CN110204697B - Process for preparing random copolymer of L-lactide and epsilon-caprolactone - Google Patents
Process for preparing random copolymer of L-lactide and epsilon-caprolactone Download PDFInfo
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Abstract
The invention relates to a method for obtaining a completely random copolymer by L-lactide and epsilon-caprolactone through one-pot boiling, which mainly comprises the following steps: under the catalytic action of a metal complex, the L-lactide and the epsilon-caprolactone are subjected to ring opening in an organic solvent at the temperature of 30-60 ℃ to realize copolymerization to obtain a random copolymer of the L-lactide and the epsilon-caprolactone; the catalyst is a Schiff base bridged bis aryloxy ligand-stabilized rare earth metal alkoxy and aryloxy complex, and the structural formula of the catalyst is as follows:
the catalyst used in the invention has the advantages of clear structure, simple synthesis method, simple post-treatment and high yield; the raw materials used in the copolymerization reaction are simple and easy to obtain, the reaction conditions are very mild, and the operation is convenient. The obtained copolymer is a highly random copolymer, makes up for the defects of respective homopolymers, and combines the advantages of the two copolymers to ensure that the copolymer can meet various industrial and living requirements. In addition, the catalyst has small dosage, and provides possibility for realizing large-scale industrial production.
Description
Technical Field
The invention relates to the technical field of polymer preparation, in particular to a method for preparing a highly random copolymer of L-lactide and epsilon-caprolactone.
Background
Some important properties of poly-L-lactide (PLLA) and poly-epsilon-caprolactone (PCL) are widely appreciated in medical and pharmaceutical applications. At the same time, they are functionally complementary in some mechanical properties. PLLA is not permeable to most drugs and has a half-life in vivo of only a few weeks. PCL has good permeability to some low molecular weight drugs, but has a half-life in vivo of up to one year. The copolymer of L-lactide and epsilon-caprolactone can organically combine the L-lactide and the epsilon-caprolactone together, so that the complementary effect of advantages and disadvantages is achieved, the high polymer material with good permeation effect and shorter degradation time is obtained, and the industrial requirement is better met. At present, there are many examples of the use of various catalysts for catalyzing the copolymerization of L-lactide and epsilon-caprolactone to obtain a block copolymer and a gradient copolymer, but there are few reports of catalysts which can obtain a highly random copolymer at ordinary temperature. The related technology mainly comprises the following steps:
in 2010, Nomura et al used geminal dimethyl bridged Salen aluminum benzyloxy complex as a catalyst to catalyze the copolymerization of lactide and caprolactone in toluene at 90 ℃, and after 10 hours of reaction, the two monomers were nearly completely converted to obtain a random copolymer, but the catalyst of the system had a high dosage of 2-3 mol% and a high temperature (see: N.Nomura, A.Akita, R.Ishii and M.Mizuno, J.Am.chem.Soc.2010,132, 1750-1751).
In 2012, Pellecchia et al selected an asymmetric bisamino aluminum methyl complex as a catalyst, and reacted in toluene at 70 ℃ for 4 days with about half of both monomers converted to obtain a random copolymer. Although the reaction temperature is reduced, the catalyst reactivity is too low (see: G.Li, M.Lamberti, D.Pappalardo and C.Pellecchaia, Macromolecules 2012,45, 8614-8620).
In the same year, the Philopsis alata et al selects amino-bridged bis (aryloxy) bis (aluminum methyl) complexes with different substituents as catalysts, and adjusts the reactivity ratios of L-lactide and epsilon-caprolactone by raising the temperature. The reactivity ratios of the two monomers are equivalent at 130 ℃, and a random polymer is obtained. However, in this system, the temperature required to obtain random copolymers is too high, and once the temperature is lowered, only block, tapered and gradient copolymers can be obtained (see: Y.Wang, H.Ma, chem.Commun.2012,48, 6729-. In 2016, the random copolymer can be obtained at high temperature in toluene by using a mononuclear aluminum complex and a binuclear aluminum complex with high steric hindrance as catalysts. The reaction temperature required for this system as high as 110 ℃ constitutes the greatest disadvantage of this catalyst (cf. C.Kan, H.Ma, RSC adv.2016,6, 47402-.
