Preparation method of polyvinyl chloride

Abstract

The invention relates to the field of polyvinyl chloride preparation methods, in particular to a polyvinyl chloride preparation method which comprises a step 1, a step 2 and a step 3. Wherein in the step 1, the cold desalted water, the compound dispersing agent, the compound initiator, the vinyl chloride monomer and the hot desalted water are stirred and react to obtain a mixture. The compound initiator is prepared from at least two of isopropyl phenyl peroxide neodecanoate, tert-amyl peroxide neodecanoate and tert-amyl peroxide isononanoic acid ester. By adding the compound initiator, the three initiators in the compound initiator can stably and continuously output free radicals in different stages of the polymerization reaction of vinyl chloride, the polymerization reaction of polyethylene monomers is promoted, the conversion rate of the vinyl chloride monomers is guaranteed, and the polymerization time of polyvinyl chloride is effectively shortened.

Description

Technical Field

[0001] This application relates to the field of polymer materials, and particularly to a method for preparing polyvinyl chloride. Background Art

[0002] Polyvinyl chloride is the third-largest synthetic polymer plastic in the world in terms of production volume, second only to polyethylene and polypropylene, and is widely used in fields such as building materials, electronic appliances, and medical supplies. With the continuous expansion of the application scope of polyvinyl chloride, the demand for polyvinyl chloride has also been continuously increasing, forcing the polyvinyl chloride production industry to continuously increase production to meet the market demand.

[0003] The existing methods for producing polyvinyl chloride mainly use suspension polymerization. Vinyl chloride monomer, deionized water, dispersant, initiator, etc. are added to a polymerization kettle. Under the action of stirring, the vinyl chloride monomer is suspended in the aqueous phase in the form of small droplets. The initiator decomposes to generate free radicals at an appropriate temperature, initiating the polymerization reaction of the vinyl chloride monomer, and finally forming polyvinyl chloride particles. However, usually a single initiator is used in the above polyvinyl chloride production process, so that the initiator cannot always maintain an efficient initiation effect throughout the polymerization process, and the reaction rate decreases in the later stage, resulting in an extended time required to reach the expected conversion rate. Summary of the Invention

[0004] In order to shorten the polymerization duration of polyvinyl chloride, this application provides a method for preparing polyvinyl chloride.

[0005] A method for preparing polyvinyl chloride provided by this application includes the following steps: A method for preparing polyvinyl chloride includes the following steps: Step 1: Stir and react cold demineralized water, compound dispersant, compound initiator, vinyl chloride monomer, and hot demineralized water to obtain a mixture; Step 2: Add a neutralizing agent and a terminator to the mixture to terminate the reaction and obtain a polyvinyl chloride slurry; Step 3: Remove the unreacted vinyl chloride monomer, and centrifuge and dry to obtain polyvinyl chloride powder; The compound initiator includes at least two of isopropylphenyl peroxyneodecanoate, tert-amyl peroxyneodecanoate, and tert-amyl peroxyisononanoate.

[0006] By adopting the above technical solution, in the preparation process of polyvinyl chloride, by compounding initiators, there are different decomposition temperature ranges among different initiators. For example, isopropylphenyl peroxyneodecanoate starts to decompose between 30-60°C, and the decomposition rate can meet the requirement of rapid initiation in the initial stage of the polyvinyl chloride polymerization reaction. The decomposition temperature range of tert-amyl peroxyneodecanoate is approximately between 40-70°C, and the decomposition temperature of tert-amyl peroxyisononanoate is usually between 45-75°C. It can provide sufficient free radicals during the polymerization of vinyl chloride, enabling the compounded initiator to continuously output free radicals at different stages of the vinyl chloride polymerization, ensuring a stable and high polymerization rate throughout the polymerization process.

[0007] In the initial stage of the vinyl chloride polymerization reaction, one component in the compounded initiator can rapidly decompose to generate free radicals, prompting the vinyl chloride monomer to quickly start the polymerization reaction and accelerating the starting speed of the polymerization reaction. In the later stage of the vinyl chloride polymerization reaction, other components in the compounded initiator can still stably output free radicals, maintaining the smooth progress of the reaction, ensuring the conversion rate of the vinyl chloride monomer, and effectively shortening the polymerization time of polyvinyl chloride.

