Ring-opening Polymerization Of Lactones Research Articles

Environmentally benign process for bulk ring opening polymerization of lactones using iron and ruthenium chloride catalysts

FeCl 3·6H 2O, RuCl 3·H 2O and FeCl 2·4H 2O are found to be bulk polymerization catalysts for the ring opening polymerization of ɛ-caprolactone, δ-valerolactone and β-butyrolactone. These polymerizations can be significantly enhanced by conducting them in the presence of appropriate amounts of different alcohols. The major initiation pathway in the polymerization is found to proceed via the activated monomer mechanism and depending on the nature of the alcohol used, poly(lactones) with different end groups can be synthesized. Such polymerizations constitute an economical process, employing readily available inorganics as catalysts and do not necessitate solvents. The overall system is green and eco friendly.

Ring-opening polymerization of lactones by rare-earth metal triflates and by their reusable system in ionic liquids

The ring-opening polymerizations (ROPs) of lactones catalyzed by rare-earth metal trifluoromethanesulfonates (triflates) (RE(OTf) 3) were examined. Among various complexes, scandium triflate (Sc(OTf) 3) emerged as an effective catalyst in toluene. The ROP of lactones by Sc(OTf) 3 proceeded in a living fashion, and the number of polymer molecules was controlled by the amount of protic additives such as benzyl alcohol and H 2O. In other words, one molecule of Sc(OTf) 3 catalytically produced a number of polymer molecules (up to 40 molecules) depending on the amount of protic additives. The plausible mechanism was depicted as an activated monomer mechanism. The polylactones with a number-average molecular weight over 25,000 were successfully synthesized. Immobilization of RE(OTf) 3 was investigated in three ionic liquids, and cerium triflate (Ce(OTf) 4) showed relatively high catalytic activity in a biphasic system of 1-butyl-3-methylimidazolium hexafluoroantimonate and toluene in the ROP of ɛ-caprolactone (CL). The ionic liquid containing Ce(OTf) 4 was used, at least three times, in the ROP of CL without losing catalytic activity.

Synthesis and characterization of biodegradable aliphatic polyesters using dibutylmagnesium as initiator

Aliphatic polyesters were synthesized via the ring opening polymerization of the corresponding lactones initiated with dibutylmagnesium both in bulk and in solution. The resulting polymers were characterized by 1H, 13C NMR, GPC and XRD. The results indicated that dibutylmagnesium is an effective initiator for the ring opening polymerization of lactones.

Investigation of Lipase-Catalyzed Ring-Opening Polymerizations of Lactones with Various Ring Sizes: Kinetic Evaluation

Lipase-catalyzed ring-opening polymerizations of lactones with various ring sizes (6- to 13- and the 16-membered ring) employing Novozym 435 demonstrate fascinating differences in their polymerization rates. These differences cannot be related to variations in physical properties such as the dipole moment of the lactones only. For example, 10-decanolactone, 11-undecanolactone, and 12-dodecanolactone show dipole moments of around 1.9 D, but the initial rate constant of their Novozym 435-catalyzed polymerization was found to be 0.10, 0.38, and 4.91 h-1, respectively. The Michaelis−Menten constants KM and Vmax were measured for all lactones, and this revealed that the KM was more or less independent of the ring size, suggesting similar affinities of the lipase for all lactones, while no obvious trend could be discerned for Vmax. However, conformational strain and transannular interactions present in medium ring lactones (ring size 8−12) affect the reactivity of these lactones in lipase catalysis in a similar...

Bis(trimethylsilyl)acetylene Complexes of Titanocenes and Zirconocenes: Their Recent Chemistry and Reactions with Lewis Acids

AbstractFor Abstract see ChemInform Abstract in Full Text.

