Method for synthesizing poly (p-dioxanone) by using continuous screw reactor

Abstract

The invention discloses a method for synthesizing poly (p-dioxanone) by using a continuous screw reactor, and belongs to the technical field of polymer synthesis, the method for synthesizing poly (p-dioxanone) by using the continuous screw reactor comprises the following specific implementation steps: pre-mixing a p-dioxanone monomer, an initiator and a catalyst; forming a raw material mixture; enabling the raw material system to sequentially pass through a temperature zone at least comprising a feeding section, a melting and mixing section, a polymerization reaction section and a devolatilization section in the twin-screw extrusion reactor to carry out ring-opening polymerization reaction; a poly (p-dioxanone) product is obtained from a discharge port of the twin-screw extrusion reactor, the number-average molecular weight of the product is 80,000-150,000, and the molecular weight distribution index is 1.5-2.0. The production efficiency and the equipment utilization rate are greatly improved, the problems of long period and low efficiency of batch production are solved, large-scale industrial continuous production is easier to realize, and the continuously increasing demand of the market on PPDO is met.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of high polymer synthesis, more particularly to a method for synthesizing poly-p-dioxanone by using a continuous screw reactor. BACKGROUND

[0002] PPDO is an important biodegradable polyester, which has been widely used in absorbable suture, stent, tissue engineering support and other fields.

[0003] At present, the main synthesis method is bulk polymerization, which usually uses batch reactors, and has the problems of long reaction time (10-24h), large batch-to-batch difference, insufficient devolatilization efficiency, limited molecular weight, and difficulty in continuous and large-scale production.

[0004] Therefore, in view of the above problems, the existing structure is improved, and a method for synthesizing poly-p-dioxanone by using a continuous screw reactor is provided, so as to achieve a more practical purpose. SUMMARY

[0005] 1. Technical problem to be solved In view of the problems in the prior art, the purpose of the present application is to provide a method for synthesizing poly-p-dioxanone by using a continuous screw reactor, which greatly improves the production efficiency and equipment utilization, solves the problems of long cycle and low efficiency in batch production, and is more suitable for large-scale industrial continuous production, meeting the growing demand of the market for PPDO.

[0006] 2. Technical scheme In order to solve the above problems, the present application adopts the following technical scheme.

[0007] A method for synthesizing poly-p-dioxanone by using a continuous screw reactor, the specific implementation steps of the method are as follows: Step S1, mixing of poly-p-dioxanone production raw materials: pre-mixing p-dioxanone monomer, initiator and catalyst to form a raw material mixture; Step S2, extrusion of the mixed raw materials: making the raw material system pass through at least the temperature zones including the feeding section, the melt mixing section, the polymerization reaction section and the devolatilization section in sequence in the twin-screw extrusion reactor for ring-opening polymerization reaction; Step S3, obtaining poly-p-dioxanone product: obtaining poly-p-dioxanone product from the discharge port of the twin-screw extrusion reactor, wherein the number average molecular weight of the product is 80-150 thousand, and the molecular weight distribution index is 1.5-2.0.

[0008] Further, in the step S1: The initiator is a diol compound of ethylene glycol or 1,4-butanediol, and the amount of the initiator is 0.1% to 1.0% of the mass of the p-dioxanone monomer.

[0009] Further, in the step S1: The catalyst is an organic base catalyst or a Lewis acid catalyst; The organic base catalyst is one of 1,8-diazabicyclo, undec-7-ene, 1,5,7-triazabicyclodec-5-ene; The Lewis acid catalyst is stannous octoate or stannous oxalate; The amount of the catalyst is 0.01% to 0.5% of the mass of the p-dioxanone monomer.

[0010] Further, in the step S1: The purity of the p-dioxanone monomer is not less than 99.5%, the moisture content is not higher than 500 ppm, and the residual acid content is not higher than 50 ppm.

[0011] Further, in the step S2: The raw material mixture is sequentially subjected to reaction in at least four temperature zones in the twin-screw extrusion reactor, and the temperature zones include: A feeding section with a temperature of 80 to 100°C; A melt mixing section with a temperature of 120 to 140°C; A polymerization reaction section with a temperature of 150 to 170°C; A devolatilization section with a temperature of 160 to 180°C, and a vacuum with an absolute pressure lower than 100 Pa is applied in the devolatilization section.

