Ring-opening Polymerization Of L-lactide Research Articles

Biodegradable thermoplastic elastomers synthesized from C7–C10 aliphatic dicarboxylic acids, 2-methyl-1,3-propanediol, and L-lactide

Elastic materials with high biodegradability should replace those with low biodegradability in some applications. We previously reported biodegradable thermoplastic elastomers (TPEs) composed of poly(l-lactide) (PLLA) as a hard segment and aliphatic polyesters from 2-methyl-1,3-propanediol (MP) and short aliphatic dicarboxylic acids as soft segments. In this study, we synthesized the biodegradable thermoplastic elastomers using longer aliphatic dicarboxylic acids to develop the TPEs with lower glass-transition temperature (Tg) and high biodegradability. A series of aliphatic polyesters were prepared by polycondensation of MP and aliphatic dicarboxylic acids bearing 7–10 carbons. Among them, poly(2-methyl-1,3-propylene azelate) (PMP9) was found to have lower Tg, amorphous nature, and high biodegradability in seawater. The ring-opening polymerization of l-lactide (LLA) using PMP9 as a macroinitiator afforded triblock copolymers, PLLA-b-PMP9-b-PLLA (TPE9). The successive addition of LLA to in-situ generated PMP9 resulted in the successful one-pot synthesis of high molecular weight TPE9. The TPE9s showed both low Tg of the PMP9 segment and high melting temperature of the PLLA segment. The TPE9s exhibited elastic behavior showing elongation at break of up to 2500 % in tensile tests and also high biodegradability in seawater. Thus, we developed potentially practical TPE with tunable physical properties and high biodegradability obtainable from easily available and renewable starting materials.

Alternating Graft Copolymer Carrying PLA Graft Chains at Every Other Unit: Sequence Impacts on Crystallization Behaviors.

Alternating graft copolymers were precisely synthesized via selective cyclopolymerization of pendant-transformable divinyl monomer (1), post-polymerization modification via aminolysis with alkylamine, and ring-opening polymerization of l-lactide (LLA) from the hydroxy pendant group in alternating sequence. The poly(LLA) (PLLA) graft chain on the alternating copolymer gave a higher crystallization degree on the isothermal treatment than that on the random counterpart likely because of the periodic sequence. The comonomer pendant group from alkylamine in the aminolysis reaction in the alternating sequence affected the crystallization behaviors, and the oligoethylene glycol (OEG) group promoted the crystallization thanks to the larger free volume effect. As for the stereocomplex formation of the racemic mixture of enantiomeric PLLA and poly(d-lactide) (PDLA) chains, the alternating graft copolymer gave a higher degree of stereocomplex crystallization in the mixture with the enantiomer homopolymer than the random analogue.

The Facile Synthesis of Nickel-Doped Composite Magnetic Ni@CoO@ZIF-67 as an Efficient Heterogeneous Catalyst for the Ring-Opening Polymerization of L-Lactide

The ring-opening polymerization of L-lactide is a crucial route for producing biodegradable polylactides (PLAs). Developing an efficient catalyst for this process poses significant challenges. Herein, we report the successful incorporation of nickel during the crystallization of ZIF-67, the derivation of the abundant and stable CoO source, to obtain the composite magnetic Ni@CoO@ZIF-67 using the solid-state thermal (SST) method. The characterization of the resulting materials revealed that nickel atoms are well dispersed in the composite CoO@ZIF-67, imparting additional magnetic properties. The composite Ni@CoO@ZIF-67 demonstrated superior performance as a heterogeneous catalyst for the ring-opening polymerization of L-lactide compared to reference materials such as Ni-Hmim, CoO, ZIF-67, and CoO@ZIF-67. Furthermore, the magnetic property of Ni@CoO@ZIF-67 offers practical advantages, enabling easier separation and recycling of the catalyst. Notably, the SST method facilitates the single-step synthesis of composite magnetic Ni@CoO@ZIF-67 under solvent-free conditions, representing a significant advancement in catalyst development. This approach not only simplifies the synthesis process but also inspires further developments of heterogeneous magnetic catalysts for a variety of effective and diverse reactions.

