A process for the preparation of a narrow molecular weight distribution polychlorotrifluoroethylene resin

Abstract

The present application provides a preparation method of narrow molecular weight distribution polytrifluorochloroethylene resin. The specific steps are as follows: a solvent, a dispersing agent, a pH buffer, a molecular weight regulator, and trifluorochloroethylene monomers and an initiator are added into a polymerization reactor, pre-polymerization is carried out under a certain temperature and pressure, the obtained pre-polymer mixture is continuously sent into a three-dimensional plug flow microcapsule reaction device for continuous polymerization reaction, the obtained crude product meeting the polymerization degree requirement is continuously extruded through a devolatilization process, while removing the solvent and other impurities, the unstable end groups of the product are capped by adding a capping agent, and the narrow molecular weight distribution polytrifluorochloroethylene resin is obtained; the solvent collected by the devolatilization process can be continuously recycled and used in the subsequent polymerization section.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of resin material preparation, and particularly relates to a preparation method of a narrow molecular weight distribution polytrifluorochloroethylene resin. BACKGROUND

[0002] Polytrifluorochloroethylene (PCTFE) is one of the first thermoplastic fluoroplastics developed for industrial production in the 1940s. It not only has good heat resistance, chemical corrosion resistance, high mechanical strength and high transparency, but also has excellent low permeability to water and gas. Therefore, it is widely used as a packaging film material in military, medical materials, pharmaceutical packaging, high-end food packaging, circuit board packaging, electronic and electrical components and parts.

[0003] PCTFE is a thermoplastic polymer material, which has flowability after heating and can be processed and shaped by traditional methods such as molding, extrusion and injection molding. The molding temperature is 225-306℃, and the initial decomposition temperature is 300℃. Therefore, the processing temperature range (window) is relatively narrow, and the thermal stability needs to be improved to meet the processing performance of the material. The reason why PCTFE is not heat stable is that the end group of the PCTFE chain end is highly reactive and unstable, and the polymerization degree also affects the activity of the end group. Under the premise of narrow polymerization degree distribution, it is necessary to reduce the reactivity of the end group by end capping to improve the thermal stability.

[0004] At present, scholars at home and abroad have carried out a large number of experiments in changing the structure of the end group (end capping is the most effective method to change the structure of the end group), improving the polymerization degree, controlling the narrow molecular weight, and then improving the heat resistance of PCTFE under the premise of meeting the processing performance. For example, patent CN103172773A uses a suspension polymerization method in the presence of a reducing agent, uses inorganic peroxide as an initiator for polymerization, and then uses F2 / N2 mixed gas for fluorination end capping treatment to obtain PCTFE resin resistant to high temperature degradation; patent US2902477 uses ozone The end group of PCTFE resin is modified at 100-150℃ for 0.5-5h, which can effectively improve the heat resistance of PCTFE resin; patent US304500 uses chlorine gas to treat the end group of PCTFE resin to solve the degradation and discoloration problem of PCTFE in the processing process; patent CN102020737B uses an azo gas initiator for suspension polymerization, and the product is treated by fluorinated cobalt for 1-3h at a temperature of 160-170℃ and a pressure of 0.6-1.5MPa to obtain PCTFE resin resistant to high temperature and high transparency.

[0005] The aforementioned technologies for addressing the thermal stability of PCTFE resin all rely on post-treatment. These processes are lengthy, have long production cycles, consume significant energy, require substantial equipment investment, and are difficult to control. Furthermore, the post-treatment process involves the use of corrosive and highly toxic substances such as fluorine and chlorine, which can harm the environment and operators, and also introduce impurities into the finished material, affecting its quality (e.g., transparency, mechanical properties). Therefore, these post-treatment technologies all cause environmental pollution, are technically challenging to operate, and carry a high risk factor.

[0006] Furthermore, traditional polymerization methods utilize suspension polymerization and emulsion polymerization. Both of these methods employ reactors for the polymerization reaction, and once equilibrium is reached, it is difficult to reverse the reaction in the forward direction. Therefore, they suffer from drawbacks such as long reaction cycles, harsh reaction conditions, low yield, high impurity content, and wide molecular weight distribution. Moreover, the reaction is intermittent, with each batch requiring feeding, which easily leads to unstable product quality, a wide molecular weight distribution, numerous side reactions, low transparency, and poor mechanical properties. Additionally, suspension polymerization and emulsion polymerization require large quantities of initiators, catalysts, and other auxiliaries (to facilitate the forward reaction and increase yield), resulting in large processing volumes, high pollution levels, and poor quality in post-processing. Summary of the Invention

[0007] (a) Technical problems to be solved

[0008] To address the shortcomings of the aforementioned technologies, this invention provides a method for preparing a narrow molecular weight distribution polychlorotrifluoroethylene resin. This method is a solution polymerization preparation method with simple operation and mild reaction conditions. To achieve the above objectives, this invention utilizes a three-dimensional plug flow microcapsule reactor. The microcapsule reaction space in this reactor not only allows for sufficient polymerization of the materials but also ensures that the degree of polymerization of the product is distributed within an extremely narrow range. The preparation method provided by this invention also employs a devolatilization process to remove the solvent while simultaneously removing unreacted monomers, impurities, and reaction byproducts from the polymer. Furthermore, a capping agent is continuously added during devolatilization to cap the active chain ends of the polymer, increasing the thermal stability of the product.

[0009] (II) Technical Solution

[0010] To achieve the above objectives, the main technical solutions adopted by the present invention are as follows.

[0011] This invention provides a method for preparing a narrow molecular weight distribution polychlorotrifluoroethylene resin, the specific steps of which include:

[0012] S1, the solvent, dispersant, pH buffer and molecular weight regulator are added to the polymerization reactor, then the inside of the polymerization reactor is evacuated and filled with protective gas, while heating and stirring are performed simultaneously;

[0013] S2, trifluorochloroethylene monomer is added to the polymerization reactor by a feed pump to maintain the pressure and temperature in the polymerization reactor, and then an initiator is added to the polymerization reactor by a metering pump. The reactor is kept at a constant temperature and a prepolymerization reaction is carried out to obtain a prepolymer mixture.