[0008] By adding the compounded initiator (isopropylphenyl peroxyneodecanoate, tert-amyl peroxyneodecanoate, and tert-amyl peroxyisononanoate) in this application, the three initiators in the compounded initiator can stably and continuously output free radicals at different stages of the vinyl chloride polymerization reaction, promoting the polymerization reaction of the polyethylene monomer, ensuring the conversion rate of the vinyl chloride monomer, and effectively shortening the polymerization time of polyvinyl chloride.

[0009] Preferably, the compounded initiator is a mixture of isopropylphenyl peroxyneodecanoate and tert-amyl peroxyneodecanoate; the mass ratio of isopropylphenyl peroxyneodecanoate to tert-amyl peroxyneodecanoate in the compounded initiator is 1:0.66-1.

[0010] By adopting the above technical solution, isopropylphenyl peroxyneodecanoate and tert-amyl peroxyneodecanoate are compounded into an initiator, and the mass ratio of isopropylphenyl peroxyneodecanoate to tert-amyl peroxyneodecanoate in the compounded initiator is 1:0.66-1. Among them, isopropylphenyl peroxyneodecanoate has higher activity, and its concentration and amount are relatively large. In the early stage of the vinyl chloride polymerization reaction, isopropylphenyl peroxyneodecanoate can rapidly decompose to generate free radicals to accelerate the initial speed of the vinyl chloride polymerization reaction. As the heating temperature rises, the decomposition rate of tert-amyl peroxyneodecanoate increases accordingly, ensuring the smooth progress of the reaction and effectively shortening the polymerization time of polyvinyl chloride.

[0011] For other combinations of components in the compound initiator, cumyl peroxyneodecanoate has high activity and can rapidly initiate the polymerization reaction of vinyl chloride at the initial stage of the reaction. Tert-amyl peroxyneodecanoate also has certain activity at the initial stage and a moderate decomposition rate. The combination of the two can, at the initial stage of the reaction, not only rapidly generate sufficient free radicals to quickly start the reaction but also avoid the reaction being too violent to control. However, the decomposition characteristics of tert-amyl peroxyisononanoate are different from those of tert-amyl peroxyneodecanoate. When combined with cumyl peroxyneodecanoate, the accuracy of regulating the initial reaction rate may be slightly inferior, which may lead to an unstable or inefficient start of the reaction.

[0012] Preferably, the compound initiator is a mixture of cumyl peroxyneodecanoate, tert-amyl peroxyneodecanoate, and tert-amyl peroxyisononanoate; in Step 1, tert-amyl peroxyisononanoate is added 2 hours after the addition of cumyl peroxyneodecanoate and tert-amyl peroxyneodecanoate.

[0013] By adopting the above technical solution, cumyl peroxyneodecanoate, tert-amyl peroxyneodecanoate, and tert-amyl peroxyisononanoate are compounded into an initiator, enabling stable and efficient initiation efficiency throughout the pre, middle, and post stages of the vinyl chloride polymerization reaction. Among them, in Step 1, tert-amyl peroxyisononanoate is added 2 hours after the addition of cumyl peroxyneodecanoate and tert-amyl peroxyneodecanoate, so that after 2 hours of the reaction, when the concentration of vinyl chloride monomer in the system decreases and the reaction activity also decreases, tert-amyl peroxyisononanoate can continuously provide free radicals at this stage to maintain the progress of the reaction, ensure that the reaction rate does not drop too rapidly, and help reduce the probability of the reaction getting out of control due to the generation of a large number of free radicals in the early stage of the polymerization reaction, enabling the polymerization reaction to be precisely controlled at different stages.

[0014] Preferably, the compound initiator comprises 55 parts by weight of cumyl peroxyneodecanoate, 35 - 40 parts by weight of tert-amyl peroxyneodecanoate, and 5 - 10 parts by weight of tert-amyl peroxyisononanoate.

[0015] By adopting the above technical solution, during the vinyl chloride polymerization reaction, isopropylphenyl peroxypivalate has relatively high activity. The proportion of 55 parts by weight can ensure a large amount of free radicals are rapidly decomposed at the initial stage of the reaction, promoting the rapid initiation of the polymerization reaction. Meanwhile, as the temperature rises, tert-amyl peroxypivalate begins to decompose. Its relatively mild activity synergizes with that of isopropylphenyl peroxypivalate, enabling the reaction to maintain a certain level of stability while starting rapidly, and reducing the probability of the polymerization reaction getting out of control. In the middle and late stages of the reaction, 5 - 10 parts by weight of tert-amyl perisononanoate begins to decompose to generate free radicals, replenishing the concentration of free radicals in the reaction system, ensuring that the reaction can proceed continuously and stably until the monomer conversion rate reaches a relatively high level, effectively shortening the duration required for the entire polymerization reaction.

