Polymerization of lactide and related cyclic esters by discrete metal complexes

O’Keefe, Brendan J.; Hillmyer, Marc A.; Tolman, William B.

doi:10.1039/b104197p

Cited by 832 publications

(469 citation statements)

References 51 publications

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“…It is worth noting that the effect of [BnOH] was investigated and it was found that an Al/BnOH molar ratio of 1:1 afforded the best activity whereas the presence of two or three equivalents of BnOH rendered the catalyst inactive. This observation is similar to that reported by Duda, wherein he used the aluminum isopropoxide trimer [Al(O i Pr) 3 ] in the presence of diol {HO(CH 2 ) 5 OH} and suggested that the alcohol reversibly coordinated to the active species leading to catalytic inhibition. 66,67 In the polymerization reactions initiated by 4 and 5 in the absence of BnOH, gelation was observed for all reactions and conversion of ε-CL did not reach completion in 5.00 mL of toluene, the volume used in ROP using 1-3/BnOH above, due to increased viscosity resulting from a rapid increase in molecular weight.…”

Section: Ring-opening Polymerization Of ε-Caprolactonesupporting

confidence: 77%

“…[1][2][3][4] Ring-opening polymerization (ROP) of cyclic esters is mainly mediated by metal complexes which afford faster polymerization rates and greater control over molecular weight of the resulting polymers. [5][6][7][8] Biocompatible metal complexes are important in the production of these polymers, where small amounts of catalyst may inevitably be incorporated.…”

Section: Introductionmentioning

confidence: 99%

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Aluminum Methyl and Chloro Complexes Bearing Monoanionic Aminephenolate Ligands: Synthesis, Characterization, and Use in Polymerizations

et al. 2012

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Abstract:A series of aluminum methyl and chloride complexes bearing 2(N-piperazinyl-N′-methyl)-2-methylene-4-R′-6-R-phenolate or 2(N-morpholinyl)-2-methylene-4-R′-6-R-phenolate ([ONE R1,R2 ]-) {[ R 1 = t Bu, R 2 = Me, E = NMe (L1); R 1 = R 2 = t Bu, E = NMe (L2); R 1 = R 2 = t Bu, 1 E = O (L3)} ligands were synthesized and characterized through elemental analysis, 1 H, 13 The catalytic activity of complexes 1-3 toward ring-opening polymerization (ROP) of ε-caprolactone was assessed. These complexes are more active than analogous Zn complexes for this reaction but less active than the Zn analogs for ROP of rac-lactide. Characteristics of the polymer as well as polymerization kinetics and mechanism were studied. Polymer end-group analyses were achieved using 1 H NMR spectroscopy and MALDI-TOF MS. Eyring analyses were performed and the activation energies for the reactions were determined, which were significantly lower for 1 and 2 compared with 3. This could be for several reasons: (1) the methylamine (NMe) group of 1 and 2, which is a stronger base than the ether (O) group of 3, might activate the incoming monomer via non-covalent interactions, and/or (2) the ether group is able to temporarily coordinate to the metal center and blocks the vacant coordination site towards incoming monomer, whilst the amine cannot do this. Preliminary studies using 4 and 5 towards copolymerization of cyclohexene oxide with carbon dioxide have been performed. 4 was inactive and 5 afforded polyethercarbonate (66.7% epoxide conversion, polymer contains 54.0% carbonate linkages).

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Section: Ring-opening Polymerization Of ε-Caprolactonesupporting

confidence: 77%

Section: Introductionmentioning

confidence: 99%

Aluminum Methyl and Chloro Complexes Bearing Monoanionic Aminephenolate Ligands: Synthesis, Characterization, and Use in Polymerizations

et al. 2012

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“…1 Industrial applications for these polymers range from disposable plastic utensils to 3D printing and biomedical tissue scaffolding. 2 Of the numerous pre-catalysts developed toward this end, indium complexes have demonstrated high activity and stereoselectivity for a number of monomers.…”

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confidence: 99%

High activity of an indium alkoxide complex toward ring opening polymerization of cyclic esters

Quan

Diaconescu

2015

Chem. Commun.