In 2014, Chimonanthus nitens et al used m-phenylenediamine to bridge Salan and Salen type aluminum methyl complex as catalyst to catalyze the copolymerization of L-lactide and epsilon-caprolactone to obtain a product very close to a random copolymer, but the catalyst activity was low (see: L.Li, B.Liu, D.Liu, C.Wu, S.Li, B.Liu, D.Cu, Organometallics 2014,33, 6474-.
In 2017, Visbeaux et al used a mixed allyl rare earth metal complex as a catalyst, and a random copolymer could be obtained in toluene at 70 ℃, but a chain transfer reagent was added to the reaction system, and the reaction time was as long as 24h (see: S.Fadlallah, J.Jothieswaran, F.Capet, F.Bonnet, M.Visbeaux, chem.Eur.J.2017,23, 15644-.
In 2018, YaoYingming and the like adopt ethylenediamine-bridged bis (aryloxy) rare earth metal complexes as catalysts, react for 24 hours at 90 ℃ and obtain a random copolymer of L-lactide and epsilon-caprolactone through an ester exchange process, and the randomization degree (%): L-LA- ε -CL link: the link of epsilon-CL-epsilon-CL is 74: 26. However, the reaction must be carried out stepwise, and only block copolymers are obtained if a "one-pot" method is employed or the reaction temperature is lowered (see: H.Ouyang, K.Nie, D.Yuan, Y.Zhang, D.Cui, Y.Yao, Sci.China chem.2018,61, 708-.
Disclosure of Invention
In order to solve the technical problems, the invention aims to provide a method for preparing a highly random copolymer of L-lactide and epsilon-caprolactone, which is a 'one-pot' method, the selected catalyst has high catalytic activity, and can catalyze the copolymerization reaction of the L-lactide and the epsilon-caprolactone under very mild conditions, and the obtained copolymer is the highly random copolymer.
The invention provides a method for preparing a random copolymer of L-lactide and epsilon-caprolactone, which comprises the following steps:
taking L-lactide and epsilon-caprolactone as raw materials, taking a rare earth metal complex with stable bis-aryloxy ligand bridged by Schiff base as a catalyst, and carrying out ring-opening copolymerization reaction in an organic solvent at 30-60 ℃ to obtain an L-lactide and epsilon-caprolactone random copolymer; the mole ratio of the rare earth metal complex stabilized by the Schiff base bridged bis aryloxy ligand to L-lactide and epsilon-caprolactone is 1: 120-500; the structural formula of the Schiff base bridged bis aryloxy ligand stable rare earth metal complex is shown as a formula (1) and/or a formula (2):
wherein THF is tetrahydrofuran molecule, R is 2, 6-di-tert-butyl-p-tolyl (C)6H2-2,6-tBu2-4-CH3) Tert-butyl group (c)tBu), isopropyl group(s) ((ii)iPr), benzyl (Bn) and ethyl (Et).
Further, the preparation method of the random copolymer of L-lactide and epsilon-caprolactone specifically comprises the following steps:
(1) dissolving a rare earth metal complex with stable Schiff base bridged bis (aryloxy) ligand in an organic solvent to obtain a catalyst solution; dissolving monomers L-lactide and epsilon-caprolactone by using an organic solvent, adding the catalyst solution into the monomers L-lactide and epsilon-caprolactone at one time, and reacting at 30-60 ℃ under a closed condition;
(2) adding a terminator to terminate the reaction, thereby obtaining the random copolymer of the L-lactide and the epsilon-caprolactone.
And (3) after the step (2), settling the polymer by using industrial alcohol, filtering and washing for a plurality of times, and extracting the solvent in a vacuum drying oven to obtain a pure and dry product.
The structural formulas of L-lactide (L-LA) and epsilon-caprolactone (epsilon-CL) are respectively as follows:
further, the reaction time is 2-7 h. Preferably, the reaction time is 2-3 h.
Further, the ratio of the catalyst to the organic solvent is 2-5mmol:1 mL. Preferably, the ratio of the catalyst to the organic solvent is 5mmol:1 mL.
Further, the molar ratio of the catalyst, L-LA and ε -CL is 1: 120-500. Preferably, the molar ratio of the catalyst, the L-lactide and the epsilon-caprolactone is 1: 120-300.
Further, the organic solvent is one of toluene, n-hexane or tetrahydrofuran.
Furthermore, the content of L-lactide in the random copolymer of L-LA and epsilon-CL is 9-90%.