[0016] Preferably, in step 1, a chain transfer agent is further added, and the chain transfer agent includes at least one of α-methylstyrene dimer, mercaptoacetic acid, and dodecyl mercaptan.

[0017] Preferably, the chain transfer agent is α-methylstyrene dimer.

[0018] By adopting the above technical solution, when α-methylstyrene dimer is used as the chain transfer agent, when the growing polymer radical encounters α-methylstyrene dimer, the polymer radical will attack the carbon-carbon double bond in the α-methylstyrene dimer molecule. The double bond opens and combines with the polymer radical, terminating the growth of the polymer chain. Meanwhile, α-methylstyrene dimer forms a new free radical due to the opening of the double bond, and this new free radical can continue to initiate the polymerization reaction of the monomer, thus realizing the function of chain transfer and effectively reducing the occurrence of side reactions in the polymerization reaction.

[0019] Mercaptoacetic acid and dodecyl mercaptan exert their effects through the mercapto group. Since the hydrogen atom on the mercapto group has relatively high activity and is easily captured by the growing polymer radical, when the growing polymer radical approaches the mercaptoacetic acid molecule, it will capture the hydrogen atom on the mercapto group, terminating the growth of the polymer chain. After the mercapto group loses the hydrogen atom, the formed sulfur radical has a certain activity and can continue to initiate the polymerization reaction of vinyl chloride monomer, thus realizing the function of chain transfer.

[0020] However, α-methylstyrene dimer can more precisely control the chain transfer process in the polymerization reaction. When it reacts with the growing polymer radical, the termination of molecular chain growth and the initiation of a new chain can proceed relatively evenly. In contrast, the chain transfer processes of mercaptoacetic acid and dodecyl mercaptan are more difficult to precisely regulate and easily lead to a wider molecular weight distribution. A narrower molecular weight distribution can endow polyvinyl chloride with more excellent and stable physical properties.

[0021] Preferably, in step 1, a heat stabilizer is further added, and the heat stabilizer includes at least one of calcium stearate, dibasic lead phosphite, and dibutyltin maleate.

[0022] Preferably, the heat stabilizer is calcium stearate.

[0023] By adopting the above technical solution, α-methylstyrene dimer acts as a chain transfer agent, participates in the chain transfer process in the polymerization reaction and may generate some free radical intermediates. Calcium stearate has a certain free radical capture ability, and it can form a synergistic effect with α-methylstyrene dimer in free radical-related reactions. Calcium stearate can timely capture the unstable free radicals generated in the reaction system, reduce the further degradation or side reactions of polyvinyl chloride caused by these free radicals, thereby improving the thermal stability of polyvinyl chloride. Dibasic lead phosphite mainly exerts its thermal stabilization effect by reacting with hydrogen chloride. Although dibutyltin maleate also has a certain stabilization mechanism, it is not as closely coordinated with α-methylstyrene dimer in terms of free radical capture as calcium stearate.

[0024] Preferably, in step 1, the reaction temperature is 54 - 56 °C; in step 2, the reaction pressure before adding the neutralizer and terminator is 0.72 - 0.74 MPaG.

[0025] By adopting the above technical solution, the reaction temperature in step 1 is controlled between 54 - 56 °C. Within this temperature range, the components in the compound initiator all have ideal activities, and the decomposition characteristics of different initiators cooperate with each other, enabling the compound initiator to decompose to generate sufficient free radicals to initiate the polymerization of vinyl chloride monomer, and not decomposing too fast to cause a large amount of free radicals to be generated instantaneously, making the reaction too violent to control. This effectively ensures the stable and continuous progress of the polymerization reaction, improves the conversion rate of vinyl chloride monomer, and shortens the polymerization time of polyvinyl chloride. When the discharge pressure is between 0.72 - 0.74 MPaG, most of the vinyl chloride monomer has participated in the polymerization reaction to form polyvinyl chloride, and the conversion rate of vinyl chloride monomer is at an ideal level. When the reaction pressure when adding the neutralizer and terminator is too high, a large amount of vinyl chloride monomer will be terminated before reaction, reducing production efficiency and product output; while when the reaction pressure when adding the neutralizer and terminator is too low, it may lead to over-polymerization and affect product quality.

