Recent views on the mechanism of diolefin polymerization with transition metal initiator systems

• Published in: Progress in polymer science 1991, Vol.16 (2), p.405-441
• Main Authors: Porri, Lido, Giarrusso, Antonino, Ricci, Giovanni
• Format: Article
• Language: English
• Subjects: Applied sciences; Exact sciences and technology; Organic polymers; Physicochemistry of polymers; Polymerization; Preparation, kinetics, thermodynamics, mechanism and catalysts
• ISSN: 0079-6700; 1873-1619
• DOI: 10.1016/0079-6700(91)90024-F

Recent views on the mechanism of formation of the stereoregular diolefin polymers with transition metal initiator systems are reported. Two aspects are examined in detail, i.e. the factors that determine the exceptionally high chemoselectivity and stereoselectivity of these initiator systems. Three classes of initiatory systems based on transition metals effective for diolefin polymerization are: systems derived from an aluminum alkyl and a transition metal compound (the Ziegler--Natta initiator systems); systems not containing preformed metal--C bonds; and systems based on allyl derivatives of transition metals. Stereoregular polymers can be obtained with initiator systems of each of the three classes. The polymerization using these systems is an insertion polymerization. Several basic aspects of the mechanism of the polymerization of diolefins with the transition metal-based initiator systems are clarified. These include the factors that determine the chemoselectivity with the most common homogeneous initiator systems; the relationship between the formation of cis-1,4 vs. trans-1,4 units and the anti /syn isomerization of the last polymerized unit; and the formation of cis-1,4 iso- or syndiotactic poly(1,3-pentadiene) and the formation of syndiotactic 1,2 polybutadiene.