Furthermore, the content of epsilon-caprolactone in the random copolymer of L-LA and epsilon-CL is 10-91%.
The content of L-LA and ε -CL in the random copolymer of L-LA and ε -CL is determined by the catalyst at the beginning of the reaction, the molar ratio of L-lactide to ε -caprolactone, the reaction time, the reaction temperature and the order of addition of each substance.
Further, the method also comprises the step of adding a terminator to terminate the polymerization reaction.
Further, the terminating agent is a hydrochloric acid solution of ethanol or a 95% ethanol aqueous solution.
In the invention, the chemical general formula of the Schiff base bridged bis aryloxy ligand stable rare earth metal compound is [ LaL (OR) (THF)n1]n2L represents a bridged Schiff base ligand, L ═ NH [ CH2CH2N＝CH(2-O-3,5-tBu2C6H2)]2(ii) a THF is tetrahydrofuran; r is 2, 6-di-tert-butyl-p-tolyl, tert-butyl, isopropyl, benzyl or ethyl-; n is1Represents the number of tetrahydrofuran, n10 or 1; n is21 or 2.
The invention utilizes the catalyst to catalyze the ring-opening copolymerization of the monomers L-LA and epsilon-CL, and the principle is as follows:
in the polymerization initiation stage, the reactivity ratios of the ring-opening polymerization of the two monomers L-LA and epsilon-CL are equivalent under the same conditions (r)LA≈rCL1). The following can be proved by the tracking of the reaction process: in the copolymerization reaction, the L-LA and the epsilon-CL start to react almost simultaneously, and even in the first 7min, the conversion rate of the epsilon-CL is slightly larger than that of the L-LA; as the reaction proceeds, the conversion rate of L-LA exceeds ε -CL, and transesterification occurs until the reaction is complete. By passing1H NMR and13the C NMR spectrum was followed to confirm that the formation of highly random copolymers was the result of approximately equal reactivity ratios of the two monomers and the transesterification reaction.
By the scheme, the invention at least has the following advantages:
1) the catalyst used in the invention has the advantages of definite structure, simple synthesis method, high yield and simple separation and purification;
2) the catalyst selected by the invention has high activity and small dosage, the dosage of the catalyst is 0.2-0.5 mol% of the reactant L-LA/epsilon-CL, and the yield of the copolymer is high. When the molar consumption of the catalyst is reduced to 0.2 mol%, higher catalytic activity can still be maintained, and the less consumption of the catalyst provides convenience for the purification of the product;
3) the preparation method disclosed by the invention has the advantages that the raw materials are easy to obtain; the reaction condition is very mild, and even the highly random copolymer can be obtained at normal temperature; the reaction time is short, the copolymers with different structures can be realized by changing the molar ratio of the two monomers, the reaction operation and the post-treatment process are simple, and the possibility is provided for realizing large-scale industrial production.
The foregoing description is only an overview of the technical solutions of the present invention, and in order to make the technical solutions of the present invention more clearly understood and to implement them in accordance with the contents of the description, the following detailed description is given with reference to the preferred embodiments of the present invention and the accompanying drawings.
Drawings
FIG. 1 is a nuclear magnetic hydrogen spectrum of highly random copolymers of L-lactide and epsilon-caprolactone prepared in example 3 in the interval of 4-5.5 ppm;
FIG. 2 is a nuclear magnetic hydrogen spectrum of the highly random copolymer of L-lactide and ε -caprolactone prepared in example 3 in the range of 169-174 ppm.
Detailed Description
The following detailed description of embodiments of the present invention is provided in connection with the accompanying drawings and examples. The following examples are intended to illustrate the invention but are not intended to limit the scope of the invention.
The following detailed description of embodiments of the present invention is provided in connection with the accompanying drawings and examples. The following examples are intended to illustrate the invention but are not intended to limit the scope of the invention.
Example 1 LaL (OC)6H2-2,6-tBu2-4-CH3) (THF) catalyzed copolymerization of L-LA and ε -CL (molar ratio 50:50) to form highly random copolymers
L-LA (0.2394g,1.66mmol) and ε -CL (0.1896g, 1.66mmol) were added to a polymerization pressure bottle under the protection of high purity nitrogen in a glove box and dissolved in 729 μ L of toluene. Weighing R ═ C6H2-2,6-tBu2-4-CH3Was dissolved in 1000. mu.L of toluene, and 755. mu.L (0.0083mmol) of the catalyst solution was charged into a polymerization flask. After reacting for 3h at 60 ℃, transferring out of a glove box, taking out 60 mu L of reaction liquid for in-situ reaction1And (3) HNMR characterization, adding a 95% ethanol solution to terminate the reaction, settling by using industrial alcohol, filtering, washing the polymer for multiple times, and drying in vacuum for 12 hours to obtain the L-lactide and epsilon-caprolactone highly random copolymer.
