A one‐step procedure for the self‐switchable block copolymerization of monomer mixtures of epoxides, cyclic anhydrides, and lactide (LA) was developed by using simple organocatalysts without an ...external stimulus. This multicomponent polymerization bridges two catalytic cycles involving ring‐opening alternating copolymerization of epoxides with anhydrides and ring‐opening polymerization (ROP) of LA, in which the presence/absence of anhydrides in mixed feedstocks switched the ROP of LA off/on. The self‐switchable terpolymerization showed distinct noncoordinating and living nature, as well as perfect chemoselectivity. Different combinations of epoxides, anhydrides, and initiators enabled the generation of a variety of new block polyester polyols.
Admirable self‐control: A self‐switchable route to multiblock copolymers from three‐component feedstocks (see picture) was developed with commercially accessible organocatalysts. The one‐step procedure showed perfect chemoselectivity, living nature, and applicability to a wide range of monomers.
Full text
Available for:
BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
A simple and highly active catalytic process for ring-opening alternating copolymerization (ROAC) of cyclic anhydrides and epoxides still remains a key challenge. Herein, we have described an ...effective group of versatile and low-toxic zinc dicarbyl/amine Lewis pairs for the ROAC. The facile route showed a high catalytic activity (TOF ≤ 210 h −1 at 110 °C) and perfectly alternating selectivity (>99%). An unexpected highly regioselective ring-opening of asymmetric epoxides (PO, ECH and SO) was also achieved by the combination of zinc alkyls (or aryls) and amines. Of note, deprotonation side reaction of α-H of anhydrides with organic bases was uncovered, and subsequently was inhibited by using nonpolar solvents and Lewis acid/base pairs. Thus, an array of polyesters was synthesized by the coupling of various anhydrides (PA, CHA, SA and NA) and epoxides (CHO, PO, ECH and SO) using the same Lewis pairs. Furthermore, variable temperature 1 H NMR spectral and MALDI TOF MS analyses were performed to understand the possible mechanism and microstructure. The experimental results indicated that zwitterionic alkoxide and carboxylate intermediates alternately formed to enhance the ester repeat units in chain initiation and propagation. This work provides a simple and green catalytic strategy to prepare diversified polyesters from the ROAC process of cyclic anhydrides and epoxides with considerable catalytic activity and alternating selectivity.
A metal-free, highly regioselective and stereoregular ring-opening alternating copolymerization (ROAC) of monosubstituted epoxides with tricyclic anhydrides remains a challenge in the advancement of ...polyester synthesis. Herein, we described an effective group of organic dual catalysts for the ROAC, exhibiting a high catalytic activity (the highest TOF = 330 h −1 at 110 °C), narrow polydispersity (PDI < 1.20) and excellent alternating selectivity (ester > 99%) in a controlled manner. The ROAC of a variety of monosubstituted epoxides and tricyclic anhydrides was carried out under mild conditions. Of importance is the fact that highly regioselective insertion of epoxides has been realized by simple and metal-free catalysts in the ROAC, where the highest regioselectivity is up to 98% for aliphatic epoxides and glycidyl ethers at 80 °C. Styrene oxide bearing electron-withdrawing phenyl also showed a good regioselectivity of 78%. Besides, the complete suppression of epimerization and transesterification was achieved even at high conversion for a variety of tricyclic anhydrides. Furthermore, block and gradient copolymers were synthesized by the sequential addition strategy and one-pot terpolymerization. Accordingly, a green, regioselective and stereoregular fabrication of functional polyesters was realized for the first time by a metal-free process.
Poly(ester-
b
-ether)s, a kind of meaningful and potentially bio-based block copolymer, are typically synthesized
via
ring-opening polymerization (ROP) of cyclic esters initiated by the pre-prepared ...polyether macroinitiator. However, a multi-step procedure is required in this traditional method. Herein, we detailed a one-step selective copolymerization process of mixed monomers to precisely prepare poly(ester-
b
-ether) block copolymers, which could minimize the additional catalytic processes and organic reagents of the multi-step procedure. The strategy enables ring-opening alternating copolymerization (ROAC) of anhydrides with epoxides and ROP of epoxides sequentially in a closed system. Organic Lewis pairs were utilized to catalyze the selective copolymerization and were easily removed from the reaction system which avoided the metal residues in the copolymers. Regioselective and living copolymerization is realized by using cooperative organocatalysts, yielding the poly(ester-
b
-ether) with a controlled monomer sequence, high isotacticity and predictable molecular weight (MW). The optimized organocatalysis exhibits broad monomer adaptability and allows fabricating structurally diverse poly(ester-
b
-ether)s. Epimerization was suppressed even when tricyclic and bicyclic anhydrides were used, which enables the synthesis of stereoregular block copolymers. Significantly, well-defined block copolymers based on renewable succinic anhydride were achieved. A tandem copolymerization is also performed by using lactide as an external trigger which could switch the selective copolymerization to lactide polymerization. The study provides a new route to the facile synthesis of poly(ester-
b
-ether) block copolymers using a metal-free catalytic system.
