Ring-opening Polymerization Of Cyclic Esters Research Articles

Development of creatine and arginine-6-oligomer for the ring-opening polymerization of cyclic esters

Natural creatine and arginine-6-oligomer have been effectively engaged as ring-opening polymerization initiators of poly(L-lactide) (PLLA) and poly(ɛ-caprolactone) (PCL) in bulk. The nonlinear structure and thermal properties of the resulted polymers were further elucidated by 1H, 13C nuclear magnetic resonance, and a modulated differencial scanning calorimetry (MDSC). Thermal analysis indicated that the synthesized polymers had lower melting points, glass-transition temperatures, fusion enthalpy, and crystallization temperature than those of linear PCL or PLLA due to the presence of the arginine-6-oligomer in the macromolecule and crystalline imperfections caused by the branched structure. This study provides an efficient and metal-free method for the synthesis of branched biodegradable polymers with incorporated compounds, which exhibit therapeutic properties, adequate for the drug carrier applications. Open image in new window

Mono-aluminum, di-magnesium and tri-zinc complexes supported by bisphenolate ligand: Synthesis, characterization and catalytic studies for ring-opening polymerization of cyclic esters

Mono-aluminum, di-magnesium and tri-zinc complexes coordinated by a Biphen2- ligand (Biphen-H2 = 3,3′-di-tert-butyl-5,5′,6,6′-tetramethylbiphenyl-2,2′-diol) were synthesized and structurally characterized by X-ray single crystal determinations. The reaction of Biphen-H2 with AlMe3 (1.0 mol equiv.) in THF produced the tetra-coordinated monomeric aluminum complex [Al(Biphen)Me(THF)] (1), but treatment of Biphen-H2 with MgnBu2 under the same stoichiometric proportion in THF gave the dimeric magnesium complex [Mg(μ-Biphen)(THF)]2 (2). Tri-zinc [Zn3(μ, μ-Biphen)2Et2(THF)2] (3) resulted from treatment of Biphen-H2 with ZnEt2 (1.5 mol equiv) in THF; it consists of two different kinds of four-coordinated Zn centers. All of metal complexes are coordinated by at least one neutral THF coligand, indicating each metal center can behave as an active site to activate monomers during ring-opening polymerization (ROP). Catalysis for ROP of ε-caprolactone (ε-CL) or β-butyrolactone (β-BL) of complexes 1–3 are investigated, and the comparative studies of ε-CL polymerization are also discussed.

Ring-opening polymerization of cyclic esters initiated by cyclodextrins

Aliphatic polyesters and cyclodextrins are widely used for biomedical applications, due to their biocompatible and biodegradable character, and to the possibility to host molecules of pharmaceutical interest for the latter. Cyclodextrins have been used as initiators or co-initiators for the ring-opening polymerization of cyclic esters these last years, leading to functionalized polyesters. This mini-review reports recent developments in this field.

Synthesis and characterization of benzoxazine-functionalized amine bridged bis(phenolate) lanthanide complexes and their application in the ring-opening polymerization of cyclic esters

The synthesis and structures of lanthanide complexes supported by benzoxazine-functionalized amine bridged bis(phenolate) ligand 6,6'-(2-(8-tert-butyl-6-methyl-2H-benzo[e][1,3]oxazin-3(4H)-yl)ethylazanediyl)bis(methylene)bis(2-tert-butyl-4-methylphenolato) (L(2-)) are described. Salt metathesis reaction between lanthanide trichloride and 2 eq of LNa(2) in THF at room temperature afforded the corresponding "ate" complexes [L(2)LnNa(THF)(2)] (Ln[double bond, length as m-dash]Y (1), Nd (2), Er (3), Yb (4)). Further treatment of the product with 18-crown-6 afforded discrete ion-pair complexes [L(2)Ln][(18-crown-6)Na(THF)(2)] (Ln[double bond, length as m-dash]Y (5), Yb (6)). The single-crystal structural analyses of 1 and 3-6 revealed that the lanthanide cation and the sodium cation were bridged by two phenolate oxygen atoms in complexes 1, 3 and 4, while in complexes 5 and 6, the anion comprises a lanthanide cation coordinated by two L(2-) and the cation is comprised of a sodium cation surrounded by an 18-crown-6 and two THF molecules. These complexes were found to exhibit distinct activities towards the ring-opening polymerization of ε-caprolactone and l-lactide.

