Phosphoric acids catalyzed asymmetric kinetic resolution polymerization of benzyl substituted ε-caprolactones: Efficient protocol for stereogradient polycaprolactones

• Published in: European polymer journal Vol. 133; p. 109792
• Main Authors: Lv, Chengdong, Yang, Rulin, Xu, Guangqiang, Zhou, Li, Wang, Qinggang
• Format: Journal Article
• Language: English
• Published: Oxford Elsevier Ltd 15.06.2020; Elsevier BV
• Subjects: Asymmetric kinetic resolution polymerization; Asymmetry; Benzyl-ε-caprolactone; Catalysis; Catalysts; Chiral phosphoric acid; Enantiomers; Molecular weight; Molecular weight distribution; Phosphoric acid; Polymerization; Reaction kinetics; Reduction; Ring opening; Selectivity; Selectivity factor; Stereogradient polycaprolactone; Steric hindrance; Benzyl-ε-caprolactone; Selectivity factor; Stereogradient polycaprolactone; Asymmetric kinetic resolution polymerization; Chiral phosphoric acid
• ISSN: 0014-3057; 1873-1945
• DOI: 10.1016/j.eurpolymj.2020.109792

[Display omitted] •An asymmetric kinetic resolution polymerization of substituted ε-caprolactones.•Chiral phosphoric acids used as bifunctional organocatalysts.•Stereogradient polycaprolactones with controlled Mns and narrow PDIs.•The highest s-factor reached 7.2 during the polymerization.•An interesting phenomenon of chirality reduction was found. An asymmetric kinetic resolution polymerization (AKRP) of 2-benzyl-ε-caprolactone (2-BnCL) and 6-benzyl-ε-caprolactone (6-BnCL) has been developed. Phosphoric acids catalyze the ring-opening polymerizations smoothly, delivering stereogradient polycaprolactones with controlled molecular weights and narrow molecular weight distributions. At 50% conversions, the selectivity factors of this AKRP process are in a range of 1.9–2.5, which indicates clear dynamic differentiations of two enantiomers. Regarding the AKRP of 6-BnCL, a high selectivity factor of 7.2 is obtained at the early stage, and an interesting chiral reduction phenomenon is observed as reaction proceeding. Kinetic studies illustrate the enantiomorphic site control plays dominate role in this AKRP process, and a mismatch of chiral induction and chain steric hindrance is proposed to be responsible for the chiral reduction issue.