A selective copolymerization strategy is developed for one-step precise synthesis of diverse poly(ester-
block
-ether)s from bio-based epoxides and anhydrides by using organocatalysts.
In this contribution, we thoroughly investigated the ring-opening alternating copolymerization (ROAC) of cyclic anhydride and epoxide by using commercially available alkali metal carboxylates (AMCs) ...as the simple and green initiators. The idea of our work is based on the coordination effects of epoxide on an AMC and the formation of AMC–epoxide adducts, which will weaken the interaction between metal cation and its carboxylate counterion and therefore render the carboxylate to feasibly attack epoxides in a nucleophilic manner at high temperature. The coordination effects of epoxide on the AMC could be proved by Fourier transform infrared (FT-IR) spectroscopy and density functional theory (DFT) calculations. AMCs could effectively catalyze the copolymerization of phthalate anhydride (PA) and cyclohexene oxide (CHO) in bulk at 110 °C, affording polyesters with perfectly alternating structure. Potassium acetate (KOAc) was able to copolymerize some common cyclic anhydrides and epoxide, allowing for the preparation of polyesters with structural diversity. Of note, KOAc could mediate ROAC of PA with propylene oxide (PO) with a high molar feed ratio of KOAc/PA/PO = 1:20 000:150 000, affording poly(PA-alt-PO) with high molecular weight (>100 kDa). Finally, two different polymerization mechanisms, including anionic polymerization and cooperative catalysis, have been proposed according to the interaction strength between metal cation and carboxylate anion. In the “cooperative catalysis” mechanism, the alkali metal cation served as the Lewis acid to activate epoxide and cyclic active species were generated.
Full text
Available for:
IJS, KILJ, NUK, PNG, UL, UM
The ring‐opening alternating copolymerization (ROAC) of biorenewable glycidyl ethers with 3,4‐dihydrocoumarin (DHC) was achieved by using metal‐free Lewis pair as catalyst. This mild process provided ...access to renewable polyesters with perfectly alternating structures and functional groups fidelity. Remarkably, we observed highly regioregular arrangement of substituents along with poly(phenol ether‐alt‐ester) backbone. A one‐step strategy to block copolymer could also be realized by terpolymerization of DHC, epoxides with cyclic anhydrides via pre‐rate‐determining selectivity. Post‐polymerization modification of the resultant polyesters was further performed by thiol‐ene click reaction of vinyl, Diels–Alder reaction of furyl, cleavage reaction of benzyl ethers and tetrazine click reaction. By incorporating two different pendant functional groups into a copolymer, combinatorial and selective functionalization was achieved for introducing additional functionality, giving a route to highly modifiable polyesters. Therefore, this work provides a paradigm for designing functional and regioregular polyesters as a green synthetic toolbox derived from organocatalysis and renewable feedstocks.
Full text
Available for:
BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
The mechanism for ring-opening polymerization (ROP) of lactide catalyzed by Zn(C 6 F 5 ) 2 –organic superbase Lewis pairs was investigated in the present work. Common organic superbases ...4-dimethylaminopyridine (DMAP), 1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene ( Mes NHC), 1,8-diazabicyclo5,4,0undec-7-ene (DBU), and 7-methyl-1,5,7-triazabicyclo4.4.0decane-5-ene (MTBD) were selected as the Lewis bases to work cooperatively with Zn(C 6 F 5 ) 2 . It was demonstrated that less sterically bulky DMAP could coordinate with the zinc atom and form classical Lewis acid–base adducts (CLA), whereas frustrated Lewis pairs (FLP) were obtained when bulky MTBD and DBU were used. Investigation into the polymerization behavior of lactide showed that the frustrated Lewis pair Zn(C 6 F 5 ) 2 /MTBD exhibited much higher activity in the polymerization of lactide and much lower temperature dependence compared with the Lewis adduct Zn(C 6 F 5 ) 2 /DMAP. Furthermore, there is a direct relationship between polymerization activity and the degree of “frustration”. The initiation reaction was further explored by in situ NMR at variable temperature. The interactions between Zn(C 6 F 5 ) 2 and the organic base in both CLA and FLP would be impaired at high temperature, and lactide was activated electronically by coordination to the Lewis acid Zn(C 6 F 5 ) 2 . In addition, NMR and MALDI-TOF analyses showed that the active species are zwitterionic species, in which each chain end bears one amine and one Zn(C 6 F 5 ) 2 moiety, respectively, and Zn(C 6 F 5 ) 2 associated with the amine closely. Based on these results, a possible mechanism involving bifunctional activation was proposed. Further kinetic studies showed that increasing the reaction temperature and solvent polarity can significantly enhance the chain initiation rate. These experimental results also demonstrated that the polymerization was initiated through the proposed mechanism.
