Zinc biguanide complex and method for preparing same, method for preparing polylactide

Abstract

The application provides a zinc biguanide complex and a preparation method thereof and a preparation method of polylactide. The chemical structural formula of the zinc biguanide complex is shown in the following formula: The application further provides a preparation method of polylactide, which comprises the following steps: uniformly mixing lactide monomers with the zinc biguanide complex, and heating to make the lactide monomers perform a polymerization reaction to obtain polylactide. The application uses a low-toxicity organic metal catalyst to replace a toxic stannous octoate catalyst, efficiently catalyzes the ring-opening of lactone, and is used for realizing a green and environment-friendly process to produce aliphatic polyester.

Description

Technical Field

[0001] This invention relates to the field of polymer catalysis technology, specifically to a biguanide zinc complex and its preparation method, and a method for preparing polylactide. Background Technology

[0002] Traditional plastic products are widely used due to their low cost and other advantages, but their slow degradation leads to a series of environmental problems, and most of their raw materials come from finite and non-renewable fossil fuels. Therefore, with the depletion of petroleum resources and the pollution caused by the extremely long degradation cycle of plastic products, the search for biodegradable, reusable, and environmentally friendly polymer materials has attracted increasing attention from researchers. Polylactide (PLA) is a polymer with good biocompatibility, biodegradability, and physical and mechanical properties. PLA has good tensile strength and ductility and can be decomposed into carbon dioxide and water in the body, making it an ideal biomedical material. PLA can be used for drug delivery, surgical sutures, and artificial tissue materials, showing broad application prospects.

[0003] Currently, industrial production of PLA mainly involves the ring-opening polymerization of lactide catalyzed by stannous octoate. However, the polymers obtained from the ring-opening polymerization of lactide catalyzed by metal complex catalysts inevitably contain some metal residues. PLA obtained from the ring-opening polymerization of lactide catalyzed by stannous octoate will contain tin residues. Tin itself is toxic and harmful to human health, which limits the application of PLA in the food and pharmaceutical fields. Therefore, developing environmentally friendly metal complex catalysts to achieve green and environmentally friendly processes for the production of polylactide is of great significance.

[0004] The ligand structure and metal type in metal complexes affect the catalytic activity and stereoselectivity of the complexes in the ring-opening polymerization of lactide. Zinc is an essential trace element for the human body, and guanidino ligands are a class of ligands with a large modulation space. Therefore, the development and application of guanidino zinc complexes in the catalytic polymerization of lactide has significant research value. Summary of the Invention

[0005] To address the aforementioned technical problems, the present invention aims to provide a biguanide zinc complex and its preparation method, as well as a method for preparing polylactide, thereby providing a low-toxicity organometallic catalyst.

[0006] To achieve the above objectives, the present invention provides a biguanide zinc complex, the chemical structural formula of which is shown in Formula I:

[0007]

[0008] The present invention also provides a method for preparing the biguanide zinc complex shown in Formula I above, which includes the following steps:

[0009] The biguanide ligand shown in Formula II was reacted with zinc trifluoromethanesulfonate in a solvent to obtain the above-mentioned biguanide zinc complex.

[0010]

[0011] The method for preparing the biguanide zinc complex of the present invention involves the following reaction formula:

[0012]

[0013] In the above-mentioned method for preparing the biguanide zinc complex, preferably, the molar ratio of zinc trifluoromethanesulfonate to the biguanide ligand is 1:1-2.5.

[0014] In the above method for preparing the biguanide zinc complex, preferably, the reaction temperature is 20-60℃ and the reaction time is 0.3-48h.

[0015] In the above method for preparing the biguanide zinc complex, preferably, the solvent is tetrahydrofuran / or acetonitrile.

[0016] In the above method for preparing the biguanide zinc complex, preferably, the reaction is carried out under a protective atmosphere. The protective atmosphere is argon or nitrogen.

