Method for increasing degradation temperature of polypropylene carbonate

Abstract

The invention discloses a method for increasing degradation temperature of poly (propylene carbonate), which is characterized by comprising the following steps: mixing poly (propylene carbonate) resin in a washing solution at 0-100 DEG C, fully washing, removing the washing solution, and drying to obtain a polymer with metal residue less than 100 ppm, molecular weight less than 3000 g / mol and mass fraction less than 5%, the addition concentration of the polypropylene carbonate in the washing solution is 10-80 wt%, and the washing solution is at least one of distilled water, methanol, acetone, a sulfonic acid aqueous solution and dichloromethane. The method has the advantages that the content of catalyst metal residues and small-molecule polymers is reduced, and the utilization rate of the catalyst is improved; and the operation is simple, and the cost is low.

Description

Technical Field

[0001] The present invention belongs to the field of chemical engineering, and particularly relates to a method for increasing the degradation temperature of poly(propylene carbonate). Background Art

[0002] Poly(propylene carbonate) (abbreviated as PPC), which is made from CO2 and propylene oxide and can be decomposed and returned to nature after use, not only can consume greenhouse gas CO2 and reduce the "greenhouse effect", but also can solve the "white pollution", and has positive significance in resource conservation and environmental protection. At present, the synthesis method of poly(propylene carbonate) is mature and has entered the stage of large-scale production. Poly(propylene carbonate) has good barrier properties against oxygen and water, and excellent biocompatibility and biodegradability, and can be used as biomedical materials, food packaging materials, barrier materials, etc. However, due to the poor thermal stability of PPC, it will degrade in the range of 150-180 °C, which limits its application. In addition, since the processing temperature of most polymer materials in industrial production is higher than 150 °C. Under such processing conditions, PPC will undergo obvious degradation, resulting in poor blending effect. Therefore, improving the thermal stability of poly(propylene carbonate) has become one of the key points in the modification research of poly(propylene carbonate).

[0003] The patent with the Chinese patent application publication number CN107573476A discloses a preparation method of a modified poly(propylene carbonate) material, which includes completely dissolving poly(propylene carbonate) in a solvent, then adding an acid anhydride capping agent and heating and reacting in a water bath; raising the temperature, adding an isocyanate capping agent and continuing the reaction; dropping the completely reacted mixture into absolute ethanol for precipitation, filtering the obtained solid and drying it under vacuum. This method improves the glass transition temperature and thermal stability of poly(propylene carbonate), but the improvement effect is not very obvious. The patent with the Chinese patent application publication number CN110283312A discloses a polyamide in-situ modified poly(propylene carbonate) and its preparation method. This method chemically caps and modifies poly(propylene carbonate) with active capping agents such as isocyanate and maleic anhydride, and then copolymerizes with a third component compound under certain conditions to obtain polyamide in-situ modified poly(propylene carbonate). The patent with the Chinese patent application publication number CN103261260A discloses a method for improving the thermal stability of poly(propylene carbonate). This method delays the thermal degradation of poly(propylene carbonate) at high temperature by adding isocyanate or diisocyanate to poly(propylene carbonate) resin by a reactive co-extrusion method and using urethane groups to cap the molecular chain of poly(propylene carbonate), thereby ensuring the required thermal stability. The above methods all add chemical reagents for capping treatment, which will inevitably introduce small molecule polymers, increase the volatile content of poly(propylene carbonate), and in addition, the residual small molecule polymers cause poly(propylene carbonate) to be easily degraded during processing and use. At the same time, the method of ensuring thermal stability by reactive capping will inevitably increase the production cost of poly(propylene carbonate) and extend the process flow. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a method for increasing the degradation temperature of poly(propylene carbonate) that reduces the content of catalyst metal residues and small molecule polymers, improves thermal stability, and is simple to operate and low in cost.

[0005] The technical solution adopted by the present invention to solve the above technical problems is: a method for increasing the degradation temperature of poly(propylene carbonate), which includes the following steps: mixing poly(propylene carbonate) resin in a washing solution at 0°C - 100°C, removing the washing solution after sufficient washing, and then drying to obtain a poly(propylene carbonate) with a metal residue less than 100 ppm, a polymer mass fraction with a molecular weight less than 3000 g / mol lower than 5%, and the temperature of thermal weight loss T 5% and T 50% both increased by 25°C or more. The addition concentration of poly(propylene carbonate) in the washing solution is 10 - 80 wt%, and the washing solution is at least one of distilled water, methanol, acetone, sulfonic acid aqueous solution, and dichloromethane.

