Synthesis of well-defined poly(p-alkoxystyrene) by anionic polymerization in the presence of di-n-butylmagnesium

This study demonstrates the necessity of introducing di-n-butylmagnesium (n-Bu₂Mg) additives to synthesize precisely controlled polymers through anionic polymerization of p-alkoxystyrene monomers at −40 °C. Without additives, 4-tert-butoxystyrene (BSt) and 4-(1-ethoxy ethoxy) styrene (EESt) are polymerized using sec-butyllithium (s-BuLi) in tetrahydrofuran (THF) solvent, yielding a molecular weight distribution (MWD) of 1.36. However, the MWD is strictly controlled to 1.05–1.06 after adding n-Bu₂Mg in more than 30 times the amount of s-BuLi, resulting in an accurately designed molecular weight. Therefore, n-Bu₂Mg effectively suppresses side reactions that could occur at the polymerization temperature of −40 °C in the Schlenk reactor. Interestingly, the polymerization reaction of styrene monomer proceeds when n-Bu₂Mg is mixed in THF solvent at −40 °C for an extended period, even without s-BuLi. This result suggests that, despite being a weak anionic initiator, n-Bu₂Mg can initiate polymerization due to the lower electron density of the styrene double bond compared to BSt or EESt. Based on these results, a precise copolymer with a narrow molecular weight distribution can be synthesized by initiating polymerization with s-BuLi within 20 s of adding n-Bu₂Mg to the mixed monomers of styrene and EESt.