From the in situ NMR chart, the L-LA and the epsilon-CL are completely converted; degree of randomization (%): L-LA- ε -CL link: the link of ε -CL- ε -CL is 81: 19. GPC analysis of the obtained solid product showed that M of the copolymer was measuredn＝18.0×103g/mol, molecular weight distribution PDI 1.99.
Example 2 LaL (OC)6H2-2,6-tBu2-4-CH3) (THF) catalyzed copolymerization of L-LA and ε -CL (molar ratio 50:50) to form highly random copolymers
Under the protection of high purity nitrogen in a glove box, L-LA (0.2263g,1.57mmol) and ε -CL (0.1792g, 1.57mmol) were added to a polymerization pressure bottle and dissolved in 688 μ L of toluene. Weighing R ═ C6H2-2,6-tBu2-4-CH3The metal lanthanum complex (10.6mg) of (2) was dissolved in 1000. mu.L of toluene, and 714. mu.L (0.0078mmol) of the catalyst solution was taken and charged into a polymerization flask. After reacting for 3h at 30 ℃, transferring out of a glove box, taking out 60 mu L of reaction liquid for in-situ reaction1And H NMR characterization is carried out, then 95% ethanol solution is added to terminate the reaction, industrial alcohol is used for settlement, the polymer is filtered and washed for many times, and vacuum drying is carried out for 12 hours to obtain the L-lactide and epsilon-caprolactone highly random copolymer.
From the in situ NMR chart, the L-LA and the epsilon-CL are completely converted; degree of randomization (%): L-LA- ε -CL link: the epsilon-CL-epsilon-CL chain link is 78: 22. GPC analysis of the obtained solid product showed that M of the copolymer was measuredn＝26.0×103g/mol, molecular weight distribution PDI 2.23.
Example 3 LaL (O)tBu) (THF) catalyzed copolymerization of L-LA and ε -CL (molar ratio 50:50) to form highly random copolymer
L-LA (0.2475g,1.72mmol) and ε -CL (0.1960g, 1.72mmol) were added to a polymerization pressure bottle under the protection of high purity nitrogen in a glove box and dissolved in 805 μ L of toluene. Weighing R ═tThe metal lanthanum complex of Bu (9.6mg) was dissolved in 1000. mu.L of toluene and 729. mu.L (0.0086mmol) of the catalyst was takenThe agent solution was added to the polymerization flask. After reacting for 3h at 60 ℃, transferring out of a glove box, taking out 60 mu L of reaction liquid for in-situ reaction1And (3) HNMR characterization, adding a 95% ethanol solution to terminate the reaction, settling by using industrial alcohol, filtering, washing the polymer for multiple times, and drying in vacuum for 12 hours to obtain the L-lactide and epsilon-caprolactone highly random copolymer.
From the in situ NMR chart, the L-LA and the epsilon-CL are completely converted; degree of randomization (%): L-LA- ε -CL link: the epsilon-CL-epsilon-CL chain link is 80: 20. GPC analysis of the obtained solid product showed that M of the copolymer was measuredn＝34.0×103g/mol, molecular weight distribution PDI 2.06.
Example 4LaL (O)tBu) (THF) catalyzed copolymerization of L-LA and ε -CL (molar ratio 50:50) to form highly random copolymer
L-LA (0.2139g,1.48mmol) and ε -CL (0.1694g, 1.48mmol) were added to a polymerization pressure bottle under the protection of high purity nitrogen in a glove box and dissolved in 687 μ L of toluene. Weighing R ═tBu metal lanthanum complex (9.5mg) was dissolved in 1000. mu.L of toluene, and 639. mu.L (0.0074mmol) of the catalyst solution was charged into a polymerization flask. After reacting for 3h at 30 ℃, transferring out of a glove box, taking out 60 mu L of reaction liquid for in-situ reaction1And H NMR characterization is carried out, then 95% ethanol solution is added to terminate the reaction, industrial alcohol is used for settlement, the polymer is filtered and washed for many times, and vacuum drying is carried out for 12 hours to obtain the L-lactide and epsilon-caprolactone highly random copolymer.
