Polymerization Of L-lactide Research Articles

Poxylated stereocomplexes from PEtOx-b-PLA diblock copolymers

An ω-hydroxyl terminated poly(2-ethyl-2-oxazoline) (PEtOx) was obtained by termination of the cationic ring-opening polymerization of 2-ethyl-2-oxazoline with acetate and subsequent transesterification with methanol. The resulting PEtOx-OH featuring a degree of polymerization (DP) of 20 was used as a macroinitiator for the ring-opening polymerization of l-lactide as well as d-lactide. The resulting PEtOx-b-PLA block copolymers featured DP values of 25, 50, 100 and 150, respectively, and were characterized by means of size exclusion chromatography, 1H NMR spectroscopy as well as matrix-assisted laser desorption ionization mass spectrometry. Differential scanning calorimetry, wide-angle x-ray scattering and polarized light microscopy indicated the formation of stereocomplexes in racemic blends of PEtOx-b-PLA with opposing chirality. Thereby, the amorphous PEtOx block did not affect the modification of the stereocomplex crystallites, as shown by comparison with data obtained from PLA homopolymer stereocomplexes. Similar to those, the degree of crystallinity and melting temperature decreased with increasing molar mass of the PLA in the stereocomplexes formed from PEtOx-b-PLA block copolymers.

Controlled cationic ring-opening polymerization of L-lactide by organic ion pair: novel approach to isotactic-rich and crystalline polylactide

Controlled cationic ring-opening polymerization of L-lactide by organic ion pair: novel approach to isotactic-rich and crystalline polylactide

Simultaneous strengthening and toughening of PLA with full recyclability enabled by resin-microsphere-modified L-lactide oligomers

Various strategies have been developed to improve the brittleness of poly (lactic acid) (PLA), most of which still suffer from the toughness-strength trade-off dilemma. Herein, we prepared phenol–formaldehyde-resin microspheres (PFM) with aliphatic hydroxyl groups to initiate L-lactide polymerization and synthesized a series of PFM-modified L-lactide oligomers (PFM-OLLA) bearing different arm lengths. PFM-OLLA were then physically blended with commercial PLA in different weight ratios to prepare synchronously strengthened and toughened PFM-OLLA/PLA composites. After blending with 4 % PFM2.5-OLLA (PFM content: 2.5 %), the mechanical properties of the PFM2.5-OLLA/PLA composites were best. PFM2.5-OLLA efficiently improved the crystallization behaviors of the PFM2.5-OLLA/PLA composites, thereby significantly enhancing their strength and toughness. The maximum tensile yield strength (40.2 MPa), elongation at break (85.7 %), and impact strength (20.8 kJ/m2) of PFM2.5-OLLA/PLA composites could respectively increase by 44.2 %, 465.7 %, and 100 %, compared to the values of neat PLA. The microscopic strengthening and toughening mechanisms were attributed to the rigidity of PFM, and the heterogeneous nucleating ability as well as larger free volume of PFM2.5-OLLA, whereas the visual toughening effects were attributed to multiple crazing and shear yielding phenomena. After simple alcoholysis and filtration, the polymer components were completely converted into methyl lactate. The recycled PFM, exhibiting excellent chemical stability, were reused to synthesize a new PFM-OLLA for strengthening and toughening PLA. This study provides a sustainable strategy for the development of high-performance PLA engineering materials showing great application potentials in the automotive, electronics and housing fields.

Polyester Adhesives via One-Pot, One-Step Copolymerization of Cyclic Anhydride, Epoxide, and Lactide.

Polyesters (PEs) are sustainable alternatives for conventional polymers owing to their potential degradability, recyclability, and the wide availability of bio-based monomers for their synthesis. Herein, we used a one-pot, one-step self-switchable polymerization linking the ring-opening alternating copolymerization (ROAC) of epoxides/cyclic anhydrides with the ring-opening polymerization (ROP) of L-lactide (LLA) to synthesize PE-based hot-melt adhesives with a high bio-based content. In the cesium pivalate-catalyzed self-switchable polymerization of glutaric anhydride (GA), butylene oxide (BO), and LLA using a diol initiator, the ROAC of GA and BO proceeded whereas the ROP of LLA simultaneously proceeded very slowly, resulting in a copolyester consisting of poly(GA-alt-BO) and poly(L-lactide) (PLLA) segments with tapered regions, that is, PLLA-tapered block-poly(GA-alt-BO)-tapered block-PLLA (PLLA-tb-poly(GA-alt-BO)-tb-PLLA). Additionally, a series of tapered-block or real-block copolyesters consisting of poly(anhydride-alt-epoxide) (A segment) and PLLA (B segment) with AB-, BAB-, (AB)3-, and (AB)4-type architectures of different compositions and molecular weights were synthesized by varying the monomer combinations, alcohol initiators, and initial feed ratios. The lap shear tests of these copolyesters revealed an excellent relationship between the adhesive strength and polymer structural parameters. The (AB)4-type star-block copolyester (poly(GA-alt-BO)-tb-PLLA)4 exhibited the best adhesive strength (6.74 ± 0.64 MPa), comparable to that of commercial products, such as PE-based and poly(vinyl acetate)-based hot-melt adhesives.

