Zinc biguanide complex, preparation method thereof and preparation method of polylactide

Abstract

The invention provides a biguanide zinc complex, a preparation method thereof and a preparation method of polylactide. The chemical structural formula of the biguanide zinc complex is as shown in # imgabs0. The invention also provides a preparation method of polylactide, which comprises the following steps: uniformly mixing a lactide monomer with the biguanide zinc complex, and heating to enable the lactide monomer to carry out polymerization reaction to obtain the polylactide. According to the method, the low-toxicity organic metal catalyst is used for replacing a toxic stannous octoate catalyst, ring opening of cyclic lactone is efficiently catalyzed, and the method is used for producing aliphatic polyester through a green and environment-friendly process.

Description

Technical Field

[0001] The invention relates to the technical field of polymer catalysis, and in particular to a biguanide zinc complex and a preparation method thereof, and a preparation method of polylactide. Background Art

[0002] Traditional plastic products are widely used due to their low cost and other advantages, but they are difficult to degrade, leading to a series of environmental problems, and most of the raw materials come from limited 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 some biodegradable, reusable and environmentally friendly polymer materials has attracted the attention of more and more 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, which makes it an ideal biomedical material. PLA can be used for drug delivery, surgical suture materials and artificial tissue materials, and has a wide range of application prospects.

[0003] At present, the industrial production of PLA is mainly through the ring-opening polymerization of lactide catalyzed by stannous octoate. However, the polymer obtained by the ring-opening polymerization of cyclic lactone catalyzed by metal complex catalysts will inevitably contain some metal residues. The PLA obtained by the ring-opening polymerization of lactide catalyzed by stannous octoate will contain tin residues. The tin element itself is toxic and harmful to the human body, which will limit the application of PLA in the food and medical fields. Therefore, it is of great significance to develop environmentally friendly metal complex catalysts and realize the green and environmentally friendly process to produce polylactide.

[0004] The ligand structure and metal type in the metal complex affect the catalytic activity and stereoselectivity of the complex in the ring-opening polymerization of lactide. Zinc is an essential trace element in the human body, and guanidine ligands are a type of ligand with a large tuning space. Therefore, the development of the preparation of guanidine zinc complexes and their application in the field of catalytic lactide polymerization has great research value. Summary of the invention

[0005] In order to solve the above technical problems, the purpose of the present invention is to provide a biguanide zinc complex and a preparation method thereof and a preparation method of polylactide, thereby providing a low-toxic organic metal catalyst.

[0006] In order to achieve the above object, the present invention provides a biguanide zinc complex, the chemical structure of which is shown in Formula I:

[0007]

[0008] The present invention also provides a method for preparing the biguanide zinc complex represented by the above formula I, which comprises the following steps:

[0009] The biguanide ligand represented by formula II is reacted with zinc trifluoromethanesulfonate in a solvent to obtain the biguanide zinc complex;

[0010]

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

[0012]

[0013] In the above 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-mentioned method for preparing the biguanide zinc complex, preferably, the reaction temperature is 20-60° C. and the reaction time is 0.3-48 h.

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

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

[0017] In the above-mentioned method for preparing the biguanide zinc complex, preferably, the preparation method further comprises washing and purifying the reaction product with ether to obtain the biguanide zinc complex.

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

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

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

[0021] The invention also uses the prepared biguanide zinc complex, a low-toxic organic metal catalyst, to replace the toxic stannous octoate catalyst, and efficiently catalyzes the ring-opening of the cyclic lactone, so as to realize the green and environmentally friendly process for producing aliphatic polyester.

[0022] In the above 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 method for preparing polylactide, preferably, the lactide monomer is selected from L-lactide or racemic lactide.

[0024] In the above method for preparing polylactide, preferably, the heating temperature (ie, polymerization reaction temperature) is 130-150°C, more preferably 130°C.

[0025] In the above-mentioned method for preparing polylactide, preferably, the endpoint of the polymerization reaction is that all the solid powders in the reaction system are converted into gel solids.

[0026] In the above method for preparing polylactide, preferably, the polymerization reaction is carried out in the absence of a solvent.

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

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

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

[0030] The biguanide zinc complex provided by the present invention is a mononuclear zinc complex with zinc as a coordination metal and chiral biguanide as a ligand. Compared with the prior art, zinc in the biguanide zinc catalyst is cheap and easy to obtain, and as one of the trace elements of the human body, it has good biocompatibility, making the polymerization process more green and environmentally friendly, and the synthesized polyester material also has less biological toxicity, so that it has a wider range of applications in the fields of biomedicine and the like.

[0031] The biguanide zinc complex catalyst of the present invention has a simple preparation method and a high yield, and the reaction product (catalyst solution) can be used directly, thereby avoiding economic losses caused by purifying the catalyst. Under the protection of anhydrous, oxygen-free, solvent-free and inert gas, even without adding a co-catalyst, the biguanide zinc complex catalyst can be heated to melt to efficiently catalyze the polymerization of lactide to prepare polylactide, and a polymer with high molecular weight and narrow molecular weight distribution can be obtained by polymerization at a relatively low reaction temperature, that is, in a relatively short time. DETAILED DESCRIPTION

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

[0033] The synthesis method of the biguanide ligand represented by 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 biguanide zinc complex, and its preparation method is as follows:

[0036] In an argon environment, 1.9 g (about 5.2 mmol) of zinc trifluoromethanesulfonate was weighed and dissolved in 20 mL of tetrahydrofuran, and 6.05 g (about 11.8 mmol) of the biguanide ligand represented by formula II was added. The resulting mixed solution was stirred at 25° C. for 24 hours to obtain a bright yellow solution. The solvent was removed in vacuo, and after the solvent was drained, it was washed and purified with ether to obtain a bright yellow powder product.

