Zum Ablauf der Niederdruckpolymerisation der α‐Olefine. Komplexpolymerisation I

Abstract

Die bisher bekannt gewordenen Befunde über die Niederdruck (ND)‐Olefinpolymerisation lassen sich unter dem einheitlichen Gesichtspunkt verstehen, daß die Polymerisation innerhalb eines „electron deficient”︁‐Komplexes abläuft.

Specific Roles of Al‐Alkyl Cocatalyst in the Origin of Isospecificity of Active Sites on Donor‐Free TiCl4/MgCl2 Ziegler‐Natta Catalyst

“…These evidences clearly show that the IS 3 sites can also be formed through the interaction between the catalyst and cocatalyst even in the absence of electron donor. As it is well known that the activation (alkylation with reduction) of TiCl 4 with TEA is an ultra-fast reaction, in which the active sites regardless of stereospecificity can be formed instantly after the instant contact of these two kinds of molecules.…”

“…[2] In spite of great research efforts in this field since 1953, the level of the mechanistic understanding of these catalysts has been far from satisfactory. Among the enormous polymerization mechanisms proposed in the literature, the most important ones are the Cossee-Arlman monometallic mechanism [3] and the bimetallic mechanism proposed by Sinn et al [4] and Natta. [5] There are a lot of experimental evidences favoring both mechanisms.…”

Catalytic Olefin Polymerization

“…Kissin et al [335,365] propose a model (cf Figure 28) where the catalytic center contains a transition metal which has two vacant octahedral coordination sites located on faces (001) of violet TiCI 3 , resulting from the reaction with the organometallic compound. Bimetallic catalytic centres have been proposed by Patat and Sinn [404] who suggest the growing polymeric chain to be bridge linked to both metal atoms (cf scheme c, Figure 24). Pino et al [372] propose a bimetallic model where the two metal atoms may also be of the same nature and where one of the metal atoms forms a 1t bond with the olefin whereas the other is bound to the growing chain (cf, scheme g, Figure 24).…”

Ziegler–Natta Catalysis

“…A similar mechanism was proposed by Pa tat and Sinn in 1958. 20 Here again the alkene is polarized, this time by a TiClJ cation, before inserting into an aluminium-alkyl bond (Scheme 9). A mechanism suggested by Boor saw the insertion as a concerted process (Scheme 10 …”