[0006] Preferably, the washing solution is at least one of distilled water, methanol and aqueous sulfonic acid solution.

[0007] Preferably, the addition concentration of poly(propylene carbonate) in the washing solution is 20 - 60 wt%.

[0008] Preferably, the temperature of the washing solution is 20 - 60 °C.

[0009] Preferably, the drying method is vacuum drying or nitrogen purge drying, the drying temperature is 40 - 100 °C, and the drying time is 30 - 60 min.

[0010] Compared with the prior art, the advantages of the present invention are as follows: 1. The method provided by the present invention does not introduce small molecule polymers additionally in the poly(propylene carbonate) system, and there is no need to further separate and remove the introduced small molecule polymers, which can avoid the problem of poly(propylene carbonate) degradation caused by the degradation of small molecule polymers at lower processing temperatures (such as 150 °C - 180 °C). 2. The catalyst residue amount of the poly(propylene carbonate) treated by the method provided by the present invention is significantly reduced, avoiding the situation that the catalyst reduces the activation energy required for the thermal decomposition of poly(propylene carbonate), thereby accelerating the thermal degradation of poly(propylene carbonate). 3. The content of small molecule polymers in the poly(propylene carbonate) treated by the method provided by the present invention is significantly reduced, and to a certain extent, the content of active end groups (-OH) is reduced, so that when poly(propylene carbonate) undergoes thermal degradation, random scission occurs first (the activation energy or temperature required for random scission is higher), and then unzipping degradation occurs, thereby effectively increasing the thermal degradation temperature of poly(propylene carbonate) and enhancing its thermal stability. 4. The process flow of the method provided by the present invention is simple, efficient and low-cost, and can maintain the high economic benefits of poly(propylene carbonate) products.

[0011] In summary, a method for increasing the degradation temperature of poly(propylene carbonate) according to the present invention mainly deeply removes catalyst metal residues and small molecule polymers in the poly(propylene carbonate) resin by physical means. The metal residues in the obtained poly(propylene carbonate) are less than 100 ppm, and the mass fraction of polymers with a molecular weight less than 3000 g / mol is less than 5%. The temperatures of thermal weight loss T 5% and T 50% are both increased by more than 25 °C, the degradation temperature of poly(propylene carbonate) is increased, the thermal stability of poly(propylene carbonate) resin is enhanced, and it has the advantages of simple operation and low cost. Specific Embodiments

[0012] The present invention will be further described in detail below with reference to the embodiments.

[0013] The following methods are used to test the structure or properties of the poly(propylene carbonate) produced in the embodiments.

[0014] Molecular weight: Determined by gel permeation chromatography (GPC).

[0015] Thermogravimetric loss T 5% and T 50% : Determined by thermogravimetric analyzer (TG).

[0016] Metal residues: Determined according to the method of GB / T 9345.1-2008 and inductively coupled plasma ICP.

[0017] For those embodiments where specific conditions are not indicated, they are carried out under conventional conditions or conditions recommended by the manufacturer. For reagents or instruments whose manufacturers are not indicated, they are all conventional products that can be obtained commercially.

[0018] Example 1: The poly(propylene carbonate) resin was transported into the aqueous sulfonic acid solution, and the addition concentration of the poly(propylene carbonate) resin in the aqueous sulfonic acid solution was 20 wt%. The temperature of the aqueous sulfonic acid solution was maintained at 20 °C. After stirring and mixing for 30 min, the aqueous sulfonic acid solution was removed, and then vacuum dried at 40 °C for 18 h to obtain poly(propylene carbonate). The product was tested by GPC, TGA and ICP, and the test results are shown in Table 1.

[0019] Example 2: The poly(propylene carbonate) resin was transported into distilled water, and the addition concentration of the poly(propylene carbonate) resin in distilled water was 20 wt%. The temperature of the distilled water was maintained at 50 °C. After stirring and mixing for 30 min, the distilled water was removed, and then vacuum dried at 40 °C for 18 h to obtain poly(propylene carbonate). The product was tested by GPC, TGA and ICP, and the test results are shown in Table 1.