[0026] In summary, the present application includes at least one of the following beneficial technical effects: 1. By adding a compound initiator (cumyl peroxyneodecanoate, tert-amyl peroxyneodecanoate, and tert-pentyl peroxyisononanoate), the three initiators in the compound initiator can stably and continuously generate free radicals at different stages of the polymerization reaction of vinyl chloride, promote the polymerization reaction of vinyl chloride monomers, ensure the conversion rate of vinyl chloride monomers, and effectively shorten the polymerization time of polyvinyl chloride; 2. In step 1 of the present application, α-methylstyrene dimer is also added as a chain transfer agent. By adding α-methylstyrene dimer, the process of chain transfer can be precisely controlled in the polymerization reaction, enabling the termination of molecular weight growth and the initiation of new chains to proceed relatively uniformly, effectively reducing the occurrence of side reactions in the polymerization reaction; 3. In step 1 of the present application, calcium stearate is also added as a heat stabilizer. Through the cooperation between calcium stearate and α-methylstyrene dimer, calcium stearate can promptly capture the unstable free radicals generated in the reaction system, reducing the further degradation or side reactions of polyvinyl chloride caused by these free radicals, and effectively improving the thermal stability of polyvinyl chloride. Detailed implementation mode

[0027] The raw materials in the present application include the following parts: Cumyl peroxyneodecanoate: A commercially available product with a CAS number of 26748-47-0; Tert-amyl peroxyneodecanoate: A commercially available product with a CAS number of 68299-16-1; Tert-pentyl peroxyisononanoate: A commercially available product with a CAS number of 2851-32-7; Compound dispersant: Polyvinyl alcohol with hydrolysis degrees of 72.5%, 88%, and 55%, a commercially available product with a CAS number of 9002-89-5; Neutralizing agent: Sodium hydroxide, a commercially available product with a CAS number of 1310-73-2; Terminator: p-tert-butylcatechol, a commercially available product with a CAS number of 98-29-3; Chain transfer agent: α-methylstyrene dimer, a commercially available product with a CAS number of 6362-80-7; Mercaptoacetic acid, a commercially available product with a CAS number of 68-11-1; Dodecyl mercaptan, a commercially available product with a CAS number of 112-55-0; Heat stabilizer: Calcium stearate, a commercially available product with a CAS number of 1592-23-0; Dibasic lead phosphite, a commercially available product with a CAS number of 12141-20-7; Dibutyltin maleate, a commercially available product with a CAS number of 78-04-6.

[0028] The present application will be further described in detail below with reference to examples and comparative examples.

[0029] Example 1 A preparation method of polyvinyl chloride, comprising the following steps: Step 1: Add 53 kg of cold demineralized water, 3 kg of compound dispersant, 0.07 kg of compound initiator, 100 kg of vinyl chloride monomer and 51 kg of hot demineralized water into a polymerization kettle for stirring reaction. The reaction temperature is 55 °C and the reaction pressure is 0.85 MPaG to obtain a mixture; Step 2: When the reaction pressure in the polymerization kettle drops to 0.73 MPaG, add a neutralizing agent and a terminator into the polymerization kettle to terminate the reaction. After discharging, a polyvinyl chloride slurry is obtained; Step 3: Strip off the unreacted vinyl chloride monomer by steam stripping and obtain polyvinyl chloride powder by centrifugal drying.

[0030] The configuration ratio of the compound initiator is as follows: 100 g of the compound initiator includes 55 g of cumyl peroxyneodecanoate and 45 g of t-amyl peroxyneodecanoate.

[0031] Examples 2-3 Based on the preparation method of Example 1, Examples 2-3 adjust the component types of the compound initiator, and the specific adjustments are shown in Table 1.

[0032] Comparative Examples 1-3 Based on the preparation method of Example 1, Comparative Examples 1-3 adjust the components of the compound initiator, and the specific adjustments are shown in Table 1.

[0033] Table 1 Component types and component ratios of the compound initiators of Examples 1-3 and Comparative Examples 1-3 (unit: g) Performance detection test Analyze the polyvinyl chloride of the above Examples 1-3 and Comparative Examples 1-3. The specific detection methods are as follows: 1. Vinyl chloride conversion rate Weigh a certain amount of vinyl chloride standard product and dilute it with a solvent into standard solutions with concentrations of 1 mg / L, 5 mg / L, 10 mg / L, 20 mg / L, and 50 mg / L. Use a syringe to respectively suck different concentrations of the standard solutions and inject them into a gas chromatograph for analysis and record the data. Take the concentration of the vinyl chloride standard solution as the abscissa and the corresponding peak area or peak height as the ordinate to draw a standard curve. Through linear regression analysis, obtain the equation of the standard curve.