From the in situ NMR chart, the L-LA and the epsilon-CL are completely converted; degree of randomization (%): L-LA- ε -CL link: the link of epsilon-CL-epsilon-CL is 76: 24. GPC analysis of the obtained solid product showed that M of the copolymer was measuredn＝23.1×103g/mol, molecular weight distribution PDI 2.03.
Example 5[ LaL (O)iPr)]2Catalyzing L-LA and epsilon-CL (molar ratio is 50:50) to be copolymerized into high random copolymer
L-LA (0.2162g,1.50mmol) and ε -CL (0.1712g, 1.50mmol) were added to a polymerization pressure bottle under the protection of high purity nitrogen in a glove box and dissolved in 556 μ L of toluene. Weighing R ═iPr Metal lanthanum Complex (7.0mg) was dissolved in 1000. mu.L of toluene, 784. mu.L (0.0075mmol) of catalyst was takenThe agent solution is added to the polymerization flask. After reacting for 3h at 60 ℃, transferring out of a glove box, taking out 60 mu L of reaction liquid for in-situ reaction1And (3) HNMR characterization, adding a 95% ethanol solution to terminate the reaction, settling by using industrial alcohol, filtering, washing the polymer for multiple times, and drying in vacuum for 12 hours to obtain the L-lactide and epsilon-caprolactone highly random copolymer.
As seen from the in situ nuclear magnetic diagram (FIGS. 1-2), no raw material remained, and the conversion of L-LA and ε -CL was complete; degree of randomization (%): L-LA- ε -CL link: the epsilon-CL-epsilon-CL chain link is 80: 20. Glass transition temperature of copolymer: -6.4 ℃, average segment length: l isLA＝0.84；LCL1.15; GPC analysis of the obtained solid product showed that M of the copolymer was measuredn＝32.9×103g/mol, molecular weight distribution PDI 1.96.
Example 6[ LaL (O)iPr)]2Catalyzing copolymerization of L-LA and epsilon-CL (molar ratio 40:60) to synthesize highly random copolymer
L-LA (0.1730g,1.20mmol) and ε -caprolactone (0.2055g,1.80mmol) were polymerized by the method of example 3 to obtain a highly random copolymer of L-LA and ε -CL. The product prepared in this example was characterized as follows:
the L-LA and the epsilon-CL are completely converted; degree of randomization (%): L-LA- ε -CL link: the epsilon-CL-epsilon-CL chain link is 67: 33; glass transition temperature of copolymer: -19.6 ℃, average segment length: l isLA＝0.59；LCL1.31,; GPC analysis of the obtained solid product showed that M of the copolymer was measuredn＝26.9×103g/mol, molecular weight distribution PDI 2.05.
Example 7[ LaL (O)iPr)]2Catalyzing copolymerization of L-LA and epsilon-CL (molar ratio 60:40) to synthesize highly random copolymer
L-LA (0.2594g,1.80mmol) and ε -caprolactone (0.1370g,1.20mmol) were polymerized by the method of example 3 to obtain a highly random copolymer of L-LA and ε -CL. The product prepared in this example was characterized as follows:
the L-LA and the epsilon-CL are completely converted; degree of randomization (%): L-LA- ε -CL link: the chain link of epsilon-CL-epsilon-CL is 86: 14; copolymer glassGlass transition temperature: 7.9 ℃, average segment length: l isLA＝1.11；LCL1.11; GPC analysis of the obtained solid product showed that M of the copolymer was measuredn＝30.7×103g/mol, molecular weight distribution PDI 2.01.
Example 8[ LaL (O)iPr)]2Catalyzing L-LA and epsilon-CL (molar ratio is 70:30) to be copolymerized into a highly random copolymer
L-LA (0.3027g,2.10mmol) and ε -caprolactone (0.1027g,0.90mmol) were polymerized by the method of example 3 to obtain a highly random copolymer of L-LA and ε -CL. The product prepared in this example was characterized as follows:
the L-LA and the epsilon-CL are completely converted; degree of randomization (%): L-LA- ε -CL link: the chain link of the epsilon-CL-epsilon-CL is 89: 11; glass transition temperature of copolymer: 19.0 ℃, average segment length: l isLA＝1.89；LCL1.02; GPC analysis of the obtained solid product showed that M of the copolymer was measuredn＝37.5×103g/mol, molecular weight distribution PDI 1.72.