Organocatalysts for L-Lactide polymerization: 2-alkyl- and 2-aryl-1,1,3,3-tetramethylguanidines

A series of 2-alkyl- and 2-aryl-1,1,3,3-tetramethylguanidine derivatives were synthesized, and their application in L-Lactide (LA) polymerization was studied. Bn-TMG was the best catalyst in LA polymerization ( [Bn-TMG] = 5 mM, conversion = 94 % after 4 h at 25 °C) compared to other monoguanidine derivatives. In addition, the catalytic activities of C2-dTMG exhibited higher catalytic activity than Bn-TMG, nBu-TMG (monoguanidine derivatives), and C3-dTMG (diguanidine derivative). Density functional theory calculations revealed that Bn-TMG deprotonated benzyl alcohol enhanced benzyl alcohol's initiation ability to LA, and the protonated Bn-TMG activated LA ring-opening process by interacting with the ether oxygen atom of LA. Bn-TMG presented excellent catalytic activity and controllability for LA polymerization at 25 °C.

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.

A comparative study of titanium complexes bearing 2-(arylideneamino)phenolates and 2-((arylimino)methyl)phenolates as catalysts for ring-opening polymerization of ε-caprolactone and L-lactide.

Titanium complexes bearing 2-(arylideneamino)phenolates and 2-((arylimino)methyl)phenolates were synthesized, and their catalytic activities in the polymerization of ε-caprolactone and L-lactide were studied. Among five-membered ring Ti complexes bearing 2-(arylideneamino)phenolates, FCl-Ti exhibited the highest level of catalytic activity ([CL] : [FCl-Ti] = 100 : 1, where [CL] = 2 M, and conv. = 86% at 60 °C after 9 h). For six-membered ring Ti complexes bearing 2-((arylimino)methyl)phenolates, SCl-Ti exhibited the highest level of catalytic activity ([CL] : [SCl-Ti] = 100 : 1, where [CL] = 2 M, and conv. = 88% at 60 °C after 118 h). The five-membered ring Ti complexes bearing 2-(arylideneamino)phenolates exhibited a higher level of catalytic activity (6.1-12.8 fold for the polymerization of ε-caprolactone and 6.2-23.0 fold for the polymerization of L-lactide) than the six-membered ring Ti complexes bearing 2-((arylimino)methyl)phenolates. The density functional theory (DFT) results revealed that the free energy of the first transition state FH-Ti-TS1 is 36.49 kcal mol-1 which is lower than that of SH-Ti-TS1 (46.58 kcal mol-1), which was ascribed to the fact that the Ti-Nim bond (2.742 Å) of FH-Ti-TS1 is longer than that of SH-Ti-TS1 (2.229 Å) and reduces the repulsion between ligands.

MICROWAVE ASSISTED LACTIDE-GLYCOLIDE HOMO AND COPOLYMERIZATION INITIATED BY MAGNESIUM LACTATE

In this work, microwave-assisted ring opening polymerization (ROP) of lactide (LA) and glycolide (GA) initiated by magnesium lactate was investigated. The influence of microwave power, temperature, and reaction time on homopolymers and copolymer’s structure and thermal properties is discussed. Polymerization of L-lactide (LLA) initiated by the magnesium compound resulted in yields up to 78% and poly(L-lactic acid) (PLLA) with average molar mass of up to 30,600 g mol-1. Homopolymerization of glycolide generate poly(glycolic acid) (PGA) in yields up to 90% and in L-lactide/glycolide copolymerizations yields between 34-82%. PLLA prepared with the initiator presented microstructure with significant amount of stereo errors as the result of a racemization process during polymerization as well as low glass transition temperature (Tg) and melting temperature (Tm), while the PGAs presented high Tg, due to high crystallinity, and Tm in accordance with the literature. LLA and GA copolymerization result in poly(lactic acid-co-glycolic acid) (PLGA) with composition close to polymerization feed composition.

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).

Bis-thiourea and macrocyclic polyamines as binary organocatalysts for the ROP of lactide

New binary catalysts formed by a bis-thiourea and a series of flexible polyaza-macrocycles are revealed to be efficient catalysts for the ring opening polymerization (ROP) of l-lactide.

Applications of low-valent compounds with heavy group-14 elements.