[0012] Further, in the step S2: The unreacted monomer or oligomer removed in the vacuum devolatilization section is recovered and then recycled to the premixing step of the raw material system.

[0013] Further, in the step S2: The length-diameter ratio of the screw of the twin-screw extrusion reactor is not less than 40:1, the screw rotation speed is 30 to 80 rpm, and the total residence time of the material in the reactor is 10 to 30 minutes.

[0014] Further, in the step S3: The conversion rate of the p-dioxanone monomer in the ring-opening polymerization reaction is not less than 95%.

[0015] 3. Beneficial effects Compared with the prior art, the advantages of the present application are: ①The reaction time of the traditional batch reactor process is as long as 10-24 hours, and the double screw extrusion reactor is used as the core equipment in the present application, so that the polymerization process is changed into a continuous process. The total residence time of the material in the reactor is shortened to 10-30 minutes, which greatly improves the production efficiency and equipment utilization, solves the problems of long cycle and low efficiency existing in batch production, and is more easy to realize large-scale industrialized continuous production, so as to meet the increasing demand of the market for PPDO; ②The conversion rate of the p-dioxanone monomer is not less than 95% by accurately controlling the reaction conditions, so that the raw material utilization rate is high, the monomer consumption cost is reduced, the unreacted monomer and low molecular weight by-products are effectively removed, and the residual monomer content in the final product is reduced, which not only improves the chemical stability of the polymer, but also significantly enhances the biological safety when the polymer is used as a medical material. BRIEF DESCRIPTION OF DRAWINGS

[0016] Figure 1 The flowchart of the method for synthesizing poly-p-dioxanone by using a continuous screw reactor in the present application is shown. DETAILED DESCRIPTION

[0017] The technical solutions in the embodiments of the present application will be described clearly and completely in combination with the drawings in the embodiments of the present application; obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the protection scope of the present application.

[0018] Embodiment 1: Please refer to Figure 1 A method for synthesizing poly-p-dioxanone by using a continuous screw reactor, and the specific implementation steps are as follows: Step S1, mixing of poly-p-dioxanone production raw materials: the p-dioxanone monomer, initiator and catalyst are premixed to form a raw material mixture; Specifically, the initiator is a diol compound of ethylene glycol or 1,4-butanediol, and the amount of the initiator is 0.1%-1.0% of the mass of the p-dioxanone monomer.

[0019] Using diol as the initiator can effectively control the end group structure and molecular weight of the polymer. The amount of the initiator is directly related to the target molecular weight.

[0020] The selected ethylene glycol and 1,4-butanediol are both biocompatible compounds, which are crucial for the application of PPDO as absorbable medical materials (such as sutures), and avoid the residual risk caused by the use of toxic initiators.

[0021] Specifically, the catalyst is an organic base catalyst or a Lewis acid catalyst; The organic base catalyst is one of 1,8-diazabicyclo, undec-7-ene, 1,5,7-triazabicyclodec-5-ene. The Lewis acid catalyst is stannous octoate or stannous oxalate. The amount of catalyst is 0.01% to 0.5% of the mass of the p-dioxanone monomer.

[0022] The listed organic base catalyst and stannous octoate are both efficient catalysts for ring-opening polymerization, which can ensure high conversion in a short residence time in a twin-screw reactor.

[0023] The organic base catalyst generally has low toxicity, and stannous octoate is also a commonly used catalyst in medical polymer synthesis, which ensures that the product can be used in the medical field.

[0024] Precise amount control can ensure that the polymerization reaction proceeds quickly, while avoiding side reactions caused by excessive catalyst, which helps to obtain products with narrow molecular weight distribution and good color.

[0025] Specifically, the purity of the p-dioxanone monomer is not less than 99.5%, the water content is not higher than 500 ppm, and the residual acid content is not higher than 50 ppm.

[0026] Moisture and residual acid impurities are ring-opening polymerization terminators that can severely hinder chain growth, resulting in a failure to increase molecular weight. Strictly limiting impurity content is a prerequisite for obtaining high molecular weight products.

[0027] High-purity monomers can reduce uncontrollable side reactions, improve reaction stability and repeatability, and are the basis for achieving high-quality continuous production.