L-Lactide ring-opening polymerization: a multi-objective optimization approach through mathematical modeling

L-Lactide ring-opening polymerization: a multi-objective optimization approach through mathematical modeling

Comparison of three elements (In, Sn, and Sb) in the same period as catalysts in the ring-opening polymerization of l-lactide: from amorphous to semicrystalline polyesters.

The ring-opening polymerization (ROP) of l-lactide (l-LA) is the main method for synthesizing poly(l-lactide) (PLLA), in which choosing the catalyst is one of the most important parameters. In this work, we focused on the systematic study of catalysts based on p-block elements from period 5, such as indium(iii), tin(ii), tin(iv) and antimony(iii) acetates, which displayed contrasting performances influenced by the oxidation state of the metal center. Analysis of the obtained oligomers by different techniques, including nuclear magnetic resonance (NMR), differential scanning calorimetry (DSC), polarized optical microscopy (POM) and matrix-assisted laser desorption ionization-time-of-flight (MALDI-TOF), revealed the selectivity of each catalyst toward the ROP of l-LA. Tin(ii) acetate showed the best performance, making it the best catalyst of this series for synthesizing PLLA. Indium(iii) and tin(ii) acetates induced an amorphous and semicrystalline polyester, respectively. The kinetic study evidenced the excellent performance of tin(ii) acetate in the ROP of l-LA. This catalyst reached high conversions in a quarter of the total reaction time, positioning it as the most catalytically active of the selected p-block acetate catalysts. Finally, the coordination-insertion mechanism by the catalyst in the initiation step was corroborated through the development of a mechanistic study applying the density functional theory (DFT).

Tunable zinc benzamidinate complexes: coordination modes and catalytic activity in the ring-opening polymerization of L-lactide.

Seven asymmetric zinc benzamidinate complexes featuring or lacking side-arm functionalities were synthesized. Using equimolar zinc reagent produced distinct dinuclear motifs [(C6H5-C = NC6H5)ZnEt]2 (R = tBu, 1; (CH2)2OMe, 2; (CH2)2NMe2, 3). Half the zinc reagent yielded dinuclear [(C6H5-C = NC6H5)2Zn]2 (R = tBu, 4) or mononuclear zinc bis(chelate) complexes (R = (CH2)2OMe, 5; (CH2)2NMe2, 6; CH2Py, 7). Molecular structures of 1-4 and 7 were determined via single-crystal X-ray diffraction. Altering benzamidinate substituents modifies both coordination modes and catalytic activities in ring-opening polymerization of L-lactide. Specifically, complex 7 exhibits enhanced catalytic activity at 25 °C using 100 equivalents of L-lactide with a turnover frequency of 1820 h-1.

Properties of PLA-co-PBSu Copolymers Rapidly Synthesized by Reactive Processing

This work describes the synthesis of poly(lactic acid) by the ring-opening polymerization of L-lactide in the presence of oligo(butylene succinate) with two different molecular weights (Mn = 6100 and 16300 g/mol) as a macroinitiator during reactive processing. The macroinitiators were added in concentrations 1 wt%, 2.5 wt%, 5 wt%, 10 wt% and 15 wt% in respect to the L-lactide mass in the premix. The properties of the received copolymers were extensively studied with spectroscopic techniques, GPC, DSC, XRD, TGA as well as nanoindentation. Blocky copolymers were received with number average molecular weights ranging from 30 to 100 kg/mol, which decreased with increasing the PBSu content in the feed. The introduction of the flexible PBSu chains decreased the single glass transition detected, while DSC and XRD gave indications that both components crystallized in the copolymers with PBSu premix content > 5 wt%. Thermal stability was maintained and depended on the composition and molecular weight. Nanoindentation showed that despite the decreasing trend of hardness and elastic modulus with increasing PBSu content, the PLA-PBSu 2.5% copolymers had simultaneously higher elasticity modulus and strength compared to the other compositions, possibly because of a complementary effect of their high molecular weight and crystallinity. These copolymers were promising for production with continuous reactive extrusion, a novel, fast and economically viable method to commercially produce PLA-based polymers.

