Conjugated Diene Monomers

This discussion of chain polymerization has centered on free-radical polymerization of an ethenic monomer. Conjugated dienes such as 1,3-butadiene often polymerize as bifunctional monomers with 1,4-addition rather than as tetrafunctional monomers. 

One double bond remains in the main chain for each monomer that reacts. Free-radical polymerization can also produce a 1,2 form of addition at the same time, so that the polymer that results may have some unsaturated side groups and perhaps even some network formation. Ionic and coordination complex schemes of 

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Conjugated dienes can be polymerized just as simple alkenes can (Section 7.10). Diene polymers are structurally more complex than simple alkene polymers, though, because double bonds remain every four carbon atoms along the chain, leading to the possibility of cis-trans isomers. The initiator (In) for the reaction can be either a radical, as occurs in ethylene polymerization, or an acid. Note that the polymerization is a 1,4-addition of the growing chain to a conjugated diene monomer. 

A wide range of polymers are obtained from the addition of conjugate diene monomers, notably 1,3-butadiene, isoprene, and chloroprene ... 

The M[ZnR4] and M[A1R4]2 ate complexes (M = Ca, Sr, Ba) polymerize vinyl and conjugated diene monomers including styrene, methylmethacrylate, acrylonitrile, vinyl-ketones, isoprene and butadiene . The bimetallic complexes produce polymers of differing microstructure to that formed by simple alkaline-earth metal initiators, so that the presence of Zn or A1 influences the stereochemistry of propagation. Thus, polybutadiene obtained in benzene from a Ba-Zn initiator contains more than 90% 1,4-bonds (trans-1,4 75-81 %) ... 

Waymouth has polymerized silyl protected alcohols and amines, and non conjugated diene monomers, with cationic Group IV metallocene single site-catalysts. He has found that chiral [(EBTHI)ZrMc] X catalysts, where EBTHI = ethylene-1,2 bis(Ti -4,5,6,7-tetrahydro-l-indenyl), are more easily poisoned by silyl ethers than are [CP2 ZrMe] ] catalysts. Also [(EBTHI)ZrMe] X catalysts are inactive for the polymerization of 4-TMSO-l,6 heptadiene but readily polymerize with the more sterically hindered TBDMS protect monomer. 

Conjugated and Non-conjugated Diene Polymerizations 1,3-Butadienes, isoprene, and 1,3-pentadiene are the conjugated diene monomers most... 

There are many possible schemes for addition reactions of diene monomers from electronical and steric viewpoints. Because the monomer molecules arrange along the direction of the channels, a,co-addition may selectively take place in one-dimensional inclusion polymerization. Therefore, conjugated polyenes, such as dienes and trienes, may selectively polymerize by 1,4- and 1,6-addi-tion, respectively. 1,3-Butadiene polymerized via 1,4-addition exclusively in the chaimels of urea and perhydrotriphenylene. while the same monomer polymerized via both 1,2- and 1,4-additions in the channels of deoxycholic acid and apocholic acid. Moreover, we have to evaluate head-to-tail or head-to-head (tail-to-tail) additions in the case of dissymmetric conjugated diene monomers such as isoprene and 1.3-pentadiene. 

Kruse, R. (1979) Polymeric poly blend compositions toughened by addition of liquid polymers of a conjugated diene monomer , U.S. Patent 4,154,715. 

Figure 17 Asymmetric synthesis poiymerization of conjugated diene monomers.

FIGURE 17.10 Other conjugated diene monomers (a) 1-substituted butadienes (b) 2-substituted butadienes. 

This section focuses on the regio- and stereostructure of CHD polymers, because very few cyclic conjugated diene monomers besides CHD can be polymerized. Although poly(cis,ds-l,3-cycloheptadiene) and poly(cty,cA-l,3-cyclooctadiene) were synthesized by cationic polymerization, the obtained products were found to be oligomers and their detailed structures were not clear. 

The NMP of conjugated diene monomers such as butadiene and more importandy isoprene was studied from the early times of the technique by both the groups of Keoshkerian et for isoprene and Pradel a for butadiene, in... 

Although conjugated diene monomers are capable of exhibiting a functionality of four in polymerization reactions, the important examples are linear or branched polymers with residual unsaturation (Appendix 16.E). Natural rubber (cis-l,4-polyisoprene)... 

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