CZ2013966A3 - Process for preparing block copolymer - Google Patents

Abstract

The present invention provides a process for preparing a block copolymer of b-poly (lactic-co-glycolic acid) -b-polyethylene glycol-b-poly (lactic-co-glycolic acid) from polyethylene glycol, and cyclic lactic acid esters of glycolic acid by ring opening polymerization. wherein the polymerization is carried out under the catalysis of organic carbenes of formula (II), wherein R @ 1 is at R @ 2 is hydrogen, alkyl of 1 to 10 carbon atoms, cycloalkyl having 3 to 6 carbon atoms , a halogen atom, an adamantane group or a phenyl group; R 3 and R 4 are hydrogen, halogen, cyano, hydroxyl, alkyl of 1 to 4 carbon atoms, or phenyl.

Description

Technical field

The present invention relates to catalysed polymerization to form a copolymer of aliphatic ester monomers and polyethylene glycol.

BACKGROUND OF THE INVENTION

There are many materials used in medicine, which can be divided into three basic groups: metal, ceramic and polymer. Each of these materials has its advantages but also limitations. The advantage of polymeric materials is corrosion resistance, often good biocompatibility with living tissue and availability in various designs. Polymers used for medical purposes can be divided into resorbable and non-resorbable. These materials are subject to high quality control requirements when in direct contact with body fluids and tissues. It must not have adverse effects on the environment. If the material is not biocompatible, it has adverse biological responses such as increased susceptibility to infections or carcinogenic reactions. The synthesis of ever-new polymers, in many cases copolymers, focuses in particular on the development of new materials with greater biocompatibility and biodegradability that guarantee successful use in medical applications.

Recently, great attention has been devoted to the development of biodegradable, biocompatible, aliphatic polyesters such as hydrophobic poly (lactic acid), poly (glycolic acid), polycaprolactone and copolymers thereof. By copolymerization of lactide and glycolide with hydrophilic polyethylene glycol, amphiphilic water-soluble triblock copolymers of poly (lactic-co-glycolic acid) -one-poly (ethylene glycol) -one-poly (lactic-co-

-glycolic acid) (PLGA-PEG-PLGA) of ABA type, wherein A is a random copolymer of poly (lactic-co-glycolic acid) and B is polyethylene glycol. These copolymers have the ability to form gels in aqueous solution at a certain temperature [MICHLOVSKÁ, L. Synthesis and characterization of multifunctionalized biodegradable copolymers. Minimum PhD thesis. Brno University of Technology, Faculty of Chemistry. 2012], This phenomenon can be used to prepare carrier systems where drugs, proteins or cells are admixed at a low temperature of the polymer solution, which, when the temperature changes (eg to the temperature of the human body) remain trapped in the gel and gradually released.

Methods for preparing these copolymers are based on ring opening polymerization in the presence of polyethylene glycol as a macroinitiator. Metal complex compounds are known as efficient and highly selective catalysts for these polymerizations. For toxicological reasons, metal residues from catalysts (eg tin and aluminum) must be removed from the polymer product before it is used in medical applications. Requirements for low or zero toxicity of catalyst traces, as well as easy removal of these compounds from the resulting polymer, are the driving force for the development of new effective green catalysts free of toxic metals [ALBERTSSON, A., VARMA, I. for biomedical applications. Biomacromolecules. 2003, vol. 4, pp. 1466-1486], Organic ring-opening polymerization of cyclic esters catalysed by organic carbene compounds represent a new alternative to the synthesis of polyesters of defined structure and molecular weight in addition to traditional organometallic catalysis.

Research and development of stable (nucleophilic) carbenes is currently a very topical topic. The first stable carbenes - imidazolin-2-ylidene and imidazol-2-ylidene - were prepared, isolated and characterized by Ardueng et al. in the early 1990s. At present, carbenes containing different ring heteroatoms (X = N or S) having different spatial arrangement of groups bound to the imidazole ring (R1-2) or nitrogen (s) (R3-4), a saturated or unsaturated hydrocarbon backbone are known .

r ₂ ^R 1 P ² ii

sk tk

K p

V Kj

The steric and electron properties of the substituents are the decisive factor for the catalytic behavior of carbene in the polymerization of various lactones and lactides [VYROUBALOVÁ, Z. Ring-Opening Polymerization of Lactones and Lactides. Minimum PhD thesis. Brno University of Technology, Faculty of Chemistry. 2012].