[0028] Step S2, extrusion of the mixed raw materials: The raw material system is subjected to ring-opening polymerization reaction in the twin-screw extrusion reactor by passing through at least temperature zones including a feeding section, a melt mixing section, a polymerization reaction section, and a devolatilization section in sequence. Specifically, the raw material mixture is subjected to reaction in the twin-screw extrusion reactor by passing through at least four temperature zones in sequence, and the temperature zones include: The feeding section has a temperature of 80-100°C. The melt mixing section has a temperature of 120-140°C. The polymerization reaction section has a temperature of 150-170°C. The devolatilization section has a temperature of 160-180°C, and a vacuum with an absolute pressure of less than 100 Pa is applied in the devolatilization section.

[0029] The melting section uniformly mixes the materials; the polymerization section accelerates the reaction at high temperature; and the devolatilization section effectively removes small molecules at high temperature and high vacuum. This gradient temperature control optimizes the reaction kinetics, ensuring high conversion rate and product quality.

[0030] The high vacuum applied in the devolatilization section can quickly and continuously remove small molecular byproducts (if any) and unreacted monomers generated during the reaction, which can significantly improve the final conversion rate of the monomers according to the principle of chemical equilibrium.

[0031] Specifically, the unreacted monomers or oligomers removed in the vacuum devolatilization section are recovered and then recycled to the premixing step of the raw material system.

[0032] Recycling valuable unreacted raw materials back into the process significantly reduces raw material consumption and production costs. At the same time, it reduces waste emissions, making the production process more environmentally friendly and sustainable Specifically, the length-diameter ratio of the screws of the twin-screw extruder reactor is not less than 40:1, the screw rotation speed is 30-80 rpm, and the total residence time of the material in the reactor is 10-30 minutes.

[0033] A larger length-diameter ratio provides sufficient length to accommodate the necessary functional zones and ensure sufficient residence time for the material to complete the polymerization reaction.

[0034] Suitable screw rotation speed and residence time range are key process parameters for achieving sufficient melt mixing, achieving the desired reaction degree (high conversion rate), and preventing material degradation due to long-term high-temperature residence. This directly affects the stability of the product's molecular weight, distribution, and color.

[0035] Step S3, obtaining the poly-p-dioxanone product: obtaining the poly-p-dioxanone product from the discharge port of the twin-screw extruder reactor, wherein the number average molecular weight of the product is 80,000-150,000, and the molecular weight distribution index is 1.5-2.0.

[0036] Specifically, the conversion rate of the p-dioxanone monomer in the ring-opening polymerization reaction is not less than 95%.

[0037] High conversion rate is an important indicator of whether the polymerization process is efficient and economical. A conversion rate of ≥95% indicates that the continuous process is very efficient and has high raw material utilization.

[0038] High conversion rate means that the residual monomer content in the final product is low, which is crucial for improving the chemical stability of PPDO resin and the biological safety when used as a medical material.

[0039] In summary, by using a twin-screw extruder reactor, the polymerization process is transformed from the traditional batch kettle reaction to a continuous process, greatly improving production efficiency, easy to scale up, and meeting the needs of industrial mass production.

[0040] The material conveying, melting, mixing, reaction, small molecule removal (devolatilization) and other chemical unit operations are integrated in one device to be completed continuously, which simplifies the process flow and reduces the equipment investment and operation steps.

[0041] By limiting the number average molecular weight and the molecular weight distribution index of the final product, it is clear that the method can stably produce high molecular weight and narrow molecular weight distribution high-quality PPDO resin. Narrow distribution means that the product performance is more uniform and predictable.

[0042] Example 2: Based on the above example 1, further description is made.

[0043] In the synthesis of poly-p-dioxanone, the addition amount of p-dioxanone monomer, initiator and catalyst is controlled as follows: PDO monomer (p-dioxanone monomer) 100 g; 1,4-Butanediol 0.5 g; DBU 0.2 g; The process parameters are as follows: Temperature zone 100 / 130 / 160 / 170℃; Speed 50 rpm; Vacuum degree 80 Pa; Residence time 18 min; The product detection results of the synthesized poly-p-dioxanone are as follows: Product PPDO Mn=10.5×10 4 ; Mw / Mn=1.72; Monomer conversion rate 96%.

[0044] Example 3: Based on the above examples 1 and 2, further description is made.