[0034] Samples were taken from the reaction system before and after the polymerization reaction started, and the samples were processed by diluting them with a suitable solvent to a suitable concentration range. The samples were injected into a gas chromatograph through a syringe for analysis, and the obtained data were recorded and substituted into the equation of the standard curve to obtain the amount of monomer vinyl chloride, thereby calculating the conversion rate of vinyl chloride.

[0035] 2. Polymerization duration After all the reagents were added in Step 1, the starting time of the polymerization reaction was recorded. When the reaction pressure dropped to a predetermined value in Step 2, the end time of the polymerization reaction was recorded, and the polymerization duration was calculated based on the starting time and the end time of the polymerization reaction.

[0036] Table 2 Performance test data table of Examples 1-3 and Comparative Examples 1-3 Referring to Table 2, by comparing Examples 1-3 and Comparative Examples 1-3, it can be seen that the initiator composed of the compounding of cumyl peroxypivalate and tert-amyl peroxypivalate has the best initiation effect. And compared with a single initiator, the compound initiator composed of two initiators can continuously and stably output free radicals at different stages of the vinyl chloride polymerization reaction, enabling the entire polymerization reaction to have a stable and high polymerization efficiency, further improving the conversion rate of vinyl chloride monomer, and effectively shortening the polymerization duration of polyvinyl chloride.

[0037] Examples 4-5 Based on the preparation method of Example 1, Examples 4-5 adjusted the component addition ratio of the compound initiator, and the specific adjustment is shown in Table 3.

[0038] Comparative Examples 4-5 Based on the preparation method of Example 1, Comparative Examples 4-5 adjusted the component addition ratio of the compound initiator, and the specific adjustment is shown in Table 3.

[0039] The polyvinyl chloride of Examples 4-5 and Comparative Examples 4-5 was subjected to the above performance tests, and the test results are shown in Table 3.

[0040] Table 3 Component addition ratio and performance test data table of the compound initiator of Example 1, Examples 4-5 and Comparative Examples 4-5 (unit: g) Referring to Table 3, by comparing Example 1 with Examples 4-7, it can be seen that when the weight ratio of cumyl peroxypivalate to tert-amyl peroxypivalate is 55:45, the conversion rate of vinyl chloride and the polymerization time of polyvinyl chloride are the most ideal. Cumyl peroxypivalate can rapidly decompose to generate free radicals in the early stage of the reaction, enabling the rapid polymerization of polyethylene, while tert-amyl peroxypivalate can stably output free radicals in the later stage to ensure the stable progress of the polymerization reaction. If the content of cumyl peroxypivalate in the compound initiator is too high, the reaction will be too fast in the initial stage of the polymerization process, and side reactions are likely to occur, resulting in a decrease in the conversion rate of vinyl chloride and an extension of the polymerization time. If the content of cumyl peroxypivalate in the compound initiator is too low, the reaction will be relatively slow in the initial stage of the polymerization process, leading to an extension of the polymerization time of polyvinyl chloride.

[0041] Example 8 On the basis of the preparation method of Example 1, in Example 8, the components and their ratios of the compound initiator were adjusted to include 55 parts by weight of cumyl peroxypivalate (concentration 75%), 40 parts by weight of tert-amyl peroxypivalate (concentration 70%), and 5 parts by weight of tert-amyl peroxyisononanoate (concentration 70%). Among them, in Step 1, tert-amyl peroxyisononanoate was added 2 hours after the addition of cumyl peroxypivalate and tert-amyl peroxypivalate.

[0042] Example 9 On the basis of the preparation method of Example 8, in Example 9, tert-amyl peroxyisononanoate was added at the same time as cumyl peroxypivalate and tert-amyl peroxypivalate for the reaction.

[0043] The polyvinyl chloride of Examples 8-9 was subjected to the above performance tests, and the test results are shown in Table 4.

