Poly(lactic acid) Controlled Drug Delivery

Li, Jiannan; Ding, Jianxun; Liu, Tongjun; Liu, Jessica F.; Yan, Lesan; Chen, Xuesi

doi:10.1007/12_2017_11

Cited by 22 publications

(11 citation statements)

References 159 publications

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“…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.…”

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

Kricheldorf

Meyer

Weidner

2021

Macro Chemistry & Physics

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“…The tacticity bias (90% isotactic) in the poly( l -lactide) produced by tin octoate thus results from chain-end control instead of the preferred enantiomorphic-site control. While the polymer does find many commercial applications, its use in food contact applications or medical devices may necessitate the challenging and costly removal of the cytotoxic tin from the product itself. − …”

Section: Introductionmentioning

confidence: 99%

Lactide Polymerization Using Zinc Dichloride Complexes Containing a Neutral Bidentate Ligand with a Diacylated Cyclic Guanidine

et al. 2022

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Zinc complexes of neutral bidentate ligands that contain an electron-poor diacylated cyclic guanidine are reported, along with their reactivity in solvent-free polymerization of rac-lactide. The diacyl groups significantly decrease the electron-donating ability of the ligand compared to the corresponding nonacylated derivative. This manifested itself through restricted rotation about the formal C−N exo double bond, with the Gibbs free-energy rotational barrier (ΔG ‡) ranging from 47.4 to 59.6 kJ mol −1 . Restricted rotation was also observed for the isopropyl substituent syn to the N exo aryl ring with ΔG ‡ values of 47.5−51.9 kJ mol −1 . Coordination of the ligands to zinc caused further π-electron delocalization from the endocyclic to the exocyclic nitrogen, thereby decreasing the Wiberg bond index of the C−N exo bond from 1.67−1.70 to 1.48−1.50 and eliminating all restricted rotations at room temperature. All three complexes were active in the solvent-free polymerization of rac-lactide with the second-order polymerization rate constant for the anthranilate-based complex of 7.30 × 10 −3 M −1 s −1 . The resulting polymers had a slight heterotactic bias (P r = 0.60) with molecular weights lower than anticipated, possibly due to transesterification, as suggested by mass spectrometry. The mass spectrum of the polymer did not show evidence of the ligand dissociating from the metal during the initiation step and its incorporation into the polymer structure. The acylation of the cyclic guanidine thus imparts advantages to the ligand, with the second building block offering additional opportunities to further improve the catalytic performance of these zinc complexes.

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“…One of the most attractive candidates is polylactide, because its production is based on natural resources and because its properties can be varied over a broad range. This broad variation can be achieved via different chain lengths, different topologies, different stereosequences, by copolymerization with various comonomers and blending with another polymer 1–8 . Almost all homo‐ and copolymers of lactic acid are produced by ring‐opening polymerization (ROP) of lactide, and for their technical production (by polymerization in bulk) tin(II) 2‐ethylhexanoate (SnOct 2 ) is the most widely used catalyst 9–11 .…”

Section: Introductionmentioning

confidence: 99%

ROP of L‐lactide and ε‐caprolactone catalyzed by tin(ii) and tin(iv) acetates–switching from COOH terminated linear chains to cycles

Kricheldorf

Weidner

2021

Journal of Polymer Science

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The catalytic potential of tin(II)acetate, tin(IV)acetate, dibutyltin‐bis‐acetate and dioctyl tin‐bis‐acetate was compared based on polymerizations of L‐lactide conducted in bulk at 160 or 130°C. With SnAc2 low‐Lac/Cat ratios (15/1–50/1) were studied and linear chains having one acetate and one carboxyl end group almost free of cyclics were obtained. Higher monomer/catalyst ratios and lower temperatures favored formation of cycles that reached weight average molecular weights (Mw's) between 100,000 and 2,500,000. SnAc4 yielded mixtures of cycles and linear species under all reaction conditions. Dibutyltin‐ and dioctyl tin bis‐acetate yielded cyclic polylactides under most reaction conditions with Mw's in the range of 20,000–80,000. Ring‐opening polymerizations performed with ε‐caprolactone showed similar trends, but the formation of COOH‐terminated linear chains was significantly more favored compared to analogous experiments with lactide. The reactivity of the acetate catalysts decreased in the following order: SnAc2 > SnAc4 > Bu2SnAc2 ~ Oct2SnAc2.

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Poly(lactic acid) Controlled Drug Delivery

Cited by 22 publications

References 159 publications

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

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

Lactide Polymerization Using Zinc Dichloride Complexes Containing a Neutral Bidentate Ligand with a Diacylated Cyclic Guanidine

ROP of L‐lactide and ε‐caprolactone catalyzed by tin(ii) and tin(iv) acetates–switching from COOH terminated linear chains to cycles

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Poly(lactic acid) Controlled Drug Delivery

Cited by 22 publications

References 159 publications

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

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

Lactide Polymerization Using Zinc Dichloride Complexes Containing a Neutral Bidentate Ligand with a Diacylated Cyclic Guanidine

ROP of L‐lactide and ε‐caprolactone catalyzed by tin(ii) and tin(iv) acetates–switching from COOH terminated linear chains to cycles

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

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