[0014] S3, the prepolymer mixture is continuously fed into the three-dimensional plug flow microcapsule reactor for deep polymerization reaction. At the same time, the crude product that has reached the degree of polymerization requirement is continuously extruded from the die head assembly of the three-dimensional plug flow microcapsule reactor. The unpolymerized reactant is continuously sent from the return port of the three-dimensional plug flow microcapsule reactor to the feed port through the metering pump to continue the polymerization reaction.

[0015] S4, the crude product that has reached the required degree of polymerization is continuously devoured through a devouring process, and the unstable end groups of the crude product that has reached the required degree of polymerization are capped by continuously adding a capping agent to obtain a polymer that has reached the required degree of polymerization.

[0016] S5, the polymer that has reached the required degree of polymerization is cooled to form a solidified product, and the solidified product is crushed, washed, filtered and dried to obtain the polychlorotrifluoroethylene resin product.

[0017] Further, in step S2, the reaction temperature of the prepolymerization reaction is 30–120°C, the reaction pressure is 0.2–0.6 MPa, and the reaction time is 1.5–3 h; in step S3, the deep polymerization reaction is a continuous solution polymerization reaction, the reaction temperature is 50–240°C, the reaction pressure is 0.1–1.2 MPa, and after reacting for 1–5 min, the crude product that has reached the required degree of polymerization is continuously extruded from the die head assembly, and separation begins while reacting.

[0018] Furthermore, the three-dimensional plug flow microcapsule reaction device includes a propulsion system, a microcapsule reaction assembly, a heating system, a cooling system, a head assembly, a circulation reflux system, a vacuum degassing system, and a reaction aid supply system;

[0019] The propulsion system continuously pushes the prepolymer mixture to the microcapsule reaction group through a gradient-type conveying screw, and pushes the crude product synthesized by the polymerization reaction that meets the degree of polymerization requirements to the head assembly;

[0020] The microcapsule reaction assembly is composed of several microcapsule reaction units; each microcapsule reaction unit includes several centrifugal rotating disks, fixed disks, and reaction unit cylinders; several involute grooves with opposite directions are formed at the mating surfaces of the centrifugal rotating disks and the fixed disks to create several microcapsule reaction spaces; the microcapsule reaction spaces are used to provide space for the polymerization reaction of the reactants;

[0021] The die head assembly is connected to the discharge section assembly and is used to continuously extrude the crude product that meets the polymerization degree requirement;

[0022] The heating system is fixedly installed on the outside of the propulsion system and the microcapsule reaction assembly, and is used to heat the reactants.

[0023] The cooling system is connected to the propulsion system and the microcapsule reaction assembly, and is used to cool and reduce the temperature of the reactants.

[0024] The recirculation system is used to recirculate the reactants from the discharge section component to the feed section component to continue participating in the polymerization reaction;

[0025] The vacuum degassing system is connected to the microcapsule reaction assembly and is used to remove small molecule impurities generated during the reaction process.

[0026] The reaction aid supply system is connected to the microcapsule reaction assembly and is used to supply the reaction aid.

[0027] Furthermore, the solvent is one or more of cyclohexane, benzene, p-xylene, o-xylene, and 1,3,5-trimethylbenzene.

[0028] Further, the solvent is cyclohexane; the molar ratio of cyclohexane to the trifluorochloroethylene monomer is (1.50~5.00):1.

[0029] Furthermore, the dispersant is selected from cellulose-based materials, including one or more of hydroxypropyl methylcellulose, hydroxyethylcellulose, and hydroxymethylcellulose;

[0030] The pH buffer is selected from one or more of triethylamine, triethylolamine, dimethylethanolamine, sodium citrate, or sodium tartrate.

[0031] The molecular weight regulator is an R-alkyl-substituted cyclopentane, wherein the R-alkyl includes methyl, ethyl, propyl, isopropyl, n-butyl, tert-butyl, 1-methyl-2-ethyl, 1,2-dimethyl, and 1,2,3-trimethyl.

[0032] Further, the dispersant is hydroxypropyl methylcellulose; the molar ratio of the hydroxypropyl methylcellulose to the solvent cyclohexane is (0.0001~0.001):1;

[0033] The pH buffer is triethylamine; the molar ratio of the triethylamine to the trifluorochloroethylene monomer is (0.0002~0.001):1;

[0034] The molecular weight regulator is methylcyclopentane; the molar ratio of methylcyclopentane to the trifluorochloroethylene monomer is (0.006~0.02):1.

[0035] Further, the initiator is perfluoropropionyl peroxide; the molar ratio of the initiator to the trifluorochloroethylene monomer is (0.0003~0.0025):1.

[0036] Furthermore, in step S4, after the solvent is removed by the devolatilization process, it is collected and recycled to subsequent polymerization reaction stages; the capping agent, dissolved in the solvent, is continuously and uniformly added to the devolatilization process via a metering pump; the capping agent is a fluorinated peroxide. RF is selected from The fluorine-containing peroxide The molar ratio of the trifluorochloroethylene monomer to the total trifluorochloroethylene monomer is (0.0001~0.01):1.

[0037] Furthermore, the polymer that meets the degree of polymerization requirement has a degree of polymerization distribution narrower than 5%.

[0038] Unless explicitly stated otherwise, all ranges referenced in this invention include extreme values. For example, "reaction temperature 30–120°C" means that the reaction temperature range T is 30°C. 120℃.

[0039] (III) Beneficial Effects

[0040] (1) The present invention uses a self-designed three-dimensional plug flow microcapsule reaction device to make the polymerization reaction proceed smoothly. At the same time, polymers that have not reached the degree of polymerization can be circulated and retained in the plug flow reaction device. Only polymers that have reached the degree of polymerization requirement can be squeezed out from the plug flow microcapsule reaction device and enter the devolatilization section, thus achieving the effect of reaction and separation at the same time and accurately controlling the narrow molecular weight distribution range of the degree of polymerization (within 5%).