Mono- and Bimetallic Aluminum Complexes Supported by Thioether-Amide Ligands: Synthesis, Characterization, and Application in the Ring Opening Polymerization of l-Lactide

Mono- and bimetallic aluminum complexes bearing bidentate NS or tetradentate NSSN ligands have been synthesized via reaction of AlMe3 with the corresponding proligand and spectroscopically characterized. In these complexes the aluminum centers are surrounded by anionic nitrogen and neutral sulfur atoms that, together with the carbon atoms of the alkyl groups, produce tetrahedral coordination geometries. In the bimetallic complexes the two metal centers are linked by a thioether-bridge of different lengths. The solid state structure of the complexes featuring the thioethyl or thiopropyl bridge were determined by X-ray diffraction studies. Both mono- and bimetallic aluminum complexes display fluxional behaviors in solution. After proper activation, all complexes were able to promote the ring opening polymerization of l-lactide in toluene solution. The polymerizations were well controlled as testified by the linear increase of the molecular weights with the conversions and the narrow polydispersity indexes. The highest activity was observed for the bimetallic complex bearing the NSSN ligand with the shortest bridge (ethyl bridge) with a turnover frequency of 11.6 molLA·molAl–1·h–1 (toluene, 80 °C). The activity decreased as the distance between the two metal centers increased. Moreover, the activity of the bimetallic complex with the ethyl bridge was higher than those of the monometallic ones. These findings suggest that a cooperative interaction between two aluminum centers is operative in the bimetallic complex with the shortest bridge.

Branched Amphiphilic Polylactides as a Polymer Matrix Component for Biodegradable Implants.

The combination of biocompatibility, biodegradability, and high mechanical strength has provided a steady growth in interest in the synthesis and application of lactic acid-based polyesters for the creation of implants. On the other hand, the hydrophobicity of polylactide limits the possibilities of its use in biomedical fields. The ring-opening polymerization of L-lactide, catalyzed by tin (II) 2-ethylhexanoate in the presence of 2,2-bis(hydroxymethyl)propionic acid, and an ester of polyethylene glycol monomethyl ester and 2,2-bis(hydroxymethyl)propionic acid accompanied by the introduction of a pool of hydrophilic groups, that reduce the contact angle, were considered. The structures of the synthesized amphiphilic branched pegylated copolylactides were characterized by 1H NMR spectroscopy and gel permeation chromatography. The resulting amphiphilic copolylactides, with a narrow MWD (1.14-1.22) and molecular weight of 5000-13,000, were used to prepare interpolymer mixtures with PLLA. Already, with the introduction of 10 wt% branched pegylated copolylactides, PLLA-based films had reduced brittleness, hydrophilicity, with a water contact angle of 71.9-88.5°, and increased water absorption. An additional decrease in the water contact angle, of 66.1°, was achieved by filling the mixed polylactide films with 20 wt% hydroxyapatite, which also led to a moderate decrease in strength and ultimate tensile elongation. At the same time, the PLLA modification did not have a significant effect on the melting point and the glass transition temperature; however, the filling with hydroxyapatite increased the thermal stability.

One-pot synthesis of liquid photocrosslinkable poly(l-lactide) with terminal triacrylate.

We synthesized a poly(l-lactide)-pentaerythritol triacrylate (PETA) polymer modified with acrylic trifunctional groups using a one-pot method based on ring-opening polymerization of l-lactide and PETA. We calculated the molecular weight and structure of PLA-PETA using gel permeation chromatography (GPC) and nuclear magnetic resonance (NMR) (1H, 13C, heteronuclear multiple bond correlation [HMBC]) spectroscopy. Photocrosslinking PLA-PETA using the Omnirad 1173 photoinitiator yielded a transparent sample with 91% crosslinkage. The crosslinked sample was analyzed using differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and thermomechanical analysis (TMA) to determine its thermal properties and thermal expansion coefficient. In vitro cell toxicity tests showed an average cell viability >90%, indicating that the PLA-PETA polymer had good biocompatibility with cells after photocrosslinking.