Over the last two decades, the low-valent compounds of group-14 elements have received significant attention in several fields of chemistry owing to their unique electronic properties. The low-valent group-14 species include tetrylenes, tetryliumylidene, tetrylones, dimetallenes and dimetallynes. These low-valent group-14 species have shown applications in various areas such as organic transformations (hydroboration, cyanosilylation, N-functionalisation of amines, and hydroamination), small molecule activation (e.g. P4, As4, CO2, CO, H2, alkene, and alkyne) and materials. This review presents an in-depth discussion on low-valent group-14 species-catalyzed reactions, including polymerization of rac-lactide, L-lactide, DL-lactide, and caprolactone, followed by their photophysical properties (phosphorescence and fluorescence), thin film deposition (atomic layer deposition and vapor phase deposition), and medicinal applications. This review concisely summarizes current developments of low-valent heavier group-14 compounds, covering synthetic methodologies, structural aspects, and their applications in various fields of chemistry. Finally, their opportunities and challenges are examined and emphasized.

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.

Titanium and Vanadium Complexes of Tridentate Phenoxy-Imine and Phenoxy-Amine Ligands and Their Application in the Ring-Opening Polymerization of Cyclic Esters.

Phenoxy-imine and phenoxy-amine proligands, with the additional OH donor groups 2,4-tBu2-6-(2-CH2(OH)-C6H4N=CH)C6H3OH (L1H2), 6-(2-CH2(OH)-C6H4N=CH)C6H3OH (L2H2), and 2,4-tBu2-6-(2-CH2(OH)-C6H4NH-CH)C6H3OH (L3H2), were synthesized and their titanium (Ti-L1-Ti-L3) and vanadium (V-L1-V-L2) complexes were prepared in reactions with Ti(OiPr)4 and VO(OiPr)3, respectively. All new compounds were characterized with the use of FTIR, 1H, and 13C NMR spectroscopy; X-ray crystallography was also used to study proligands. All the complexes proved to be active catalysts in the ring-opening polymerization (ROP) of ε-caprolactone, rac-lactide, and L-lactide in the melt. The effects of the complex structure (transition metal type, presence of tBu substituents, and type of nitrogen donor group), as well as the polymerization time and temperature, on the monomer conversion and polymer properties were investigated in detail.

Ring-Opening Polymerization of rac-β-Butyrolactone Promoted by New Tetradentate Thioether-Amide Ligand-Type Zinc Complexes.

In this work, thioether-amide ligands featuring a combination of hard amide groups with soft donor groups have been employed to develop new zinc catalysts for the ring-opening polymerization of cyclic esters. All complexes were prepared in high yields through alkane elimination reactions with diethyl zinc and characterized using nuclear magnetic resonance (NMR) spectroscopy. Density functional theory (DFT) characterization provided insight into the parameters that influence catalytic activity, such as steric hindrance at the metal center, Lewis acidity and electronic density of thioether-amide ligands. In the presence of one equivalent of isopropanol, all complexes were active in the ring-opening polymerization of rac-β-butyrolactone. Quantitative conversion of 100 monomer equivalents was achieved within 1 h at 80 °C in a toluene solution. Number-average molecular weights increased linearly with monomer conversion; the values were in optimal agreement with those expected, and polydispersity index values were narrow and relatively constant throughout the course of polymerization. The most active complex was also effective in the ring-opening polymerization of ε-caprolactone and L-lactide. To propose a reliable reaction path, DFT calculations were undertaken. In the first step of the reaction, the acidic proton of the alcohol is transferred to the basic nitrogen atom of the amide ligand coordinated to the zinc ion. This leads to the alcoholysis of the Zn-N bond and the formation of an alcoholate derivative that starts the polymerization. In subsequent steps, the reaction follows the classical coordination-insertion mechanism.

Alcohol-initiated and Tin(II) 2-ethylhexanoate-catalyzed polymerization of l-lactide in bulk – About separate crystallization of cyclic and linear Poly(l-lactide)s

Alcohol-initiated ROPs of l-Lactide were performed at 140 °C in bulk with variation of the initiator/catalyst ratio and time. Lower ratios favor the formation of cycles which upon annealing display a change of the MALDI mass peak distribution towards a new maximum with a “saw-tooth pattern” of the mass peaks representing the cycles. Such a pattern was not observed for the mass peak of the linear chains. The coexistence of these patterns indicate that linear and cyclic poly (l-lactide)s (PLA) crystallize in separate crystals, and that the crystallites of the cycles are made up by extended rings. High Tm and ΔHm values confirm that these extended-ring crystallites represent a thermodynamically optimized form of PLA. Experiments with preformed cyclic and linear PLAs support this interpretation.

L-Lactide Polymerization Kinetics in the Presence of Ti(Tbse)2 by Differential Scanning Calorimetry

L-Lactide Polymerization Kinetics in the Presence of Ti(Tbse)2 by Differential Scanning Calorimetry

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.

Preparation of high-molecular-weight polylactide by ring-opening polymerization of l-lactide using base/bisurea binary organocatalyst

Preparation of high-molecular-weight polylactide by ring-opening polymerization of l-lactide using base/bisurea binary organocatalyst