[0041] (2) The present invention uses alkylcyclopentane as a molecular weight regulator to control the relative molecular weight of the polymer. It has good compatibility with polychlorotrifluoroethylene monomers and prepolymers, which further controls the degree of polymerization of polychlorotrifluoroethylene polymers within the set range. At the same time, it improves the flexibility of the product and is conducive to improving its corrosion resistance.

[0042] (3) The molecular weight regulator, dispersant, pH buffer, initiator and end-capping agent used in this invention are used in very small amounts, the water consumption in the post-treatment washing section is small, and the environmental pollution is small; the product has high purity, good toughness and excellent comprehensive performance, which meets the production process requirements of extrusion film stretching, injection molding, compression molding and other processes. It can be used as an encapsulation film and is widely used in military, chemical, medical materials, high-end food, electrical and electronic components, circuit boards, field-induced photoelectronic components and other industries.

[0043] (4) Since the present invention uses perfluorinated peroxide as the end-capping agent, it has a higher end-capping speed, which can enable the prepolymer to undergo final polymerization and end-capping in a short time, effectively reducing the occurrence of side reactions and controlling the degree of polymerization, resulting in a narrow molecular weight distribution of the product. At the same time, the end groups of polychlorotrifluoroethylene resin are perfluorinated, which has good thermal stability. The product does not require complicated subsequent processing, resulting in higher purity and better quality of the product.

[0044] (5) The polymerization reaction is continuous. Two or more polymerization reactors are fed alternately to maintain the continuous and uninterrupted entry of the prepolymer mixture into the three-dimensional push flow microcapsule reactor. There is no need to stack a large number of microcapsule reaction groups to meet the requirements of large-scale production. It is efficient and low-cost.

[0045] (6) The devolatilization process of the present invention can continuously remove the solvent and recycle it to the subsequent polymerization reaction stage; at the same time, it can also remove unreacted monomers, impurities and reaction by-products, which not only improves the purity and quality of the polymer, but also optimizes the production process and reduces the production cost. Attached Figure Description

[0046] Figure 1 This is a flowchart illustrating the preparation process of polychlorotrifluoroethylene resin with a narrow molecular weight distribution. Detailed Implementation

[0047] To better explain and facilitate understanding of the present invention, the technical solutions of the present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0048] The following describes preferred embodiments of the present invention, but the present invention is not limited to these preferred embodiments. It should be noted that, for those skilled in the art, any modifications and alterations made based on this inventive concept are within the scope of protection of the present invention.

[0049] The PCTFE resins prepared in the following examples were tested for fluorine content, high-temperature yellowing resistance, strength loss time, and refractive index. The specific test procedures are as follows:

[0050] Fluorine content test: A certain amount of PCTFE resin is placed in an oxygen combustion flask and burned. The gas produced by combustion is absorbed by the solution. Then, the fluoride ion content in the solution is tested using the F-selective electrode method, and the fluorine content in the PCTFE resin is calculated. The theoretical fluorine content of pure PCTFE resin should be 48.94%.

[0051] High-temperature yellowing resistance test: After heating the molded specimen at 300℃ for 10 hours, observe the color change of the sample.

[0052] Time of failure (ZST) test: Tested according to American standard ASTM D1430-03.

[0053] Melt Flow Index (MFR) Test: Tested according to national standard GB / T3682-2000.

[0054] Tensile strength test: Tested according to national standard GB / T1040-2018.

[0055] Refractive index test: Tested according to the national standard GB / T39691-2020.

[0056] Example 1

[0057] (1) A 50L vertical low-pressure stainless steel polymerization reactor (with jacket, screw anchor composite agitator, pressure gauge, oxygen content analyzer, thermometer, and viscometer) was used, and 20kg of cyclohexane was added to the polymerization reactor as a solvent.

[0058] (2) Add 12g of triethylamine as a pH buffer, 20g of hydroxymethyl cellulose as a dispersant, and 65g of 1,2-dimethylcyclopentane as a molecular weight regulator to the polymerization reactor;

[0059] (3) The polymerization reactor was then evacuated multiple times and filled with nitrogen (protective gas). The oxygen content was indicated by the online oxygen content meter on the reactor to reach ≤30ppm. At the same time, heat transfer oil was introduced into the jacket to make the temperature reach 50℃. Then the stirring motor was started and the speed was 79~108rpm.

[0060] (4) 10 kg of CTFE monomer is fed into the polymerization reactor by a feed pump, and the pressure in the reactor is maintained at 0.6 MPa and the temperature at 50 °C.

[0061] (5) 30g of perfluoropropionyl peroxide was injected as an initiator using a metering pump, and then the mixture was kept at a constant temperature for 2 hours to carry out the prepolymerization reaction;

[0062] (6) Then, by heating, the prepolymerization temperature in the polymerization reactor reaches 75°C, the pressure is 0.8MPa, and the residence time is 20min. Then, the prepolymer mixture in the polymerization reactor is continuously fed into the three-dimensional plug flow microcapsule reactor for deep polymerization reaction.

[0063] (7) The temperature of the three-dimensional plug flow microcapsule reactor is controlled at 62℃±2℃. After the deep polymerization reaction is 1 min, the product is extruded from the die head assembly of the three-dimensional plug flow microcapsule reactor. The basic product is the crude product that meets the degree of polymerization requirement. The die head pressure is controlled at 0.4~0.5MPa and the rotation speed is controlled at 50rpm.

[0064] (8) Then the crude product extruded from the three-dimensional plug flow microcapsule reactor is continuously pumped into the feed port of the devolatilization twin-screw extruder by a metering pump, while 2g of end-capping agent is simultaneously pumped into the feed port of the devolatilization twin-screw extruder by another metering pump. The solution formed by dissolving in 500g of cyclohexane is continuously, uniformly, and quantitatively pumped into the feed port of the devolatilization twin-screw extruder;

[0065] (9) The rotation speed of the devolatilized twin-screw extruder is controlled at 120 rpm, and the temperature is controlled at 60℃ in zone 1, 80℃ in zone 2, 120℃ in zone 3, 200℃ in zones 4 to 9, 200℃ in zone 10, 190℃ in zone 11, and 185℃ at the die head. The volatiles (solvents) are removed, collected, stored, and reused.

