Suspension polymerization method for preparing polyvinylidene fluoride and application thereof

Abstract

The invention provides a suspension polymerization method for preparing polyvinylidene fluoride and application thereof, and the method comprises the following steps: polymerizing polyvinylidene fluoride in a polymerization reactor containing a dispersant, an initiator system, at least one chain transfer agent and water to form a polyvinylidene fluoride suspension; the initiator system comprises at least one first initiator and at least one second initiator, the first initiator being selected from one or more of the following: a peroxide C2-C12 carboxylic acid ester, a peroxide C2-C12 carboxylic acid, a persulfate, a C2-C10 alkyl peroxide, a C2-C12 acyl peroxide; the second initiator is a peroxide carbonate. Polyvinylidene fluoride prepared by the suspension polymerization method has higher molecular weight, higher melting point and wider molecular weight distribution, not only has excellent mechanical property, but also has good processability, wider use temperature range, good corrosion resistance and permeation resistance, excellent heat resistance and ageing resistance, and can be used for preparing the polyvinylidene fluoride material. The method is suitable for preparing the lining layer of the marine dynamic flexible riser.

Description

Technical Field

[0001] The present application relates to the field of polymers, and more specifically to a suspension polymerization method for preparing polyvinylidene fluoride resin, the polyvinylidene fluoride synthesized by the method, and its application in marine dynamic flexible risers. Background Art

[0002] The oil and gas reserves in the ocean are extremely rich worldwide, and the production of marine oil and gas is steadily increasing year by year, accounting for an increasing proportion. Marine dynamic flexible risers are the main structural form connecting underwater production systems and deepwater floating facilities. Compared with steel sea pipes, they are laid in actual complex and harsh marine environments, have short construction periods, are recyclable, and have low engineering costs. They are one of the important facilities for deepwater oil and gas field development projects and play a vital role in deep-sea oil and gas exploitation. With the increase in demand for marine oil and gas resources, deep-sea oil and gas development, exploration and production activities are increasing, and the industry's demand for flexible risers suitable for use in marine environments is also continuing to grow. As of 2017, the global use of marine oil and gas hoses has accumulated 15,341 km, of which 57.4% is used for deepwater oil and gas field development with a water depth of more than 300 meters. At present, with the improvement of domestic deep-sea oil and gas exploitation technology, the annual demand for marine flexible risers is about 2,000 kilometers or more. Among them, there are strict requirements on the selection of materials for the inner lining of marine flexible risers. It is not only required to have a wide operating temperature, good corrosion resistance and permeability resistance, but also high heat resistance and anti-aging performance.

[0003] Among many engineering plastics, polyvinylidene fluoride (PVDF) has good chemical stability and aging resistance, and is more suitable for the inner lining of such flexible pipes. For example, for a 12-inch marine flexible riser, an average of 20 kg of PVDF is required per meter, 40,000 tons of PVDF are required each year, and the market value exceeds 20 billion. However, there are still many serious problems with the PVDF materials in the prior art, such as poor heat resistance, poor environmental stress cracking resistance, and processing performance and mechanical properties that cannot simultaneously meet the use requirements of the inner lining materials for marine flexible risers. People are eager to develop PVDF resins with further improved performance. One idea is to prepare PDVF resins with a wide-bimodal molecular weight distribution. The so-called "wide-bimodal molecular weight distribution" means that the PVDF resin has a wide molecular weight distribution (PDI) and has two peaks of different molecular weights in the molecular weight distribution. These two peaks provide various properties for the PVDF resin, such as excellent mechanical properties, processing properties, etc.

[0004] The existing technical processes for achieving such molecular weight distribution mainly include physical methods and chemical methods. The physical method refers to obtaining PVDF resin with the above molecular weight distribution by physically blending several batches of products with different molecular weights and molecular weight distributions. However, this method is prone to uneven mixing, obvious differences between different batches, and poor stability.

[0005] The chemical method is to specially design the reagents, steps and processes used in the polymerization reaction to make the PVDF product have the desired molecular weight distribution. However, so far, there are very few reports on such chemical methods, and none of them can achieve the expected molecular weight distribution and expected purpose. The common problems of the chemical methods reported in the prior art are: low molecular weight, poor mechanical properties, weather resistance or processing performance, unable to meet the performance requirements of marine flexible risers, and poor durability when used in marine environments.

