Polymerization of butadiene with π‐allylic catalysts

Abstract

The polymerization of butadiene‐1,3 with π‐allylic nickel complexes has been studied. π‐Allyl(crotyl) nickel halides themselves are shown to initiate stereospecific polymerization. The stereospecificity of the catalysts is determined by the nature of halogen bonded to metal. In the presence of chlorine complexes cis‐1,4‐polybutadienes are obtained, the iodine ones giving trans‐1,4‐polybutadienes. Lewis acids change the stereospecificity of π‐crotyl nickel bromide and iodide, favoring cis‐1,4‐structure formation. The polymerization of butadiene with rhodium compounds has been investigated. The experimental evidence indicates that the polymerization involves π‐allylic complexes. An attempt is made to explain the mechanism of polymer chain unit formation on the basis of π‐allylic structure of active sites in diene polymerization by transition metal compounds.

The Mechanism of Polymerization of Butadiene by “Ligand-Free” Nickel(II) Complexes

“…The stereoselective polymerization of butadiene (BD) has been investigated using a variety of transition metal [1][2][3][4] and lanthanide catalysts. 5 Numerous Ni(II) π-allyl complexes have been used as initiators, [6][7][8][9] but the most reactive one identified to date is "ligandfree" Ni(II) wrap-around complex A (Scheme 1), which yields polybutadiene (PBD) exhibiting 93% cis-1,4 enchainment. 10,11 The chain growth mechanism proposed by Taube and Tobisch, based largely on DFT calculations, [12][13][14][15] is shown in Scheme 1.…”

Recent Advances in Polybutadienes

“…Polybutadiene controlled almost completely to trans-1,4 microstructure is obtained with rhodium catalysts [4] and vanadium catalysts [5]. The polybutadiene of 80-90% trans-1,4 content produced with vanadium catalysts [6] has outstanding roll processability and extrudability; although the wear resistance of vulcanisates was some 20-70 times better than that of styrene-butadiene copolymer rubber (SBR) or natural rubber, the material had drawbacks of highly temperature dependent hardness and large hysteresis loss and is no longer produced.…”

The Polymerization of 2,4-Hexadiene. Stereoregular Polymer and the Mechanistic Study for Its Preparation

“…To elucidate the difference in stereocontrol in the polymerization of diene compounds, several mechanisms have been proposed from the point of the coordination of the monomer or the structure of the propagating active end. [11][12][13][14][15][16][17][18] Recently, much information has been derived on the structure of the terminal active unit by the nmr technique.19,20 Nevertheless, the mechanism of stereoregular polymerization of diene compounds by transition-metal catalysts still remains unsolved. It would be desirable for clarification of the polymerization mechanism to examine the polymerization of 2,4-hexadiene, which has three isomeric forms, by transition-metal catalysts.…”