[0066] (10) The product extruded from the devolatilization twin-screw extruder is cooled by a cooling belt machine, crushed by a pulverizer, and put into a washing tank. A certain amount of deionized water is added, the stirring is turned on, the washing tank speed is 79 rpm, the liquid in the washing tank is heated to 55~65℃ and washed for 2~3 hours, and then filtered by a plate and frame filter press. The filter cake is put back into the washing tank and washed again under the same conditions. The second filter cake is dried at 105~110℃ and finally crushed to 80~100 mesh to obtain the powdered PCTFE resin product.

[0067] Comparative Example 1-1

[0068] Compared with Example 1, in step (1), 20 kg of benzene was used instead of 20 kg of cyclohexane as a solvent added to the polymerization reactor, and the other experimental steps were the same as steps (2) to (10) of Example 1.

[0069] Comparative Examples 1-2

[0070] Compared with Example 1, in step (1), 20 kg of p-xylene was used instead of 20 kg of cyclohexane as a solvent added to the polymerization reactor, and the other experimental steps were the same as steps (2) to (10) of Example 1.

[0071] Comparative Examples 1-3

[0072] Compared with Example 1, in step (1), 20 kg of p-xylene was used instead of 20 kg of cyclohexane as a solvent added to the polymerization reactor, and the other experimental steps were the same as steps (2) to (10) of Example 1.

[0073] Comparative Examples 1-4

[0074] Compared with Example 1, in step (1), 20 kg of p-1,3,5-trimethylbenzene was used instead of 20 kg of cyclohexane as a solvent added to the polymerization reactor, and the other experimental steps were the same as steps (2) to (10) of Example 1.

[0075] Comparative Examples 1-5

[0076] Compared with Example 1, in step (1), 15 kg of cyclohexane was added to the polymerization reactor as a solvent, and the other experimental steps were the same as steps (2) to (10) of Example 1.

[0077] Comparative Examples 1-6

[0078] Compared with Example 1, in step (1), 25 kg of cyclohexane was added to the polymerization reactor as a solvent, and the other experimental steps were the same as steps (2) to (10) of Example 1.

[0079] This embodiment and its series of comparative examples use different solvents for polymerization reactions. By analyzing the comprehensive performance of PCTFE resins prepared under different solvents, the solvents are optimized.

[0080] The PCTFE resins synthesized by polymerization reactions of Example 1 and Comparative Examples 1-1, 1-2, 1-3, 1-4, 1-5, and 1-6 using different solvents were tested for fluorine content, high-temperature yellowing resistance, loss of strength time, melt index (MFR), tensile strength, and refractive index. The test results are shown in Table 1.

[0081] Table 1 Properties of PCTFE resins prepared using different solvents

[0082]

[0083] As shown in Table 1, under different solvent conditions, the PCTFE resin prepared by using cyclohexane as the solvent has the best overall performance. This is because cyclohexane, as a common hydrocarbon compound, has relatively stable chemical properties and a relatively small chain transfer constant. In the polymerization reaction, it does not participate in typical chain transfer reactions, which is beneficial for obtaining high-molecular-weight PCTFE resin products with better performance.

[0084] Furthermore, based on a comparison of product performance using different amounts of cyclohexane as solvent, a cyclohexane to CTFE monomer mass ratio of 2:1 (molar ratio 2.77:1) is the optimal amount, exhibiting good overall performance. This is because the solvent amount only needs to be sufficient to dissolve the CTFE monomer. Insufficient solvent affects the solubility of the CTFE monomer in the solvent, preventing the polymerization reaction from proceeding in a homogeneous phase. This results in the presence of monomers and oligomers in the finished product, reducing its mechanical properties, anti-aging properties, and transparency. Simultaneously, the product yield is low, hindering the forward polymerization reaction. Excessive solvent does not significantly improve product performance but increases the amount of other reaction aids, reaction time and space requirements, impacting equipment utilization, reducing production capacity, and increasing the cost of the polymerization stage. It also increases the workload of devolatilization, leading to increased energy consumption and costs in the devolatilization stage. Therefore, a moderate amount of solvent is sufficient.

[0085] Example 2

[0086] (1) Same as step (1) in Example 1;

[0087] (2) Add 20g of triethylalkanolamine as a pH buffer, 20g of hydroxypropyl methylcellulose as a dispersant, and 70g of 1,2,3-trimethylcyclopentane as a molecular weight regulator to the polymerization reactor;

[0088] Steps (3) to (10) are the same as steps (3) to (10) in Example 1.

[0089] Comparative Example 2-1

[0090] (1) Same as step (1) in Example 1;

[0091] (2) Compared with step (2) of Example 2, 20g of hydroxymethyl cellulose was added to the polymerization reactor instead of 20g of hydroxypropyl methyl cellulose as a dispersant, and the pH buffer and molecular weight regulator added were the same as those in step (2) of Example 2.

[0092] Steps (3) to (10) are the same as steps (3) to (10) in Example 1.

[0093] Comparative Example 2-2

[0094] (1) Same as step (1) in Example 1;

[0095] (2) Compared with step (2) of Example 2, 20g of hydroxyethyl cellulose was added to the polymerization reactor instead of 20g of hydroxypropyl methyl cellulose as a dispersant, and the pH buffer and molecular weight regulator added were the same as those in step (2) of Example 2.

[0096] Steps (3) to (10) are the same as in Example 1.

[0097] Comparative Examples 2-3

[0098] (1) Same as step (1) in Example 1;

[0099] (2) Compared with step (2) of Example 2, 10g of hydroxypropyl methylcellulose was added to the polymerization reactor instead of 20g of hydroxypropyl methylcellulose as a dispersant, and the pH buffer and molecular weight regulator added were the same as those in step (2) of Example 2.

[0100] Steps (3) to (10) are the same as in Example 1.

[0101] Comparative Examples 2-4

[0102] (1) Same as step (1) in Example 1;

[0103] (2) Compared with step (2) of Example 2, 15g of hydroxypropyl methylcellulose was added to the polymerization reactor instead of 20g of hydroxypropyl methylcellulose as a dispersant, and the pH buffer and molecular weight regulator added were the same as those in step (2) of Example 2.

