Polymerization Of L-lactide Research Articles

Polymerization of l-lactide with SnCl2: A Low Toxic and Eco-friendly Catalyst

Polymerizations of l-lactide catalyzed either by neat SnCl2 or by SnCl2 + difunctional cocatalysts were conducted in bulk at 180, 160 and 140 °C with variation of the Lac/Cat ratio and time. With neat SnCl2 poly(L-lactide) having weight average molecular weights (uncorrected Mw’s) up to 190 000 g mol−1 were obtained mainly consisting of linear chains. Addition of salicylic acid or 1,1-bisphenol yielded a higher fraction of cyclic polylactides but lower molecular weights. Furthermore, SnCl2 was compared with Bu2SnCl2 and various other metal chlorides and the best results were obtained with SnCl2. With ethyl L-lactate as initiator SnCl2-catalyzed ROPs were performed at 120 °C and the lac/initiator ratio was varied. All these experiments were conducted under conditions allowing for comparison with ROPs catalyzed with neat Sn(II)-2-ethyhexanoate. Such a comparison was also performed with ε-caprolactone as monomer.

Polylactide materials with ultraviolet filtering function by introducing natural compound

ABSTRACT Through ring-opening polymerization of L-lactide, aloin, a natural compound, was bonded to the polymeric chains and the molecular structures of obtained PLA-An were characterized by FT-IR and NMR. Measurements on the UV-Vis absorption and fluorescence emission spectroscopy show that PLA-An has a characteristic absorption of aloin and a large Stokes shift at the state of solution in the PL, being capable of absorbing UV light and dissipating some of UV energy. Additionally, due to chemical bonds, aloin groups aren’t easy to be extracted by solvent, which allows aloin to play the role of ultraviolet absorption for a long time.

Synthesis, Properties, and Biodegradability of Thermoplastic Elastomers Made from 2-Methyl-1,3-propanediol, Glutaric Acid and Lactide.

An innovative type of biodegradable thermoplastic elastomers with improved mechanical properties from very common and potentially renewable sources, poly(L-lactide)-b-poly(2-methyl-1,3-propylene glutarate)-b-poly(L-lactide) (PLA-b-PMPG-b-PLA)s, has been developed for the first time. PLA-b-PMPG-b-PLAs were synthesized by polycondensation of 2-methyl-1,3-propanediol and glutaric acid and successive ring-opening polymerization of L-lactide, where PMPG is an amorphous central block with low glass transition temperature and PLA is hard semicrystalline terminal blocks. The copolymers showed glass transition temperature at lower than −40 °C and melting temperature at 130–152 °C. The tensile tests of these copolymers were also performed to evaluate their mechanical properties. The degradation of the copolymers and PMPG by enzymes proteinase K and lipase PS were investigated. Microbial biodegradation in seawater was also performed at 27 °C. The triblock copolymers and PMPG homopolymer were found to show 9–15% biodegradation within 28 days, representing their relatively high biodegradability in seawater. The macromolecular structure of the triblock copolymers of PLA and PMPG can be controlled to tune their mechanical and biodegradation properties, demonstrating their potential use in various applications.

Photocontrolled lactide ROP by the light-regulated release of potassium acetate from an azobenzene-bridged crown ether

An azobenzene-bridged crown ether was successfully used as a photoswitch for modulating the catalytic activity of potassium acetate (KOAc) in the ring-opening polymerization (ROP) of l-lactide (l-LA) when initiated from an exogenous alcohol.

Copolyesters of ε-caprolactone and l-lactide catalyzed by a tetrabutylammonium phthalimide-N-oxyl organocatalyst.

Aliphatic polyesters are biocompatible materials that can be used in biomedical applications. We report here the use of tetrabutylammonium phthalimide-N-oxyl catalyst (TBAPINO), as a thermally stable organocatalyst for the ring-opening polymerization (ROP) of cyclic esters under mild conditions. In the solution ROP of ε-caprolactone (ε-CL), quantitative conversion and Mn of ∼20 000 g mol−1 are achieved in a wide temperature range from −15 to 60 °C. Under bulk condition, the conversion of ε-CL reaches over 85% at 120 °C within 2 h. The living ROP character of l-lactide (l-LA) catalyzed over TBAPINO is proved by multiple additions of monomer in the bulk polymerization. The catalyst shows comparable selectivity towards the ring-opening polymerization of l-LA and ε-CL. Their copolymerization over TBAPINO is carried out in one-pot bulk condition in terms of the reaction time, monomer feed ratio, and sequence of addition. The colorless poly(ε-caprolactone-co-lactide) (PCLA) is obtained with considerable conversion of both monomers with the Mn over 22 000 g mol−1.