[0017] Preferably, the preparation method of the above-mentioned biguanide zinc complex further includes washing and purifying the reaction product with diethyl ether to obtain the biguanide zinc complex.

[0018] The present invention also provides a method for preparing polylactide, which includes the following steps:

[0019] Under inert gas protection, lactide monomer and biguanide zinc complex are mixed evenly and heated to allow the lactide monomer to undergo a polymerization reaction to obtain polylactide.

[0020] The biguanide zinc complex is the above-mentioned biguanide zinc complex or the biguanide zinc complex obtained by the above preparation method.

[0021] This invention also uses the prepared biguanide zinc complex, a low-toxicity organometallic catalyst, to replace the toxic stannous octoate catalyst, which efficiently catalyzes the ring-opening of cyclic lactones, enabling the production of aliphatic polyesters through a green and environmentally friendly process.

[0022] In the above-mentioned method for preparing polylactide, preferably, the molar ratio of the lactide monomer to the biguanide zinc complex is 100-500:1.

[0023] In the above-mentioned method for preparing polylactide, preferably, the lactide monomer is selected from L-lactide or racemic lactide.

[0024] In the above-mentioned method for preparing polylactide, preferably, the heating temperature (i.e., the polymerization reaction temperature) is 130-150℃, more preferably 130℃.

[0025] In the above-mentioned method for preparing polylactide, preferably, the polymerization reaction endpoint is when all the solid powder in the reaction system is converted into a gel solid.

[0026] In the above-mentioned method for preparing polylactide, preferably, the polymerization reaction is carried out under solvent-free conditions.

[0027] In the above-mentioned method for preparing polylactide, preferably, the inert gas is argon.

[0028] In the above-mentioned method for preparing polylactide, preferably, a co-catalyst is added to the polymerization reaction system, wherein the co-catalyst is benzyl alcohol.

[0029] The technical solution provided by this invention has the following beneficial effects:

[0030] The biguanide zinc complex provided by this invention is a mononuclear zinc complex with zinc as the coordinating metal and chiral biguanide as the ligand. Compared with the prior art, zinc in the biguanide zinc catalyst is inexpensive and readily available, and as one of the trace elements in the human body, it has good biocompatibility, making the polymerization process more green and environmentally friendly. The synthesized polyester material also has less biotoxicity, making it more widely used in biomedicine and other fields.

[0031] The biguanide zinc complex catalyst of this invention has a simple preparation method, high yield, and the reaction product (catalyst solution) can be used directly, avoiding the economic losses caused by catalyst purification. Under anhydrous, oxygen-free, solvent-free, and inert gas protection, even without the addition of a co-catalyst, heating the biguanide zinc complex catalyst to melt it can efficiently catalyze the polymerization of lactide to prepare polylactide. Polymers with high molecular weight and narrow molecular weight distribution can be obtained in a relatively short time at a relatively low reaction temperature. Detailed Implementation

[0032] In order to provide a clearer understanding of the technical features, objectives and beneficial effects of the present invention, the technical solution of the present invention will now be described in detail below, but it should not be construed as limiting the scope of implementation of the present invention.

[0033] The method for synthesizing the biguanide ligand shown in Formula II used in the embodiments of the present invention can be found in Angew. Chem. Int. Ed. 2009, 48, 7387-7390.

[0034] Example 1

[0035] This embodiment provides a zinc biguanide complex, the preparation method of which is as follows:

[0036] In an argon atmosphere, 1.9 g (approximately 5.2 mmol) of zinc trifluoromethanesulfonate was weighed and dissolved in 20 mL of tetrahydrofuran. 6.05 g (approximately 11.8 mmol) of the biguanide ligand shown in Formula II was added. The resulting mixture was stirred at 25 °C for 24 hours. The reaction yielded a bright yellow solution. The solvent was removed under vacuum, and after drying, the solution was washed and purified with diethyl ether to obtain a bright yellow powder product.

