Crown effect in stereospecific polymerisation of dienes employing ziegler-natta heterogeneous catalysts

• Published in: European polymer journal 1985, Vol.21 (11), p.973-979
• Main Authors: Minsker, K.S., Karpasas, M.M., Monakov, Yu.B., Zaikov, G.E.
• Format: Article
• Language: English
• ISSN: 0014-3057; 1873-1945
• DOI: 10.1016/0014-3057(85)90184-3

The formation dynamics and the structure of polymerisation active sites (AS) of the catalyst systems α-TiCl 3 (γ-, δ-TiCl 3, VCl 3), β-TiCl 3 with metal alkyls (R 3Al, R 2Be, R 2Mg, RLi, R 2Zn, R 2AlCl), as well as various models for growing polymeric chains, have been studied using the methods of “diatomic complexes” in molecules, CNDO/2 and “atom-atomic” potentials. The formation of AS is preceded by physical adsorption of an organometallic compound (the homogeneous component) on the surface of the crystals of Ti and V trichlorides (the heterogeneous component). At this stage, the composition and the relative numbers of active sites different in their stereoregulating functions are clearly defined. During the chemisorption step, active sites of polymerisation are formed. For the most part they have a specific bimetallic crown structure of the “tunnel” (the U'-site) on α-(γ-, δ-)TiCl 3 (VCl 3) or the “flower” type on β-TiCl 3 and are formed by the atoms of Ti, Al (Be, Mg, Li), R and Cl. The stereospecific structure of the AS of polymerisation determines the stereospecific action of catalysts and the polymerisation rate. Stereospecific polymerisation of dienes involves the participation of two metal atoms and the surrounding ligands (bimetallic catalysis), with the monomeric molecules activated via the “push-pull” mechanism followed by “stapling” at the TiR bond of the bridge bond TiRMe.