[0104] Steps (3) to (10) are the same as in Example 1.

[0105] Comparative Examples 2-5

[0106] (1) Same as step (1) in Example 1;

[0107] (2) Compared with step (2) of Example 2, 25g of hydroxypropyl methylcellulose was added to the polymerization reactor instead of 20g of hydroxypropyl methylcellulose as a dispersant, and the pH buffer and molecular weight regulator added were the same as those in step (2) of Example 2.

[0108] Steps (3) to (10) are the same as in Example 1.

[0109] Comparative Examples 2-6

[0110] (1) Same as step (1) in Example 1;

[0111] (2) Compared with step (2) of Example 2, 30g of hydroxypropyl methylcellulose was added to the polymerization reactor instead of 20g of hydroxypropyl methylcellulose as a dispersant, and the pH buffer and molecular weight regulator added were the same as those in step (2) of Example 2.

[0112] Steps (3) to (10) are the same as in Example 1.

[0113] This embodiment and its series of comparative examples use different dispersants and dosages for polymerization reactions. By analyzing the comprehensive performance of the prepared PCTFE, the dispersant is optimized.

[0114] The PCTFE resin products prepared by polymerization reactions using different dispersants in Example 1 and Comparative Examples 2-1 and 2-2, as well as Comparative Examples 2-3, 2-4, 2-5, and 2-6 using different amounts of hydroxypropyl methylcellulose as dispersants, were tested for fluorine content, high-temperature yellowing resistance, loss of strength time, melt index (MFR), tensile strength, and refractive index. The test results are shown in Table 2.

[0115] Table 2 Properties of PCTFE resins prepared using different dispersants

[0116]

[0117] As shown in Table 2, under the same dosage, the PCTFE resin prepared using hydroxypropyl methylcellulose as the dispersant exhibits the best overall performance, indicating that hydroxypropyl methylcellulose has the best dispersing effect. This may be because hydroxypropyl methylcellulose has an asymmetric molecular structure, similar to the asymmetric molecular structure of CTFE, with similar polarity, but a very large difference in polarity compared to PCTFE. This allows hydroxypropyl methylcellulose to blend well with and disperse CTFE monomers. As the polymer PCTFE is continuously generated, it gradually separates out, further dispersing the monomers that did not participate in the polymerization reaction. In contrast, hydroxyethyl cellulose and hydroxymethyl cellulose have weaker molecular polarity, resulting in weaker fusion with monomers but stronger fusion with polymers. Consequently, they cannot effectively disperse CTFE monomers in the polymerization system. Therefore, hydroxypropyl methylcellulose is the optimal dispersant in the preparation method provided by this invention.

[0118] Further optimization of the dosage of dispersant hydroxypropyl methylcellulose (HPMC) was conducted. Table 2 shows that in Example 2, when the dosage of HPMC was 15g (molar ratio to monomer was 0.0003:1), the PCTFE resin prepared by the polymerization reaction exhibited better overall performance. Insufficient HPMC resulted in a weak steric hindrance mechanism, high suspension viscosity, instability, and potential agglomeration, affecting the dispersion effect. Conversely, excessive HPMC left residual ions in the suspension. Excessive ions compress the electric double layer, reducing the absolute value of the Zeta potential and thus decreasing the stabilizing effect of electrostatic repulsion. This affects the stability of the slurry, increases the viscosity of the suspension, and may cause agglomeration, reducing the dispersion effect. Furthermore, excessive dispersant dosage can lead to residual dispersant in the finished PCTFE product.

[0119] Example 3

[0120] (1) Same as step (1) in Example 1;

[0121] (2) Add 25g of triethylamine as a pH buffer, 15g of hydroxypropyl methylcellulose as a dispersant, and 70g of tert-butylcyclopentane as a molecular weight regulator to the polymerization reactor;

[0122] Steps (3) to (10) are the same as steps (3) to (10) in Example 1.

[0123] Comparative Example 3-1

[0124] (1) Same as step (1) in Example 1;

[0125] (2) Compared with step (2) of Example 3, 25g of triethylolamine was added to the polymerization reactor instead of 25g of triethylamine as a pH buffer, and the dispersant and molecular weight regulator added were the same as in step (2) of Example 3.

[0126] Steps (3) to (10) are the same as steps (3) to (10) in Example 1.

[0127] Comparative Example 3-2

[0128] (1) Same as step (1) in Example 1;

[0129] (2) Compared with step (2) of Example 3, 25g of dimethylethanolamine was added to the polymerization reactor instead of 25g of triethylamine as a pH buffer, and the dispersant and molecular weight regulator added were the same as in step (2) of Example 3.

[0130] Steps (3) to (10) are the same as steps (3) to (10) in Example 1.

[0131] Comparative Example 3-3

[0132] (1) Same as step (1) in Example 1;

[0133] (2) Compared with step (2) of Example 3, 25g sodium citrate was added to the polymerization reactor instead of 25g triethylamine as pH buffer, and the added dispersant and molecular weight regulator were the same as in step (2) of Example 3.

[0134] Steps (3) to (10) are the same as steps (3) to (10) in Example 1.

[0135] Comparative Examples 3-4

[0136] (1) Same as step (1) in Example 1;

[0137] (2) Compared with step (2) of Example 3, 25g sodium tartrate was added to the polymerization reactor instead of 25g triethylamine as pH buffer, and the added dispersant and molecular weight regulator were the same as in step (2) of Example 3.

[0138] Steps (3) to (10) are the same as steps (3) to (10) in Example 1.

[0139] Comparative Examples 3-5

[0140] (1) Same as step (1) in Example 1;

[0141] (2) Compared with step (2) of Example 3, 15g of triethylamine was added to the polymerization reactor as a pH buffer, and the dispersant and molecular weight regulator added were the same as in step (2) of Example 3;

[0142] Steps (3) to (10) are the same as steps (3) to (10) in Example 1.

