Bifunctional Squaramides as Organocatalysts for Lactide Polymerization: Catalytic Performance and Comparison with Monofunctional Analogues

Specklin, David; Hild, Frédéric; Chen, Li; Thevenin, Lucas; Munch, Maxime; Dumas, Françoise; Bideau, Franck Le; Dagorne, Samuel

doi:10.1002/cctc.201700272

Cited by 17 publications

(16 citation statements)

References 69 publications

(38 reference statements)

Supporting

Mentioning

Contrasting

Order By: Relevance

“…In addition, the activity and controllability of catalysts can be further improved by using multiurea instead of monourea . In general, HBDs are tailored by electronic and steric effects of catalyst substituents to manipulate their catalysis performance . Typical electron withdrawing substituents of HBDs include trifluoromethyl and sulfonyl groups, which can enhance the electrophilicity of HBD moiety and facilitate the activation of the monomer's carbonyl group.…”

Section: Introductionmentioning

confidence: 99%

Solvent‐free ring‐opening polymerization of lactones with hydrogen‐bonding bisurea catalyst

Zheng

Yuan

et al. 2018

J. Polym. Sci. Part A: Polym. Chem.

View full text Add to dashboard Cite

Development of effective organocatalysts for the living ring‐opening polymerization (ROP) of lactones is highly desired for the preparation of biocompatible and biodegradable polyesters with controlled microstructures and physical properties. Herein, a new class of hydrogen‐bond donating bisurea catalysts is reported for the ROP of lactones under solvent‐free conditions. ROP of lactones mediated by the bisurea/7‐methyl‐1,5,7‐triazabicyclo[4.4.0]dec‐5‐ene (MTBD) catalyst exhibits a living/controlled manner, affording the polymers and copolymers with the well‐defined structure, predictable molecular weight, narrow molecular weight distribution, and high selectivity for monomer at low catalyst loadings at ambient temperature. The possible mechanism of bisurea/MTBD‐catalyzed ROP of lactones is proposed, in which the bisurea activates the carbonyl group of lactones while MTBD facilitates the nucleophilic attack of the initiating/propagating alcohol by hydrogen bonding. Moreover, the poly(ε‐caprolactone‐co‐δ‐valerolactone) [P(CL‐co‐VL)] random copolymers with various compositions were synthesized using the bisurea/MTBD catalyst. The measurements of thermal properties and crystalline structure demonstrate that the CL and VL units are cocrystallized in the crystalline phase of P(CL‐co‐VL) copolymers. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019, 57, 90–100

show abstract

Section: Introductionmentioning

confidence: 99%

Solvent‐free ring‐opening polymerization of lactones with hydrogen‐bonding bisurea catalyst

Zheng

Yuan

et al. 2018

J. Polym. Sci. Part A: Polym. Chem.

View full text Add to dashboard Cite

show abstract

“…The reason for this can be explained by the fact that the stronger interaction between H-bond donor and H-bond acceptor groups could neutralize their activating effects on the monomer and alcohol . (iv) It was also shown that bifunctional catalysts were faster in polymerization than monofunctional squaramides operated by adding a base such as a triethylamine externally . (v) It was found that the catalytic activity is extremely sensitive to substituents on both the squaramide part and the basic site.…”

Section: Introductionmentioning

confidence: 99%

“…11 The aforementioned obstacles to binary independent catalytic systems and the necessity of expensive HBA cocatalysts (such as (−)-sparteine) have prompted many researchers to investigate bifunctional systems (double action in a single molecule) providing polymerization without these disadvantages. 11,12 A stronger alternative to chiral thiourea catalysts is chiral squaramides, 13,14 showing H-bond donor Lewis acid activity like thioureas, as well. This type of bifunctional catalyst, first developed by Rawal et al in 2008, generally consists of a combined H-bond donor (Lewis acid, squaramide) and a Hbond acceptor (Brønsted base, amine) in the presence of a chiral scaffold 13 and catalyzes a wide range of organic reactions.…”

Section: ■ Introductionmentioning

confidence: 99%

“…12,27 (iii) Although the catalyst structure was designed as bifunctional, unless a steric structure such as a cyclohexyl bridge, which prevents the interaction of these groups with each other, was inserted between the squaramide part and the basic part, the conversion slowed down again. 12 The reason for this can be explained by the fact that the stronger interaction between H-bond donor and H-bond acceptor groups could neutralize their activating effects on the monomer and alcohol. 30 (iv) It was also shown that bifunctional catalysts were faster in polymerization than monofunctional squaramides operated by adding a base such as a triethylamine externally.…”

Section: ■ Introductionmentioning

confidence: 99%

See 1 more Smart Citation

trans- and cis-DACH-Based Bifunctional Squaramides Catalyzed Ring-Opening Polymerizations of Asymmetric Substituted Glycolides