[0037] The product was characterized by NMR.

[0038] Yield of biguanide zinc complex: 6.2 g (86%).

[0039] NMR characterization results: 1 H NMR (400 MHz, CDCl 3 ): 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 prepared in this example is the biguanide zinc complex shown in Formula I.

[0041] Example 2

[0042] This embodiment provides a biguanide zinc complex, and its preparation method is as follows:

[0043] In an argon environment, 1.9 g (about 5.2 mmol) of zinc trifluoromethanesulfonate was weighed and dissolved in 20 mL of acetonitrile at 60° C., 2.7 g (about 5.2 mmol) of the biguanide ligand represented by formula II was added, and the resulting mixed solution was stirred at 60° C. for 20 min to obtain a bright yellow solution. The solvent was removed in vacuo, and after the solvent was drained, it was washed and purified with ether to obtain a bright yellow powder product.

[0044] Example 3

[0045] This embodiment provides a method for preparing polylactide (PLA), which comprises 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, and the two (the molar ratio of the monomer to the biguanide zinc complex was 500:1) were fully stirred in a reactor without solvent, and the temperature was raised to 130° C. The reaction system was carefully observed until all the solid powder was converted into a gel solid, and the reaction was stopped. The reaction time t=1 h was recorded, and the lactide ring-opening polymerization to prepare PLA reaction was completed.

[0047] Open the lid of the reactor, cool it in an ice-water bath, and add a small amount (2 ml) of CH2 Cl 2 The sample was completely dissolved to obtain a sample for performance testing. A small amount of sample was taken to remove volatiles in vacuum. 1 The lactide monomer conversion rate calculated by H NMR was conv.=94%.

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

[0049] Example 4

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

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

[0052] Example 5

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

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

[0055] Example 6

[0056] This embodiment provides a method for preparing polylactide (PLA), which is the same as that of Embodiment 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 Embodiment 2.

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

[0058] Example 7

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

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

[0061] Comparative Example 1

[0062] This comparative example provides an existing complex, 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 metal ion, but the difference is that the biguanide ligand structure is different. In a molten state at 135° C., the compound shown in formula III is used as a catalyst, the molar ratio of racemic lactide monomer to biguanide zinc complex is 500:1, and the reaction is carried out for 24 hours, and the number average molecular weight of the polymer is 21379.

[0065] Compared with Example 3, the reaction time is longer and the molecular weight of the obtained polymer is smaller.

[0066] Comparative Example 2

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

[0068]

[0069] The above-mentioned complexes C3 and C4 are complexes reported in the literature (Chem. Eur. J. 2009, 15, 2362-2376), which have the same catalyst metal ions as the present invention, but different guanidine ligand structures, and chloride ions are coordinated with zinc. In a molten state at 130° C. and 150° C., the above-mentioned complexes are used as catalysts, the molar ratio of racemic lactide monomer to biguanide zinc complex is 500:1, and the reaction is carried out for 24 hours or 48 hours. The polymer yield is zero, and the complexes C3 and C4 have no activity in catalyzing the polymerization of racemic lactide.

[0070] In summary, the biguanide zinc complex provided by the present invention is more efficient in catalyzing the polymerization of lactide to prepare polylactide, and can obtain a polymer with a high molecular weight and a narrow molecular weight distribution at a lower reaction temperature, that is, in a shorter time.

Claims

1. A biguanide zinc complex, the chemical structure of which is shown in Formula I:

2. A method for preparing the biguanide zinc complex according to claim 1, comprising the following steps: The biguanide ligand represented by formula II is reacted with zinc trifluoromethanesulfonate in a solvent to obtain the biguanide zinc complex; 3. The method for preparing the biguanide zinc complex according to claim 2, wherein: The molar ratio of zinc trifluoromethanesulfonate to biguanide ligand is 1:1-2.

5.

4. The method for preparing the biguanide zinc complex according to claim 2, wherein: The reaction temperature is 20-60°C, and the reaction time is 0.3-48h.

5. The method for preparing the biguanide zinc complex according to claim 2, wherein: The solvent is tetrahydrofuran and / or acetonitrile.

6. A method for preparing polylactide, comprising the following steps: Under the protection of inert gas, the lactide monomer and the biguanide zinc complex are uniformly mixed, and heated to allow the lactide monomer to undergo a polymerization reaction to obtain polylactide; in, The biguanide zinc complex is the biguanide zinc complex according to claim 1 or the biguanide zinc complex obtained by the preparation method according to any one of claims 2 to 5.

7. The method for preparing polylactide according to claim 6, wherein: The molar ratio of the lactide monomer to the biguanide zinc complex is 100-500:

1.

8. The method for preparing polylactide according to claim 6, wherein: The lactide monomer is selected from L-lactide or racemic lactide.

9. The method for preparing polylactide according to claim 6, wherein: The heating temperature is 130-150°C.

10. The method for preparing polylactide according to claim 6, wherein: The end point of the polymerization reaction is when all the solid powders in the reaction system are converted into gel solids.

11. The method for preparing polylactide according to claim 6, wherein: The polymerization reaction is carried out in the absence of a solvent.

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