Stereoregulation in the polymerization of methyl α‐ethylacrylate by n‐BuLi in toluene

Abstract

The polymerization of methyl α‐ethylacrylate was carried out in toluene by n‐BuLi at various temperatures. The yield of the polymer decreased with increase in the polymerization temperature and at 30°C and above no polymer was obtained, indicating that the ceiling temperature of this monomer lay between 0 and 30°C. The isotacticity increased with an increase in the polymerization temperature and at 0°C a highly isotactic polymer was obtained. The fractionation of the polymer obtained at −78°C showed that the polymer was a mixture of isotactic and syndiotactic ones. Upon the addition of a small amount of methanol or water in the polymerization mixture the isotacticity of the polymer increased while the yield decreased. Syndiotactic polymer was obtained in the polymerization by n‐BuLi in tetrahydrofuran as well as by diisobutyl aluminum diphenylamide in toluene.

Revisiting the Anionic Polymerization of Methyl Ethacrylate

“…This finding was corroborated with 13 C NMR analysis of PMEA in CDCl 3 at 25 °C where the quarternary carbon of the PMEA backbone exhibits primarily an rm triad sequence and smaller rr and mm signals of roughly equal size (Figures S8 and S9, Supporting Information). This contrasts the mostly syndiotactic microstructure reported following polymerization in THF at −78 °C using n ‐BuLi as initiator; it should be noted that only a 2% yield was reported and a 36:1 monomer to initiator ratio was used . PMMA is typically syndiotactic under these conditions .…”

“… 1 H NMR spectrum (CDCl 3 , 25 °C) of PMEA homopolymer. The left inset enlarges the methyl ester proton peaks (3H per repeat unit, δ: 3.60–3.50 ppm) which provide qualitative insight on PMEA backbone tacticity ( I – isotactic, H – heterotactic, S – syndiotactic, as reported by Hatada et al) . The right inset enlarges the peak associated with two DPHLi end‐group methyl protons (6H per polymer chain, δ: 0.57–0.45 ppm) which was integrated versus the methyl ester protons for calculation of final PMEA M n .…”

“…The . [6] The right inset enlarges the peak associated with two DPHLi end-group methyl protons (6H per polymer chain, δ: 0.57-0.45 ppm) which was integrated versus the methyl ester protons for calculation of final PMEA M n . same procedure was used to retrieve a sample of the PtBS seg ment and M n was determined by MALLSSEC analysis using the dn/dc value of 0.141 mL g −1 for PtBS in THF at 25 °C.…”

“…Two reports by Yuki and co‐workers describe attempts to anionically polymerize MEA with n ‐BuLi in different solvents (toluene, THF, diethyl ether) and varying temperatures (−78 to 30 °C). Yields were generally low (<50%) and characterization limited to the resulting tacticity of the PMEA backbone (vide infra) …”

“…Yields were generally low (<50%) and characterization limited to the resulting tac ticity of the PMEA backbone (vide infra). [6,7] Over the decades since those reports, large strides have been taken toward the improvement of purification, reagents, equipment, and strategies for anionic polymerization. [8][9][10][11] This is especially true for alkyl (meth)acrylate based mono mers which often present challenges due to the electrophilicity of the ester carbonyl and the propensity for competing eno late chemistry.…”