End-functionalized diblock copolymers by mix and match of poly(2-oxazoline) and polyester building blocks

2-(4-(Iodomethyl)benzyl)isoindoline-1,3-dione was utilized as a protected amine-functionalized initiator for the cationic ring opening-polymerization (CROP) of 2-ethyl-2-oxazoline. As kinetic studies indicated a well-controlled polymerization, the CROP was terminated with sodium azide. Subsequent deprotection of the α-end group enabled successive attachment of a targeting ligand, e.g., retinoic acid or a proteogenic amino acid as a peptide model at the α-chain end. The heterotelechelic PEtOx were coupled to cyclooctyne end-functionalized polylactide, which was obtained by initiating the ring opening polymerization of l-lactide via a cyclooctyne based alcohol, utilizing strain-promoted azide-alkyne cycloaddidtion. In-depth characterization via mass spectrometry, 1H NMR spectroscopy, size exclusion chromatography, and infrared spectroscopy investigations verified the success of all synthetic steps and the preservation of retinoyl and leucine moieties also in the end-functionalized PEtOx-b-PLA block copolymers. Circumventing potential degradation of the polyester block during ligand attachment, the heterotelechelic PEtOx represents a universal building block useful for modular approaches towards tailored materials for nanomedicine.

In Situ Ring-Opening Polymerization of L-lactide on the Surface of Pristine and Aminated Silica: Synthesis and Metal Ions Extraction.

The development of functional materials from food waste sources and minerals is currently of high importance. In the present work, polylactic acid (PLA)/silica composites were prepared by in situ ring-opening polymerizations of L-lactide onto the surface of pristine (Silochrom) and amine-functionalized (Silochrom-NH2) silica. The characteristics of the ring-opening polymerization onto the surface of modified and unmodified silica were identified and discussed. Fourier transform infrared spectroscopy was used to confirm the polymerization of lactide onto the silica surface, and thermogravimetric analysis determined that PLA constituted 5.9% and 7.5% of the composite mass for Silochrom/PLA and Silochrom-NH2/PLA, respectively. The sorption properties of the composites with respect to Pb(II), Co(II), and Cu(II) ions were investigated, and the effect of contact time, initial metal ion concentration, and initial pH were evaluated. Silochrom-NH2/PLA composites were found to have a higher adsorption capacity than Silochrom/PLA for all chosen ions, with the highest adsorption value occurring for Pb2+ at 1.5 mmol/g (90% removal efficiency). The composites showed the highest performance in the neutral or near-neutral pH (created by distilled water or buffer pH 6.86) during the first 15 min of phase contact. The equilibrium characteristics of adsorption were found to follow the Langmuir isotherm model rather than the Freundlich and Temkin models. Perspective applications for these PLA/silicas include remediation of industrial wastewater or leaching solutions from spent lead-acid and Li-ion batteries.

The Effect of Solvent Hydrophilicity on the Enzymatic Ring-Opening Polymerization of L-Lactide by Candida rugosa Lipase.

Contradictions have been reported on the effect of organic solvents, especially toluene, on enzymatic ring-opening polymerization (eROP) of L-lactide. Studies have shown that log P, a common measure of hydrophilicity, affects enzyme activity. This study examines the effect of solvents with various log P values on the eROP of L-lactide, performed using Candida rugosa lipase (CRL). N,N-dimethylacetamide (DMA), 1,2-dimethoxybenzene, 1,4-dimethoxybenzene, diphenyl ether, and dodecane were used as the organic solvents. The eROP in ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIM][PF6]) was also conducted to compare its performance with the organic solvents. The results show that [BMIM][PF6]-mediated eROP gave better conversion and molecular weight than the organic solvent-mediated eROP. In this study, the effects of solvents hydrophilicity are discussed, including the possibility of hexafluorophosphate ion ([PF6]−) hydrolysis to occur.