Samarium enolate on crosslinked polystyrene beads. III. Anionic initiator for well‐defined synthesis of poly(hydroxyethyl methacrylate) on solid support

AbstractA solid‐supported samarium enolate successfully initiated the polymerization of 2‐(trimethylsilyloxy)ethyl methacrylate (TMS‐HEMA) through the living anionic process. In addition, the silyl group was readily removed by treatment of the beads with a weak acid to afford the corresponding well‐defined poly(methacrylate) having a hydroxyethyl group in the side chain (PHEMA). The hydroxyl group of the immobilized PHEMA on the beads was successfully acetylated to give poly(2‐acetoxyethyl methacrylate), which could be quantitatively isolated from the beads by trifluoroacetic acid treatment. Moreover, the hydroxyl group of the immobilized PHEMA could be utilized as an initiator for acid promoted ring opening polymerization of lactone to yield the corresponding graft copolymer. In this method, the residual and excess reagents could be removed by filtration, which demonstrated the applicability of the present technique to a novel method for construction of functional polymers. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 4417–4423, 2004

Enzyme-Catalyzed Ring-Opening Polymerization of ε-Caprolactone in Supercritical Carbon Dioxide

We report the ring-opening polymerization reaction of e-caprolactone in supercritical carbon dioxide (scCO2) using an enzyme catalyst, Lipase B from Candida antarctica supported on macroporous beads (Novozym-435). Ring-opening polymerization of lactones is more commonly performed in organic solvents or in bulk using a Lewis acid catalyst. Recently there has been much interest in the replacement of such catalysts by enzymes. We demonstrate that the enzymatic route is viable in scCO2, yielding poly(e-caprolactone) (Mn = 12 000−37 000 g mol-1) with molecular weights very similar to those obtained from the same enzyme catalysts in organic solvents, but with lower polydispersities (typical PDI = 1.4−1.6) and higher yields of polymer product (typically 95−98%). In the same process the unique “gaslike” mass transfer properties of scCO2 can also be exploited to remove quantitatively any unconverted monomer and low molecular weight oligomers by scCO2 extraction. It is also shown that the enzyme catalyst can be cle...

Synthesis of novel types of graft copolymers by a “grafting-from” method using ring-opening polymerization of lactones and lactides

Polystyrene and polystyrene- block-poly(methyl methacrylate) densely grafted with poly(ϵ-caprolactone) or poly(DL-lactide) in the benzene rings were synthesized by a “grafting-from” method using hydroxylated precursors of the above styrene polymers as macroinitiators of the ring-opening polymerization of appropriate monomers. The poly(ϵ-caprolactone) grafts of the polystyrene- graft-poly(ϵ-caprolactone) copolymer were lengthened with poly(methyl methacrylate) by atom transfer radical polymerization. All the synthesized graft copolymers were characterized by 1H and 13C NMR spectroscopy and by size exclusion chromatography.

Recent developments in ring opening polymerization of lactones for biomedical applications.

Aliphatic polyesters prepared by ring-opening polymerization of lactones are now used worldwide as bioresorbable devices in surgery (orthopaedic devices, sutures, stents, tissue engineering, and adhesion barriers) and in pharmacology (control drug delivery). This review presents the various methods of the synthesis of polyesters and tailoring the properties by proper control of molecular weight, composition, and architecture so as to meet the stringent requirements of devices in the medical field. The effect of structure on properties and degradation has been discussed. The applications of these polymers in the biomedical field are described in detail.

Well-organized phase-separated nanostructured surfaces of hydrophilic/hydrophobic ABA triblock copolymers.

The emerging need for new synthetic materials for soft tissue engineering applications encourages the search for innovative polymers having interesting properties. Ring-opening polymerization of lactones and lactides initiated by tin alkoxides has received particular attention due to the versatility of the method for building up well-defined biodegradable structures. The controlled reactions together with a careful choice of comonomers and copolymer composition make it possible to create materials with desired molecular architecture and properties.The aim of the work described in this thesis was to design aliphatic bioresorbable copolymers with new structures and controlled properties for potential application in soft tissue engineering. The first part of the work was focused on the surface properties of the materials synthesized for biomedical application. Solution-cast film triblock copolymers of L-lactide (LLA) and 1,5-dioxepan-2-one (DXO), subjected to thermal treatment have been studied. The effects of molecular weight, polymer composition, cooling rate, and casting solution concentration on the nanostructure surface morphology and topography have been investigated by atomic force microscopy (AFM). The surface characterization of the annealed triblock copolymers revealed well-defined fiber features formed as a result of a melt-induced micro-phase separation during crystallization. The dimensions and shape of the formations could be related to the copolymer composition and annealing conditions, and this makes it possible to create controlled and well-defined surface structure. The results of cell adhesion studies on annealed triblock copolymers indicate that these materials favor fibroblast growth and spreading, which makes them promising candidates for applications as bioresorbable membranes.In the next stage of the work, linear and network copolymers of e-caprolactone (CL) and DXO with a controlled composition and controlled hydrophilicity have been synthesized. The molar fraction of DXO in the copolymers affected their mechanical, thermal and surface properties. The hydrophilicity was tailored by changing the monomer composition in the copolymers. The AFM measurements on the linear copolymers showed that short fibrillar structures were formed upon crystallization from the melt. The supple CL-DXO networks were easy to cast and could easily be removed from the mould surface, so that it is possible to use this material for embossing procedures without the risk of damaging the surface pattern during removal from the mould.