23 structural types of carbenes used for the study of ring opening polymerization of lactide, caprolactone, valerolactob and butyrolactone were found in the literature. The most studied carbene catalysts are 1,3-bis (2,4,6- (trimethylphenyl) imidazol-2-ylidene, 1,3,4-triphenyl-4,5-dihydro-1H-1,2-triazole-5-one). -ylidene and 1,3-dimethylimidazol-2-ylidene Hendrick et al. have studied various structural types of carbenes for the homopolymerization of lactide, epsilon-caprolactone, ii »·

delta-valerolactone and beta-butyrolactone in the presence of benzyl alcohol, pyrenbutane and polyfluent ethylene glycols as initiators [DOVE, A. P., et al. N-Heterocyclic carbenes: Effective organic catalyst for living polymerization. Polymer. 2006, 47, pp. 4018 ^ 025; NYCE, G., et al. In the generation of carbenes: A general and versatile platform for organocatalytic living polymerization. Joumal of the American chemical society. 2003, 125, pp. 3046X3056; COULEMBIER, O. et al. Alcohol Adducts of N-Heterocyclic Carbenes: Latent Catalysts for Thermally-Controlled Living Polymerization of Cyclic Esters. Macromolecules 2006, 39, pp. 5617-5628; KAMBER, N.E. et al. N-Heterocyclic Carbenes for Organocatalytic Ring-Opening Polymerization of ε-Caprolactone. Macromolecules 2010, x

42, pp. 1634-1639; CONNOR, E.F., et al. First Example of N-Heterocyclic Carbenes as Catalysts for Living Polymerization: Organocatalytic Ring-Opening Polymerization of Cyclic Esters. Joumal of the American Chemical Society. 2002, 124, pp. 914-915; CSIHONY, S., et al. Brederecks Reagent Revisited: Latent Anionic Ring-Opening Polymerization and Transesterification Reactions. Advanced Synthesis & Catalysis 2004, 346, pp. 1081-1086]. The same team of scientists have also studied 1,3-dimethylimidazol-2-ylidene for block copolymerization of lactide and epsilon-caprolactone in the presence of benzyl alcohol as initiator [NYCE, G., et al. Joumal of the American chemical society. 2003, 125, pp. 3046-3056], Li et al. Have studied the polymerization and copolymerization of cyclic monomers using carbon dioxide carbon adducts [USÉ0110152493, US 20110144296]. Nemoto et al. Used a variety of organic catalysts, including 1,3-di-tert-butylimidozol-2-ylidene, to prepare polylactide and polycaprolactone [USj20110218301].

It is apparent from the literature review that a number of polymerizations leading to the preparation of lactide homopolymers and various types of lactones using carbene catalysts are known. In contrast, copolymerization of other cyclic aliphatic esters with a block polymer by means of carbene catalysts has not been known or studied.

SUMMARY OF THE INVENTION

An object of the present invention is a process for preparing a block copolymer of b-poly (lactic-co-glycolic acid) -b-polyethylene glycol-b-poly (lactic-co-glycolic acid) from polyethylene glycol, and cyclic esters of lactic acid and glycolic acid (especially lactide and glycolide) by ring-opening polymerization, characterized in that the polymerization is carried out under catalysis with an organic carbene of formula (II).

* (II) ^R1 * 2

VZ

IN/

/ .....

Rr \ / r ₃ * ♦ wherein Ri and R ₂ represent hydrogen, an alkyl group having 1 to 10 carbon atoms, cycloalkyl having 3 to 6 carbon atoms, a halogen atom, an adamantane or a phenyl group;

R 3 and R 4 represent hydrogen, halogen, cyano, hydroxyl, alkyl 1i.

a group having 1-4 carbon atoms or a phenyl group.

In a preferred embodiment, R 1 and R 2 in formula (II) are hydrogen or alkyl having 1-4 carbon atoms.

Preferably R3 and R4 in formula (II) are alkyls having 1 / carbon atoms or phenyl, more preferably tert-butyl.

Preferably, the polymerization is carried out in the presence of an organic carbene catalyst with a content by weight of 0.04 to 2.00%, preferably 1.70%, based on the total weight of the reaction mixture.