[0143] Comparative Examples 3-6

[0144] (1) Same as step (1) in Example 1;

[0145] (2) Compared with step (2) of Example 3, 40g of triethylamine was added to the polymerization reactor as a pH buffer, and the dispersant and molecular weight regulator added were the same as in step (2) of Example 3;

[0146] Steps (3) to (10) are the same as steps (3) to (10) in Example 1.

[0147] This embodiment and its series of comparative examples used different pH buffers and dosages for polymerization reactions. By analyzing the overall performance of the prepared PCTFE, the pH buffers were optimized.

[0148] The fluorine content, high-temperature yellowing resistance, loss of strength time, melt index (MFR), tensile strength and refractive index of PCTFE resins prepared by polymerization reactions using different pH buffers in Example 3 and Comparative Examples 3-1, 3-2, 3-3, and 3-4, as well as Comparative Examples 3-5 and 3-6 using different amounts of triethylamine as pH buffers, were tested. The test results are shown in Table 3.

[0149] Table 3 Properties of PCTFE resins prepared using different pH buffers

[0150]

[0151] Therefore, it is evident that when triethylamine is used as the pH buffer, the PCTFE resin prepared by polymerization exhibits better overall performance. The main purpose of the pH buffer is to adjust the pH value of the reaction system and absorb F ions from CTFE. While sodium citrate and sodium tartrate, as pH buffers, have good buffering effects, they introduce sodium ions into the system, increasing the inorganic sodium ion content in the finished PCTFE and severely affecting its quality. Dimethylethanolamine and triethylolamine have moderate pH buffering effects because their molecules contain hydroxyl groups, which can create transition bonds at the end groups of PCTFE, resulting in a decrease in refractive index. Triethylamine has the best buffering effect because it reacts rapidly with free F ions, stabilizes the pH value of the system, and does not react or form intermolecular hydrogen bonds with CTFE, PCTFE, solvent cyclohexane, dispersant hydroxypropyl methylcellulose, etc., in the reaction system. Therefore, triethylamine is the optimal pH buffer in the preparation method provided by this invention.

[0152] As shown in Table 3, in this embodiment, when the amount of triethylamine is 25g (molar ratio to monomer is 0.00034:1), the PCTFE resin prepared by the polymerization reaction has better overall performance. This is because an appropriate amount of pH buffer can maintain a suitable pH value in the polymerization reaction system, which is beneficial for more complete and faster decomposition of the initiator, facilitates control of the polymerization rate, reduces initiator residue in the PCTFE resin product, and improves the thermal stability of the resin. Too much or too little triethylamine will result in an excessively high or low pH value, which will damage the dispersing and binding abilities of the dispersant, leading to coarser polyvinyl chloride resin particles that cannot be properly sieved. In severe cases, this can cause explosive polymerization and other extreme situations, posing serious safety hazards to the stable operation of the polymerization reactor.

[0153] Example 4

[0154] (1) Same as step (1) in Example 1;

[0155] (2) Add 25g of triethylamine as a pH buffer, 15g of hydroxypropyl methylcellulose as a dispersant, and 70g of methylcyclopentane as a molecular weight regulator to the polymerization reactor;

[0156] Steps (3) to (10) are the same as steps (3) to (10) in Example 1.

[0157] Comparative Example 4-1

[0158] (1) Same as step (1) in Example 1;

[0159] (2) Compared with step (2) of Example 4, 70g of ethylcyclopentane was added to the polymerization reactor instead of 70g of methylcyclopentane as a molecular weight regulator, and the added dispersant and pH buffer were the same as in step (2) of Example 4.

[0160] Steps (3) to (10) are the same as steps (3) to (10) in Example 1.

[0161] Comparative Example 4-2

[0162] (1) Same as step (1) in Example 1;

[0163] (2) Compared with step (2) of Example 4, 70g of propylcyclopentane was added to the polymerization reactor instead of 70g of methylcyclopentane as a molecular weight regulator, and the added dispersant and pH buffer were the same as in step (2) of Example 4.

[0164] Steps (3) to (10) are the same as steps (3) to (10) in Example 1.

[0165] Comparative Example 4-3

[0166] (1) Same as step (1) in Example 1;

[0167] (2) Compared with step (2) of Example 4, 70g of isopropylcyclopentane was added to the polymerization reactor instead of 70g of methylcyclopentane as a molecular weight regulator, and the added dispersant and pH buffer were the same as in step (2) of Example 4.

[0168] Steps (3) to (10) are the same as steps (3) to (10) in Example 1.

[0169] Comparative Example 4-4

[0170] (1) Same as step (1) in Example 1;

[0171] (2) Compared with step (2) of Example 4, 70g of n-butylcyclopentane was added to the polymerization reactor instead of 70g of methylcyclopentane as a molecular weight regulator, and the dispersant and pH buffer added were the same as in step (2) of Example 4.

[0172] Steps (3) to (10) are the same as steps (3) to (10) in Example 1.

[0173] Comparative Example 4-5

[0174] (1) Same as step (1) in Example 1;

[0175] (2) Compared with step (2) of Example 4, 70g of tert-butylcyclopentane was added to the polymerization reactor instead of 70g of methylcyclopentane as a molecular weight regulator, and the added dispersant and pH buffer were the same as in step (2) of Example 4.

[0176] Steps (3) to (10) are the same as steps (3) to (10) in Example 1.

[0177] Comparative Examples 4-6

[0178] (1) Same as step (1) in Example 1;

[0179] (2) Compared with step (2) of Example 4, 70g of 1-methyl-2-ethylcyclopentane was added to the polymerization reactor instead of 70g of methylcyclopentane as a molecular weight regulator, and the dispersant and pH buffer added were the same as those in step (2) of Example 4.

[0180] Steps (3) to (10) are the same as steps (3) to (10) in Example 1.

[0181] Comparative Examples 4-7

[0182] (1) Same as step (1) in Example 1;

[0183] (2) Compared with step (2) of Example 4, 70g of 1,2-dimethylcyclopentane was added to the polymerization reactor instead of 70g of methylcyclopentane as a molecular weight regulator, and the dispersant and pH buffer added were the same as in step (2) of Example 4.

[0184] Steps (3) to (10) are the same as steps (3) to (10) in Example 1.

