New Paradigms for Organic Catalysts: The First Organocatalytic Living Polymerization

Nederberg, Fredrik; Connor, Eric F.; Möller, Michael; Glauser, Thierry; Hedrick, James L.

doi:10.1002/1521-3773(20010716)40:14<2712::aid-anie2712>3.0.co;2-z

Cited by 442 publications

(335 citation statements)

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“…If a guest ion was present that selectively bound to one of the rings then the system could be moved to favor the presence of that host-guest complex ion. To test for this hypothesis, we introduced an isolated group of A n molecules in benzene solution to a suspension of NaBPh 4 . Upon heating to 60°C the A 6 rings were selectively removed from the solution as is evident from the mass spectra shown in Fig.…”

Section: Resultsmentioning

confidence: 99%

“…We have found that when the polymer support (1 eq based on N atom content) is allowed to react with L-LA (24 eq) in the presence of a suspension of NaBPh 4 (10 eq) in benzene at 80°C for 20 h, the A 6 rings are removed from solution with the formation of NaBPh 4 (MeCHC(O)O) 6 . The latter is soluble in acetonitrile, and based on the integration of the proton signals arising from BPh 4 Ϫ and A 6 in the 1 H NMR spectrum recorded in CD 3 CN the conversion of LA to A 6 is Ͼ80% based on NaBPh 4 .…”

Section: Resultsmentioning

confidence: 99%

“…For a reaction involving the 2,5-morpholinedione where R ϭ i Pr, we isolated a crystalline component from a set of (AB) 4 rings and determined its structure by single-crystal x-ray crystallography. An Oak Ridge Thermal Ellipsoid Plot (ORTEP) drawing of this 24-membered cyclodepsipeptide is shown in Fig.…”

Section: Resultsmentioning

confidence: 99%

“…This is commonly brought about by the use of metal catalyst precursors, although organic catalysis is possible by employing a nucleophilic base such as 4-dimethyl aminopyridine or an N-heterocyclic carbene with alcohol initiators (2)(3)(4)(5). It is now generally accepted that metal-alkoxide species are the key reactive intermediates in the propagation steps and, furthermore, that these, too, play a role in the competing side reactions of transesterification and chain transfer (6).…”

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Cyclic esters and cyclodepsipeptides derived from lactide and 2,5-morpholinediones

Chisholm

Gallucci

Yin

2006

Proc. Natl. Acad. Sci. U.S.A.

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The reaction between Bu n Li in benzene and the solid polystyrene support PS-C 6H4CH2NH2 leads to a lithiated species that can be represented as PS-C 6H4CH2NHLi(LiBu)x, where x ϳ 4, which is active in the ring-opening of the cyclic esters L-lactide, rac-lactide, and 2,5-morpholinediones. With Ϸ10 eq of these monomeric six-membered rings and with heating, cyclic esters (MeCHC ( dynamic combinatorial library ͉ ring enlarging T he ring-opening polymerization of cyclic esters such as lactides (LA) is a well established procedure for the production of polyesters (1). This is commonly brought about by the use of metal catalyst precursors, although organic catalysis is possible by employing a nucleophilic base such as 4-dimethyl aminopyridine or an N-heterocyclic carbene with alcohol initiators (2-5). It is now generally accepted that metal-alkoxide species are the key reactive intermediates in the propagation steps and, furthermore, that these, too, play a role in the competing side reactions of transesterification and chain transfer (6). These reactions are collectively shown in Scheme 1.Transesterification is normally a deleterious side reaction because it leads to a loss of control of molecular mass in a living polymerization and, because in a stereoselective ring-opening polymerization, transesterification scrambles the stereocenters along a chain. As shown in Scheme 1, transesterification can occur by a bimolecular mechanism or a reaction involving a single chain. The latter reaction, intrachain transesterification leads to cycles. Previously, we found that the polymerization of lactide by Ph 2 SnX 2 initiators, where X ϭ OPr i or NMe 2 , gave different ratios of chains to cycles with the cycles being significantly more prominent for X ϭ NMe 2 . This apparently arises because of the favorable chelation of the SnOCHMeC(O)NMe 2 groups (7).Prompted by these observations, we set out to explore a synthetic route for cyclic oligoesters derived from LA and we describe herein our findings. It is worthy of mention that others have synthesized cyclic esters and carbonates principally as a route for the formation of polyesters and polycarbonates (8). Brunelle and coworkers (9) at GE Corporate Research andDevelopment specifically developed high-yielding syntheses of cyclic esters derived from 1,4-aromatic acyl chlorides and diols. These ringed compounds melt to yield low viscous media, which by a thermo-neutral ring-opening polymerization give polyesters with no elimination products. This chemistry forms the technology platform of Cyclics Corporation. 2. Kricheldorf and coworkers (10, 11) have used principally tin(IV) diolates as initiators for the ring-opening polymerization and the reaction with dicarboxylic acid chlorides to cleave the cyclic esters. 3. Hodge and coworkers (12) used a solid support and step growth polymerization to produce a polyester chain followed by treatment with a metal catalyst, most often Bu n 2 SnO, to affect intrachain transesterification and release of the cyclic esters to the solution phase. 4....

