Microstructures of polydienes prepared from alkyllithium

The stereochemistry of polymerization of isoprene and butadiene by means of alkyllithium initiators was examined. The stereochemistry of polybutadiene and polyisoprene responded to the same variables in anionic polymerization. Microstructure of both polymers is sensitive to initiator level, solvent type, and polymerization temperature, but is independent of monomer concentration, conversion and initiator structure. The heat activation energy leading to 1,2 addition is greater than that leading to trans‐1,4 addition (1200 cal./mole). The exact pictorial sequence leading to stereospecific polymerization of dienes by means of alkyllithium is still not clear. However, it seems to involve the orientation of the incoming monomer units by association and passage through a transition complex in which all bonds are largely covalent in character and within which polymerization occurs.