[0185] Comparative Examples 4-8

[0186] (1) Same as step (1) in Example 1;

[0187] (2) Compared with step (2) of Example 4, 70g of 1,2,3-trimethylcyclopentane was added to the polymerization reactor instead of 70g of methylcyclopentane as a molecular weight regulator, and the dispersant and pH buffer added were the same as in step (2) of Example 4.

[0188] Steps (3) to (10) are the same as steps (3) to (10) in Example 1.

[0189] Comparative Examples 4-9

[0190] (1) Same as step (1) in Example 1;

[0191] (2) Compared with step (2) of Example 4, 50g of methylcyclopentane was added to the polymerization reactor as a molecular weight regulator, and the dispersant and pH buffer added were the same as in step (2) of Example 4.

[0192] Steps (3) to (10) are the same as steps (3) to (10) in Example 1.

[0193] Comparative Examples 4-10

[0194] (1) Same as step (1) in Example 1;

[0195] (2) Compared with step (2) of Example 4, 90g of methylcyclopentane was added to the polymerization reactor as a molecular weight regulator, and the dispersant and pH buffer added were the same as in step (2) of Example 4.

[0196] Steps (3) to (10) are the same as steps (3) to (10) in Example 1.

[0197] Comparative Example 4-11

[0198] (1) Same as step (1) in Example 1;

[0199] (2) Same as step (2) in Example 4;

[0200] (3) Same as step (3) in Example 1;

[0201] (4) is the same as step (4) in Example 1;

[0202] (5) Use a metering pump to inject 20g of perfluoropropionyl peroxide as an initiator, and then keep it at the temperature for 2 hours for prepolymerization reaction;

[0203] Steps (6) to (10) are the same as steps (6) to (10) in Example 1.

[0204] Comparative Example 4-12

[0205] (1) Same as step (1) in Example 1;

[0206] (2) Same as step (2) in Example 4;

[0207] (3) Same as step (3) in Example 1;

[0208] (4) is the same as step (4) in Example 1;

[0209] (5) Use a metering pump to inject 40g of perfluoropropionyl peroxide as an initiator, and then keep it at the temperature for 2 hours for prepolymerization reaction;

[0210] Steps (6) to (10) are the same as steps (6) to (10) in Example 1.

[0211] This embodiment and its series of comparative examples use different molecular weight regulators and dosages, as well as different dosages of initiators, to carry out polymerization reactions. By analyzing the comprehensive performance of the prepared PCTFE, the molecular weight regulators and initiators are optimized.

[0212] The fluorine content, high-temperature yellowing resistance, decompression time, melt index (MFR), tensile strength, and refractive index of PCTFE resin products prepared by polymerization reactions using different molecular weight regulators in Example 4 and Comparative Examples 4-1, 4-2, 4-3, 4-4, 4-5, 4-6, 4-7, and 4-8, different amounts of methylcyclopentane as molecular weight regulator in Comparative Examples 4-9 and 4-10, and different amounts of perfluoropropionyl peroxide as initiator were tested. The test results are shown in Tables 4 and 5, respectively.

[0213] Table 4 Performance Test Table of PCTFE Resins Prepared Using Different Molecular Weight Regulators

[0214]

[0215] As shown in Table 4, the PCTFE resin prepared by polymerization in the preparation method provided by this invention exhibits the best overall performance when methylcyclopentane is selected as the molecular weight regulator. This is because methylcyclopentane has the smallest branched chain and the largest molar number for the same weight, making its molecular weight adjustment predictable and controllable. Furthermore, methylcyclopentane is a colorless, volatile, and flammable liquid with high reactivity under specific conditions, allowing it to disperse rapidly and uniformly in the reaction system, thereby effectively regulating the polymer's molecular weight. Moreover, it is easily removed from the vacuum devouring screw compressor after the reaction.

[0216] The overall performance of the PCTFE resins prepared by polymerization reactions in Example 4, Comparative Examples 4-9, and 4-10 was compared, as shown in Table 4. When methylcyclopentane was used as a molecular weight regulator at a dosage of 70 g (molar ratio to monomer 0.0097:1), the PCTFE resin prepared by polymerization showed the best overall performance. Excessive use of the molecular weight regulator resulted in a decrease in the molecular weight of the polymer. This is because the regulator reduces the relative molecular mass of the polymer obtained through chain transfer reaction, while the newly generated active centers continue chain growth, thus maintaining the polymerization rate but decreasing the polymer's molecular weight. This decrease in molecular weight may lead to a decline in the polymer's physical and mechanical properties, such as strength, elasticity, toughness, and hardness. Furthermore, the decrease in molecular weight also affects the processing performance of the polymer material, as a lower molecular weight may lead to increased flowability during processing, reducing the thermal stability and durability of the finished product. Conversely, insufficient molecular weight regulator may result in an excessively large molecular weight. While an excessively large molecular weight can improve certain physical properties of the polymer, such as tensile strength and impact strength, it may also lead to increased viscosity, affecting flowability and moldability during processing. In addition, excessively large molecular weights may cause polymers to exhibit undesirable properties in applications, such as reduced material flexibility or increased brittleness.

[0217] The properties of PCTFFE prepared by polymerization reactions using different amounts of perfluoropropionyl peroxide as an initiator, including content, deterioration time, refractive index, and tensile strength, were compared, as shown in Table 5. Table 5 shows that PCTFE prepared with 30g of perfluoropropionyl peroxide as an initiator (molar ratio to monomer of 0.00045:1) exhibited the best overall performance. This is because excessive initiator leads to a relatively higher number of free radicals generated per unit time, resulting in a faster reaction rate, shorter polymerization time, and higher equipment utilization. However, the heat of reaction cannot be removed in time, potentially leading to explosive polymerization, coarser product particles, and reduced porosity. Furthermore, excessive initiator reduces the stability of the polymerization process, causing a rapid decrease in the polymer's molecular weight. Conversely, insufficient initiator results in a slow reaction rate, longer polymerization time, lower equipment utilization, and a reduced number of free radicals, leading to excessively large polymers, higher molecular weight, increased system viscosity, lower monomer conversion rate, and poor system stability. The amount of initiator is a key factor in regulating the polymerization rate, degree of polymerization, molecular weight, and particle size distribution. Appropriate initiator dosage is crucial for optimizing the polymerization process.