Synthesis of paramylon ester-graft-PLA copolymers and its two-step enzymatic degradation by proteinase K and β-1,3-glucanase

Paramylon ester-graft-poly(lactic acid) (PLA) copolymers were synthesized by the ring opening polymerization of l-lactide with paramylon acetate (PaAc) samples having an acetate degree of substitution (DS) from 0.5 to 2.2 (PaAc-g-PLA) or paramylon propionate (PaPr) samples with a propionate DS of 1.6 or 2.0 (PaPr-g-PLA). These copolymers exhibited thermoplasticity and some formed self-supporting melt-pressed films. Analyses of annealed films using differential scanning calorimetry showed that their thermal properties varied with the PLA DS. The enzymatic degradation behaviors of the neat paramylon as well as the PaAc and PaPr were investigated by treating these materials with β-1,3-glucanase followed by spectrometric analysis of the glucose levels in the buffer solutions, prior to the investigation of the copolymers. The data showed that 9 wt% glucose was obtained from the neat paramylon after 7 d and that the PaAc and PaPr were also degraded by β-1,3-glucanase. The concentration of liberated glucose was also found to decrease as the DS increased. Two-step enzymatic degradation tests were subsequently carried out with PaAc-g-PLA and PaPr-g-PLA specimens. In the first step, proteinase K was applied to degrade the PLA side-chains and high performance liquid chromatography (HPLC) was used to assess the release of lactic acid. Both HPLC and nuclear magnetic resonance (NMR) analyses established that the PLA side-chains of both the PaAc-g-PLA and PaPr-g-PLA specimens were successfully degraded. In the second step, β-1,3-glucanase was employed to decompose the remaining paramylon ester backbones. Monitoring the release of glucose showed that these backbones were successfully degraded in trials using the PaAc0.5-g-PLA and PaAc1.0-g-PLAs after 7 d These results confirmed that both copolymers could be broken down via this two-step enzymatic treatment, and that degradation by β-1,3-glucanase was dependent on the DS of the paramylon ester backbone. The results of this work show that PaAc1.0-g-PLA is a plastic material capable of thermal processing and is also completely biodegradable.

One-step synthesis of sequence-controlled multiblock polymers with up to 11 segments from monomer mixture

Switchable polymerization holds considerable potential for the synthesis of highly sequence-controlled multiblock. To date, this method has been limited to three-component systems, which enables the straightforward synthesis of multiblock polymers with less than five blocks. Herein, we report a self-switchable polymerization enabled by simple alkali metal carboxylate catalysts that directly polymerize six-component mixtures into multiblock polymers consisting of up to 11 blocks. Without an external trigger, the catalyst polymerization spontaneously connects five catalytic cycles in an orderly manner, involving four anhydride/epoxide ring-opening copolymerizations and one L-lactide ring-opening polymerization, creating a one-step synthetic pathway. Following this autotandem catalysis, reasonable combinations of different catalytic cycles allow the direct preparation of diverse, sequence-controlled, multiblock copolymers even containing various hyperbranched architectures. This method shows considerable promise in the synthesis of sequentially and architecturally complex polymers, with high monomer sequence control that provides the potential for designing materials.

Elitist Genetic Algorithm Strategy for Multi-Objective Optimization of L-Lactide Ring Opening Polymerization in Batch Reactor

Elitist Genetic Algorithm Strategy for Multi-Objective Optimization of L-Lactide Ring Opening Polymerization in Batch Reactor

Biodegradable PCL-b-PLA Microspheres with Nanopores Prepared via RAFT Polymerization and UV Photodegradation of Poly(Methyl Vinyl Ketone) Blocks.

Biodegradable triblock copolymers based on poly(ε-caprolactone) (PCL) and poly(lactic acid) (PLA) were synthesized via ring-opening polymerization of L-lactide followed by reversible addition–fragmentation chain-transfer (RAFT) polymerization of poly(methyl vinyl ketone) (PMVK) as a photodegradable block, and characterized by FT-IR and 1H NMR spectroscopy for structural analyses, and by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) for their thermal properties. Porous, biodegradable PCL-b-PLA microspheres were fabricated via the oil/water (O/W) emulsion evaporation method, followed by photodegradation of PMVK blocks by UV irradiation. The macro-chain transfer agent (CTA) synthesized by reacting a carboxylic-acid-terminated CTA—S-1-dodecyl-S′-(a,a′-dimethyl-a′′-acetic acid)trithiocarbonate (DDMAT)—with a hydroxyl-terminated PCL-b-PLA block copolymer was used to synthesize well-defined triblock copolymers with methyl vinyl ketone via RAFT polymerization with controlled molecular weights and narrow polydispersity. Gel permeation chromatography traces indicated that the molecular weight of the triblock copolymer decreased with UV irradiation time because of the photodegradation of the PMVK blocks. The morphology of the microspheres before and after UV irradiation was investigated using SEM and videos of three-dimensional confocal laser microscopy, showing a change in their surface texture from smooth to rough, with high porosity owing to the photodegradation of the PMVK blocks to become porous templates.