[0006] Specifically, the above chemical methods include emulsion polymerization and suspension polymerization. The drawback of emulsion polymerization is that the molecular weight of the PVDF resin product is small and the mechanical properties are poor. Although the molecular weight of the PVDF polymer produced by the suspension polymerization method reported so far is relatively higher than that of the emulsion polymerization method, the molecular weight distribution is very narrow, the processing performance is poor, and it is difficult to granulate and extrude, which seriously restricts its industrial application.

[0007] Therefore, the art particularly hopes to develop a novel suspension polymerization method for preparing PVDF resin, which can effectively synthesize polyvinylidene fluoride resin with both wide distribution and bimodal properties. Such PVDF resin also has excellent mechanical properties, processing properties, chemical corrosion resistance, heat resistance and weather resistance, and meets the requirements for the use of marine flexible riser lining materials used in deeper water (water depth>3000m) oil and gas exploration and transportation applications.

[0008] In view of the problems existing in the above-mentioned prior art, the inventors of the present application have unexpectedly developed a suspension polymerization method suitable for preparing PVDF resin through extensive and in-depth research. The PVDF resin synthesized by this method has a wide-bimodal molecular weight distribution and the required properties, solving a long-standing problem in the prior art that has been urgently needed to be solved. Summary of the invention

[0009] The first aspect of the present application provides a suspension polymerization method for preparing polyvinylidene fluoride, the method comprising: in a polymerization reactor containing a dispersant, an initiator system, at least one chain transfer agent and water, allowing vinylidene fluoride to polymerize to form a polyvinylidene fluoride suspension; the initiator system comprises at least one first initiator and at least one second initiator, the first initiator is selected from one or more of the following: peroxidized C2-C12 carboxylic acid ester, peroxidized C2-C12 carboxylic acid, persulfate, C2-C10 alkyl peroxide, C2-C12 acyl peroxide; the second initiator is a peroxidized carbonate.

[0010] According to one embodiment of the first aspect of the present application, the first initiator is selected from at least one of the following: 3-hydroxy-1,1-dimethylbutyl peroxyneodecanoyl, ammonium persulfate, potassium persulfate, isobutyl peroxide, tert-butyl peroxyneodecanoate, benzoyl peroxide, tert-butyl peroxyisobutyrate, tert-butyl peroxypivalate, tert-amyl peroxypivalate, succinic acid peroxide, acetyl peroxide, octanoyl peroxide, decanoyl peroxide, lauroyl peroxide; the first initiator is optionally used together with one or more reducing agents selected from the following: sodium sulfite, sodium bisulfite, sodium trifluoromethylsulfinate, potassium trifluoromethylsulfinate.

[0011] According to one embodiment of the first aspect of the present application, according to another embodiment of the first aspect of the present application, the second initiator is selected from one or more of the following: diisopropyl peroxydicarbonate, di-n-propyl peroxydicarbonate.

[0012] According to one embodiment of the first aspect of the present application, based on 100 wt % of the weight of vinylidene fluoride, the amount of the initiator system is 0.01-1 wt %.

[0013] According to one embodiment of the first aspect of the present application, the weight ratio of the first initiator to the second initiator is 1:20 to 5:1.

[0014] According to one embodiment of the first aspect of the present application, the initiator system is added to the reactor in a manner selected from the following:

[0015] The first initiator is added all at once at the start of the reaction, a portion of the second initiator is added all at once at the start, and the remaining second initiator is added intermittently or continuously during the polymerization reaction;

[0016] The first initiator is added all at once at the start of the reaction, and all the second initiators are added intermittently or continuously during the polymerization reaction;

[0017] At least a portion of the first initiator is added all at once at the start, and the remaining first initiator is added intermittently or continuously during the polymerization reaction, and at least a portion of the second initiator is added all at once at the start, and the remaining second initiator is added intermittently or continuously during the polymerization reaction; or

[0018] All of the first initiator is added intermittently or continuously during the polymerization reaction, and all of the second initiator is added intermittently or continuously during the polymerization reaction.