Preferably, the polymerization is carried out in the presence of an aprotic organic solvent, for example tetrahydrofuran, dimethylsulfoxide or xylene, up to 95% by weight based on the weight of the reaction mixture, preferably 75%.

Preferably, in the resulting copolymer, the weight ratio of poly (lactic-co-glycolic acid) / polyethylene glycol (PLGA / PEG) is in the range of 2 to 2.5, more preferably 2.3, and the molar ratio of lactic acid / glycolic acid (PLA / PGA). it is in the range of 2.3 to 4.7, more preferably 3.1.

In the present invention, N-heterocyclic carbenes have recently been used to prepare a triblock copolymer of poly (lactic-co-glycolic acid) -α-polyethylene glycol-6-poly (lactic-co-glycolic acid) ensuring the non-toxicity of the resulting hydrogel. The prepared 7-hydrogel is biodegradable and thermosensitive with a sol-gel transition temperature in the range of 28 to ° C allowing its use as an injectable drug carrier.

; 4

Overview of illustrations

Giant. 1 shows the 1 H NMR spectrum of the carbene prepared according to Example 1.

Giant. 2 shows the ¹ H NMR spectrum of the copolymers prepared according to Example 2.

Giant. 3 shows a sol-gel phase diagram

Giant. 4 illustrates the inverse vial method: a) sol solution, b) gel phase at 37 ° C, c) separation into two copolymer-water phases.

Giant. 5 shows the effect of the polymer solution concentration (18-42% w / v) on the elastic modulus of shear.

Giant. 6 shows the effect of the polymerization temperature on the elastic shear modulus of the polymer solution (concentration 42% w / v).

Giant. 7 shows the effect of the polymeric medium on the elastic shear modulus of the polymer solution (concentration 42% w / v).

DETAILED DESCRIPTION OF THE INVENTION

Example 1: Preparation of Carbene

Carbene 1,3-di-tert-butylimidazolidene was prepared according to the following reference [DENK, M.K., et al. Joumal of Organometallic chemistry. 2001, 617-618, pp. 242-253].

To the sublimation apparatus was weighed 3.22 g of the chloride salt of the carbene precursor, 42.00 mL of tetrahydrofuran was added thereto, and the apparatus was immersed in a cooling bath (-78 ° C). Subsequently, 15.00 ml of butyllithium was slowly added to the suspension over a period of 30 minutes. The brown suspension was allowed to warm slowly to room temperature. After tempering, the slurry was bubbled with nitrogen to remove solvent and light derivatives for 1 h. Subsequently, sublimation was performed under reduced pressure at 40 ° C.

J / hz.

54% rotting carbene was obtained as a white crystalline powder which was further used for ring opening polymerization.

The chemical composition of the prepared carbene was verified by 1 H NMR (see Fig. 1). Peaks corresponding to protons of methyl groups with a shift of δ = 1.52 ppm and peaks corresponding to protons bound to the imidazole ring with a shift of δ = 6.79 ppm were found in this spectrum.

Example 2: Polymerization reactions

The poly (lactic-co-glycolic acid) - β-polyethylene glycol-poly (lactic-co-glycolic acid) (PLGA-PEG-PLGA) triblock copolymer was prepared by ring opening polymerization in tetrahydrofuran solution. The polymerization was conducted in a Schlenk flask equipped with a magnetic stirrer under a nitrogen atmosphere. Prior to polymerization, the occluded moisture reactor was annealed 3 times under vacuum. Thereafter, 0.93 g of a polyethylene glycol macroinitiator was charged into the reactor from which air and moisture were removed by heating in an oil bath at 130 ° C under vacuum for 3 hours. After cooling, 1.82 g of cyclic lactic acid diester and 0.49 g of cyclic glycolic diester were added under a stream of nitrogen, which were left under vacuum for 30 minutes. 11.50 ml of tetrahydrofuran was added and the solution was allowed to homogenize. After complete dissolution of all components, 0.22 g of 1,3-di-tert-butylimidazolidene carbene catalyst was added to the solution. The reaction was allowed to proceed for 1 hour and was then terminated with a few drops of ultrapure water. THF was removed from the solution by a stream of air and the obtained polymer was washed 3 times with ultrapure water from the residual unreacted monomers, then dried under reduced pressure at 30 ° C to constant weight and weighed on an analytical balance.