[0020] Example 3: The poly(propylene carbonate) resin was transported into the aqueous sulfonic acid solution, and the addition concentration of the poly(propylene carbonate) resin in the aqueous sulfonic acid solution was 40 wt%. The temperature of the aqueous sulfonic acid solution was maintained at 60 °C. After stirring and mixing for 30 min, the aqueous sulfonic acid solution was removed, and then vacuum dried at 40 °C for 18 h to obtain poly(propylene carbonate). The product was tested by GPC, TGA and ICP, and the test results are shown in Table 1.

[0021] Example 4: The poly(propylene carbonate) resin was transported into methanol, and the addition concentration of the poly(propylene carbonate) resin in methanol was 20 wt%. The temperature of the methanol was maintained at 40 °C. After stirring and mixing for 30 min, the methanol was removed, and then vacuum dried at 40 °C for 18 h to obtain poly(propylene carbonate). The product was tested by GPC, TGA and ICP, and the test results are shown in Table 1.

[0022] Example 5: Poly(propylene carbonate) resin was transported into distilled water, and the addition concentration of poly(propylene carbonate) resin in distilled water was 20 wt%. The temperature of distilled water was maintained at 60 °C, and after stirring and mixing for 30 min, the distilled water was removed. Then, it was dried in vacuum at 40 °C for 18 h to obtain poly(propylene carbonate). The products were tested by GPC, TGA and ICP, and the test results are shown in Table 1.

[0023] Comparative Example 1: Poly(propylene carbonate) resin was dried in vacuum at 40 °C for 18 h. After drying, poly(propylene carbonate) was tested by GPC, TGA and ICP, and the test results are shown in Table 1.

[0024] The test results of the poly(propylene carbonate) products finally obtained in Examples 1-5 and Comparative Example 1 are shown in Table 1 below.

[0025] Table 1 Test results of poly(propylene carbonate) products

[0026] As can be seen from Table 1, after the poly(propylene carbonate) resin with the same molecular weight was treated by the method provided by the present invention, the contents of small molecules and metal residues were significantly reduced, and the degradation temperatures of T 5% and T 50% were significantly increased. The maximum temperature increase was 74 °C, and the thermal stability was significantly better than that of the poly(propylene carbonate) resin material. The method provided by the present invention can directly remove small molecules and metal residues deeply in the industrial production process without adding other small molecule polymers additionally, avoiding the degradation problem of poly(propylene carbonate) caused by small molecule polymers in subsequent processing and use. The method provided by the present invention can improve the thermal stability of the product and obtain good economic benefits while retaining the original structure and excellent properties of poly(propylene carbonate).

[0027] The above description is not a limitation of the present invention, nor is the present invention limited to the above examples. Changes, modifications, additions or substitutions made by those of ordinary skill in the art within the scope of the essence of the present invention shall also fall within the protection scope of the present invention.

Claims

1. A method for increasing the degradation temperature of poly(propylene carbonate), characterized in that The method includes the following steps: mixing poly(propylene carbonate) resin in a washing solution at 0°C - 100°C, removing the washing solution after sufficient washing, and then drying to obtain a polymer with a metal residue less than 100 ppm and a mass fraction of polymers with a molecular weight less than 3000 g / mol lower than 5%, and a poly(propylene carbonate) with the temperature of T 5% and T 50% both increased by 25°C or more. The addition concentration of poly(propylene carbonate) in the washing solution is 10 - 80 wt%, and the washing solution is at least one of distilled water, methanol, acetone, sulfonic acid aqueous solution, and dichloromethane.

2. The method for increasing the degradation temperature of poly(propylene carbonate) according to claim 1, characterized in that: The washing solution is at least one of distilled water, methanol and aqueous sulfonic acid solution.

3. A method for increasing the degradation temperature of poly(propylene carbonate) according to claim 1, characterized in that: The added concentration of poly(propylene carbonate) in the washing solution is 20-60 wt%.

4. A method for increasing the degradation temperature of poly(propylene carbonate) according to claim 1, characterized in that: The temperature of the washing solution is 20-60 °C.

5. A method for increasing the degradation temperature of poly(propylene carbonate) according to claim 1, characterized in that: The drying method is vacuum drying or nitrogen purge drying, the drying temperature is 40-100 °C, and the drying time is 30-60 min.

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