Vardar,

Erdebil,

Mert

et al. 2023

Macromolecules

View full text Add to dashboard Cite

A broad scope of the library of squaramide organocatalysts was prepared starting from two geometric isomers (trans- and cis-(1,2-diaminocyclohexane) (DACH)) with various numbers of −CH2– linkages between the squaramide core and the aromatic group, different numbers of electron-withdrawing −CF3 groups on the aromatic ring, and different sizes of cyclic tertiary amines from piperidine to pyrrolidine on the DACH ring. Then, the ring-opening polymerizations of asymmetrically substituted glycolides (ASGs) such as isobutyl glycolide (IBG), isobutyl methyl glycolide (IBMG), and isobutyl ethyl glycolide (IBEG) were achieved with bifunctional squaramide organocatalysts at ambient temperature (20 °C) in dichloromethane (DCM) or in 1,2-dichloroethane (DCE) at 50 °C. Predictable molecular weights of poly(substituted glycolide) (PSG) homopolymers in accordance with monomer/initiator ratios, high conversions up to 100%, narrow polydispersity (PDI) values as low as 1.04, and high yields up to 93% were acquired. IBG, IBMG, and IBEG monomers showed much better polymerization activity in the presence of trans-DACH-based catalysts when compared to cis-DACH-based derivatives. It was revealed that the change of chemical shifts in the NHCH 2 and NH Cy amine peaks in the trans catalyst were 4.6 and 2.2 times higher than that of the cis catalyst upon addition of the monomer according to 1H NMR titration analyses, which proves that the monomer interacts better with the trans-DACH-based catalyst, probably due to the proximity of the trans-organocatalyst to the monomer, thus opening the ring more easily. The relative reactivities within three monomers toward polymerization are closely related to the sterically crowded groups of alkyl substituents on monomers. For instance, the IBG monomer having less sterically crowded groups led to polymerization faster when compared to IBMG and IBEG monomers. Thus, all trans catalysts 19–25 were very efficient in the polymerization of IBG at 20 °C. On the other hand, the existence of the steric group in IBMG and IBEG monomers made the catalyst selectivity important in their polymerizations. The most effective trans- and cis- catalysts in the polymerization of both IBMG and IBEG monomers were found to be trans 22 and cis 34 with two −CF3 groups and no −CH2– groups probably due to their high acidity, respectively. One or two different asymmetric centers leading to structural isomers in the chains (H–H, T–T, and H–T segments) in PIBG, PIBMG, and PIBEG homopolymers were analyzed in depth by single-frequency decoupled 1H NMR.

show abstract

“…This proposed catalyst system bears many similarities to cooperative catalysis, with both acids and bases being present in the reaction mixture, often in equilibrium between the individual components and the homoconjugated species. While the field of cooperative catalysis in polymerization is established, especially regarding ring-opening polymerization of cyclic esters and carbonates, − there are relatively few instances of cooperative catalysis to affect silanol polycondensation in the literature, and no mention of cyclosiloxane levels generated using these approaches. ,,, Homoconjugated acid catalysts are cheap, simple to make, relatively mild, and commercially available. This provides ample room to develop new catalyst compositions and explore how the base and acid component of the homoconjugate relate to reactivity and selectivity.…”

Section: Introductionmentioning

confidence: 99%

Homoconjugated Acids as Low Cyclosiloxane-Producing Silanol Polycondensation Catalysts

et al. 2020

View full text Add to dashboard Cite

Polycondensation of α,ω-disilanols is a foundational technology for silicones producers. Commercially, this process is carried out with strong Brønsted acids and bases, which generates cyclosiloxane byproducts. Homoconjugated acids (a 2:1 complex of acid:base or a 1:1 complex of acid:salt), a seldom used class of silanol polycondensation catalysts, were evaluated for their ability to polymerize α,ω-disilanols while forming low levels of cyclosiloxane byproducts. Homoconjugated acid catalysts were highly active for silanol polycondensation, even when made from relatively mild acids such as acetic acid. Both the acid and base (or cation) component of the homoconjugated species was important for activity and avoiding cyclosiloxane byproduct formation. Stronger acids and bases were found to positively affect reactivity, and the p K a of the acid was found to correlate with cyclosiloxane byproduct formation. The individual components of the homoconjugated species (the acid and base) were ineffective as catalysts by themselves, and compositions with fewer than 2 mol of acid to 1 mol of base were much less reactive. Homoconjugated trifluoroacetic acid tetramethylguanidinium and tetrabutylphosphonium complexes were found to be privileged catalysts, able to give high-molecular-weight siloxanes ( M n > 60 kDa) while generating less than 100 ppm of octamethylcyclotetrasiloxane byproduct. Finally, a mechanism has been proposed where silanols are electrophilically and nucleophilically activated by the homoconjugated species, leading to silanol polycondensation.

show abstract

Bifunctional Squaramides as Organocatalysts for Lactide Polymerization: Catalytic Performance and Comparison with Monofunctional Analogues

Cited by 17 publications

References 69 publications

Solvent‐free ring‐opening polymerization of lactones with hydrogen‐bonding bisurea catalyst

Solvent‐free ring‐opening polymerization of lactones with hydrogen‐bonding bisurea catalyst

trans- and cis-DACH-Based Bifunctional Squaramides Catalyzed Ring-Opening Polymerizations of Asymmetric Substituted Glycolides

Homoconjugated Acids as Low Cyclosiloxane-Producing Silanol Polycondensation Catalysts

Contact Info

Product

Resources

About