The molecular weight Mn and the polydispersity Mw / Mn of the resulting copolymer were determined by gel permeation chromatography (GPC) using polystyrene as the standard and tetrahydrofuran as the mobile phase. The results were compared with proton nuclear magnetic resonance (1 H NMR) analysis, from which the exact composition of the copolymer was determined (Table 1).

• 4 4

Tab. 1: Overview of properties of prepared copolymer.

M _n ^a M _w / M _n ^a M _n ^b p (%) ^c LA / GA ^b PLGA / PEG ^b PLGA-PEG-PLGA 5648 1.17 5007 79 3.10 2.34

t = 120 min, Temperature = 25 C, Cat / I = 2, S / M = 3, [D, L-LA] ₀ = 1.10 moldm ³ , [GA] ₀ = 0.37 moldm ³ "Analyzed by GPC with PS standards in THF ^h Analyzed by 1 H NMR spectroscopy ^c Gravimetric conversion of monomer to polymer

In the 1 H NMR spectrum of the PLGA-PEG-PLGA copolymer shown in FIG. 2, peaks corresponding to protons of lactic acid monomer units with a shift of δ = 1.5 to 1.75 ppm (e) and δ = 5.1 to 5.35 ppm (a) were found, peaks corresponding to protons of glycolic acid monomer units in the δ regions - 4.6 to 4.9 ppm (b) as well as peaks corresponding to the poly (ethylene glycol) macroinitiator units in the δ = 3.55 to 3.75 ppm (d) regions. Peaks in the δ = 1.67 ppm and δ = 7.40 ppm (unlabeled) peaks belong to the protons of the residual organic catalyst. The peak corresponding to the residual protons of the deuterochloroform solvent used was found to be δ = 7.25 ppm.

For the prepared sample, a sol-gel phase diagram (Fig. 3) was constructed based on visual observation - inverse vial method (Fig. 4) to verify hydrogel gelation. A solution of PLGA-PEG-PLGA in MilliQ water was prepared in a concentration range of 6 to 42%. At higher concentrations above 20% w / v. as the temperature of the copolymer gradually increases, the liquid solution of the copolymer becomes a viscous solution, around 37 ° C a transparent gel is formed, which becomes a white gel with increasing temperature. At temperatures around 43 ° C, the copolymer precipitates and divides the sample into two phases (copolymer and water). Upon re-cooling, the copolymer sample is redissolved and again exhibits a sol-gel transition. At lower concentrations, with increasing temperature, only the viscosity of the solution increases.

The rheological behavior of thermosensitive triblock copolymers has been described by the elastic modulus of shear elasticity G '. Giant. 5 shows an increase in the modulus of elasticity of the hydrogel with increasing temperature and increasing sample concentration.

Example 3: Polymerization reactions

Example 3 was technically carried out as Example 2 except that the reaction was carried out at temperatures of 0 ° C, 10 ° C and 40 ° C for an optimal period of 5 min in THF solution. The copolymers prepared had a monomer conversion of 70 to 79%. As the polymerization temperature decreases, the molecular weight of the copolymers decreases and their polydispersity indexes widen. The LA / GA and PLGA / PEG ratios approached theoretically set values (LA / GA = 3.0 and PLGA / PEG = 2.5) except for the reaction conducted. at 40 ° C where the PLGA / PEG ratio is lower (2.13) and the molecular weights determined by both GPC and NMR are lower than theoretical (5250). Obviously, transesterification side reactions occur at this temperature. The properties of the prepared copolymers at different temperatures are given in Tab. 2.

Tab. 2: Overview of the properties of the prepared PLGA-PEG-PLGA copolymer at various temperatures (25 ° C Example 2).

temperature M * MM M ^b p (%) ^c LA / GA ^b PLGA / PEG ^b 0 4133 1.39 5003 74 3.23 2.34 10 4609 1.26 5042 71 3.09 2.36 25 5648 1.17 5007 79 3.10 2.34 40 4312 1.14 4689 77 3.12 2.13

1 = 5 min, THF, Cat / I = 2, S / M = 5, [D, L-LA] ₀ = 1.10 mol · dm, [GA] ₀ = 0.37 mol · dm ”Analyzed by GPC with PS standards in THF ^h Analyzed by 1 H NMR spectroscopy ^L Gravimetric conversion of monomer to polymer

The rheological behavior of PLGA-PEG-PLGA copolymers prepared at various polymerization temperatures has been described by the elastic modulus of shear elasticity G '. Giant. 6 shows different values of the modulus of elasticity of the hydrogel for individual copolymers. The greatest stiffness of 176 Pa was achieved by the copolymer prepared at a polymerization temperature of 25 ° C.

