Block Copolymerization of Lactide and an Epoxide Facilitated by a Redox Switchable Iron-Based Catalyst

• Published in: Angewandte Chemie 2016-04, Vol.128 (17), p.5337-5340
• Main Authors: Biernesser, Ashley B., Delle Chiaie, Kayla R., Curley, Julia B., Byers, Jeffery A.
• Format: Article
• Language: eng ; ger
• Subjects: Block copolymers; Blockcopolymere; Catalysts; Cationic polymerization; Chemistry; Conducting polymers; Copolymerization; Copolymers; Cyclohexene; Eisen; Epoxides; Iron; Monomers; NMR; Nuclear magnetic resonance; Oxidation; Oxides; Polymerization; Redoxchemie; Redoxschalter; Ringöffnungspolymerisation; Solubility; Valence
• ISSN: 0044-8249; 1521-3757
• DOI: 10.1002/ange.201511793

A cationic iron(III) complex was active for the polymerization of various epoxides, whereas the analogous neutral iron(II) complex was inactive. Cyclohexene oxide polymerization could be “switched off” upon in situ reduction of the iron(III) catalyst and “switched on” upon in situ oxidation, which is orthogonal to what was observed previously for lactide polymerization. Conducting copolymerization reactions in the presence of both monomers resulted in block copolymers whose identity can be controlled by the oxidation state of the catalyst: selective lactide polymerization was observed in the iron(II) oxidation state and selective epoxide polymerization was observed in the iron(III) oxidation state. Evidence for the formation of block copolymers was obtained from solubility differences, GPC, and DOSY‐NMR studies. Die redoxkontrollierte Blockcopolymerisation von Cyclohexenoxid und Lactid beruht auf der Eigenschaft eines Bis(imino)pyridin‐Eisen‐Bisalkoxid‐Komplexes, das Lactid im Eisen(II)‐ und das Epoxid im Eisen(III)‐Zustand zu polymerisieren, nicht jedoch umgekehrt. Diblockcopolymere wurden in Gegenwart beider Monomere hergestellt, indem entweder mit dem Eisen(II)‐ oder dem Eisen(III)‐Katalysator angefangen und ein Redoxschalter in situ eingesetzt wurde.