Lanthanide amidinates and guanidinates in catalysis and materials science: a continuing success story

Today the rare-earth elements play a critical role in numerous high-tech applications. This is why various areas of rare-earth chemistry are currently thriving. In organolanthanide chemistry the search for new ligand sets which are able to satisfy the coordination requirements of the large lanthanide cations continues to be a hot topic. Among the most successful approaches in this field is the use of amidinate and guanidinate ligands of the general types [RC(NR')(2)](-) (R = H, alkyl, aryl; R' = alkyl, cycloalkyl, aryl, SiMe(3)) and [R(2)NC(NR')(2)](-) (R = alkyl, SiMe(3); R' = alkyl, cycloalkyl, aryl, SiMe(3)), which can both be regarded as steric cyclopentadienyl equivalents. Mono-, di- and trisubstituted lanthanide amidinate and guanidinate complexes are all readily available. Various rare earth amidinates and guanidinates have turned out to be very efficient homogeneous catalysts e.g. for the polymerization of olefins and dienes, the ring-opening polymerization of cyclic esters or the guanylation of amines. Moreover, certain alkyl-substituted lanthanide tris(amidinates) and tris(guanidinates) were found to be highly volatile and are thus promising precursors for ALD (= atomic layer deposition) and MOCVD (= metal-organic chemical vapor deposition) processes in materials science, e.g. for the production of lanthanide nitride thin layers. This tutorial review covers the continuing success story of lanthanide amidinates and guanidinates which have undergone an astonishing transition from mere laboratory curiosities to efficient homogeneous catalysts as well as ALD and MOCVD precursors within the past 10 years.

Phenalenyl‐Based Molecules: Tuning the Lowest Unoccupied Molecular Orbital to Design a Catalyst

Phenalenyl in action: The cationic state of the phenalenyl system can be used to design Lewis acidic catalysts. The phenalenyl backbone can tune the energy of the lowest unoccupied molecular orbital (LUMO) of the molecule, which in turn controls the catalytic activity in the ring-opening polymerization of cyclic esters (see figure).

Ring-opening polymerization of cyclic esters in the presence of choline/SnOct2 catalytic system

Low-molecular weight poly(ε-caprolactone), polylactides, and copolymers of ε-caprolactone and lactide were synthesized by ring-opening polymerization of cyclic monomers with choline (CHOL) as a initiator and SnOct2 as a catalyst. Polymerization was conducted in bulk (120–160 °C) with high yield. Effects of temperature, reaction time, and CHOL dosage on the polymerization process were examined. Structure of products was characterized by means of MALDI-TOF, IR, and NMR.

Synthesis, characterization of carbon-bridged Bis(phenolate) neodymium complexes and their catalytic activity for ring-opening polymerization of cyclic esters

Three carbon-bridged bis(phenolate) neodymium complexes, [(MBMP)2Nd(μ3–Cl)Li(THF)2Li(THF)] (1), [(MBBP)2Nd(μ3-Cl)Li(THF)2Li(THF)] (2) and [(THF)2Nd(EDBP)2Li(THF)] (3) have been synthesized by one-pot reaction of NdCl3 and LiCH2SiMe3 with 6,6′-methylenebis(2-tert-butyl-4-methylphenol) (MBMP-H2), 6,6′-methylenebis(2,4-di-tert-butylphenol) (MBBP-H2) or 6,6′-(ethane- 1,1-diyl)bis(2,4-di-tert-butylphenol) (EDBP-H2), respectively, in a molar ratio of 1:4:2. The definitive structures of complexes 2 and 3 were determined by X-ray diffraction studies. Experimental results show that 1–3 efficiently initiate the ring-opening polymerization (ROP) of ε-caprolactone and ROP of L-lactide.

A Strategy for Control of "Random" Copolymerization of Lactide and Glycolide: Application to Synthesis of PEG-b-PLGA Block Polymers Having Narrow Dispersity.

Poly(lactic-co-glycolic acid) (PLGA) is a biodegradable copolymer that is also acceptable for use in a variety of biomedical applications. Typically, a random PLGA polymer is synthesized in a bulk batch polymerization using a tin-based catalyst at high temperatures. This methodology results in relatively broad polydispersity indexes (PDIs) due to transesterification, and the polymer product is often discolored. We report here the use of 1,8-diazabicyclo[5.4.0]-undec-7-ene (DBU), a known, effective, and convenient organocatalyst for the ring-opening polymerization of cyclic esters, to synthesize random copolymers of lactide and glycolide. The polymerization kinetics of the homo- and copolymerizations of lactide and glycolide were explored via NMR spectroscopy. A novel strategy that employs a controlled addition of the more reactive glycolide monomer to a solution containing the lactide monomer, the poly(ethylene glycol) (PEG) macroinitiator, and DBU catalyst was developed. Using this tactic (semi-batch polymerization), we synthesized a series of block copolymers that exhibited excellent correlation of the expected and observed molecular weights and possessed narrow PDIs. We also measured the thermal properties of these block copolymers and observed trends based on the composition of the block copolymer. We also explored the need for experimental rigor in several aspects of the preparations and have identified a set of convenient reaction conditions that provide polymer products that retain the aforementioned desirable characteristics. These polymerizations proceed rapidly at room temperature and without the need for tin-based catalysts to provide PEG-b-PLGAs suitable for use in biomedical investigations.

