A preparation method of high molecular weight polycaprolactone

Abstract

The present invention belongs to the technical field of biodegradable polymer material synthesis and discloses a method for preparing high molecular weight polycaprolactone. The method uses a ketimine ligand and diethylzinc to react in situ to catalyze the ring-opening polymerization of caprolactone to prepare polycaprolactone. Under bulk conditions, the polymerization of ε-caprolactone can be catalyzed to prepare polycaprolactone without the participation of an initiator. This method has the advantages of in situ catalysis, short polymerization reaction time, high molecular weight of the obtained polymer, and narrow distribution. Through the synthesis technology of polycaprolactone disclosed in the present invention, the molecular weight of the synthesized polycaprolactone is more than 179,000, and the molecular weight distribution is between 1.55 and 1.70. The molecular weight reaches a maximum of 246,000, and the corresponding polymer molecular weight distribution is 1.65.

Description

Technical Field

[0001] The invention belongs to the technical field of biodegradable polymer material synthesis, and particularly relates to a method for preparing high-molecular-weight polycaprolactone. Background Art

[0002] In recent years, with the increasing scarcity of petroleum resources, the search for renewable, biodegradable, and environmentally friendly polymers to replace petroleum-based polyolefins has become a research hotspot in materials science. Polycaprolactone is a biodegradable polymer with a wide range of applications in packaging, biopharmaceuticals, and the pharmaceutical industry.

[0003] The commonly used synthesis method for high molecular weight polycaprolactone is the ring-opening polymerization of caprolactone catalyzed by a metal catalyst. Stannous octoate is commonly used as a catalyst in industry. Stannous octoate has certain cytotoxicity, and the metal residues of the catalyst in the polymer are difficult to completely remove. In addition, most polycaprolactone synthesis processes in the prior art have defects such as low polymer molecular weight and long reaction times, which limit their application and promotion in fields such as medicine. Zinc is a non-toxic metal element that is beneficial to the human body. Using new and friendly zinc metal catalysts to prepare high molecular weight polyester has become a research direction for scientific researchers. Summary of the Invention

[0004] In order to overcome the shortcomings of the prior art, the present invention provides a method for preparing high molecular weight polycaprolactone, which adopts the method of preparing polycaprolactone by in-situ catalytic ring-opening polymerization of ε-caprolactone. The catalyst is generated in situ, the preparation method of the raw material ketimine required for the catalyst is simple, diethyl zinc is a commercially available compound, and the zinc element is non-toxic.

[0005] The above object of the present invention is achieved through the following technical solution: A method for preparing high molecular weight polycaprolactone, comprising the steps of:

[0006] ε-caprolactone, a ketimine ligand and diethylzinc are mixed and then subjected to ring-opening polymerization to obtain polycaprolactone.

[0007] The ketimine ligand has a structure as shown in general formula I.

[0008]

[0009] Furthermore, the molar ratio of the ε-caprolactone:ketimine ligand:diethylzinc is (5000-30000):1:1.

[0010] Furthermore, the ring-opening polymerization temperature is 80-200° C., and the time is 3 seconds to 60 minutes.

[0011] In a further preferred embodiment of the present invention, the high molecular weight polycaprolactone is prepared by mixing ketimine ligands and diethylzinc in equal molar ratios and then in situ catalyzing the ring-opening polymerization of ε-caprolactone to prepare the polycaprolactone.

[0012] The beneficial effects of the present invention compared with the prior art are: the present invention adopts a method for preparing polycaprolactone by in-situ catalytic ring-opening polymerization of ε-caprolactone, the catalyst is generated in situ, the preparation method of the raw material ketimine required for the catalyst is simple, diethyl zinc is a commercially available compound, and the zinc element is non-toxic. In anhydrous and oxygen-free environment and under inert gas protection, under bulk conditions, ε-caprolactone is used as a monomer, and ketimine and diethyl zinc react for a period of time before in-situ catalyzing the ring-opening polymerization of ε-caprolactone, and no initiator is required during the polymerization process. The polymerization reaction time is short, and the obtained polycaprolactone has a high molecular weight, a high yield, and a narrow polymer molecular weight distribution. The molecular weight of polycaprolactone reaches up to 246,000, and the corresponding polymer molecular weight distribution is is 1.65. DETAILED DESCRIPTION

[0013] The present invention is described in detail below with reference to the examples. However, the following examples are only preferred embodiments of the present invention, and the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field, within the technical scope disclosed in the present invention, who makes equivalent replacements or changes according to the technical scheme and inventive concept of the present invention, should be covered by the protection scope of the present invention. The experimental methods adopted in the present invention are all conventional methods, and the experimental equipment, materials, reagents, etc. used can be obtained from commercial channels.