[0019] According to one embodiment of the first aspect of the present application, the chain transfer agent is a liquid phase chain transfer agent, or a combination of a liquid phase chain transfer agent and a gas phase chain transfer agent.

[0020] According to one embodiment of the first aspect of the present application, the liquid phase chain transfer is selected from one or more of the following: methyl acetate, ethyl acetate, propyl acetate, butyl acetate, dimethyl malonate, diethyl malonate, dipropyl malonate, dibutyl malonate, diethyl carbonate, n-butyl mercaptan, tert-butyl mercaptan, isopropanol, methanol, ethanol, n-butanol, acetone, chloroform, and cyclohexane.

[0021] According to one embodiment of the first aspect of the present application, the gas phase chain transfer agent is selected from one or more of the following: methane, ethane, propane, butane, and hydrogen.

[0022] According to one embodiment of the first aspect of the present application, when the chain transfer agent is a combination of a liquid phase chain transfer agent and a gas phase chain transfer agent, the weight ratio of the liquid phase chain transfer agent to the gas phase chain transfer agent is 30:1 to 6:1.

[0023] According to one embodiment of the first aspect of the present application, based on 100% by weight of vinylidene fluoride, the amount of the chain transfer agent is 0.01-1% by weight.

[0024] According to one embodiment of the first aspect of the present application, the chain transfer agent is added to the reactor in a manner selected from the following:

[0025] The chain transfer agent only includes a liquid chain transfer agent, which is added once at the start of the reaction;

[0026] The chain transfer agent comprises only a liquid chain transfer agent, at least a portion of which is added once at the beginning, and the remaining liquid chain transfer agent is added intermittently or continuously during the polymerization reaction;

[0027] The chain transfer agent only includes liquid chain transfer agent, and all the liquid chain transfer agent is added in an intermittent or continuous manner during the polymerization reaction;

[0028] The chain transfer agent includes a liquid chain transfer agent and a gas chain transfer agent, at least a portion of the liquid chain transfer agent is added once at the start, and the remaining liquid chain transfer agent is added intermittently or continuously during the polymerization reaction, and the gas chain transfer agent is added once at the start of the reaction;

[0029] The chain transfer agent includes a liquid chain transfer agent and a gas chain transfer agent, at least a portion of the liquid chain transfer agent is added once at the start, and the remaining liquid chain transfer agent is added intermittently or continuously during the polymerization reaction; at least a portion of the gas chain transfer agent is added once at the start, and the remaining gas chain transfer agent is added intermittently or continuously during the polymerization reaction;

[0030] The chain transfer agent includes a liquid chain transfer agent and a gas chain transfer agent, and all of the liquid chain transfer agent and the gas chain transfer agent are added at once at the beginning.

[0031] According to one embodiment of the first aspect of the present application, the dispersant is selected from one or more of the following: hydroxymethyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, hydroxypropyl methyl cellulose, cellulose acetate, cellulose acetate phthalate, cellulose phosphate, polyanionic cellulose, polycationic cellulose, polyvinyl alcohol, polyethylene glycol, polypropylene glycol, polyethylene glycol-propylene glycol copolymer, fatty acid polyethylene glycol ester, and polyacrylamide.

[0032] According to one embodiment of the first aspect of the present application, based on 100 weight % of the weight of vinylidene fluoride, the amount of the dispersant used is 0.01-5 weight %.

[0033] According to one embodiment of the first aspect of the present application, the polymerization reaction temperature is 30-70° C., and the polymerization reaction pressure is 6.0-8.0 MPa.

[0034] The second aspect of the present application provides a polyvinylidene fluoride resin having a weight average molecular weight of 1 million to 4 million, a PDI of 3-20, and a molecular weight distribution including two peaks; a melting point of 168-175° C., and a melt index of 0.1-4 g / 10 min.

[0035] According to an embodiment of the second aspect of the present application, the polyvinylidene fluoride resin is prepared by the method of the present invention described above.

[0036] The third aspect of the present application provides a marine dynamic flexible riser, the inner lining of which is made of the polyvinylidene fluoride resin of the present invention.