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Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

mentioning

confidence: 99%

See 2 more Smart Citations

Cyclic esters and cyclodepsipeptides derived from lactide and 2,5-morpholinediones

Chisholm

Gallucci

Yin

2006

Proc. Natl. Acad. Sci. U.S.A.

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“…[5][6][7] Since the biomedical application of the polymers demands extremely high purity and the absence of any toxic compounds, the development and use of biocompatible low-toxic or non-toxic catalysts/initiators, one of which is the metal-free organo-catalyst, may have significant benefits. [8][9][10] The most studied organo-catalytic compounds for the ROP of cyclic esters are some well-known transesterification agents such as 4-(dimethylamino) pyridine, 11 nucleophilic tertiary phosphines, 12 N-heterocyclic carbenes, 13 bifunctional aminothioureas, 14 and 1,5,7-triazabicyclo-[4.4.0]dec-5-ene. 15 Among these organocatalyst, the nucleophilic tertiary phosphines are quite interesting for their catalytic mechanism.…”

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confidence: 99%

Microwave-assisted Ring-Opening Polymerization of ε-Caprolactone in Presence of Hydrogen Phosphonates

et al. 2009

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Polylactides

Degée

Dubois

2004

Kirk-Othmer Encyclopedia of Chemical Technology

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This article focuses on the controlled synthesis and properties of polylactide (PLA) in regard to its microstructure and the design of new related materials, with particular attention on nanocomposites built up from PLA and organoclays, ie, organo‐modified layered silicates (OMLS). As far as the ring‐opening polymerization of lactide is concerned, the selectivity and stereoelectivity of novel (catalytic) initiating systems are discussed using different combinations of lactide isomers, catalysts–initiators, and ligands. A series of biodegradable PLA/OMLS nanocomposites prepared by either solution mixing, melt intercalation, or in situ intercalative polymerization is described. All these nanocomposites exhibit dramatic improvements in mechanical and many other materials key‐properties as compared with those of unfilled pristine PLA. These improvements include flexural and thermal properties, heat distortion temperature, oxygen permeability barrier, and rate of crystallization. The future of PLA‐based materials is also discussed with special attention to the environmental impact.

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New Paradigms for Organic Catalysts: The First Organocatalytic Living Polymerization

Cited by 442 publications

References 41 publications

Cyclic esters and cyclodepsipeptides derived from lactide and 2,5-morpholinediones

Cyclic esters and cyclodepsipeptides derived from lactide and 2,5-morpholinediones

Microwave-assisted Ring-Opening Polymerization of ε-Caprolactone in Presence of Hydrogen Phosphonates

Polylactides

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