[0037] The product was characterized by nuclear magnetic resonance.

[0038] Biguanide zinc complex yield: 6.2 g (86%).

[0039] NMR characterization results: 1 H NMR (400MHz, CDCl3): δ7.35-7.21(m,20H),4.84(br,4H),3.48-3.30(m,32H),2.05-1.93(m,16H),1.80-1.75(m,16H).

[0040] This proves that the bright yellow powder product obtained in this embodiment is the biguanide zinc complex shown in Formula I.

[0041] Example 2

[0042] This embodiment provides a zinc biguanide complex, the preparation method of which is as follows:

[0043] In an argon atmosphere, 1.9 g (approximately 5.2 mmol) of zinc trifluoromethanesulfonate was weighed and dissolved in 20 mL of acetonitrile at 60 °C. 2.7 g (approximately 5.2 mmol) of the biguanide ligand shown in Formula II was added. The resulting mixture was stirred at 60 °C for 20 min. The reaction yielded a bright yellow solution. The solvent was removed under vacuum, and after drying, the solution was washed and purified with diethyl ether to obtain a bright yellow powder product.

[0044] Example 3

[0045] This embodiment provides a method for preparing polylactide (PLA), which includes the following steps:

[0046] Under argon protection, 4.5 mmol of L-lactide (lactide monomer) and 0.009 mmol of the biguanide zinc complex provided in Example 1 were accurately weighed. Under solvent-free conditions, the two (monomer to biguanide zinc complex molar ratio of 500:1) were thoroughly stirred in the reactor, heated to 130°C, and the reaction system was carefully observed until the solid powder was completely converted into a gel solid. The reaction was stopped, and the reaction time was recorded as t = 1 h, thus completing the ring-opening polymerization of lactide to prepare PLA.

[0047] Open the reactor lid, cool in an ice-water bath, and add a small amount (2 ml) of CH2Cl2 to the reaction mixture until completely dissolved to obtain a sample for performance testing. Take a small amount of sample, remove volatiles under vacuum, and then... 1 ¹H NMR calculations showed that the lactide monomer conversion rate was conv. = 94%.

[0048] The remaining sample solution was subjected to vigorous stirring, and a large amount (20 mL) of cold methanol solution was added for precipitation to obtain crude polymer. The polymer was then separated and washed with a small amount of cold methanol to remove residual catalyst and oligomers. This washing operation was repeated three times. The polymer was then vacuum dried at 60 °C to constant weight to obtain a film-like plastic polymer sample. The molecular weight of the polymer, Mn, was determined by gel permeation chromatography (GPC) to be 37439 g / mol, and the molecular weight distribution (PDI) was 1.6.

[0049] Example 4

[0050] This embodiment provides a method for preparing polylactide (PLA), which is the same as that in Example 2, except that racemic lactide is used instead of L-lactide in Example 2.

[0051] Reaction results: reaction time t = 3 h, lactide monomer conversion conv. = 95%, molecular weight Mn = 34261 g / mol and molecular weight distribution PDI = 1.6 as determined by gel permeation chromatography (GPC).

[0052] Example 5

[0053] This embodiment provides a method for preparing polylactide (PLA), which is the same as that in Example 3, except that 0.009 mmol of benzyl alcohol is added to the reaction system (the molar ratio of lactide monomer: biguanide zinc complex: benzyl alcohol is 500:1:1).

[0054] Reaction results: reaction time t = 3 h, lactide monomer conversion conv. = 97%, molecular weight Mn = 22134 g / mol and molecular weight distribution PDI = 2.0 as determined by gel permeation chromatography (GPC).

[0055] Example 6

[0056] This embodiment provides a method for preparing polylactide (PLA), which is the same as that in Example 2, except that the molar ratio of lactide monomer to biguanide zinc complex is 100:1, and racemic lactide is used instead of L-lactide in Example 2.