[0037] In the following specific implementation section, the method, polyvinylidene fluoride resin and application of the present application are further introduced in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 The gel permeation chromatography curve of the PVDF resin prepared in one embodiment of the present application is shown. DETAILED DESCRIPTION

[0039] "Range" disclosed herein is in the form of lower limit and upper limit. It can be one or more lower limits, and one or more upper limits respectively. A given range is defined by selecting a lower limit and an upper limit. The selected lower limit and upper limit define the boundaries of a particular range. All ranges that can be defined in this way are inclusive and combinable, i.e. any lower limit can be combined with any upper limit to form a range. For example, a range of 60-120 and 80-110 is listed for a particular parameter, and it is understood that a range of 60-110 and 80-120 is also expected. In addition, if the minimum range values ​​1 and 2 are listed, and if the maximum range values ​​3, 4 and 5 are listed, the following ranges can all be expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5.

[0040] In this application, unless otherwise specified, the numerical range "ab" represents an abbreviation of any real number combination between a and b, where a and b are real numbers. For example, the numerical range "0-5" means that all real numbers between "0-5" are listed in this document, and "0-5" is just an abbreviation of these numerical combinations.

[0041] In this application, unless otherwise specified, all embodiments and preferred embodiments mentioned herein can be combined with each other to form a new technical solution.

[0042] In this application, unless otherwise specified, all technical features and preferred features mentioned herein can be combined with each other to form a new technical solution.

[0043] In this application, if there is no special explanation, the "including" mentioned herein means open or closed. For example, the "including" may mean that other components not listed may also be included, or only the listed components may be included.

[0044] In the present invention, gaseous vinylidene fluoride monomer is transported into a polymerization reactor, and vinylidene fluoride is polymerized in the presence of a dispersant, an initiator system, at least one chain transfer agent and water to form a polyvinylidene fluoride resin suspension, and the prepared polyvinylidene fluoride resin has the desired ultra-high molecular weight, wide-bimodal molecular weight distribution and the desired properties for marine applications.

[0045] The PVDF polymerization method of the present invention is a suspension polymerization method, and the product generated by the reaction is a PVDF suspension. Unlike the emulsion polymerization method used to prepare PVDF, the method of the present invention does not form a PVDF emulsion after the polymerization reaction due to the absence of an emulsifier, but forms a PVDF suspension in the presence of a dispersant, and the PVDF resin product prepared by the method of the present invention has a molecular weight, molecular weight distribution, processing performance and mechanical strength performance that are significantly different from those of the PVDF resin prepared by the emulsion method. According to a preferred embodiment of the present application, the method of the present invention does not use an emulsifier during the polymerization reaction. According to a preferred embodiment of the present application, the method of the present invention does not use an emulsifier and a stabilizer during the polymerization reaction.

[0046] According to one embodiment of the present application, the initiator system comprises at least one first initiator and at least one second initiator, wherein the first initiator and the second initiator have different properties (such as decomposition temperature, free radicals of different activities), and the (ultra-high) molecular weight and molecular weight distribution of the product polyvinylidene fluoride resin are adjusted by the specially designed initiator type, dosage and addition method of the present invention.

[0047] According to one embodiment of the present application, the first initiator is selected from one or more of the following: peroxidized C2-C12 carboxylic acid esters (preferably peroxidized C2-C12 carboxylic acid C1-C6 alkyl esters), peroxidized C2-C12 carboxylic acids (including monocarboxylic acids, dicarboxylic acids or tricarboxylic acids or higher, etc., preferably dicarboxylic acids), persulfates (preferably ammonium salts, sodium salts or potassium salts), C2-C10 alkyl peroxides, C2-C12 acyl peroxides. According to a preferred embodiment of the present application, the first initiator is selected from one or more of the following: 3-hydroxy-1,1-dimethylbutyl peroxyneodecanoate, ammonium persulfate, potassium persulfate, isobutyl peroxide, tert-butyl peroxyneodecanoate, benzoyl peroxide, tert-butyl peroxyisobutyrate, tert-butyl peroxypivalate, tert-amyl peroxypivalate, peroxysuccinic acid, acetyl peroxide, octanoyl peroxide, decanoyl peroxide, lauroyl peroxide; and the first initiator is optionally used with one or more reducing agents selected from the following: sodium sulfite, sodium bisulfite, sodium trifluoromethylsulfinate, potassium trifluoromethylsulfinate. For example, when the first initiator used is ammonium persulfate, potassium persulfate, or a combination thereof, the first initiator (oxidant) can be used in combination with the above-mentioned one or more reducing agents.

