-Natta polymerization of α-olefins. In spite of this almost 25 years old activity many points do not appear entirely clarified and firmly established. Indeed these catalysts join unique and very interesting properties to a very large complexity. Thus the field is under constant development and also the aspects generally accepted (1) are often put in debate. For istance the α-olefin insertion in a transition metal-carbon bond, considered as one of the fixed step of the mechanism, has been questioned very recently by proposing (2) a mechanism proceeding via a 1,2 hydrogen shift from the α-carbon of the growing chain and formation of metallocycle and carbene intermediates. Even if this last proposal does not explain end group nature, particularly when using AlPh3, large predominance of primary insertion in isotactic polymerization and different role of growing chain end and metal complex in the steric control, it however indicates that several problems are still open as discussed in other chapters.

Living anionic lithium-ended polymer is transformed into a soluble Ziegler-Natta Ti (III)/Li-based system. The latter exhibits a high efficiency as at least 80% of C-Ti bonds participate in the homo- and co-polymerization of ethylene and propene, leading to vinylicolefinic type block copolymers.

For a long time homogeneous Ziegler-catalysts basing on bis(cyclopentadienyl)titanium or zirconium dialkyls and trialkylaluminiums were assumed to be inactive for olefin polymerization. In the case of biscyclopentadienyl-ethyl-titanium chloride and triethylaluminium very fast aging reactions take place which end up before long with titaniumIII-compounds. These titaniumIII-compounds are as inactive as mixtures of biscyclopentadienyltitanium-dimethyl and trimethylaluminium.

Stereoregular polymers constitute a large class of macromolecular compounds that are endowed with many interesting and valuable properties. The natural ones are of vital importance. The properties that these polymers possess are determined in large part by their steric regularity. The essential role of stereochemistry in determining the physical and chemical properties of chemical compounds was envisaged by Wislicenus (1) more than one hundred years ago. That this applies to high as well as to low molecular weight compounds was recognized early during the development of macromolecular science. In the late twenties Meyer and Mark (2,3) interpreted the differences between natural rubber and gutta-percha by suggesting that the former represents the eis- and the latter the trans-form of 1,4-polyisoprene, and Staudinger proposed stereoirregularity as the cause of the non-crystallizability of polyindene (4,5), polystyrene (5) and polyvinylacetate (5). At that time researchers were gradually beginning to realize that all organic polymers found in nature and containing sites of stereoisomerism were stereoregular. The development in the understanding of the structure of various natural polymers has been described by Meyer (6). Thus it must have become obvious that stereoregularity is an essential condition in order for these natural polymers to carry out their specific biologic functions. However, fundamental studies on the influence of stereochemistry on the physical and chemical properties of polymers started only in the late forties, when the first stereoregular polymers were synthesized from monomers non containing stereoisomerism sites. Great impetus to developments in this area was given by the first synthesis of a highly stereoregular polypropylene by Natta and his group in 1955 (7). This originated a large interest in the synthesis and the study of other stereoregular polymers, thus forming the basis for the remarkable progresses achieved in this area in the last 20 years. From this development it clearly emerged that stereochemistry strongly influences the reactivity, the conformational equilibria and many physical properties of polymers in dilute solution and in the melt. For chemically regular polymers, stereochemistry determines the type of crystal structure and the degree of crystallinity, and thus determines the properties of these polymers in the solid state. Therefore, it is not surprising that, in some cases (e.g. polypropylene) stereochemistry may even determine the success of the industrial application of a polymeric product. The relevance of synthetic stereoregular polymers is by no means limited to the study and applications of the relationships between polymer stereochemistry and properties. Progress in many other areas of polymer science has been made possible or has been accelerated by studies on stereoregular synthetic polymers. In particular, significant advances in the understanding of the mechanism of various polymerization processes have been achieved through the efforts made to elucidate the factors that determine the formation of stereoregular polymers. Furthermore, some factors influencing the mode of crystallization of the polymer chains and the morphology of the polymers have been clarified by the investigation of the large number of stereoregular polymers which have been synthesized.