[0014] The ketimine ligand of the present invention is shown in general formula I. The ketimine ligand and diethylzinc in the present invention are commercially available products or prepared according to existing methods, and the present invention has no particular limitation on this.

[0015]

[0016] To further understand the present invention, the following examples describe in detail the methods for preparing polycaprolactone provided herein. The scope of the present invention is not limited by the following examples. The raw materials used in the following examples are all commercially available, except for ketimine, which was prepared with reference to a known reference (Journal of Organometallic Chemistry 2004, 689, 224–237).

[0017] Example 1

[0018] In an argon environment, take ketimine 1a (0.001mmol) and put it in a schlenk bottle, add anhydrous and oxygen-free treated toluene, heat the reaction solution to 60°C, add diethylzinc (0.001mmol), and stir the reaction at 60°C for 30min to obtain a colorless clear solution. Vacuum the solvent to obtain a white powder. Add 10.0mmol of ε-caprolactone that has been distilled under reduced pressure to the above reaction bottle, heat and stir the resulting mixture at 110°C, and observe the reaction system until its magnetic particle no longer stirs or the powder is completely converted into a gel solid, then stop the reaction. Record the reaction time (t = 50s). Open the bottle cap, cool naturally, add a minimum amount (10mL) of CH2Cl2 to completely dissolve, take a small amount of sample from the reaction mixture and vacuum remove volatiles, and then use 1 The monomer conversion was calculated by HNMR (conv.=100%).

[0019] The reaction mixture was stirred vigorously and then added to a large amount (100 mL) of cold ethanol solution to precipitate the crude polymer. To separate and purify the polymer, a small amount of cold ethanol was used to wash away residual ketimine, diethylzinc, ε-caprolactone, and oligomers. This washing process was repeated three times. The polymer was vacuum-dried at 60°C to a constant weight to obtain a film-like plastic polymer sample.

[0020] The yield of polycaprolactone obtained in the present invention is 98%. The present invention uses polystyrene as a standard and uses gel permeation chromatography to analyze the polycaprolactone obtained in this embodiment. The measured number average molecular weight Mn of the polycaprolactone is 184,000 and the molecular weight distribution is is 1.66.

[0021] Example 2

[0022] A method for in-situ catalytic polymerization of caprolactone is provided, wherein the raw materials are ε-caprolactone, ketimine 1a, and diethylzinc, and the molar ratio of ε-caprolactone:1a:diethylzinc is 20,000:1:1. The method is the same as Example 1. The method differs from Example 1 in that the polymerization reaction time t is 1 min, the ε-caprolactone conversion rate conv. is 99%, the polymer yield is 96%, the polymer molecular weight Mn is 235,000, and the polymer molecular weight distribution is 1.58.

[0023] Example 3

[0024] A method for catalytic polymerization of caprolactone is provided, wherein the raw materials are ε-caprolactone, ketimine 1b, and diethylzinc, and the molar ratio of ε-caprolactone:1b:diethylzinc is 5000:1:1. The method is the same as Example 1. The differences from Example 1 are: the catalytic reaction time t = 1.5 min, the ε-caprolactone conversion rate conv. = 100%, the polymer yield is 95%, the polymer molecular weight Mn is 231,000, and the polymer molecular weight distribution is 1.69.

[0025] Example 4

[0026] A method for catalytic polymerization of caprolactone is provided, wherein the raw materials are ε-caprolactone, ketimine 1b, and diethylzinc, and the molar ratio of ε-caprolactone:1b:diethylzinc is 10,000:1:1. The method is the same as Example 1. The method differs from Example 1 in that the catalytic reaction time t is 2.5 min, the ε-caprolactone conversion rate conv. is 91%, the polymer yield is 97%, the polymer molecular weight Mn is 246,000, and the polymer molecular weight distribution is 1.65.