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Abstract. An indium complex supported by a ferrocene-derived Schiff base ligand has an unprecedented high activity toward ε-caprolactone, δ-valerolactone, and β-butyrolactone. L-lactide, D,L-lactide, and trimethylene carbonate polymerizations also showed moderate to high activity.Over the past two decades, the ring-opening polymerization of cyclic esters has been increasingly studied because of the promise to produce biodegradable polymers from biomass. In our recent studies, a cerium complex supported by a Schiff base ligand with a ferrocene backbone polymerized L-lactide in a controlled fashion. 24 Phosphinimine analogues with yttrium and indium also demonstrated good activity in lactide and trimethylene carbonate polymerizations. 22 Therefore, we decided to combine indium's activity with the Schiff base, ferrocene-derived ligand in order to study the activity of the resulting complexes toward a broad range of cyclic ester polymerizations. Additional motivation was found from recent studies that point to the biocompatibility, robustness, and high activity of indium catalysts in the ring opening polymerization of cyclic esters. 10,25 Herein, we report a ferrocene-derived Schiff base indium complex that possesses a remarkable range of activity toward cyclic esters and exceptionally fast polymerization rates with lactones. Compound (salfen)In(O t Bu) (salfen = 1,1'-di(2,4-di-tert-butyl-6-iminephenoxy)ferrocene) represents the first indium precatalyst capable of δ-valerolactone polymerization and the most active indium catalyst to date in the polymerization of β-butyrolactone and ε-caprolactone. The polymerization rates of ε-caprolactone are even competitive with those of current industrial catalysts.Compound (salfen)In(O t Bu) was synthesized from the reaction of (salfen)InCl and freshly sublimed KO t Bu. In turn, (salfen)InCl was synthesized by combining InCl3 with K2(salfen), which was generated from H2(salfen) and two equivalents of KH (Eq 1). Needle crystals of (salfen)InCl were isolated from a diethyl ether solution. The solid state molecular structure (Figure 1) shows a distorted octahedral indium center and a THF molecule coordinated trans to the chloride ligand. Similarly to the phosphinimine indium chloride analogue previously reported by us, 22 a long In-Fe distance (3.98 Å) and a staggered configuration of the Cp rings were apparent. Elongation of the In-heteroatom distances compared to other compounds, such as (salen)InCl (salen = N,N ' -bis(3,5-di-tert-butylsalicylidene)-1,2-cyclohexanediamine (rac-or (R,R)-H2(ONNO))) 9 and (phosfen)In(OPh) (phosfen = 1,1'-di(2-tert-butyl-6-diphenylphosphiniminophenoxy)ferrocene), 22 by about 0.25 Å possibly compensates for the distortion caused by the staggered Cp rings.

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“…Metal alkoxide species, M-OR, have been shown to be the true active species in numerous ROP processes. [1][2][3][4][5][6][7][8][9][10][11][12][13][18][19][20][21][22][23][24] For example, in 2004, Lewiński and co-workers reported the first structurally characterized aluminum ε-caprolactone complex, indicating that the Al-Me group has poor reactivity with CL. 77 Thus, in most ROP cases, an alcohol is used as an initiator and is essential in order to start the polymerization.…”

Section: Introductionmentioning

confidence: 99%

A Comparison of Gallium and Indium Alkoxide Complexes as Catalysts for Ring-Opening Polymerization of Lactide

et al. 2017

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ABSTRACT:The synthesis, characterization, and reactivity of an aluminum alkoxide complex supported by a ferrocene-based ligand, (thiolfan*)Al(O t Bu) (1 red , thiolfan* = 1,1'-di(2,4-di-tert-butyl-6-thiophenoxy)ferrocene), are reported. The homopolymers of L-lactide (LA), ε-caprolactone (CL), δ-valerolactone (VL), cyclohexene oxide (CHO), trimethylene carbonate (TMC), and their copolymers were obtained in a controlled manner by using redox reagents. Detailed DFT calculations and experimental studies were performed to investigate the mechanism. Mechanistic studies show that after the insertion of the first monomer, the coordination effect of the carbonyl group, which has usually been ignored in previous reports, can significantly change the energy barrier of the propagation steps, thus playing an important role in polymerization and copolymerization processes.

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Polymerization of lactide and related cyclic esters by discrete metal complexes

Cited by 832 publications

References 51 publications

Aluminum Methyl and Chloro Complexes Bearing Monoanionic Aminephenolate Ligands: Synthesis, Characterization, and Use in Polymerizations

Aluminum Methyl and Chloro Complexes Bearing Monoanionic Aminephenolate Ligands: Synthesis, Characterization, and Use in Polymerizations

High activity of an indium alkoxide complex toward ring opening polymerization of cyclic esters

A Comparison of Gallium and Indium Alkoxide Complexes as Catalysts for Ring-Opening Polymerization of Lactide

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