Synthesis and characterization of new Na+ complexes of N-benzyl cyclic peptoids and their role in the ring opening polymerization of l-lactide

Na+ complexes of cyclic peptoid were employed for the first time as catalyst for the l-lactide polymerization.

Investigation of the influence of impurities on the ring-opening polymerisation of L-Lactide from biogenous feedstock

In order to use a L-lactide monomer that is derived from fermentation processes it is necessary to understand, how the polymerisation process is influenced by impurities which derive from the production process. We have selected a group of likely contaminants and added them at various concentrations to the polymerisation of L-lactide using tin (II)-2-ethylhexanoate as catalyst and 2-methoxyethanol as initiator. The effect of impurities onto the global properties of the polymers such as glass transition temperature, melting point and molecular mass distribution were investigated and NMR and MALDI mass spectrometry were used to identify structural changes within the polymers. Thus, it could be shown that in reference experiments cyclic polymers and linear polymers with different starting groups are formed. Addition of ethanol and sodium carbonate showed the strongest influence on molecular masses as well as polymer structures, which could be elucidated by interpretation of the MALDI mass spectra and NMR data.

Novel Temperature/Reduction Dual-Stimulus Responsive Triblock Copolymer [P(MEO2MA-co- OEGMA)-b-PLLA-SS-PLLA-b-P(MEO2MA-co-OEGMA)] via a Combination of ROP and ATRP: Synthesis, Characterization and Application of Self-Assembled Micelles.

Novel temperature/reduction dual stimulus-responsive triblock copolymers, poly [2-(2-methoxyethoxy) ethyl methacrylate-co-oligo (ethylene glycol) methacrylate]-b-(L-polylactic acid)-SS-b-(L-polylactic acid)-b-poly[2-(2-methoxyethoxy) ethyl methacrylate-co-oligo(ethylene glycol)methacrylate] [P(MEO2MA-co-OEGMA)-b-PLLA-SS-PLLA-b-P(MEO2MA-co-OEGMA)] (SPMO), were synthesized by ring opening polymerization (ROP) of L-lactide and 2,2’-dithio diethanol (SS-DOH), and random copolymerization of MEO2MA and OEGMA monomers via atom transfer radical polymerization (ATRP) technology. The chemical structures and compositions of the novel copolymers were demonstrated by proton nuclear magnetic resonance (1H NMR) and Fourier transform infrared spectroscopy (FTIR). The molecular weights of the novel copolymers were measured by size exclusive chromatography (SEC) and proved to have a relatively narrow molecular weight distribution coefficient (ÐM ≤ 1.50). The water solubility and transmittance of the novel copolymers were tested via visual observation and UV–Vis spectroscopy, which proved the SPMO had a good hydrophilicity and suitable low critical solution temperature (LCST). The critical micelle concentration (CMC) of the novel polymeric micelles were determined using surface tension method and fluorescent probe technology. The particle size and morphology of the novel polymeric micelles were characterized by dynamic light scattering (DLS) and transmission electron microscopy (TEM). The sol–gel transition behavior of the novel copolymers was studied via vial flip experiments. Finally, the hydrophobic anticancer drug doxorubicin (DOX) was used to study the in vitro release behavior of the novel drug-loaded micelles. The results show that the novel polymeric micelles are expected to become a favorable drug carrier. In addition, they exhibit reductive responsiveness to the small molecule reducing agent dithiothreitol (DTT) and temperature responsiveness with temperature changes.

A One-Pot Strategy to Synthesize Block Copolyesters from Monomer Mixtures Using a Hydroxy-Functionized Ionic Liquid.

One-pot transformation of monomer mixtures into block copolymers remains a key challenge. Herein, a metal-free route to prepare block copolymers from monomer mixtures by a hydroxyl functionalized ionic liquid of 3-(2-hydroxyl-ethyl)-1-methylimidazolium bromide (HEMIMB) is described. HEMIMB can bridge two catalytic cycles including ring-opening alternating copolymerization (ROAC) of phthalic anhydride (PA) with epoxides and ring-opening polymerization (ROP) of L-lactide (LA), and enable a selective copolymerization from PA, LA, and epoxides. The selective copolymerization depends on the presence of PA in mixed feedstocks, exhibits the first ROAC of PA with epoxides and then ROP of LA to the formation of block polyesters in one-pot strategy. This work is beneficial to the development of metal-free catalysts for sequence-controlled polymerization that enable block architectures from mixtures of monomers.

