Butadiene and 2-Substituted 1,3-Butadienes

The polymerization of a 1,3-diene such as 1,3-butadiene, isoprene, and chloroprene can lead to cis and trans isomers when polymerization occurs by a 1,4-polymerization. On the 

The situation is exactly analogous to the polymerization of monosubstituted alkenes the various polymer structures would be those in Fig. 8-1 with R = — CH=CH2. With chloroprene and isoprene, the possibilities are enlarged since the two double bonds are substituted differently. Polymerizations through the 1,2- and 3,4-double bonds do not yield the same product as they would in 1,3-butadiene polymerization. There are, therefore, a total of six structures possible—corresponding to isotactic, syndiotactic, and atactic structures for both 1,2- and 

From the practical viewpoint, the more important products from 1,3-dienes are those that occur by 1,4-polymerization of the conjugated diene system, for example, for isoprene, we obtain 

4-Polymerization leads to a polymer structure (VII) with a repeating alkene double bond in the polymer chain. The double bond in each repeating unit of the polymer chain is a site of steric isomerism since it can have either a cis or a trans configuration. The polymer chain segments on each carbon atom of the double bond are located on the same side of the double 

It should be noted that both carbon atoms of the double bond in VIII and IX are achir-otopic stereocenters. Interchange of the groups attached to one or the other carbon of the double bond converts VIII into IX and vice versa. 

---