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Sidearm effect in (thio)urea/alkoxide‐mediated ring‐opening polymerization of cyclic esters
Author(s) -
Zhu Ningning,
Behzadi Shabnam,
Si Guifu,
Tan Chen
Publication year - 2021
Publication title -
polymer international
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.592
H-Index - 105
eISSN - 1097-0126
pISSN - 0959-8103
DOI - 10.1002/pi.6169
Subject(s) - thio , moiety , lewis acids and bases , chemistry , polymerization , polymer chemistry , catalysis , alkoxide , bifunctional , ring opening polymerization , thiourea , medicinal chemistry , organic chemistry , polymer
Abstract Thiourea and urea catalysts have received much attention in the field of ring‐opening polymerization. In the (thio)urea/alkoxide catalytic system, sidearm groups can influence the catalytic performance of the organocatalyst moiety. In this work, a series of (thio)ureas bearing 2‐, 3‐ and 4‐pyridyl moieties were designed and synthesized. The (thio)ureas bearing a 2‐pyridyl group exhibited much higher catalytic activities than the (thio)ureas bearing 3‐ or 4‐pyridyl groups, suggesting a sidearm effect. Both crystal data and computational studies indicated that 2‐pyridyl can form an intramolecular hydrogen bond with the NH moiety, resulting in a Brønsted base/Lewis acid bifunctional catalytic system. Furthermore, the catalyst was stimuli‐responsive in Lewis acid/base‐modulated ring‐opening polymerization. Coordination between the Lewis acid BEt 3 and the catalyst was found to terminate the polymerization. Subsequently, the coordinated species was cleaved using the Lewis base bicyclo[2.2.2]‐1,4‐diazaoctane, resulting in the reactivation of the catalyst. © 2020 Society of Chemical Industry