Internal Lewis pair enhanced H-bond donor: boronate-urea and tertiary amine co-catalysis in ring-opening polymerization. Issue 44 (25th October 2016)

• Record Type: Journal Article
• Authors: Xu, Songquan; Sun, Herui; Liu, Jingjing; Xu, Jiaxi; Pan, Xianfu; Dong, He; Liu, Yaya; Li, Zhenjiang; Guo, Kai
• Is Part Of: Polymer chemistry. Volume 7:Issue 44(2016)
• Page Start: 6843
• Page End: 6853
• Publication Date: 2016-10-25
• Subjects: Polymers -- Periodicals; Macromolecules -- Periodicals; Polymerization -- Periodicals; 547.705
• DOI: 10.1039/c6py01436d
• Languages: English
• ISSNs: 1759-9954

Abstract

Abstract : A new protocol of internal Lewis pair enhanced H-bond (LPHBD) catalysis for ring opening polymerisation was developed using boronate-urea (BU) as a representative LPHBD combined with tertiary amines. Abstract : Co-catalysis with an H-bond donor (HBD) and base has been an important bifunctional catalytic system for polymerizations. The development of strong HBDs is a continuing quest in the design of more efficient H-bonding catalysts. Internal Lewis pair enhanced H-bond donors (LPHBDs) as strong HBDs have not been explored for polymerizations. Here we report that boronate-urea (BU) as a representative LPHBD, combined with (−)-sparteine as the base, promoted fast ring-opening polymerization (ROP) ofl -lactide (LLA) at room temperature, which featured high conversions (up to 99%), predicted molecular weights (from 2.58 to 17.2 kg mol −1 ), and narrow dispersities ( Đ ≤ 1.16). A bifunctional synergistic activation mechanism was proposed and supported by NMR titrations. The controlled/living nature of the ROP for LLA was confirmed by kinetics and chain extension experiments. 1 H NMR, SEC, and MALDI-ToF MS analyses strongly indicated that the obtained PLAs were the designated ones. The successful synthesis of well-defined poly(trimethylene carbonate)- block -poly(l -lactide) verified that the catalytic ROP was of a controlled/living nature, and suggested that the LPHBD binary catalysis system is generally applicable. Taken together, we present a new protocol of internal Lewis pair enhanced H-bond (LPHBD) catalysis in ROP. Boronate-urea (BU) as a representative LPHBD is mild, tunable and it is more efficient than the common urea; it is nicely compatible with tertiary amines. BU combined with tertiary amines is a generally workable polymerization tool.