The stereoregular polymerization of isoprene with lithium and organolithium compounds

Abstract

All of the alkali metals catalyze the polymerization of dienes such as butadiene and isoprene. A stereoregular polymer is obtained when the polymerization of isoprene is catalyzed by lithium or organolithium compounds in the absence of oxygen contaning solvents. The polymer has molecular structure, configuration, and physical properties similar to Hevea rubber, and a microstructure comprised of 93–95% cis‐1,4 and 5–7% 3,4 addition. The polymerization appears to proceed by way of an homogeneous catalytic mechanism. Stereoregularity is a result of cis coordination between a monomer molecule with a carbon bound lithium atom and formation of a six membered, cyclic, activated complex. This complex owes its relative stability to the capability of the lithium atom to undergo hybridization and to behave as an atom with considerable divalent character. The observed effects of temperature, catalyst concentration, type of solvent, and effect of Lewis bases such as ethers on the microstructure of these isoprene polymers are consistent with the catalytic reaction mechanism advanced.