Variably Isotactic Poly(hydroxybutyrate) from Racemic β‐Butyrolactone: Microstructure Control by Achiral Chromium(III) Salophen Complexes

Zintl, Manuela; Molnár, F.; Urban, Tobias; Bernhart, Volker; Preishuber‐Pflügl, Peter; Rieger, Bernhard

doi:10.1002/anie.200703859

Cited by 109 publications

(83 citation statements)

References 32 publications

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“…[9] The observation of stereocontrol in the ROP of racemic BL by achiral Cr-salphen catalysts was explained originally in terms of ab imetallic mechanism of polymerization, which leads to the formation of ac hiral cage aroundt he interacting metal centers. [8,9] In accordance with this mechanism, it was shown that dinuclear disalphen complexes Cr-1 g-i with aflexible bridge catalyze the ROP of BL more effectively by af actor of five than the analogousm ononuclear species Cr-1 f under typical polymerization conditions. [10] However,t hese dinuclear complexes produced only atactic PHB in contrastt oc atalysts Cr-1 a-d.…”

Section: Introductionmentioning

confidence: 61%

“…Peculiarities of the microstructure of PHBs obtained withCrsalphens Under standard polymerizationc onditions (100 8C, 5h,1 :1000 catalyst/monomer ratio), halogen-substituted Cr-salphen complexes Cr-1 b-d were reported to produce PHBs of very high M w values that reachedn early 800 kg mol À1 [8,9] ands howed isotactic enrichment. Depending on the batches of the catalysta nd of the monomer,h owever,t he P m value, determined as ar atio of the m-diad signalt ot he overall signal of the carbonyl group in 13 CNMR spectrumo ft he polymer, [11] was found to vary and reached0 .54 in some cases.…”

Section: Resultsmentioning

confidence: 99%

“…The reason for this may lie in ab imetallic mechanism proposed earlier. [8] The formation of as olid phase from m-OH-bridged coordination polymers/oligomers guarantees the spatialp roximity and low mobility of two (or more) metallic centers at the active sites as well as the control of the stereochemistry.…”

Section: Mechanistic Considerationsmentioning

confidence: 99%

“…This is the case if other substituted Cr-salphen catalysts of poor activity,f or example, Cr-1 e and Cr-1 f are applied (Scheme 2). [8,9,13] In the investigationo ft he origin of the opalescence, we focused on Cr-1 c.BLpolymerization experimentsu sing this catalyst were performed,t he reaction was cooled rapidly after the appearance of the opalescence( % 5min heating at 100 8C), and the mixture was centrifuged.C hanges upon such treatments are illustrated in Figure S2. By this procedure, ap recipitate (Cr-2)c omposed mainly of Cr-salphen complex can be isolated (Scheme 3).…”

Section: Catalysis-related Transformations Of Cr-salphensmentioning

confidence: 99%

“…[8] Subsequently,t he influence of the salphen ligand structure on the polymerization performance was studied extensively,w hich revealed the nontrivial relationship of the substitution pattern and the catalytic characteristics in the ROP of BL. [9] Thus, the exchange of R = H( Cr-1 a)b yatertbutyl group (Cr-1 e) not only decreasest he catalytic activity and the M w of the resulting polymer but also influences the molecular weight distribution dramatically and yields atactic polymer.…”

Section: Introductionmentioning

confidence: 99%

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New Insights into the Ring‐Opening Polymerization of β‐Butyrolactone Catalyzed by Chromium(III) Salphen Complexes

et al. 2015

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The heterogeneous nature of β‐butyrolactone (BL) polymerization towards tactic poly(3‐hydroxybutyrate) (PHB) in the presence of chromium(III) salphen (salphen=N,N′‐disalicylidene‐o‐phenylenediamine) complexes is supported by a number of experimental observations. Depending on the substitution pattern, initially soluble chromium(III) salphen chloride complexes can generate microcrystalline agglomerates under the polymerization conditions, driven by formation of μ‐OH bridges between metal centers. Coordinated water molecules are suggested to be the source of such bridging ligands. The formation of these/this heterogeneous species is a prerequisite for the stereocontrolled ring‐opening polymerization (ROP) of BL, whereas both iso‐ and syndioselective enchainment occurs simultaneously. According to the analysis of the 13C NMR spectra of the polymers, the ratio of the corresponding triads depends on a number of parameters in a not yet understood manner. Besides dual stereoselectivity, the heterogeneous chromium(III) salphen species feature catalytic sites with different activities, which is reflected in the very broad molecular mass distribution of the produced PHB. Highly active catalytic sites cause the formation of polymer chains with a high molecular mass at the beginning of polymerization. The described behavior is not inherent to truly homogeneous chromium salphen complexes and is more in line with a bimetallic ROP mechanism proposed earlier, which requires a particular mutual spatial orientation of two salphen complexes for the efficient catalysis of BL polymerization.