Ring-opening Polymerization of Lactones Catalyzed by Surfactant-Coated Lipases in Organic Solvents.

We have performed the ring-opening polymerization of lactones catalyzed by surfactant-coated lipases in organic solvents. A great improvement in the number-average molecular weight (Mn) of the produced polymer was observed compared to that of the lyophilized native lipase. The Mn vs monomer conversion profile suggests that the polymerization catalyzed by the surfactant-coated lipase is a step polymerization, whereas that catalyzed by lyophilized lipase powder is a chain polymerization. The effects of reaction temperature and the reaction solvent on the polymerization of lactones were also investigated.

Homoleptic lanthanide complexes of chelating bis(phosphanyl)amides: synthesis, structure, and ring-opening polymerization of lactones.

Treatment of the bis(phosphanyl)amide (Ph2P)2NH with KH in boiling THF followed by crystallization from THF/n-pentane leads to [K(thf)n][N(PPh2)2] (n = 1.25, 1.5). Reaction of [K(thf)n][N(PPh2)2] with anhydrous yttrium or lanthanide trichlorides in a 3:1 molar ratio afforded homoleptic bis(phosphanyl)amide complexes [Ln[N(PPh2)2]3] (Ln = Y, Er) as large crystals in good yields. [Ln[N(PPh2)2]3] can also be obtained by reaction of the homoleptic bis(trimethylsilyl)amides of Group 3 metals and lanthanides [Ln[N(SiMe3)2]3] (Ln = Y, La, Nd) with three equivalents of (Ph2P)2NH in boiling toluene. The single-crystal X-ray structures of these complexes always show eta 2 coordination of the ligand. Dynamic behavior of the ligand is observed in solution and is caused by rapid exchange of the two different phosphorus atoms. [Ln[N(PPh2)2]3] was used as catalyst for the polymerization of epsilon-caprolactone. Significant differences in terms of correlation of theoretical and experimental molecular weights as well as polydispersities were observed depending on the nature of Ln. On the basis of the crystal structure of the heteroleptic complex [Lu[N(PPh2)2]3(thf)], we suggest that in the initiation step of epsilon-caprolactone polymerization the lactone adds to the lanthanide atom to form a sevenfold coordination sphere around the central atom.

Recognition by Lipases of ω-Hydroxyl Macroinitiators for Diblock Copolymer Synthesis

The mono-terminal hydroxyl groups of polybutadiene of varying chain length were studied as sites for initiation of lactone ring-opening polymerization by lipase catalysis. Novozyme-435 (immobilized Candida antarctica lipase B) was an effective catalyst for this acylation. Monohydroxyl-terminated polybutadiene with Mn of 2.6, 10, and 19 kg/mol efficiently initiated ω-pentadecalactone (PDL) and e-caprolactone (CL) polymerization in toluene at 55 °C to give polybutadiene-b-polypentadecalactone and polybutadiene-b-polycaprolactone, respectively. For example, monohydroxyl-terminated polybutadiene with Mn 2.6 kg/mol initiated PDL ring-opening polymerization (1:25, OH:PDL) and formed a product with Mn 9.6 kg/mol in 19 h with 17 mol % chains initiated by water and >90% initiator efficiency. This method circumvented previously published chemical methods that required a metal catalyst and strict exclusion of moisture. A fractionation method was developed to separate the oligomers and to reduce the homopolymer conta...