Bis(phenyl-β-diketonato)titanium(IV) ethoxide complexes: Ring-opening polymerization of l-lactide by solvent-free microwave irradiation

A range of functionalized bis(phenyl-β-diketonato)titanium(IV) ethoxide complexes of the type [Ti(L)2(OEt)2], containing two asymmetric or symmetric phenyl-β-diketonate ligands (L), have been synthesized and fully characterized. Single crystal X-ray diffraction has been used to confirm that all structures crystallize with the ethoxide ancillary ligands in a cis arrangement and NMR spectra show characteristic ligand rearrangement in solution. The complexes have been screened as catalysts in the ring-opening polymerization (ROP) of l-lactide (L-LA) to yield polylactide (PLA), by using microwave (MW) and conventional heating. The resulting polymers have high molecular weights but a high polydispersity index (PDI) which is suggestive of transesterification. However, unlike conventional heating methods, the polymerization by MW reaction leads to a retention in stereochemistry of the resulting polymer in significantly shorter time periods.

Synthesis of well-defined ABC2, AB2C3, (ABC2)4, and (ABC2)6 miktoarm star-branched polymers by combining organocatalyzed group transfer polymerization and ring-opening polymerization using multialdehydes as chain linkers

A series of well-defined ABC2, AB2C3, (ABC2)4, and (ABC2)6 type miktoarm star branched polymers consisting of poly(methyl methacrylate) (PMMA), poly(methyl acrylate) (PMA), and poly(L-lactide) (PLLA) were obtained by the combination of organocatalyzed group transfer polymerization (GTP) and ring-opening polymerization (ROP) using bi and trialdehydic aromatic compounds, 4-(diethoxymethyl)benzaldehyde and benzene-1,3,5-tricarbaldehyde respectively, as the chain end coupling agents. The entire synthetic route includes three main steps. The first one is an arm-first route in which the Mukaiyama aldol-type end coupling reaction between a living PMMA obtained through the t-Bu-P4-catalyzed GTP of MMA and an excess amount of a coupling agent was implemented to afford the aromatic aldehyde-bearing PMMA macroterminator. The second one is still an arm-first route in which a further aldol-type end coupling reaction between the aldehyde group left in the aforementioned PMMA macroterminator and a living PMA obtained by the dimethylphenylsilane-mediated B(C6F5)3-catalyzed GTP of MA to produce the multihydroxyl functionalized PMMA and PMA based copolymers, which were later used as the macroinitiators. Therefore, the third one is the ROP of L-lactide (LLA) using the above macroinitiators to give the final star branched polymers in a core-first way. Interestingly, the PMA and PMMA arms could be readily cleaved from the end-coupling bonds using fluoride anion. The resulting star branched polymers were well characterized by SEC, 1H NMR, MALLS, and TGA measurements.

Enhancing catalytic activity via metal tuning of zeolitic imidazole frameworks for ring opening polymerization of l-lactide

A catalyst series of zeolitic imidazole frameworks (ZIFs) with a sodalite (SOD) structure was explored as an effective heterogeneous catalyst for l-lactide polymerization into biodegradable polylactides (PLAs). The catalyst series of ZIF-8, ZIF-67, and bimetallic ZnCo-ZIF was synthesized under the green method (room temperature synthesis), which contained a variance in the metal species/contents. The chemical and physical properties of catalysts were characterized by several techniques to illustrate the relation between catalyst properties and catalytic performance. The results indicated that the metals in the ZIF structure revealed an influencing role in catalytic activities, kinetic rates, and properties of polymer products under bulk ring-opening polymerization of l-lactide. Moreover, the best performing ZIF showed potential as a heterogeneous catalyst since it could be reused at least four times without significant loss of catalytic activity.