About the transformation of low Tm into high Tm poly(<scp>l</scp>-lactide)s by annealing under the influence of transesterification catalysts

Weidner, Steffen M.; Meyer, Andreas; Chatti, Saber; Kricheldorf, Hans R.

doi:10.1039/d0ra10012a

Cited by 15 publications

(23 citation statements)

References 37 publications

(64 reference statements)

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“…2, 6, Table 4) Since the T m also depends on the thickness of the lamellar crystal (l c ) and on the surface free energy (s e ) according to the Gibbs-Thomson equation (eqn (1)), nature and extent of transesterification catalyst across the surface of the crystallites play an important role for the morphology and thus, for the T m . Evidence for such transesterification reactions in solid PLLA has been presented and discussed in several previous publications [29][30][31][32] and thus, should not be repeated here again.…”

Section: Annealing Experimentsmentioning

confidence: 90%

“…It has recently been demonstrated by the authors 30 Furthermore, the PLLAs listed in Tables 6 and 7 were characterized by SAXS measurements. Interestingly, the data recorded from DSTL catalyzed PLLAs displayed a systematic difference.…”

Section: Evaluation Of Saxs Measurementsmentioning

confidence: 92%

“…This aspect was recently discovered by the authors and needs further studies. [29][30][31][32] In this context it was the purpose of this work to find reaction conditions allowing for an optimization of T m and DH m . Variation of structure and activity of catalysts of primary interest.…”

Section: Introductionmentioning

confidence: 99%

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Poly(l-lactide): optimization of melting temperature and melting enthalpy and a comparison of linear and cyclic species

2022

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Section: Annealing Experimentsmentioning

confidence: 90%

Section: Evaluation Of Saxs Measurementsmentioning

confidence: 92%

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Poly(l-lactide): optimization of melting temperature and melting enthalpy and a comparison of linear and cyclic species

2022

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“…247 Scheme 58 Transesterification resulting in shortening or growing of linear chains sticking out from the surface of a crystallite. 247 Scheme 59 Transesterification resulting in formation of a loop and cleavage of a tie molecule. 247 Scheme 60 Simplified model of "smoothing" of lamellar surfaces combined with thickness growth.…”

Section: Reviewmentioning

confidence: 99%

“…247 Scheme 59 Transesterification resulting in formation of a loop and cleavage of a tie molecule. 247 Scheme 60 Simplified model of "smoothing" of lamellar surfaces combined with thickness growth. 247 Polymer Chemistry Review tures, so that esterification is self-catalyzed, the mechanism outlined in Scheme 50 is the most likely reaction pathway.…”

Section: Reviewmentioning

confidence: 99%

Syntheses of polylactides by means of tin catalysts

Kricheldorf

Weidner

2022

Polym. Chem.

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High T_m Poly(l‐lactide)s by Means of Bismuth Catalysts?

Kricheldorf

Meyer

Weidner

2021

Macro Chemistry & Physics

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and reduction of environmental pollution, even when this substitution cannot reach the level of 100%. In addition to the substitution of fuel-based, plastics homoand copolymers of lactic acid have found numerous applications in medicine and pharmacy. [6][7][8] This situation justifies to explore new methods and catalysts useful for the preparation of high molecular polylactides (poly-LAs) and to explore their chemical and physical properties in more detail.In contrast to the classical polymer chemistry mainly based on polymers of α-olefins and vinyl monomers, the production of biodegradable environmentally friendly polymers makes only sense, when the catalysts used for their production possess a low toxicity. The commercial polylactides are all produced by ringopening polymerization (ROP) of l-lactide (sometimes containing also D-units) by means of tin(II) 2-ethylhexanoate (SnOct 2 ) as catalyst in combination with an alcohol as initiator. This tin(II)salt, like any other tin compound, possess a considerable broad cytotoxicity, which concerns almost all microorganisms. Since its toxicity for humans is rather low, SnOct 2 has been accepted by the U. S. Food and Drug Administration (FDA) as antifouling food additive. Nonetheless, for medical and pharmaceutical applications any contamination of polylactides by tin compounds is unwanted and substitution by a less toxic catalyst is desirable.Over the past 20 years an increasing number of research groups has focused its work on ROPs of l-or d,l-lactide catalyzed by metal-free organocatalysts claiming that they are less toxic than metal-based catalyst. [9][10][11] However, those authors have rarely published toxicity data of their catalysts and in cases were such data are available (e.g., N,N-dimethyl-4-aminopyridine) its toxicity is significantly higher than that of SnOct 2 . The most promising alternative of tin is bismuth, first, because its toxicity is extremely low [12][13][14] (even lower than that of zinc [13] ) and second, because its tendency to racemize l-lactide at high reaction temperatures is as low or lower than that of tin salts. [14] It has been demonstrated (and reviewed) that various bismuth(III) salts combined with alcohols enable syntheses of linear homo and copolymers of lactide and glycolide. [15,16] Furthermore, the authors have reported that that the combination of BiSub and salicylic acid also allows for a racemization-free synthesis of cyclic poly(l-lactide) under optimized reaction conditions. [17] In addition to the exploration of preparative methods, studies of physical properties of polylactides are of interest. Regardless of the thermal history, optically pure, commercial poly(l-lactide) One series of BiSub-catalyzed ring-opening polymerizations (ROPs) is performed at 160 °C for 3 days with addition of difunctional cocatalysts to find out, if poly(l-lactide) crystallizes directly from the reaction mixture. An analogous series is performed with monofunctional cocatalysts. High T m crystallites (T m > 190 °C) are obtained from all bifunction...

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About the transformation of low T_m into high T_m poly(l-lactide)s by annealing under the influence of transesterification catalysts

Abstract: Cyclic polylactides were prepared in bulk at 170 °C, crystallized at 120 °C and then annealed at temperatures between 130 and 170 °C with variation of catalyst, catalyst concentration and annealing time.

Cited by 15 publications

References 37 publications

Poly(l-lactide): optimization of melting temperature and melting enthalpy and a comparison of linear and cyclic species

Poly(l-lactide): optimization of melting temperature and melting enthalpy and a comparison of linear and cyclic species

Syntheses of polylactides by means of tin catalysts

High T_m Poly(l‐lactide)s by Means of Bismuth Catalysts?

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About the transformation of low Tm into high Tm poly(l-lactide)s by annealing under the influence of transesterification catalysts

Abstract: Cyclic polylactides were prepared in bulk at 170 °C, crystallized at 120 °C and then annealed at temperatures between 130 and 170 °C with variation of catalyst, catalyst concentration and annealing time.

Cited by 15 publications

References 37 publications

Poly(l-lactide): optimization of melting temperature and melting enthalpy and a comparison of linear and cyclic species

Poly(l-lactide): optimization of melting temperature and melting enthalpy and a comparison of linear and cyclic species

Syntheses of polylactides by means of tin catalysts

High Tm Poly(l‐lactide)s by Means of Bismuth Catalysts?

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Product

Resources

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About the transformation of low T_m into high T_m poly(l-lactide)s by annealing under the influence of transesterification catalysts

High T_m Poly(l‐lactide)s by Means of Bismuth Catalysts?