Example 9[ LaL (O)iPr)]2Catalyzing L-LA and epsilon-CL (molar ratio is 50:50) to be copolymerized into high random copolymer
Under the protection of high-purity nitrogen in a glove box, L-LA (0.2274g,1.58mmol) and ε -CL (0.1801g, 1.58mmol) were added to a polymerization pressure bottle and dissolved in 549 μ L of toluene. Weighing R ═iThe metal lanthanum complex of Pr (6.7mg) was dissolved in 1000. mu.L of toluene, and 861. mu.L (0.0079mmol) of the catalyst solution was taken and charged into a polymerization flask. After reacting for 3h at 30 ℃, transferring out of the glove box, adding 95% ethanol solution to terminate the reaction, settling with industrial alcohol, filtering and washing the polymer for many times, and drying in vacuum for 12h to obtain the L-lactide and epsilon-caprolactone highly random copolymer.
The product was characterized, the conversion of L-LA was 88% and the conversion of ε -CL was 94%; degree of randomization (%): L-LA- ε -CL link: the epsilon-CL-epsilon-CL link is 77: 23.
Example 10[ LaL (OBn)]2Catalyzing L-LA and epsilon-CL (molar ratio is 50:50) to be copolymerized into high random copolymer
Glove box high purity nitrogen protectionNext, L-LA (0.2291g,1.59mmol) and ε -CL (0.1814g, 1.59mmol) were added to a polymerization pressure bottle and dissolved in 593. mu.L of toluene. Lanthanum metal complex (7.5mg) of R ═ Bn was weighed out and dissolved in 1000 μ L of toluene, and 827 μ L (0.0080mmol) of the catalyst solution was taken and charged into a polymerization flask. After reacting for 3h at 60 ℃, transferring out of a glove box, taking out 60 mu L of reaction liquid for in-situ reaction1And (3) HNMR characterization, adding a 95% ethanol solution to terminate the reaction, settling by using industrial alcohol, filtering, washing the polymer for multiple times, and drying in vacuum for 12 hours to obtain the L-lactide and epsilon-caprolactone highly random copolymer.
From the in situ NMR chart, the L-LA and the epsilon-CL are completely converted; degree of randomization (%): L-LA- ε -CL link: the epsilon-CL-epsilon-CL chain link is 80: 20. GPC analysis of the obtained solid product showed that M of the copolymer was measuredn＝17.7×103g/mol, molecular weight distribution PDI 1.81.
Example 11[ LaL (OBn)]2Catalyzing L-LA and epsilon-CL (molar ratio is 50:50) to be copolymerized into high random copolymer
L-LA (0.2899g,2.01mmol) and ε -CL (0.2296g, 2.01mmol) were added to a polymerization pressure bottle under the protection of high purity nitrogen in a glove box and dissolved in 953 μ L of toluene. Lanthanum metal complex (9.3mg) of R ═ Bn was weighed out and dissolved in 1000 μ L of toluene, and 843 μ L (0.0100mmol) of the catalyst solution was added to a polymerization flask. After reacting for 3h at 30 ℃, transferring out of a glove box, taking out 60 mu L of reaction liquid for in-situ reaction1And H NMR characterization is carried out, then 95% ethanol solution is added to terminate the reaction, industrial alcohol is used for settlement, the polymer is filtered and washed for many times, and vacuum drying is carried out for 12 hours to obtain the L-lactide and epsilon-caprolactone highly random copolymer.
From the in situ NMR chart, the L-LA and the epsilon-CL are completely converted; degree of randomization (%): L-LA- ε -CL link: the epsilon-CL-epsilon-CL chain link is 75: 25. GPC analysis of the obtained solid product showed that M of the copolymer was measuredn＝19.4×103g/mol, molecular weight distribution PDI 1.86.