[0218] Table 5. Comprehensive properties of PCTFE resins prepared using different amounts of initiator

[0219]

[0220] This invention also experimentally analyzed the effects of polymerization temperature, time, and pressure on the overall properties of the prepared PCTFE. The experimental results show that by adjusting the reaction temperature, time, and pressure, polymers with specific structures and properties can be prepared to meet different application requirements. Therefore, during the polymerization process, the polymerization temperature, time, and pressure can be precisely controlled according to the specific requirements of the product. Furthermore, the amount of end-capping agent used in this invention can be determined based on the required molecular weight of the prepared polymer; the higher the required molecular weight, the less end-capping agent is needed, and the lower the required molecular weight, the more end-capping agent is needed.

[0221] In summary, the method for preparing narrow molecular weight distribution PCTFE resin provided by this invention uses cyclohexane as a solvent, hydroxypropyl methylcellulose as a dispersant, triethylamine as a pH buffer, methylcyclopentane as a molecular weight regulator, fluorinated compound RFCO2 as a capping agent, and perfluoropropionyl peroxide as an initiator, resulting in PCTFE resin with the best overall performance.

Claims

1. A process for the production of a narrow molecular weight distribution polychlorotrifluoroethylene resin, characterized in that, Specific steps of the preparation method include: S1, a solvent, a dispersing agent, a pH buffer, and a molecular weight regulator are added into a polymerization reactor, then the inside of the polymerization reactor is vacuumized, and protective gas is filled in, while heating and stirring are carried out; S2, trifluorochloroethylene monomers are added into the polymerization reactor through a feeding pump, the pressure and temperature in the polymerization reactor are maintained, and an initiator is added into the polymerization reactor through a metering pump, and pre-polymerization is carried out, to obtain a pre-polymer mixture; S3, the pre-polymer mixture is continuously punched into a three-dimensional plug flow microcapsule reaction device, and a deep polymerization reaction is carried out, while the crude product reaching the required polymerization degree is continuously extruded from a head assembly of the three-dimensional plug flow microcapsule reaction device, and the reaction material not completing the polymerization reaction is continuously sent from a return port of the three-dimensional plug flow microcapsule reaction device to a feeding port through a metering pump, and the polymerization reaction is continuously carried out; S4, the crude product reaching the required polymerization degree is continuously devolatilized through a devolatilization process, and unstable end groups of the crude product reaching the required polymerization degree are capped by continuously adding a capping agent, to obtain a polymer reaching the required polymerization degree; S5, the polymer reaching the required polymerization degree is cooled to form a solidified product, and the solidified product is crushed, washed, filtered, and dried, to obtain a polytrifluorochloroethylene resin finished product; The solvent is cyclohexane; the molar ratio of the cyclohexane to the trifluorochloroethylene monomers is (1.50-5.00):1; The dispersing agent is hydroxypropyl methyl cellulose; the molar ratio of the hydroxypropyl methyl cellulose to the solvent cyclohexane is (0.0001-0.001):1; The pH buffer is triethylamine; the molar ratio of the triethylamine to the trifluorochloroethylene monomers is (0.0002-0.001):1; The molecular weight regulator is methylcyclopentane; the molar ratio of the methylcyclopentane to the trifluorochloroethylene monomers is (0.006-0.02):

1.

2. The process for producing a narrow molecular weight distribution polychlorotrifluoroethylene resin according to claim 1, characterized by, In S2, the reaction temperature of the pre-polymerization is 30-120℃, the reaction pressure is 0.2-0.6 MPa, and the reaction time is 1.5-3 h; in S3, the deep polymerization reaction is a continuous solution polymerization reaction, the reaction temperature is 50-240℃, the reaction pressure is 0.1-1.2 MPa, and after 1-5 min of reaction, the crude product reaching the required polymerization degree is continuously extruded from the head assembly, and the separation is started while the reaction is carried out.

3. The process for producing a narrow molecular weight distribution polychlorotrifluoroethylene resin according to claim 1, characterized by, The three-dimensional plug flow microcapsule reaction device includes a propulsion system, a microcapsule reaction group, a heating system, a cooling system, a head assembly, a circulating reflux system, a vacuum degassing system, and a reaction aid supply system; The propulsion system continuously pushes the pre-polymer mixture to the microcapsule reaction group through a gradually changing conveying screw, and pushes the crude product reaching the required polymerization degree synthesized by the polymerization reaction to the head assembly. The microcapsule reaction group is composed of several microcapsule reaction units; the microcapsule reaction unit comprises several centrifugal driving discs, fixed discs and reaction unit cylinders; several involute grooves with opposite directions are opened on the cooperation surface of the centrifugal driving disc and the fixed disc to form several microcapsule reaction spaces; the microcapsule reaction spaces are used to provide polymerization reaction spaces for the reactant materials; The head assembly is connected with the discharge section assembly and is used to continuously extrude the crude product reaching the polymerization degree requirement; The heating system is fixedly installed outside the propelling system and the microcapsule reaction group and is used to heat the reactant materials; The cooling system is connected with the propelling system and the microcapsule reaction group and is used to cool the reactant materials; The circulating reflux system is used to circulate the reactant materials from the discharge section assembly to the feeding section assembly to continue to participate in the polymerization reaction; The vacuum degassing system is connected with the microcapsule reaction group and is used to remove small molecular impurities generated in the reaction process; The reaction aid supplement system is connected with the microcapsule reaction group and is used to supplement the reaction aids.

4. The process for producing a narrow molecular weight distribution polychlorotrifluoroethylene resin according to claim 1, characterized by, The initiator is peroxide total fluorine propionyl; the molar ratio of the initiator to the trifluoro chloroethylene monomer is (0.0003-0.0025):

1.

5. The process for producing a narrow molecular weight distribution polychlorotrifluoroethylene resin according to claim 1, characterized by, The polymer reaching the polymerization degree requirement has a narrowness of polymerization degree distribution within 5%.

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