[0044] Table 4 Performance test data table of Examples 1, 8-9 Project Example 1 Example 8 Example 9 Vinyl chloride conversion rate / % 82.4 83.1 82.8 Polymerization duration / min 360 337 348 Referring to Table 4, by comparing Example 1 with Examples 8-9, it can be seen that when three initiators, namely cumyl peroxypivalate, tert-amyl peroxypivalate, and tert-amyl peroxyisononanoate, are compounded into a compound initiator, compared with the compound initiator compounded by two initiators, it can more effectively improve the conversion rate of vinyl chloride and shorten the polymerization reaction of polyvinyl chloride. And by adding tert-amyl peroxyisononanoate 2 hours after the addition of cumyl peroxypivalate and tert-amyl peroxypivalate, when the concentration of vinyl chloride monomer in the reaction system decreases and the reaction activity also decreases, tert-amyl peroxyisononanoate can continue to provide free radicals to ensure the stable progress of the polymerization reaction.

[0045] Examples 10-11 Example 10 - 11 Based on the preparation method of Example 8, the ratio of components in the compound initiator was adjusted, and the specific adjustment is shown in Table 5.

[0046] The polyvinyl chloride of Examples 10 - 11 was subjected to the above performance tests, and the test results are shown in Table 5.

[0047] Table 5 Data table of the component ratio and performance test of the compound initiator in Examples 8 and 10 - 11 (unit: g) Project Example 8 Example 10 Example 11 Cumyl peroxypivalate 55 55 55 Tert-Amyl peroxypivalate 40 35 30 Tert-Pentyl perisononanoate 5 10 15 Vinyl chloride conversion rate / % 83.1 83.5 82.9 Polymerization duration / min 337 348 352 Referring to Table 5, comparing Example 8 and Examples 10 - 11, it can be seen that when the ratio of cumyl peroxyneodecanoate, tert - amyl peroxyneodecanoate, and tert - pentyl peroxyisononanoate is 55:40:5, the polymerization time of polyvinyl chloride is the shortest. On the premise that the content of cumyl peroxyneodecanoate is determined, reducing the content of tert - amyl peroxyneodecanoate will result in insufficient free radicals in the middle stage of the polymerization reaction to promote the polymerization of vinyl chloride, leading to an extended polymerization time.

[0048] Example 12 Example 12 Based on the preparation method of Example 8, α - methylstyrene dimer was added as a chain transfer agent in Step 1 and was added and mixed with other reagents in Step 1, and other conditions remained unchanged.

[0049] Examples 13 - 14 Examples 13 - 14 Based on the preparation method of Example 12, the type of chain transfer agent was adjusted, and the specific adjustment is shown in Table 6.

[0050] The polyvinyl chloride of Examples 13 - 14 was subjected to the above performance tests, and the test results are shown in Table 6.

[0051] Table 6 Types of chain transfer agents and their performance test data tables in Examples 8 and 12 - 14 Referring to Table 6, comparing Example 8 and Examples 12 - 14, it can be seen that adding a chain transfer agent to the reaction system can effectively reduce the side reactions occurring during the polymerization reaction, thereby improving the conversion rate of vinyl chloride. Among them, adding α - methylstyrene dimer as a chain transfer agent is more effective in improving the conversion rate of vinyl chloride in the polymerization reaction.

[0052] Example 15 Example 15 Based on the preparation method of Example 12, calcium stearate was added as a heat stabilizer in Step 1 and was added and mixed with other reagents in Step 1, and other conditions remained unchanged.

[0053] Example 16 Example 16 Based on the preparation method of Example 15, the heat stabilizer was adjusted to dibasic lead phosphite.

[0054] Example 17 Example 17 Based on the preparation method of Example 15, the heat stabilizer was adjusted to dibutyltin maleate.

[0055] Example 18 Example 18 Based on the preparation method of Example 16, the chain transfer agent was adjusted to mercaptoacetic acid.

[0056] The polyvinyl chloride of Examples 15 - 18 was subjected to the above performance tests, and the test results are shown in Table 7.

[0057] Table 7 Performance test data table of Examples 12 and Examples 15 - 18 Referring to Table 7, by comparing Example 12 and Examples 15 - 18, it can be seen that adding calcium stearate as a heat stabilizer in the reaction system has a more significant effect on improving the conversion rate of vinyl chloride. The presence of the heat stabilizer can improve the stability of polyvinyl chloride at high temperatures, making it less likely to degrade at high temperatures and reducing the loss of vinyl chloride monomer caused by chain breakage, thereby increasing the conversion rate of vinyl chloride. Among them, although the effect obtained by the combination of mercaptoacetic acid and dibasic lead phosphite is better than that obtained by the combination of other heat stabilizers and chain transfer agents in this application, the conversion rate of vinyl chloride and the polymerization duration obtained by the combination of calcium stearate and α-methylstyrene dimer are more ideal.