Controlled Ring-Opening Polymerization of Lactones and Lactides Initiated by Lanthanum Isopropoxide, 1. General Aspects and Kinetics

Ring-opening polymerization of various lactones and lactides initiated by lanthanum isopropoxide has been investigated. Analysis of molecular weights and molecular-weight distributions of the resulting polymers shows that the ring-opening process is a controlled reaction, which is initiated by a variable number of isopropoxy groups. This number depends on both the monomer and the [monomer]/[initiator] ratio. Kinetic studies indicate that all the polymerizations are equilibrated, and the corresponding thermodynamic parameters and the equilibrium monomer concentrations have been calculated. Comprehensive kinetics carried out for e-caprolactone abd δ-valerolactone polymerizations allows the determination of kinetic order relative to both monomer and initiator concentrations, along with that of the apparent rate constants of polymerization. It is also demonstrated that propagation occurs on aggregated (δ-valerolactone) or unaggregated (e-caprolactone) active polymer chains and that the ring-opening process proceeds via [O-acyl] bond cleavages.

Synthesis and characterization of (C 5H 9C 9H 6) 2Yb(THF) 2(II) ( 1) and [(C 5H 9C 5H 4) 2Yb(THF)] 2O 2 ( 2), and ring-opening polymerization of lactones with 1

Reaction of YbI 2 with two equivalents of cyclopentylindenyl lithium (C 5H 9C 9H 6Li) affords ytterbium(II) substituted indenyl complex (C 5H 9C 9H 6) 2Yb(THF) 2 ( 1) which shows high activity to ring-opening polymerization (ROP) of lactones. The reaction between YbI 2 and cyclopentylcyclopentadienyl sodium (C 5H 9C 5H 4Na) gives complex [(C 5H 9C 5H 4) 2Yb(THF)] 2O 2 ( 2) in the presence of a trace amount of O 2, the molecular structure of which comprises two (C 5H 9C 5H 4) 2Yb(THF) bridged by an asymmetric O 2 unit. The O 2 unit and ytterbium atoms define a plane that contains a C i symmetry center.

Ring-Opening Polymerization of Lactones and Lactides with Sn(IV) and Al(III) Initiators

A theoretical study is presented of the ring-opening polymerization (ROP) mechanism of 1,5-dioxepan-2-one (DXO) and glycolide with Sn(II) and Al(III) alkoxide initiators (SnMe3MeO, SnMe2(MeO)2, and AlMe2MeO). The B3LYP density functional method has been used to perform the quantum chemical calculations. A coordination−insertion mechanism is presented with two principal reaction steps. First, the alkoxide of the initiator performs a nucleophilic attack on the carbonyl carbon, and the carbonyl bond is broken. An intermediate is formed at this point, where the former carbonyl oxygen of the monomer is coordinated to tin via an alkoxide bond, while the carbonyl carbon assumes a sp3 bonding geometry. The second step involves the acyl−oxygen cleavage of the monomer. For all three initiators it was found that the transition state involving the breaking of the carbonyl double bond (TS1) represented the highest point on the potential energy surface for DXO. For glycolide, however, the transition state of the acyl−oxygen cleavage (TS2) was the least stable structure. The reaction barriers were calculated to 17.1 kcal/mol for DXO/SnMe3MeO, 18.7 kcal/mol for glycolide/SnMe3MeO, 14.3 kcal/mol for DXO/SnMe2(MeO)2, 14.5 kcal/mol for glycolide/SnMe2(MeO)2, 13.6 kcal/mol for DXO/AlMe2MeO, and 9.3 kcal/mol for glycolide/AlMe2MeO. Both electronic and steric properties of the monomer affect the reaction barriers. It was found that the more electrophilic initiators polymerized cyclic esters faster.