Example 4: Polymerization reactions

Example 4 was technically carried out as Example 2 except that the reaction was carried out at a temperature of 0 ° C for 5 minutes in various aprotic solvents (basic solvents capable of

bind a proton or inert, which the proton cannot cleave or bind). in THF, dimethylsulfoxide (DMSO), xylene as well as solvent-free melt. The copolymers prepared in the melt and DMSO showed low molecular weight and a broader polydispersity, also the LA / GA and PLGA / PEG ratios differed from theoretically set (LA / GA = 3.0 and PLGA / PEG = 2.5). The copolymer prepared in THF achieved the highest monomer conversion with a molecular weight close to the set theoretical molecular weight (5250) and a narrow polydispersity (MJM _n = 1.17). The LA / GA and PLGA / PEG ratios were close to the theoretically set values. In a xylene solution, a copolymer was prepared with a molecular weight close to the set theoretical molecular weight, but with a broader polydispersity and low monomer conversion (45%). The LA / GA and PLGA / PEG ratios were very different from the theoretical values. In Tab. 3 provides an overview of the properties of prepared copolymers in the environment of various solvents.

Tab. 3: Overview of the properties of the prepared PLGA-PEG-PLGA copolymer in various solvents.

solvent M _n ^a M _w / M _n ^a M _n ^b p (%) ^c LA / GA ^b PLGA / PEG ^b melt 3876 1.32 4825 73 2.83 2.21 THF 5648 1.17 5007 79 3.10 2.34 DMSO 3901 1.30 4550 53 2.37 2.03 Xylene 5151 1.30 4416 45 4.74 1.94

t = 5 min, ^25 ° C, Cat / 1 = 2, S / M = 5, [D, L-LA] ₀ = 1.10 moldm *. [GA] ₀ = 0.37 moldm * ^a Analyzed by GPC with PS standards in THF ^h Analyzed by 1 H NMR spectroscopy ^c Gravimetric conversion of monomer to polymer

The rheological behavior of PLGA-PEG-PLGA copolymers prepared in various solvents has been described by the elastic modulus of shear elasticity G '. Giant. 7 shows different hydrogel modulus values for individual copolymers. The greatest stiffness of 176 Pa was achieved by the copolymer prepared in THF solution. The copolymers prepared in the melt and DMSO did not show viscoelastic properties, they did not form solid gels - only viscous solutions.

Claims (5)

PATENT CLAIMS A process for the preparation of block copolymers of b-poly (lactic-co-glycolic acid) -b-polyethylene glycol-b-poly (lactic-co-glycolic acid) from polyethylene glycol, and cyclic esters of lactic acid and glycolic acid by ring opening polymerization, characterized by in that the polymerization is carried out by catalysis with an organic carbene of formula (II) (II) wherein R 1 and R 2 are hydrogen, alkyl having 140 carbon atoms, cycloalkyl having 3-6 carbon atoms, halogen, adamantane or phenyl; R 3 and R 4 represent hydrogen, halogen, cyano, hydroxyl, alkyl. a group having 1-4 carbon atoms or a phenyl group in an amount of 0.04 to 2.00% by weight. 2. The process of claim 1 wherein R1 and R2 are hydrogen or alkyl having 14 carbon atoms. The process according to claim 1, characterized in that R 3 and R 4 are alkyl having 14 carbon atoms or phenyl, more preferably tert-butyl. Process according to any one of the preceding claims, characterized in that the reaction is carried out in the presence of an aprotic organic solvent of up to 95% by weight, based on the weight of the reaction mixture, preferably 75%. Method according to any one of the preceding claims, characterized in that the starting ratios of the starting materials are such that in the resulting copolymer the weight ratio of poly (lactic-glycolic acid) / polyethylene glycol (PLGA / PEG) is in the range of 2 to 2.5, more preferably 2.3, and the lactic acid / glycolic acid (PLA / PGA) molar ratio is in the range of 2.3 to 4.7, more preferably 3.1.