Example 12[ LaL (OEt)]2Catalyzing L-LA and epsilon-CL (molar ratio is 50:50) to be copolymerized into high random copolymer
Adding into a polymerization pressure-resistant bottle under the protection of high-purity nitrogen in a glove boxL-LA (0.2061g,1.43mmol) and ε -CL (0.1632g, 1.43mmol) were dissolved in 412 μ L of toluene. Lanthanum metal complex of R ═ Et (5.9mg) was weighed out and dissolved in 1000 μ L of toluene, and 865 μ L (0.0071mmol) of the catalyst solution was added to the polymerization flask. After reacting for 3h at 60 ℃, transferring out of a glove box, taking out 60 mu L of reaction liquid for in-situ reaction1And (3) HNMR characterization, adding a 95% ethanol solution to terminate the reaction, settling by using industrial alcohol, filtering, washing the polymer for multiple times, and drying in vacuum for 12 hours to obtain the L-lactide and epsilon-caprolactone highly random copolymer.
From the in situ NMR chart, the L-LA and the epsilon-CL are completely converted; degree of randomization (%): L-LA- ε -CL link: the link of ε -CL- ε -CL is 83: 17. GPC analysis of the obtained solid product showed that M of the copolymer was measuredn＝19.9×103g/mol, molecular weight distribution PDI 1.87.
Example 13[ LaL (OEt)]2Catalyzing L-LA and epsilon-CL (molar ratio is 50:50) to be copolymerized into high random copolymer
L-LA (0.2532g,1.76mmol) and ε -CL (0.2005g, 1.76mmol) were added to a polymerization pressure bottle under the protection of high purity nitrogen in a glove box and dissolved in 932 μ L of toluene. Lanthanum metal complex of R ═ Et (9.9mg) was weighed out and dissolved in 1000 μ L of toluene, and 637 μ L (0.0088mmol) of the catalyst solution was added to a polymerization flask. After reacting for 3h at 30 ℃, transferring out of a glove box, taking out 60 mu L of reaction liquid for in-situ reaction1And H NMR characterization is carried out, then 95% ethanol solution is added to terminate the reaction, industrial alcohol is used for settlement, the polymer is filtered and washed for many times, and vacuum drying is carried out for 12 hours to obtain the L-lactide and epsilon-caprolactone highly random copolymer.
From the in situ NMR chart, the L-LA and the epsilon-CL are completely converted; degree of randomization (%): L-LA- ε -CL link: the epsilon-CL-epsilon-CL chain link is 73: 27. GPC analysis of the obtained solid product showed that M of the copolymer was measuredn＝20.7×103g/mol, molecular weight distribution PDI 1.89.
The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention, it should be noted that, for those skilled in the art, many modifications and variations can be made without departing from the technical principle of the present invention, and these modifications and variations should also be regarded as the protection scope of the present invention.
Claims (8)
1. A process for the preparation of random copolymers of L-lactide and epsilon-caprolactone comprising the steps of:
(1) taking L-lactide and epsilon-caprolactone as raw materials, taking a rare earth metal complex with stable bis-aryloxy ligand bridged by Schiff base as a catalyst, and carrying out ring-opening copolymerization reaction in an organic solvent at 30-60 ℃ to obtain an L-lactide and epsilon-caprolactone random copolymer; the mole ratio of the rare earth metal complex stabilized by the Schiff base bridged bis aryloxy ligand to L-lactide and epsilon-caprolactone is 1: 120-500; the structural formula of the Schiff base bridged bis aryloxy ligand stable rare earth metal complex is shown as a formula (1) and/or a formula (2):
wherein THF is tetrahydrofuran molecule, R is one of 2, 6-di-tert-butyl-p-tolyl, tert-butyl, isopropyl, benzyl and ethyl; the reaction time is 2-7 h.
2. The method of claim 1, wherein: the ratio of the catalyst to the organic solvent is 2-5mmol:1 mL.
3. The method of claim 1, wherein: the organic solvent is one of toluene, n-hexane or tetrahydrofuran.
4. The method of claim 1, wherein: in the L-lactide and epsilon-caprolactone random copolymer, the content of L-lactide is 9-90%.
5. The method of claim 1, wherein: in the L-lactide and epsilon-caprolactone random copolymer, the content of epsilon-caprolactone is 10-91 percent.
6. The method of claim 1, wherein: the molar ratio of the catalyst, the L-lactide and the epsilon-caprolactone is 1: 120-300.
7. The method of claim 1, wherein: also comprises a step of adding a terminator to terminate the polymerization reaction.
8. The method of claim 7, wherein: the terminating agent is ethanol hydrochloric acid solution or 95% ethanol solution.
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