[0048] According to a preferred embodiment of the present application, the first initiator is selected from: tert-amyl peroxypivalate, ammonium persulfate / sodium trifluoromethanesulfinate, or a combination thereof.

[0049] According to another embodiment of the present application, the second initiator is a peroxycarbonate, preferably di(C1-C6 alkyl peroxydicarbonate), more preferably diisopropyl peroxydicarbonate or di-n-propyl peroxydicarbonate, most preferably diisopropyl peroxydicarbonate.

[0050] According to a specific embodiment of the present application, the weight ratio of the first initiator to the second initiator is 1:20 to 5:1, preferably 1:15 to 4:1. According to a preferred embodiment of the present application, when the first initiator is a peroxycarboxylic acid ester (such as tert-amyl peroxypivalate), the weight ratio of the first initiator to the second initiator is 1:1 to 5:1, more preferably 2:1 to 4:1. According to another preferred embodiment of the present application, when the first initiator is a persulfate (such as sodium persulfate, potassium persulfate, ammonium persulfate, or a combination of these persulfates and the above-mentioned reducing agent), the weight ratio of the first initiator to the second initiator is 1:20 to 1:2, more preferably 1:10 to 1:5.

[0051] In the present invention, at least one of the first initiator and the second initiator is not added all at once at the start of the reaction, but is added continuously or intermittently during the polymerization of vinylidene fluoride.

[0052] According to a specific embodiment of the present application, the initiator system is added to the reactor in a manner selected from the following:

[0053] Mode 1: The first initiator is added all at once at the start of the reaction, a portion of the second initiator (e.g., 30% to 90%, preferably 40% to 60%) is added all at once at the start, and the remaining second initiator is added intermittently or continuously during the polymerization reaction;

[0054] Method 2: The first initiator is added at once at the beginning of the reaction, and the second initiator is not added at the beginning of the reaction. Instead, all the second initiator is added intermittently or continuously during the polymerization reaction;

[0055] Mode 3: At least a portion (e.g. 30% to 90%, preferably 40% to 60%) of the first initiator is added at once at the start, and the remaining first initiator is added intermittently or continuously during the polymerization reaction, at least a portion (e.g. 30% to 90%, preferably 40% to 60%) of the second initiator is added at once at the start, and the remaining second initiator is added intermittently or continuously during the polymerization reaction;

[0056] Method 4: The first initiator and the second initiator are not added at the beginning of the reaction, but all of the first initiator is added intermittently or continuously during the polymerization reaction, and all of the second initiator is added intermittently or continuously during the polymerization reaction.

[0057] According to a preferred embodiment of the present application, the initiator system is added in the above-mentioned method 1 or method 2. According to a more preferred embodiment of the present application, when the first initiator is a persulfate (such as sodium persulfate, potassium persulfate, ammonium persulfate, or a combination of these persulfates and the above-mentioned reducing agent), the above-mentioned method 2 is selected to add the initiator system; in other cases, especially when the first initiator is a peroxycarboxylic acid ester (such as tert-amyl peroxypivalate), the above-mentioned method 1 is selected to add the initiator system.

[0058] According to one embodiment of the present application, the ratio of the total weight of the initiator system (all the first initiators and the second initiators) added to the reaction system during the entire polymerization reaction to the total weight of the vinylidene fluoride monomer added to the reaction system during the entire polymerization reaction is 0.01:100 to 1:100, preferably 0.1:100 to 0.8:100, and more preferably 0.3:100 to 0.6:100.

[0059] According to one embodiment of the present application, the chain transfer agent is a liquid phase chain transfer agent, or a combination of a liquid phase chain transfer agent and a gas phase chain transfer agent.

