Synthesis of Liquid Polyisoprene via Anionic Chain Transfer Polymerization and Its 100-Fold Scale-Up in a 2-Liter Reactor

Abstract

The primary synthesis of liquid rubber via anionic polymerization requires substantial alkali metal initiators, resulting in high costs. This study introduces a metal-free chain transfer agent (CTA), 9,10-dihydroanthracene (DHA), into the anionic polymerization of isoprene (Ip). A series of liquid polyisoprenes (PIp) with number-average molecular weights (M_n) ranging from 2100 to 6800 g/mol were synthesized. Furthermore, the correlation between DHA, THF dosage, and reaction temperature and the resulting polymer structures was established. The results indicate that at 20°C, DHA induces chain transfer during the anionic polymerization of Ip. Moreover, higher dosages of both DHA and THF led to lower M_n and polydispersity index (PDI) of the resulting PIp, corresponding to a lower degree of polymerization (${\overline{X}}_n$). Concurrently, the initiator efficiency (E_I) and chain transfer constant (C_M) increased. Conversely, −25°C effectively suppressed chain transfer, while 60°C did not significantly promote the process. To validate its practical potential, a 100-fold scale-up experiment was performed. This yielded a series of liquid PIp with M_n below 2500 g/mol, PDI below 1.21, E_I greater than 20.0, and C_M greater than 2.8 × 10⁻². It provides crucial theoretical and experimental foundations for advancing the preparation technology of liquid rubber.