Catalyse de polymérisation par des composés d'insertion

Abstract

The first polymerizations by graphite inclusion compounds were indicated in 1958 by Podall et al. (KC 8, ethylene) and by Parrod and Beinert (KC 8, KC 24, styrene, dienes). In 1962, Stein and his collaborators prepared inclusion compounds by electronic transfer from metal-naphthalene in a polar solvent. This new method had the advantage of leading to the inclusion of lithium, the latter being solvated (ternary inclusion). These ternary compounds, as well as the binary ones, allow polymerization of vinyl or diene compounds by an anionic process. There are some differences in stereospecificities of the resulting polymers from those obtained by a homogeneous process in the same solvent. In 1970, Panayotov and Rashkov, revising the work concerning binary inclusions, showed the importance of the π interaction between monomer and graphitic planes in the polymerization process. They assumed that polymerization takes place between the planes. Moreover, they noticed that copolymerizations did not take place as in anionic copolymerization in a homogeneous medium, in which one of the monomers is generally unpolymerized. They also studied ethyloxide and acroleine polymerization. In a common work between Panayotov et al. (Sofia) and Golé et al. (Lyon) there was developed a process for the ternarization of binary inclusions with n and π donors. In fact, there are no differences between these n-donor ternarized inclusion compounds and those obtained directly by Stein's method. On the other hand, π-donor ternarised inclusion leads to new compounds in which the interaction does not take place between alkali ion and solvent, but between graphite and solvent. This new method has an important application with the LiC n binary compounds first prepared by Hérold and Guérard in 1972. They produced new lithium catalysts utilisable in non-polar media. So it is possible to polymerize isoprene with a high cis-1–4 percentage (90%), and styrene-isoprene in an alternating copolymer. This later factor confirms the abnormal behaviour of anionic graphite catalysts. n-Donor ternarization leads to numerous interesting catalysts. For instance, the metal-graphite inclusion ternarized with polyethylene oxide gives surprisingly high cis-1–4 polyisoprene. In conclusion we can say that: 1. (1) polymerization seems to take place between the graphitic planes; 2. (2) the influence of these planes is very important on account of the interaction of graphite with the monomer, and this is sometimes a determining factor in the case of the copolymerizations; 3. (3) binary inclusions or binary ternarized inclusions by aromatic solvents seem to provide some interest.