Homopolymerization and Copolymerization of Substituted Butadienes other than Isoprene

Homopolymerization and Copolymerization of Substituted Butadienes (other than Isoprene) 

Substituted conjugated 1,3-butadienes are especially interesting with regard to conclusions about the mechanism of the polyinsertion reaction. From the substitution pattern of the monomers and the microstructure of the formed polymers mechanistic conclusions can be drawn. These issues are addressed in detail in review articles by Porri et al. [50,141,486]. 

Monomers such as E-l,3-pentadiene (piperylene) and E-2-methyl-l,3-pentadiene give 1,4-polymers with an asymmetric carbon atom. Therefore, these monomers in principle will result in polymers with an isotactic, syndio-tactic or atactic structure. 

Early studies on the homopolymerization of E-l,3-pentadiene yielded polymers with a high cis-1,4-content and an isotactic structure, whereas E-2-methyl-l,3-pentadiene resulted in a polymer with a mixed czs-1,4/transit-structure [487-492]. Investigations on the polymerization of E-1,3-pentadiene with the system NdN/TIBA/DEAC partially support these findings as a poly(l,3-pentadiene) with a cis- 1,4-threo-disyndiotactic structure was obtained [492]. A somewhat lower cis- 1,4-content of 70% was obtained when the polymerization of E-l,3-pentadiene was catalyzed by (CF3COO)2NdCl/TEA [493,494]. When 2,3-Dimethyl-1,3-butadiene is polymerized with the catalyst NdN/TIBA/EtAlC the resulting poly(2,3-dimethyl-butadiene) predominantly contains cis-1,4-units [495,496]. 

A study in which BD and E-l,3-pentadiene were homopolymerized by the application of the same ternary Nd-carboxylate-based system revealed a significant drop in cis- 1,4-structures from 95% (BD) to 80% (E-1,3-pentadiene) [490,491]. 

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