Polymerization catalysis

The second half of the 20th century saw considerable progress in the chemistry and technology of plastic materials. A few figures suffice to convince us of this. In 1940, global plastics production stood at around one million tonnes; today, it's close to one hundred million tonnes! Initially conceived as substitutes for natural products, plastics have rapidly established themselves in many fields, to the detriment of other materials such as metals. One important reason for this breakthrough is the relatively low cost of the raw materials and energy required to manufacture and shape plastics, combined with new properties, the first of which is the favorable weight/performance ratio.

Polymerization catalysis using transition metal complexes occupies a very important place among all synthesis methods, whether for mass-produced polymers (polyolefins) or specialty polymers (carbon monoxide-ethylene copolymers or polycycloolefins). Known since the 1950s, with the discovery of catalytic systems based on chromium (Phillips) or titanium (Ziegler), this type of catalysis has never ceased to evolve, leading to more productive, more selective processes and enriching the range of plastics with new products. The reason for this is undoubtedly the abundance and low cost of the raw materials used (olefins, carbon monoxide).

Polyolefins account for a significant proportion of polymers produced by polymerization catalysis. In the late 1950s, catalytically produced polyolefins accounted for only a small share of thermoplastic materials. By 1960, this share had already risen to 20% worldwide! In a short space of time, the discovery of Ziegler catalysis had an enormous impact on the chemical industry, with polyolefins rapidly becoming widely available.

In recent years, a further step has been taken with the arrival on the market of polymers obtained using new catalysts (metallocene catalysis, Shell's palladium catalysis). Some predict that these new products could eventually compete with conventional plastics such as ethylene-vinyl acetate (EVA) copolymers, polyamides and polycarbonates. Organometallic chemistry has made a considerable contribution to explaining and elucidating the mechanisms involved, and above all to synthesizing new, well-defined organometallic species.

The aim of this article is to present the main polymerization catalysts involving transition metals and the polymer materials derived from them.