A one‐step procedure for the self‐switchable block copolymerization of monomer mixtures of epoxides, cyclic anhydrides, and lactide (LA) was developed by using simple organocatalysts without an ...external stimulus. This multicomponent polymerization bridges two catalytic cycles involving ring‐opening alternating copolymerization of epoxides with anhydrides and ring‐opening polymerization (ROP) of LA, in which the presence/absence of anhydrides in mixed feedstocks switched the ROP of LA off/on. The self‐switchable terpolymerization showed distinct noncoordinating and living nature, as well as perfect chemoselectivity. Different combinations of epoxides, anhydrides, and initiators enabled the generation of a variety of new block polyester polyols.
Bewundernswerte Selbstbeherrschung: Ein selbstschaltender Weg zu Multiblockcopolymeren aus Dreikomponenten‐Rohstoffen (siehe Bild) wurde mit kommerziell verfügbaren Organokatalysatoren entwickelt. Das einstufige Verfahren zeigt eine perfekte Chemoselektivität und „lebendes” Verhalten und ist auf ein breites Spektrum von Monomeren anwendbar.
Full text
Available for:
BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
A simple and highly active catalytic process for ring-opening alternating copolymerization (ROAC) of cyclic anhydrides and epoxides still remains a key challenge. Herein, we have described an ...effective group of versatile and low-toxic zinc dicarbyl/amine Lewis pairs for the ROAC. The facile route showed a high catalytic activity (TOF ≤ 210 h
−1
at 110 °C) and perfectly alternating selectivity (>99%). An unexpected highly regioselective ring-opening of asymmetric epoxides (PO, ECH and SO) was also achieved by the combination of zinc alkyls (or aryls) and amines. Of note, deprotonation side reaction of α-H of anhydrides with organic bases was uncovered, and subsequently was inhibited by using nonpolar solvents and Lewis acid/base pairs. Thus, an array of polyesters was synthesized by the coupling of various anhydrides (PA, CHA, SA and NA) and epoxides (CHO, PO, ECH and SO) using the same Lewis pairs. Furthermore, variable temperature
1
H NMR spectral and MALDI TOF MS analyses were performed to understand the possible mechanism and microstructure. The experimental results indicated that zwitterionic alkoxide and carboxylate intermediates alternately formed to enhance the ester repeat units in chain initiation and propagation. This work provides a simple and green catalytic strategy to prepare diversified polyesters from the ROAC process of cyclic anhydrides and epoxides with considerable catalytic activity and alternating selectivity.
Simple and low-toxic Lewis pairs were introduced for ring-opening alternating copolymerization of anhydrides and epoxides to prepare diversified polyesters.
A metal-free, highly regioselective and stereoregular ring-opening alternating copolymerization (ROAC) of monosubstituted epoxides with tricyclic anhydrides remains a challenge in the advancement of ...polyester synthesis. Herein, we described an effective group of organic dual catalysts for the ROAC, exhibiting a high catalytic activity (the highest TOF = 330 h
−1
at 110 °C), narrow polydispersity (PDI < 1.20) and excellent alternating selectivity (ester > 99%) in a controlled manner. The ROAC of a variety of monosubstituted epoxides and tricyclic anhydrides was carried out under mild conditions. Of importance is the fact that highly regioselective insertion of epoxides has been realized by simple and metal-free catalysts in the ROAC, where the highest regioselectivity is up to 98% for aliphatic epoxides and glycidyl ethers at 80 °C. Styrene oxide bearing electron-withdrawing phenyl also showed a good regioselectivity of 78%. Besides, the complete suppression of epimerization and transesterification was achieved even at high conversion for a variety of tricyclic anhydrides. Furthermore, block and gradient copolymers were synthesized by the sequential addition strategy and one-pot terpolymerization. Accordingly, a green, regioselective and stereoregular fabrication of functional polyesters was realized for the first time by a metal-free process.
A metal-free, highly regioselective and stereoregular ring-opening alternating copolymerization of monosubstituted epoxides with tricyclic anhydrides was achieved to yield well-defined polyesters.
