Reaching High Stereoselectivity and Activity in Organocatalyzed Ring-Opening Polymerization of Racemic Lactide by the Combined Use of a Chiral (Thio)Urea and a N-Heterocyclic Carbene.
Materials Chemistry; Inorganic Chemistry; Polymers and Plastics; Organic Chemistry
Abstract :
[en] Stereochemical control during polymerization is a key strategy of polymer chemistry to achieve semicrystalline engineered plastics. The stereoselective ring-opening polymerization (ROP) of racemic lactide (rac-LA), which can lead to highly isotactic polylactide (PLA), is one of the emblematic examples in this area. Surprisingly, stereoselective ROP of rac-LA employing chiral organocatalysts has been under-leveraged. Here we show that a commercially available chiral thiourea (TU1), or its urea homologue (U1), can be used in conjunction with an appropriately selected N-heterocyclic carbene (NHC) to trigger the stereoselective ROP of rac-LA at room temperature in toluene. Both a high organic catalysis activity (>90% monomer conversion in 5-9 h) and a high stereoselectivity (probability of formation of meso dyads, Pm, in the range 0.82-0.93) can be achieved by thus pairing a NHC and a chiral amino(thio)urea. The less sterically hindered and the more basic NHC, that is, a NHC bearing tert-butyl substituents (NHCtBu), provides the highest stereoselectivity when employed in conjunction with the chiral TU1 or U1. This asymmetric organic catalysis strategy, as applied here in polymerization chemistry, further expands the field of possibilities to achieve bioplastics with adapted thermomechanical properties.
Disciplines :
Chemistry
Author, co-author :
Zaky, Mohamed Samir; Laboratoire de Chimie des Polymères Organiques (LCPO), UMR 5629, Université de Bordeaux, INP-ENSCBP, 16 av, Pey Berland, 33607 PESSAC Cedex France
Wirotius, Anne-Laure; Laboratoire de Chimie des Polymères Organiques (LCPO), UMR 5629, Université de Bordeaux, INP-ENSCBP, 16 av, Pey Berland, 33607 PESSAC Cedex France
Coulembier, Olivier ; Université de Mons - UMONS > Faculté des Sciences > Service des Matériaux Polymères et Composites
Guichard, Gilles ; Univ. Bordeaux, CNRS, CBMN, UMR 5248, Institut Européen de Chimie et Biologie, 2 rue Robert Escarpit, F-33607 Pessac, France
Taton, Daniel ; Laboratoire de Chimie des Polymères Organiques (LCPO), UMR 5629, Université de Bordeaux, INP-ENSCBP, 16 av, Pey Berland, 33607 PESSAC Cedex France
Language :
English
Title :
Reaching High Stereoselectivity and Activity in Organocatalyzed Ring-Opening Polymerization of Racemic Lactide by the Combined Use of a Chiral (Thio)Urea and a N-Heterocyclic Carbene.
Minist?re de l'Enseignement sup?rieur, de la Recherche et de l'Innovation Agence Nationale de la Recherche Centre National de la Recherche Scientifique
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