Amidinium pyridinolate ion pair organocatalyst for ring-opening polymerizations of cyclic esters

Fengzhen Guo, Yaling Yin, Zhenjiang Li, Yue Xu, Shaoju Cao, Ziqi Liu, Yanqi Shi, Chunyu Li, Kai Guo

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Abstract

Ion pair organocatalyst composed of a positively charged hydrogen-bond donor (HBD+) and a nucleophilic anion (A) was proposed for ring-opening polymerizations (ROPs) of cyclic esters. The HBD+/A ion pair catalyst was readily accessible by mixing stoichiometric of super strong nitrogen bases (i.e. DBU, TBD, and MTBD) with 2-, 3-, and 4-pyridinols (4-PyOH). Nine ion pair catalysts were evaluated in bulk ROPs of L-lactide (LLA) by ratios of 25: 1: 1 of the monomer to the initiator and to the catalyst at 140 °C, in which the DBUH+/4-PyO pair showed optimal performances in producing polylactide (PLLA) by high conversion (95 %) in 15 min. Under the catalysis of DBUH+/4-PyO ion pair, PLLA of predicted molecular weights (Mn,NMR = 3.3–23.9 kg·mol−1) and narrow dispersity (Ð = 1.10–1.25) was prepared; ROPs of trimethylene carbonate (TMC), δ-valerolactone, and ε-caprolactone, as well as diblock-copolymers of TMC and LLA were all successful in the bulk. Bifunctional catalytic mechanism of the ion pair via activation of the monomer with the cationic HBD+ and activation of the initiator/chain-end with anion A was suggested and validated by NMR titrations. The design principle of H-bonding cation and nucleophilic anion ion pair organocatalyst featured easy access and multiple combinations paved avenues to wider scope of catalytic polymerizations.

Original languageEnglish
Article number113848
JournalEuropean Polymer Journal
Volume229
DOIs
StatePublished - 16 Apr 2025

Keywords

  • Amidine
  • Ion pair
  • Organocatalysis
  • Pyridinol
  • Ring-opening polymerizations

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