Biodegradable poly (lactic acid)-poly (ε-caprolactone)-nanolignin composite films with excellent flexibility and UV barrier performance

In this work, poly(lactide-ε-caprolactone) copolymer grafted lignin nanoparticles (LNP-g-P(LA-CL) were synthesized, through a ring-open polymerization (ROP) of L-lactide and ε-caprolactone, initiated from the hydroxyl groups on LNP surface. Then PLA, PCL and various amounts of the copolymer were blended via a facile solvent casting approach. Mechanical tests showed that the addition of 6 wt% LNP-g-P(LA-CL) copolymer made a significant contribution to the toughness of PLA/PCL blend, which was enhanced by 4 folds in comparison with neat PLA. Meanwhile, the crystallization ability of both PLA and PCL were improved due to the better interfacial adhesion and mobility of PLA and PCL chains. Well-distributed elongated-fibrils and crazes, observed after tensile measurements for the nanocomposites, were responsible for absorbed energy, improved toughness and flexibility of PLA. Furthermore, UV–Vis spectroscopy measurements showed that the incorporation of 12 wt% of LNP-g-P(LA-CL) copolymer make PLA/PCL film able to shield almost 100 wt% of UV-B and UV-C irradiation. PLA/PCL-LNP nanocomposites can be used as impact resistance materials and in UV-resistance fields, such as sunshade and food packaging areas.

Macromolecular Dyes by Chromophore-Initiated Ring Opening Polymerization of L-Lactide.

End functionalized polylactides are prepared by ring opening polymerization of L-lactide in the presence of stannous octoate (Sn(Oct)2). Three chromophores, 9H-carbazol-ethanol (CA), 9-fluorenyl-methanol (FM), and 2-(4-(2-chloro-4-nitrophenylazo)-N-ethylphenylamino)ethanol (Disperse Red 13, DR), are for the first time used as co-initiators in the polymerization process. The polymerization reaction is initiated by conventional thermal treatment, but in the case of FM, microwave-assisted polymerization is also carried out. CA and FM absorb and emit in the UV portion of the electromagnetic spectrum, whereas DR absorbs in the visible part. The obtained end-capped polylactides derivatives show the same photophysical properties as the initiator, so they are “macromolecular dyes” (MDs) that can be used “as synthesized” or can be blended with commercial poly(lactic acid) (PLA). The blends of PLA with MDs have ultraviolet-visible (UV-Vis) absorption and fluorescence emission features similar to that of MDs and thermal properties typical of PLA. Finally, migration tests, carried out onto the blends of PLA with MDs and PLA with free chromophores, show that MDs are less released than free chromophores both in solution and in the solid phase.

Enhancing the Crystallization Performance of Poly(L-lactide) by Intramolecular Hybridizing with Tunable Self-assembly-type Oxalamide Segments

In this work, hydroxyl-terminated oxalamide compounds N1,N2-bis(2-hydroxyethyl)oxalamide (OXA1) and N1, N1′-(ethane-1,2-diyl)bis(N2-(2-hydroxyethyl)oxalamide (OXA2) were synthesized to initiate the ring-opening polymerization of L-lactide for preparation of oxalamide-hybridized poly(L-lactide) (PLAOXA), i.e., PLAOXA1 and PLAOXA2. The crystallization properties of PLA were improved by the self-assembly of the oxalamide segments in PLAOXA which served as the initial heterogeneous nuclei. The crystal growth kinetics was studied by Hoffman-Lauritzen theory and it revealed that the nucleation energy barrier of PLAOXA1 and PLAOXA2 was lower than that of PLA. Consequently, PLAOXA could crystallize much faster than PLA, accompanied with a decrease in spherulite size and half-life crystallization time by 74.8% and 86.5% (T = 125 °C), respectively. In addition, the final crystallinity of PLAOXA1 and PLAOXA2 was 6 and 8 times higher, respectively, in comparison with that of neat PLA under a controlled cooling rate of 10 °C/min. The results demonstrate that the hybridization of oxalamide segments in PLA backbone will serve as the self-heteronucleation for promoting the crystallization rate. The higher the content of oxalamide segments (PLAOXA2 compared with PLAOXA1) is, the stronger the promotion effect will be. Therefore, this study may provide a universal approach by hybridizing macromolecular structure to facilitate the crystallization of semi-crystalline polymer materials.

