AM2Net Advanced Macromolecular Materials By Transition Metal Catalysis; Group 3: "Ring-opening Polymerization Catalysis"; Alkaline-earth (and lanthanide) metal-alkoxide catalysts for oxygenate polymerization

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Industrially, there is an increasing interest in the development of new polymeric materials from classical monomers. During the last decade of polymer research, the keyword in the rational design of new materials from "old" monomers has been stereoselective polymerisation. The last few years, however, there is an increasing tendency in designing new materials by means of copolymerisation. Many research groups concentrate on statistical copolymerisation of monomer mixtures as a way to influence the physical properties of the polymer. We like to concentrate on a very powerful method in rational polymer design: block-copolymerization. In order to achieve the syntheses of block-copolymers the polymerization reactions need to be living. Therefore, block-copolymers are traditionally prepared by anionic polymerisation using alkalimetal alkyls as initiator. It is our aim to combine the advantages of living block-copolymerisation with those of stereoselektive polymerisation. Preliminary work of our group has shown that this goal can be reached partially by the use of divalent alkaline-earth initiators. These complexes polymerize styrene in a living fashion with syndiotacticities up to r = 91%. We could show that the remaining errors are due to inversion of the chiral chain-end, which leads to racemisation of the stereocenters. One approach to retard these chain-end inversions is the use of initiators with trivalent metals: the bond between polymer chain and metal is stronger and this leads to slower inversion. We therefore like to extend our research with the syntheses of trivalent metal initiators that are isolobal to the divalent alkaline-earth initiators. There are two possible approaches that will be pursued: i) the use of isolobal cationic initiators and ii) the use of isolobal neutral initiators with dianionic ligand systems. The metall will be preferably aluminium for which recently considerable potential in alkene polymerisation has been shown. We also like to venture into lanthanide metal chemistry, which has been shown quite useful in polymerisation catalyses lately. Apart from the syntheses and structures of new catalysts based on trivalent metals, the polymerization properties and especially their mechanisms will be investigated as well. We like to concentrate especially on the block-copolymers of styrene and butadiene. It is expected that stereoregular styrene blocks within atactic butadiene blocks will result in elastomeric materials that are transparent and have an unusual high impact.