ChemInform Abstract: Aliphatic Polyester Polymer Stars: Synthesis, Properties and Applications in Biomedicine and Nanotechnology

AbstractReview: 262 refs.

Zinc and magnesium complexes supported by bulky multidentate amino-ether phenolate ligands: potent pre-catalysts for the immortalring-opening polymerisation of cyclic esters

A family of heteroleptic complexes of zinc and magnesium supported by bulky multidentate amino-ether phenolate ligands has been developed; in combination with external chain transfer agents, they constitute efficient binary catalytic systems for the immortal ring-opening polymerisation of cyclic esters.

Neodymium borohydride complexes supported by diamino-bis(phenoxide) ligands: diversity of synthetic and structural chemistry, and catalytic activity in ring-opening polymerization of cyclic esters

New heterobimetallic borohydrido neodymium complexes {[OONN]1Nd(BH4)(μ-BH4)Li(THF)}2 (1) and [OONN]3Nd(BH4)(μ-BH4)Li(THF)2 (3) supported by diamino-bis(phenoxide) ligands ([OONN]1 = {CH2N(Me)CH2-3,5-Me,t-Bu-C6H2O}2; [OONN]3 = C5H4NCH2N{CH2-3,5-Me,t-Bu-C6H2O}2) were synthesized by the reactions of Nd(BH4)3(THF)2 with equimolar amounts of dilithium derivatives of diamino-bis(phenol)s Li2[OONN]n and isolated in high yields. In the case of Li2[OONN]2 ([OONN]2 = Me2NCH2CH2N{CH2-3,5-t-Bu-C6H2O}2), the same synthetic procedure afforded the heterobimetallic bis(phenoxide) complex Li{Nd[OONN2]2} (2). The structures of complexes 1–3 were established by X-ray diffraction studies. Compounds 1–3 act as single-site initiators for the ring-opening polymerization (ROP) of racemic lactide and racemic β-butyrolactone under mild conditions (20 °C), providing atactic polymers with controlled molecular weights and relatively narrow polydispersities (Mw/Mn = 1.07–1.82). While 1 and 3 initiate polymerizationvia their borohydride groups, ROP with 2 proceeds viainsertion into the Nd–O(ligand) bond.

Aliphatic polyester polymer stars: synthesis, properties and applications in biomedicine and nanotechnology

A critical review: the ring-opening polymerization of cyclic esters provides access to an array of biodegradable, bioassimilable and renewable polymeric materials. Building these aliphatic polyester polymers into larger macromolecular frameworks provides further control over polymer characteristics and opens up unique applications. Polymer stars, where multiple arms radiate from a single core molecule, have found particular utility in the areas of drug delivery and nanotechnology. A challenge in this field is in understanding the impact of altering synthetic variables on polymer properties. We review the synthesis and characterization of aliphatic polyester polymer stars, focusing on polymers originating from lactide, ε-caprolactone, glycolide, β-butyrolactone and trimethylene carbonate monomers and their copolymers including coverage of polyester miktoarm star copolymers. These macromolecular materials are further categorized by core molecules, catalysts employed, self-assembly and degradation properties and the resulting fields of application (262 references).

Heteroscorpionate rare-earth initiators for the controlled ring-opening polymerization of cyclic esters

A series of neutral rare-earth metal amides containing different achiral and chiral heteroscorpionate ligands was synthesized and characterized and these compounds were employed in the polymerization of cyclic esters. Thus, treatment of [Ln{N(SiHMe(2))(2)}(3)(thf)(2)] (Ln = Nd, Sm) with acetamide or thioacetamide heteroscorpionate ligands for 2 h at 0 °C afforded the α-agostic silylamido dimeric rare-earth compounds [Ln{N(SiHMe(2))(2)}(NNE)](2) (Ln = Nd and Sm; NNE = heteroscorpionate ligands, E = O, S) (1-8), some as enantiopure complexes. Complexes 1-8 contain dianionic heteroscorpionate pseudoallyl ligands resulting from C-H activation of the bridging methine group of the bis(pyrazol-1-yl)methane moiety and subsequent coordination to the metal center. However, when the reaction was carried out for 1 h at lower temperature new bis(silylamido) dimeric lanthanide compounds [Ln{N(SiHMe(2))(2)}(2)(NNE)](2) (Ln = Nd and Sm; E = O) (9 and 10) were obtained. The structures of the complexes were determined by spectroscopic methods and the X-ray crystal structures of 1, and 4 were also established. Neodymium complexes are active initiators for the ring-opening polymerization (ROP) of lactide (LA) and lactones, giving rise to medium-high molar mass polymers under mild conditions and with narrow polydispersities. These complexes were well suited for achieving well-controlled polymerization through an insertion-coordination mechanism. Achiral and racemic complexes did not affect stereocontrol in the polymerizarion of rac-LA but the enantiomerically pure complex 1 was found to exhibit a homosteric preference for one of the two enantiomers of rac-LA at low conversions.