Reactions of 2,2‘-Methylenebis(4-chloro-6-isopropyl-3-methylphenol) with Trimethylaluminum: Highly Efficient Catalysts for the Ring-Opening Polymerization of Lactones

The reaction of 2,2‘-methylenebis(4-chloro-6-isopropyl-3-methylphenol) (MCIMP-H2) with 1.2 molar equiv of AlMe3 in THF yields [(MCIMP)AlMe(THF)] (1), which further reacts with a stoichiometric amount of 2-propanol (IPA), affording the isopropoxy-bridged dimer [(MCIMP)Al(μ-OiPr)]2 (2). Compound 2 can also be obtained by the treatment of MCIMP-H2 with a stoichiometric amount of Al(OiPr)3 in refluxing toluene. However, the reaction of 1 with another 1 equiv of AlMe3 in CH2Cl2 furnishes [Me2Al(μ-MCIMP)AlMe2(THF)] (3), in which the MCIMP2- ligand is acting as a bridging ligand. Further treatment of compound 3 with 2 molar equiv of 2-propanol results in the formation of the isopropoxy-bridged dinuclear aluminum complex [(MCIMP)Al(μ-OiPr)2AlMe2] (4). Compound 4 can be directly obtained from the reaction of 1 with AlMe3 in the presence of 2-propanol. However, in the presence of a stoichiometric amount of H2O, hydrolysis of 1 in THF gives the trimeric aluminum compound [(MCIMP)Al(μ-OH···THF)]3 (5), in which the hy...

Bimetallic Titanocene or Zirconocene/Aluminium Complexes as Active Catalysts in Lactone Polymerization Reactions

The metallocene alkyne complexes [Cp2M(L)(η2-Me3SiC2R)] react with diisobutylaluminium hydride at room temp. by addition of HAl(iBu)2 to yield the heterobimetallic complexes [{Cp2M}(μ-η1:η2-RCCSiMe3)(μ-H){Al(iBu)2}] [{Cp2M}: (η5-C5H5)2Ti, R = Ph 1, R = SiMe32; {Cp2M}: (η5-C5H5)2Zr, R = SiMe33; {Cp2M}: (ebthi)Zr, R = SiMe34] {ebthi: rac-[1,2-ethylene-1,1′-bis(η5-tetrahydroindenyl)]}. Complexes 1−4 were characterized by NMR spectroscopy and 1, 2 and 4 investigated by X-ray crystal structure analysis. Compounds 1−4 were tested as initiators in the ring-opening polymerization of lactones. The results are discussed in comparison to the corresponding monometallic titanocene and zirconocene alkyne complexes.

Ring-opening polymerization of lactones in the presence of hydroxyapatite

The ring-opening polymerization of ε-caprolactone, δ-valerolactone (VL) and d, l-lactide, respectively, in the presence of different proportions of hydroxyapatite (HA) was catalyzed by stannous (II)octoate (SnOct 2) at 130°C and resulted in composites. The lactones were almost completely converted to the polymers within a reaction time of 70 up to 240 min. The number-average molecular weights M n as determined by size exclusion chromatography decreased with increasing content of HA. The initiating efficiency of HA as calculated from the difference of the polymerization degrees P n obtained with and without HA turned out to be relatively low with ca. 11 to 0.5% for 1 to 80 wt% HA, respectively. For the polymerization of VL, the initiating efficiency of HA was on the average threefold higher. The quantitative proof of non-extractable polymer on HA by means of thermogravimetric analysis, fourier transform infrared spectroscopy with photoacoustic detection and differential scanning calorimetry confirmed the initiating efficiency of HA as mentioned above. This poly(lactone) can be debound from HA by treatment with aqueous HCl. Hence it is assumed to be ionically bound.

Lipase-Catalyzed Ring-Opening Polymerization of Lactones in the Presence of Aliphatic Polyesters to Ester Copolymers

Ring-opening polymerization of macrolides in the presence of aliphatic polyesters has been performed using Pseudomonas lipase as catalyst to produce ester copolymers with molecular weights of several thousands. The polymerization behavior was monitored by SEC and NMR. 13C NMR analysis showed that the resulting polymer was not a mixture of the starting polyester and the polymer from the macrolide, but a random copolymer consisting of both units. These data indicate that the lipase catalyzed the polymerization of the macrolide as well as the intermolecular transesterification of the starting and resulting polymers. The random copolymer was found to be highly crystalline by DSC and WAXD measurement. The present specific catalysis of the lipase was applied to the synthesis of ester copolymers by transesterification between two different polyesters.