Titanium complexes bearing 2,6-Bis(o-hydroxyalkyl)pyridine ligands in the ring-opening polymerization of L-Lactide and ε-caprolactone

A series of titanium (Ti) compounds bearing 2,6-bis(o-hydroxyalkyl)pyridine ligands were synthesized and investigated as catalysts for the ring-opening polymerization of ε-caprolactone (CL) and L-lactide (LA). The Ti complexes with electron-withdrawing groups in pyridine rings or steric bulky groups in hydroxymethyl groups reduced the catalytic activity in CL and LA polymerizations, and MeLPh-TiOPr2 exhibited the highest catalytic activity ([CL] = 0.5 M, [CL]:[Cat] = 100:8, 60 °C, 7.5 h, conversion = 93%; [LA] = 0.5 M, [LA]:[Cat] = 100:8, 60 °C, 3.5 h, conversion = 98%). The density functional theory calculation results revealed that CL interacted with the ligand through weak hydrogen bonds, and then approached the Ti center. After being attacked by isopropyl oxide, the carbonyl group of CL bonded to the Ti center. After the rearrangement and ring opening of CL ring, CL was converted to poly-ε-caprolactone.

Ring-opening polymerization of L-lactide by using sodium complexes bearing amide as catalysts in high polar solvent

In this study, a series of sodium complexes with amidate ligands, including sulfonamide, acylamide, and aryl carbamate, were synthesized. These sodium complexes were used as catalysts to study the L-lactide (LA) polymerization in high polar solvent (dimethyl sulfoxide: tetrahydrofuran = 1:4). Among these sodium complexes, CTolOMe-Na (5) exhibited the highest catalytic activity (10 s, conversion > 99% with the ratio [LA]:[CTolOMe-Na (5)]:[BnOH] = 800:1:120, [CTolOMe-Na (5)] = 1.25 mM at 0 °C) and controllability (Đ = 1.10). To prove that CTolOMe-Na (5) can polymerize LA with special initiators in polar solvent, 1,4-benzenedimethanol and pentaerythritol were used as initiators in LA polymerization. The polymerization results revealed that end-chain-modified poly(lactides) with a precise molar mass (MnGPC: 3000–8800) and narrow dispersity (1.04–1.28) can be synthesized.

Comparison of L-lactide polymerization by using magnesium complexes bearing 2-(arylideneamino)phenolate and 2-((arylimino)methyl)phenolate ligands

A series of magnesium complexes bearing 2-(arylideneamino)phenolate (forming 5-membered ring Mg complexes) and 2-((arylimino)methyl)phenolate (forming 6-membered ring Mg complexes) ligands were synthesized, and their application in the ring-opening polymerization of L-lactide (LA) was investigated. The Mg complexes with 5-membered rings exhibit a higher polymerization rate and controllability for polylactide production than those with 6-membered rings do (one-fold to three-fold for LA polymerization). The density function theory calculation results revealed that benzyl alcohol approaches LA through the hydrogen bond with phenolate oxygen, and then initiates LA, with the proton transferring to phenolate oxygen to form the LA-OBn adduct. The LA-OBn adduct was activated using the proton present on phenolate oxygen to open the ring of the LA-OBn adduct. Moreover, the LA polymerization using L5ThioMg as a catalyst needs to overcome a 17.7 kcal/mol activation free energy that is lower than that of L6ThioMg (21.0 kcal/mol)

Synthesis and characterization of biocompatible poly (L-lactide) using zinc (II) salen complex

A biocompatible zinc (II) complex based on a tetradentate N,N,O,O-type salen ligand was synthesized, characterized and used for the solvent-free ring-opening polymerization (ROP) of L-lactide in bulk at 180 °C to prepare high molecular weight poly(L-lactide) (Mn : 82,600 Da; Mw : 140,000 Da; PDI: 1.70). Poly(L-lactide) (PLLA) was characterized using FTIR, 1H NMR, 13C NMR, GPC, TGA, DSC, WAXD, and MALDI-ToF. Kinetic measurement was carried out and first-order behavior to monomer was observed. The k app was found as 6 ± 0.001 × 10−4 s−1. The biocompatibility of the PLLA was confirmed by in vitro cytotoxicity against NIH/3T3 fibroblast cell line and can be used in biomedical applications.

