Investigation of the mechanism of chain termination and transfer by 1,2‐butadiene in the butyllithium‐initiated polymerization of 1,3‐butadiene in non‐polar solvents

Abstract 1,2‐Butadiene (BD‐1,2) was shown to be a chain terminating/transferring agent in the butyllithium (nBuLi)‐initiated polymerization of 1,3‐butadiene in hexane solvent by Adams et al. Based on model reactions and circumstantial evidence they proposed that BD‐1,2 terminates the polymerization by extracting Li from the living chain end. The lithiated BD‐1,2 formed may initiate new chains causing chain transfer or isomerize to lithiated ethylacetylene (system. name: 1‐butyne), a nonactive species. This paper proposes a modification of the mechanism suggested by Adams et al. Kinetic investigations of the model reaction between nBuLi and BD‐1,2 by infrared spectroscopy have shown that the first, and rate‐determining, step is the isomerization of BD‐1,2 to ethylacetylene, followed by lithiation. It is proposed that the lithiated ethylacetylene can initiate new chains, thereby causing chain transfer.