[0058] Examples 19 - 22 Examples 19 - 22 Based on the preparation method of Example 8, the reaction temperature in Step 1 and the reaction pressure before adding the neutralizing agent and terminating agent in Step 2 were adjusted, and the specific adjustments are shown in Table 8.

[0059] The polyvinyl chloride of Examples 19 - 22 was subjected to the above performance tests, and the test results are shown in Table 8.

[0060] Table 8 Temperature and performance test data table of Example 1 and Examples 19 - 22 Referring to Table 8, by comparing Example 1 with Examples 19 - 22, it can be seen that when the temperature is in the range of 54 - 56 °C, the movement of molecules in the reaction system speeds up, increasing the effective collision frequency between molecules, thereby accelerating the polymerization reaction. At this time, the initiation efficiency of the compound initiator is relatively high, which can quickly decompose to generate free radicals, thus shortening the polymerization time of polyvinyl chloride. And when the pressure is between 0.72 - 0.74 MPaG, the conversion rate of vinyl chloride is at an ideal level. When the pressure is too high when adding the neutralizer and terminator, a large amount of vinyl chloride monomers will be terminated without reaction. When the pressure is too high when adding the neutralizer and terminator, it will lead to over-polymerization of polyvinyl chloride, hindering the diffusion of vinyl chloride monomers to the active center, thereby affecting the conversion rate of vinyl chloride.

[0061] This specific embodiment is only an interpretation of the present application, and it does not limit the present application. After reading this specification, those skilled in the art can make modifications to this embodiment without creative contributions as needed, but as long as it is within the scope of the claims of the present application, it is protected by the patent law.

Claims

1. A method for preparing polyvinyl chloride, characterized in that: The following steps are involved: Step 1: stirring cold desalted water, a compound dispersant, a compound initiator, vinyl chloride monomer and hot desalted water to obtain a mixture; Step 2: adding a neutralizing agent and a terminator to the mixture to terminate the reaction and obtain a polyvinyl chloride slurry; Step 3: removing unreacted vinyl chloride monomer and centrifugally drying to obtain polyvinyl chloride powder; The composite initiator comprises at least two of cumyl peroxyneodecanoate, tert-amyl peroxyneodecanoate and tert-amyl peroxyisononanoate.

2. The method for preparing polyvinyl chloride according to claim 1, characterized in that: The composite initiator is a mixture of cumyl peroxyneodecanoate and tert-amyl peroxyneodecanoate; the mass ratio of cumyl peroxyneodecanoate to tert-amyl peroxyneodecanoate in the composite initiator is 1:0.66-1.

3. The method for preparing polyvinyl chloride according to claim 1, characterized in that: The composite initiator is a mixture of cumyl peroxyneodecanoate, tert-amyl peroxyneodecanoate and tert-amyl peroxyisononanoate; in step 1, cumyl peroxyneodecanoate and tert-amyl peroxyneodecanoate are added for 2 hours before tert-amyl peroxyisononanoate is added.

4. The method for preparing polyvinyl chloride according to claim 3, characterized in that: The composite initiator comprises 55 parts by weight of cumyl peroxyneodecanoate, 35-40 parts by weight of tert-amyl peroxyneodecanoate and 5-10 parts by weight of tert-amyl peroxyisononanoate.

5. The method for preparing polyvinyl chloride according to claim 1, characterized in that: In step 1, a chain transfer agent is also added, and the chain transfer agent includes at least one of α-methylstyrene dimer, thioglycolic acid, and dodecyl mercaptan.

6. The method for preparing polyvinyl chloride according to claim 5, characterized in that: The chain transfer agent is α-methylstyrene dimer.

7. The method for preparing polyvinyl chloride according to claim 1, characterized in that: In step 1, a heat stabilizer is also added, and the heat stabilizer includes at least one of calcium stearate, dibasic lead phosphite, and dibutyltin maleate.

8. The method for preparing polyvinyl chloride according to claim 7, characterized in that: The heat stabilizer is calcium stearate.

9. The method for preparing polyvinyl chloride according to claim 3, characterized in that: In step 1, the reaction temperature is 54-56° C.; in step 2, the reaction pressure before adding the neutralizing agent and the terminator is 0.72-0.74 MPaG.

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