N-heterocyclic ligand optimization for aluminum complexes in ε-caprolactone and L-Lactide polymerization

A series of aluminum complexes bearing heterocyclic amine ligands were synthesized, and their application in ε-caprolactone (CL) and L-Lactide (LA) polymerization and copolymerization were studied. The CL polymerization results revealed that ligands containing the higher electronegativity atom increased the polymerization rate of CL polymerization. Among these Al complexes, NON-AlMe3 bearing benzofurazan ligand was the best catalyst in CL polymerization ([NON-AlMe3] = 10 mM, conversion = 94% after 4 min at room temperature). In LA polymerization, the catalytic trend of Al complexes was random, and NCN-AlMe3 bearing 1-benzylbenzimidazole ligand was the best catalyst ([NCN-AlMe3] = 10 mM, conversion = 90% after 45 min at 80 °C). The selectivity of the production of a PLA-gradual-PCL copolymer could be controlled by different Al complexes. Our study revealed that the four-coordinated trimethyl Al complexes bearing heterocyclic amine ligands were easily synthesized and constitute an ideal catalyst design in CL polymerization.

Synthesis of Polylactic Acid Initiated through Biobased Antioxidants: Towards Intrinsically Active Food Packaging.

Polylactide (PLA)-based polymers, functionalized with biobased antioxidants, were synthesized, to develop an intrinsically active, biobased and potentially biodegradable material for food packaging applications. To achieve this result, phenolic antioxidants were exploited as initiators in the ring opening polymerization of l-lactide. The molecular weight, thermal properties and in vitro radical scavenging activity of the polymers obtained were compared with the ones of a PLA Natureworks 4043D, commonly used for flexible food packaging applications. The most promising synthesized polymer, bearing vanillyl alcohol as initiator (PLA-VA), was evaluated for active food packaging applications. Packaging with PLA-VA films reduced color and fat oxidation of salami during its shelf life.

ABA triblock copolyesters composed of poly(l-lactide) A hard blocks: comparison of amorphous and crystalline unsaturated aliphatic polyesters as B soft blocks

The property profiles of ABA triblock copolymers can be precisely customized by changing the chemical structure of the components. The identification of the midblock is the key point in the development of PLLA-containing ABA triblock copolymers. Two kinds of unsaturated aliphatic polyesters, crystalline poly(cis-butene succinate) (PcBS) and amorphous poly(cis-butene glutarate) (PcBG) with dihydroxyl end groups were prepared by polycondensation reactions. Then, dihydroxyl-terminated PcBS and PcBG were used as macroinitiators to initiate ring opening of polymerization of L-lactide toward two series of fully biobased biodegradable PLLA-b-PcBS-b-PLLA and PLLA-b-PcBG-b-PLLA triblock copolymers with PLLA as hard end-blocks. The influences of the midblocks and the endblocks length on microstructure, thermal and tensile properties of the triblock copolymers were studied. Compared to homopolymer PLLA, all the triblock copolymers had a much higher elongation at break with lower tensile strength and tensile modulus, depending on the length of PLLA blocks. It was found that the amorphous PcBG midblock plays a greater role than the crystalline PcBS midblock in enhancing the tensile toughness of ABA triblock copolymers. PLLA-b-PcBG-b-PLLA composed of shorter PLLA hard block displayed typical elastomeric behavior without yield, which is a promising aliphatic polyester-based thermoplastic elastomer. The unsaturated carbon–carbon double bonds in these polyesters backbone provide a variety of opportunities for further modifications.

Comparison study of ε‐caprolactone, L‐lactide, and ε‐decalactone polymerizations using aluminum complexes bearing pyrazole derivatives, and synthesis of polylactide‐gradual‐poly‐ε‐caprolactone copolymer

AbstractThis study compared ε‐caprolactone (CL), L‐lactide (LA), and ε‐decalactone (DL) polymerizations, where aluminum complexes bridged by two pyrazole ligands was used as catalysts. The reactivites of these Al complexes between CL, LA, and DL polymerization were different that L Bu 2Al 2Me 4, with the distort boat form, exhibits the greatest catalytic activity for LA and DL polymerization at 60°C but the lowest catalytic activity for CL polymerization at room temperature. This may be because dinuclear L Bu 2Al 2Me 4 cannot react with BnOH to form aluminum benzyl oxide at room temperature, making it unable to reduce catalytic activity. Because these aluminum complexes had different reactivities for LA and CL polymerizations, the selectivity of polylactide‐gradual‐poly‐ε‐caprolactones (PLA(10–80%)‐gradual‐PCL(59–79%)) (PLA‐g‐PCLs) was observed.