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Section: Introductionmentioning

confidence: 61%

Section: Resultsmentioning

confidence: 99%

Section: Mechanistic Considerationsmentioning

confidence: 99%

Section: Catalysis-related Transformations Of Cr-salphensmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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New Insights into the Ring‐Opening Polymerization of β‐Butyrolactone Catalyzed by Chromium(III) Salphen Complexes

et al. 2015

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Stereoselective Ring‐Opening Polymerization of Heterocyclic Monomers

Takeuchi

2014

Encyclopedia of Polymer Science and Technology

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Recent progress in stereoselective ring‐opening polymerization of heterocyclic monomers, especially polymerization and copolymerization of epoxides and lactones, is summarized. Zn, Al, Co, and Cr complexes promote stereospecific ring‐opening polymerization of epoxides as well as copolymerization of epoxides with carbon dioxide. Enantioselective polymerization of epoxide is also achieved to afford optically active polyethers. Cr and lanthanide complexes promote stereoselective polymerization of β‐butyrolactone. Stereospecific polymerization of lactide has been achieved by using varieties of metal catalysts, including Al, Ga, In, Mg, Ca, Sn, Zn, Ti, Zr, Hf, Ge, and rare earth metals. Organic catalysts such as carbenes and phosphazene bases are also utilized for the synthesis of stereoregular polylactide. By utilizing those stereoselective polymerizations, more stereogradient and stereoblock copolymers have been synthesized. Polylactides with high degree of stereoregularity show high melting points. One‐to‐one mixtures of isotactic poly( l ‐lactide) and poly( d ‐lactide) or stereoblock copolymer of l ‐lactide and d ‐lactide show higher melting points compared with the polymer of homochiral monomer, due to the formation of stereocomplex.

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Ionic and Coordination Ring‐Opening Polymerization

Penczek¹,

Biela²,

Cypryk³

et al. 2022

Macromolecular Engineering

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This article provides the up‐to‐date and comprehensive review (over 700 citations) of all the important subjects of the ring‐opening polymerization (ROP) methods of polymers syntheses. This is the method of synthesis of several important classes of polymers that cannot be prepared in a different way (e.g., polyethers). It also complements known methods of polycondensation and ROP often is the method of choice. ROP is particularly important in syntheses of the biodegradable polymers‐polylactide and poly(ε‐caprolactone), discussed in details. Applications of these polymers, as well as polysiloxanes in biomedical applications are irreplaceable in the modern medicine. Either as bulk polymers or as nano‐ and microspheres, described In this article separately. There are sections in the present version that were not presented in the previous editions. This is description of polyoxazolines, polymers with phosphorus atoms in the chains, as well as mentioned above polysiloxanes an microspheres. We introduced also section describing novel analytical methods, particularly useful in studies of polymers with various architectures (star shape, multibranched etc.). Besides the synthetic aspects of ROP, this article describes thermodynamics and kinetic features of the living/controlled polymerizations, particularly by activated monomer mechanism and importance of dormant polymers in precision syntheses of desired structures.

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Variably Isotactic Poly(hydroxybutyrate) from Racemic β‐Butyrolactone: Microstructure Control by Achiral Chromium(III) Salophen Complexes

Cited by 109 publications

References 32 publications

New Insights into the Ring‐Opening Polymerization of β‐Butyrolactone Catalyzed by Chromium(III) Salphen Complexes

New Insights into the Ring‐Opening Polymerization of β‐Butyrolactone Catalyzed by Chromium(III) Salphen Complexes

Stereoselective Ring‐Opening Polymerization of Heterocyclic Monomers

Ionic and Coordination Ring‐Opening Polymerization

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