[0057] Reaction results: reaction time t = 0.5 h, lactide monomer conversion conv. = 90%.

[0058] Example 7

[0059] This embodiment provides a method for preparing polylactide (PLA), which is the same as that in Example 5, except that benzyl alcohol (lactide monomer: biguanide zinc complex: benzyl alcohol molar ratio of 100:1:1) is added to the reaction system.

[0060] Reaction results: reaction time t = 0.5 h, lactide monomer conversion conv. = 95%.

[0061] Comparative Example 1

[0062] This comparative example provides an existing coordination compound, as follows:

[0063]

[0064] The compound shown in Formula III is a complex reported in the literature (Eur. J. Inorg. Chem. 2007, 5645-5651). Compared with the biguanide zinc complex catalyst of the present invention, it has the same anion and the same metal ion, the difference being the biguanide ligand structure. In the molten state at 135°C, using the compound shown in Formula III as a catalyst, with a racemic lactide monomer to biguanide zinc complex molar ratio of 500:1, and a reaction time of 24 h, the polymer number-average molecular weight was 21379.

[0065] Compared to Example 3, the reaction time was longer and the resulting polymer had a smaller molecular weight.

[0066] Comparative Example 2

[0067] This comparative example provides an existing coordination compound, as follows:

[0068]

[0069] Complexes C3 and C4 are those reported in the literature (Chem. Eur. J. 2009, 15, 2362-2376), and have the same metal ion as the catalyst described in this invention, but different guanidine ligand structures, with chloride ions coordinating with zinc. In the molten state at 130°C and 150°C, using the above complexes as catalysts, with a molar ratio of racemic lactide monomer to biguanide zinc complex of 500:1, and a reaction time of 24 h or 48 h, the polymer yield was zero. Neither complex C3 nor C4 exhibited catalytic activity for the polymerization of racemic lactide.

[0070] In summary, the biguanide zinc complex provided by this invention has a higher efficiency in catalyzing the polymerization of lactide to prepare polylactide, and can polymerize polymers with high molecular weight and narrow molecular weight distribution in a shorter time at a lower reaction temperature.

Claims

1. A zinc bisguanide complex having a chemical structure as shown in Formula I: 2.A method for preparing the zinc bisguanide complex of claim 1, comprising the following steps: reacting a bisguanide ligand shown in Formula II with zinc triflate in a solvent to obtain the zinc bisguanide complex; 3. The method of preparing a zinc complex of a biguanide according to claim 2, wherein, the molar ratio of zinc triflate to the bisguanide ligand is 1:1-2.

5.

4. The method of preparing a zinc complex of a bisguanide according to claim 2, wherein, the reaction temperature is 20-60℃, and the reaction time is 0.3-48h.

5. The method of preparing a zinc complex of a bisguanide according to claim 2, wherein, the solvent is tetrahydrofuran and / or acetonitrile. 6.A method for preparing poly-L-lactide, comprising the following steps: mixing lactide monomers with the zinc bisguanide complex under the protection of inert gas, and heating to make the lactide monomers undergo polymerization to obtain poly-L-lactide; wherein, the zinc bisguanide complex is the zinc bisguanide complex of claim 1 or the zinc bisguanide complex obtained by the preparation method of any one of claims 2-5.

7. The method of preparing poly-L-lactide according to claim 6, wherein, the molar ratio of the lactide monomers to the zinc bisguanide complex is 100-500:

1.

8. The method of preparing poly-L-lactide according to claim 6, wherein, the lactide monomers are selected from L-lactide or racemic lactide.

9. The method of preparing poly-L-lactide according to claim 6, wherein, the heating temperature is 130-150℃.

10. The method of preparing poly-L-lactide according to claim 6, wherein, the end of the polymerization is that all the solid powders in the reaction system are converted into gel solids.

11. The method of preparing poly-L-lactide according to claim 6, wherein, the polymerization is carried out under solvent-free conditions.

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