Oznaczanie pozostalosci cyny w syntetyzowanych biomedycznych poliestrach alifatycznych metoda elektrotermicznej absorpcyjnej spektrometrii atomowej

The synthesis of the aliphatic polyesters — polylactide (PLA) and poly (e-caprolactanes) (PCL) in the ring-opening polymerization of cyclic esters in the presence tin(II) 2-ethylhexanoate (SnOct 2 ) has been presented. The obtained products were subjected to multiple purification procedures to remove residual organo-tin catalyst (Tables 2 and 3). The tin content in the polyesters was then determined by Electrothermal Atomic Absorption Spectroscopy (ET-AAS) (Tables 3 and 4) after each purification process. The results of the analysis were discussed taking into consideration the requirements placed by the European Pharmacopoeia regarding the amount of tin allowed in aliphatic biomedical polyesters. It was confirmed, that a four-stage purification of the polyreaction product led to a three-fold decrease in the concentration of tin to a level less than the value required by Pharmacopoeia for materials designated for contact with blood. Moreover, the purification process did not generate any degradation of the polymer.

ChemInform Abstract: Ring‐Opening Polymerization by Lithium Catalysts: An Overview

AbstractReview: 143 refs.

Synthesis and Organocatalytic Ring-Opening Polymerization of Cyclic Esters Derived from l-Malic Acid

The synthesis of 3-(S)-[(benzyloxycarbonyl)methyl]-1,4-dioxane-2,5-dione (BMD) and 3,6-(S)-[di(benzyloxycarbonyl)methyl]-1,4-dioxane-2,5-dione (malide) from commercially available l-malic acid is reported. Ring-opening polymerization (ROP) studies of BMD are reported showing that the controlled ROP of this monomer is possible in the absence of transesterification side reactions, despite the presence of side-chain esters, using 1-(3,5-bis(trifluoromethyl)phenyl)-3-cyclohexylthiourea and (-)-sparteine to catalyze the polymerization. The ROP of malide with this system was ineffective. Investigation of the effect of initiating species revealed that the electronic nature of the alcohol had a greater effect on the ultimate molecular weight and hence initiator efficiency than steric considerations. Deprotection of the resultant poly(BMD) using H(2) and Pd/C resulted in hydrophilic poly(glycolic-co-malic acid)s (PGMAs) that were able to undergo autocatalytic degradation in dilute H(2)O solution such that complete degradation was observed within 6 days.

Synthesis and characterization of polyester conjugates of ciprofloxacin

Two-, three-, four and six-arm, star-shaped poly(ɛ-caprolactone) and polylactide homopolymers were synthesized via ring-opening polymerization of cyclic esters in the presence of glycerol, penthaerythritol, dipentaerythritol and poly(ethylene glycol) as initiators and stannous octoate as a catalyst. Thus obtained oligomers were successfully used in the synthesis of novel polyester conjugates of ciprofloxacin. The structures of the polymers and conjugates were determined by means of GPC, MALDI-TOF MS, NMR and IR studies. The in vitro release of ciprofloxacin from obtained conjugates was investigated.

Seeking Polymeric Prodrugs of Norfloxacin. Part 2. Synthesis and Structural Analysis of Polyurethane Conjugates

Oligo(ε-caprolactone) and oligolactide were synthesized via ring-opening polymerization of cyclic esters in the presence of creatinine as initiators. Thus obtained oligomers were successfully used in the synthesis of novel polyurethane conjugates of norfloxacin. The structures of the polymers and conjugates were elucidated by means of MALDI-TOF MS, NMR and IR studies.

Stereocontrolled ring-opening polymerization of cyclic esters: synthesis of new polyester microstructures

Synthesis of aliphatic polyesters has been studied intensively due to their biocompatible and biodegradable properties and their potential applications in medical and agricultural fields. There has been particular emphasis over the past decade on the synthesis of discrete, well-characterized complexes that are active polymerization initiators for the ring-opening polymerization (ROP) of lactide (LA) and beta-butyrolactone (BBL) to give, respectively, poly(lactide) (PLA) and poly(3-hydroxybutyrate) (PHB). These recent advances in catalyst design have led to a variety of polyester microstructures. This tutorial review focuses on the use of metal-based complexes for the stereoselective ROP of rac-LA and rac-BBL.