Chain transfer in anionic polymerization. Determination of chain‐transfer constants by using carbon‐14‐labeled chain transfer agents

Abstract

A method is described in which ¹⁴C‐labeled chain‐transfer agents are employed to measure chain‐transfer constants in anionic polymerization as low as 10⁻⁶. Each chain‐transfer step incorporates one molecule of the chain‐transfer agent into the polymer so that measurement of the activity and conversion allows evaluation of the chain‐transfer constant. This method is independent of the initiator concentration and efficiency, making the technique especially useful when problems with the initiator are encountered. The experimental procedure is described in detail for the case of chain transfer to toluene in the n‐butyllithium‐initiated polymerization of styrene, where C_RH was found to be 5 × 10⁻⁶. A mathematical treatment is given showing the relationship between the degree of polymerization (DP_n) and chain transfer.