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Lewis Pair Polymerization of Epoxides via Zwitterionic Species as a Route to High‐Molar‐Mass Polyethers
Author(s) -
Walther Patrick,
Krauß Annabelle,
Naumann Stefan
Publication year - 2019
Publication title -
angewandte chemie international edition
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 5.831
H-Index - 550
eISSN - 1521-3773
pISSN - 1433-7851
DOI - 10.1002/anie.201904806
Subject(s) - monomer , polymerization , molar mass , chemistry , polymer chemistry , epoxide , propylene oxide , nucleophile , copolymer , anionic addition polymerization , ring opening polymerization , catalysis , degree of polymerization , organic chemistry , polymer , ethylene oxide
A dual catalytic setup based on N‐heterocyclic olefins (NHOs) and magnesium bis(hexamethyldisilazide) (Mg(HMDS) 2 ) was used to prepare poly(propylene oxide) with a molar mass ( M n ) >500 000 g mol −1 , in some cases even >10 6 g mol −1 , as determined by GPC/light scattering. This is achieved by combining the rapid polymerization characteristics of a zwitterionic, Lewis pair type mechanism with the efficient epoxide activation by the Mg II species. Transfer‐to‐monomer, traditionally frustrating attempts at synthesizing polyethers with a high degree of polymerization, is practically removed as a limiting factor by this approach. NMR and MALDI‐ToF MS experiments reveal key aspects of the proposed mechanism, whereby the polymerization is initiated via nucleophilic attack by the NHO on the activated monomer, generating a zwitterionic species. This strategy can also be extended to other epoxides, including functionalized monomers.