[0027] Example 5

[0028] A method for catalytic polymerization of caprolactone is provided, wherein the raw materials are ε-caprolactone, ketimine 1c, and diethylzinc, and the molar ratio of ε-caprolactone:1c:diethylzinc is 30,000:1:1. The method is the same as Example 1. The method differs from Example 1 in that the catalytic reaction time t is 40 seconds, the ε-caprolactone conversion rate conv. is 100%, the polymer yield is 97%, the polymer molecular weight Mn is 207,000, and the polymer molecular weight distribution is 1.70.

[0029] Example 6

[0030] A method for catalytic caprolactone polymerization is provided, wherein the raw materials are ε-caprolactone, ketimine 1d, and diethylzinc, and the molar ratio of ε-caprolactone:1d:diethylzinc is 20,000:1:1. The method is the same as Example 1. The method differs from Example 1 in that the catalytic reaction time t is 20 seconds, the ε-caprolactone conversion rate conv. is 100%, the polymer yield is 99%, the polymer molecular weight Mn is 179,000, and the polymer molecular weight distribution is 1.55.

[0031] Example 7

[0032] A method for catalyzing the homopolymerization of caprolactone using ε-caprolactone, ketimine 1d, and diethylzinc as the raw materials, and a molar ratio of ε-caprolactone:1d:diethylzinc of 30,000:1:1 is provided. The method is the same as that in Example 1. The method differs from Example 1 in that the catalytic reaction time t is 30 seconds, the ε-caprolactone conversion rate conv. is 100%, the polymer yield is 96%, the polymer molecular weight Mn is 203,000, and the polymer molecular weight distribution is 1.64.

[0033] The various test data of the in-situ catalytic ring-opening polymerization of ε-caprolactone in the above examples are shown in Table 1.

[0034] Table 1 Data of ε-caprolactone ring-opening polymerization

[0035]

[0036] Note:

[0037] 1 Monomer conversion rate 1 H-NMR spectrum determination.

[0038] 2 The molecular weight was measured by gel permeation chromatography (GPC) using polystyrene as the standard substance and tetrahydrofuran as the eluent.

[0039] 3 The conversion frequency TOF calculation formula is: TOF = conversion × ([monomer] / [initiator]) / time.

[0040] 4 The bulk catalysis was carried out at 110°C without solvent.

[0041] As can be seen from Table 1, the molecular weight of the synthesized polycaprolactone prepared by the ring-opening polymerization of caprolactone disclosed in the present invention is above 179,000, and the molecular weight distribution is between 1.55-1.70. The molecular weight of the polycaprolactone reaches up to 246,000, and the molecular weight distribution of the corresponding polymer is is 1.65.

[0042] The in-situ ring-opening polymerization of caprolactone catalyzed by ketimine 1d and diethylzinc was achieved with extremely low metal raw material dosage (monomer: ketimine 1d: diethylzinc = 30,000:1:1) and within a very short time (30 seconds), caprolactone was completely converted (up to 100%), with a high polymer yield (96%), a high polymer molecular weight (203,000 g / mol), and a narrow molecular weight distribution. Very high conversion frequency (TOF=3600000h -1 ), which has great application value.

[0043] The above-described embodiments are only preferred embodiments of the present invention, and are not intended to be all feasible embodiments of the present invention. Any obvious modifications made by a person skilled in the art without departing from the principles and spirit of the present invention should be considered to be included within the scope of protection of the claims of the present invention.

Claims

1. A method for preparing high molecular weight polycaprolactone, characterized in that the steps include: A ketimine ligand and diethylzinc are mixed in equal molar ratios and reacted for a period of time, followed by in-situ catalytic ring-opening polymerization of ε-caprolactone to obtain polycaprolactone. The ketimine ligand has a structure as shown in general formula I:

2. The method for preparing high molecular weight polycaprolactone according to claim 1, wherein The molar ratio of the ε-caprolactone:ketimine ligand:diethylzinc is (5000-30000):1:

1.

3. The method for preparing high molecular weight polycaprolactone according to claim 1, wherein The ring-opening polymerization temperature is 80-200° C., and the time is 3 seconds to 60 minutes.

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