Coordination polymerization dienes

Stereoregular Polymerization of Dienes. Coordination polymerization exhibiting high degree of chemo- and stereoselectivity is the method of choice to synthe-size c -1,4-polybutadiene the commercially most important product (see... 

Other mechanistic pathways have been proposed, in particular a so-called outer-sphere mechanism (similar to a pericyclic allylic transposition) by Hugues and Powell. Although they are probably relevant to some stoichiometric reactions of -allyl complexes with dienes, they do not seem to fit the characteristic experimental features of these dienes coordination polymerizations. 

Coordination polymerization of isoprene using Ziegler-Natta catalyst systems (Section 6 21) gives a material similar in properties to natural rubber as does polymerization of 1 3 butadiene Poly(1 3 buta diene) is produced in about two thirds the quantity of SBR each year It too finds its principal use in tires... 

Stereochemistry Coordination Polymerization. Stereoisomerism is possible in the polymerization of alkenes and 1,3-dienes. Polymerization of a monosubstituted ethylene, such as propylene, yields polymers in which every other carbon in the polymer chain is a chiral center. The substituent on each chiral center can have either of two configurations. Two ordered polymer structures are possible — isotactic (XII and syndiotactic (XIII) — where the substituent R groups on... 

Osakada, K. and Takeuchi, D. Coordination Polymerization of Dienes, Allenes, and Methyl-enecydoalkanes. Vol. 171, pp. 137-194. 

The ionic chain polymerization of unsaturated linkages is considered in this chapter, primarily the polymerization of the carbon-carbon double bond by cationic and anionic initiators (Secs. 5-2 and 5-3). The last part of the chapter considers the polymerization of other unsaturated linkages. Polymerizations initiated by coordination and metal oxide initiators are usually also ionic in nature. These are called coordination polymerizations and are considered separately in Chap. 8. Ionic polymerizations of cyclic monomers is discussed in Chap. 7. The polymerization of conjugated dienes is considered in Chap. 8. Cyclopolymerization of nonconjugated dienes is discussed in Chap. 6. 

The importance of coordination polymerization of alkenes and dienes is evident when it is noted that more than 40 billion pounds of polymers were produced by this route in the United States in 2001. This corresponds to 35 10% of the total industrial production of polymers from monomers containing carbon-carbon double bonds. 

Conjugated dienes (1,3-butadiene, isoprene) have suitable nucleophilicity to undergo cationic polymerization. There is, however, not much practical interest in these processes since the polymers formed are inferior to those produced by other (free-radical, coordination) polymerizations. A significant characteristic of these polymers is the considerably less than theoretical unsaturation due to cyclization processes.132 A fully cyclized product of isoprene has been synthesized163 by constant potential electrolysis in CH2C12. 

The mechanism of coordination polymerization of 1,3-butadiene and, in general, that of conjugated dienes follows the same pathway discussed for alkene polymerization that is, monomer insertion into the transition metal-carbon bond of the growing polymer chain occurs. One important difference, however, was recognized very early.47,378,379 In the polymerization of dienes the growing chain end is tt-allyl complexed to the transition metal ... 

Polydienes. The most important diene homopolymers are polybutadiene and polyisoprene produced by anionic or coordination polymerization.184,186,187,487 189 Highly purified starting materials free from acetylenes, oxygen, and sulfur compounds are required. 

Otsuka et al. (110, 112) studied the polymerization of butadiene in the presence of an aged Co2(CO)8/2 MoC15 catalyst. The product obtained was predominantly an atactic poly(l,2-butadiene), the 1,2-structure being favored by low reaction temperature (e.g., at 40° C, 97% 1,2 at 30° C, > 99% 1,2). Similar experiments with a Ni(CO)4/MoCl5 catalyst yielded a polymer with 85% cis- 1,4-structure. The results of Otsuka et al. have been confirmed by Babitski and co-workers (8), who studied the polymerization of butadiene by a large number of binary catalysts, based on transition metal halide, transition metal carbonyl combinations. These systems are of interest as further examples of alkyl-free coordination polymerization catalysts for dienes (9, 15a, 109). Little is known of the origins of stereospecificity of these reactions. 

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