[0045] On the basis of the raw materials and their amounts in example 2, a 500 mL batch reactor is used, wherein: temperature: 160℃; time: 12h; The final PPDO has Mn=7.8×10 4 , distribution 2.3, conversion rate 90%.

[0046] In the synthesis of poly-p-dioxanone, a comparative experiment group is set up, and the experimental results are compared, as shown in the following table: Comparative Experiment 1 Conventional batch reactor conditions Low efficiency Comparative Experiment 2 Screw reactor but no vacuum devolatilization High monomer residue Comparative Experiment 3 Screw reactor but only 2-zone heating Low molecular weight Poly-p-dioxanone synthesis 500 mL batch reactor High conversion Compared with the traditional process, the application greatly improves the production efficiency and equipment utilization, solves the problems of long cycle and low efficiency existing in batch production, is easier to realize large-scale industrial continuous production, and meets the increasing demand of market for PPDO.

[0047] The above merely describes the preferred embodiments of the present application; however, the protection scope of the present application is not limited thereto. Any person skilled in the art, according to the technical solution and the improvement concept of the present application, makes equivalent replacement or change within the technical range disclosed by the present application, and should be covered within the protection scope of the present application.

Claims

1. A method for synthesizing poly(p-dioxanone) using a continuous screw reactor, characterized in that: The specific implementation steps of the method are as follows: Step S1, Mixing of raw materials for the production of polydioxanone: The polydioxanone monomer, initiator and catalyst are premixed to form a raw material mixture; Step S2, Extrusion of mixed raw materials: The raw material system is subjected to ring-opening polymerization reaction in a twin-screw extruder, passing sequentially through temperature zones including at least a feeding section, a melt mixing section, a polymerization reaction section and a devolatilization section; Step S3: Obtain polydioxanone product: Obtain polydioxanone product from the outlet of the twin-screw extruder reactor, wherein the number average molecular weight of the product is 80,000 to 150,000 and the molecular weight distribution index is 1.5 to 2.

0.

2. The method for synthesizing poly(p-dioxanone) using a continuous screw reactor according to claim 1, characterized in that: In step S1: The initiator is a diol compound of ethylene glycol or 1,4-butanediol, and the amount of initiator used is 0.1% to 1.0% of the mass of the dioxane monomer.

3. The method for synthesizing poly(p-dioxanone) using a continuous screw reactor according to claim 1, characterized in that: In step S1: The catalyst is an organic base catalyst or a Lewis acid catalyst; The organic base catalyst is one of 1,8-diazabicyclo, undec-7-ene, and 1,5,7-triazabicyclodec-5-ene; The Lewis acid catalysts are stannous octoate and stannous oxalate; The amount of catalyst used is 0.01% to 0.5% of the mass of the dioxane monomer.

4. The method for synthesizing poly(p-dioxanone) using a continuous screw reactor according to claim 1, characterized in that: In step S1: The purity of the dioxane monomer is not less than 99.5%, the water content is not more than 500 ppm, and the residual acid content is not more than 50 ppm.

5. The method for synthesizing poly(p-dioxanone) using a continuous screw reactor according to claim 1, characterized in that: In step S2: The feed mixture is reacted sequentially through at least four temperature zones within a twin-screw extruder reactor, including: The temperature in the feeding section is 80–100℃. The melting and mixing section has a temperature of 120–140℃. The polymerization reaction section has a temperature of 150–170℃; The devolatilization section is at a temperature of 160–180°C, and a vacuum with an absolute pressure of less than 100 Pa is applied in the devolatilization section.

6. The method for synthesizing poly(p-dioxanone) using a continuous screw reactor according to claim 1, characterized in that: In step S2: Unreacted monomers or oligomers removed in the vacuum devolatilization section are recovered and then recycled to the premixing step of the feed system.

7. The method for synthesizing poly(p-dioxanone) using a continuous screw reactor according to claim 1, characterized in that: In step S2: The screw length-to-diameter ratio of the twin-screw extrusion reactor is not less than 40:1, the screw speed is 30-80 rpm, and the total residence time of the material in the reactor is 10-30 minutes.

8. The method for synthesizing poly(p-dioxanone) using a continuous screw reactor according to claim 1, characterized in that: In step S3: The conversion rate of p-dioxanone monomer in the ring-opening polymerization reaction is not less than 95%.

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