[0060] The liquid phase chain transfer is selected from one or more of the following: methyl acetate, ethyl acetate, propyl acetate, butyl acetate, dimethyl malonate, diethyl malonate, dipropyl malonate, dibutyl malonate, diethyl carbonate, n-butyl mercaptan, tert-butyl mercaptan, isopropanol, methanol, ethanol, n-butanol, acetone, chloroform, cyclohexane; preferably diethyl carbonate, ethyl acetate, or a combination thereof.

[0061] The gas phase chain transfer agent is selected from one or more of the following: methane, ethane, propane, butane, hydrogen; preferably propane.

[0062] According to one embodiment of the present application, when the chain transfer agent is a combination of a liquid phase chain transfer agent and a gas phase chain transfer agent, the weight ratio of the liquid phase chain transfer agent to the gas phase chain transfer agent is 30:1 to 6:1, preferably 20:1 to 10:1.

[0063] According to one embodiment of the present application, the ratio of the total weight of all chain transfer agents added to the reaction system during the entire polymerization reaction to the total weight of the vinylidene fluoride monomer added to the reaction system during the entire polymerization reaction is 0.01:100 to 1:100, preferably 0.08:100 to 0.8:100, and more preferably 0.2:100 to 0.5:100.

[0064] In the polymerization reaction of the present invention, at least one of the gas chain transfer agent and the liquid chain transfer agent is added to the polymerization reactor at one time at the start of the reaction; or at least a portion of at least one of the gas chain transfer agent and the liquid chain transfer agent is added to the reactor at the start of the polymerization reaction, and the remaining portion is added to the reactor continuously or intermittently during the polymerization reaction.

[0065] According to one embodiment of the present application, the chain transfer agent is added to the reactor in a manner selected from the following:

[0066] Mode A: The chain transfer agent only includes a liquid chain transfer agent, which is added once at the start of the reaction;

[0067] Mode B: The chain transfer agent comprises only a liquid chain transfer agent, at least a portion of the liquid chain transfer agent (e.g., 30-60%, preferably 40-50%) is added at once at the beginning, and the remaining liquid chain transfer agent is added intermittently or continuously during the polymerization reaction;

[0068] Mode C: The chain transfer agent includes only a liquid chain transfer agent, and no liquid chain transfer agent is added at the beginning of the reaction, and all the liquid chain transfer agent is added intermittently or continuously during the polymerization reaction;

[0069] Mode D: The chain transfer agent comprises a liquid chain transfer agent and a gas chain transfer agent, at least a portion (e.g. 30-60%, preferably 40-50%) of the liquid chain transfer agent is added all at once at the start, the remaining liquid chain transfer agent is added intermittently or continuously during the polymerization reaction, and the gas chain transfer agent is added all at once at the start of the reaction;

[0070] Mode E: The chain transfer agent comprises a liquid chain transfer agent and a gas chain transfer agent, at least a portion (e.g. 30-60%, preferably 40-50%) of the liquid chain transfer agent is added once at the start, and the remaining liquid chain transfer agent is added intermittently or continuously during the polymerization reaction, at least a portion (e.g. 30-60%, preferably 40-50%) of the gas chain transfer agent is added once at the start, and the remaining gas chain transfer agent is added intermittently or continuously during the polymerization reaction;

[0071] Mode F: The chain transfer agent comprises a liquid chain transfer agent and a gas chain transfer agent, and all of the liquid chain transfer agent and the gas chain transfer agent are added at once at the beginning.

[0072] According to a preferred embodiment of the present application, the chain transfer agent is added by selecting the above-mentioned method B, method C or method D.

[0073] The dispersant used in the polymerization reaction of the present application is preferably an environmentally friendly dispersant of natural origin. According to one embodiment of the present application, the dispersant used for the polymerization reaction is selected from one or more of the following: hydroxymethyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, hydroxypropyl methyl cellulose, cellulose acetate, cellulose acetate phthalate, cellulose phosphate, polyanionic cellulose, polycationic cellulose, polyvinyl alcohol, polyethylene glycol, polypropylene glycol, polyethylene glycol-propylene glycol copolymer, fatty acid polyethylene glycol ester, polyacrylamide; preferably hydroxymethyl cellulose.

[0074] According to one embodiment of the present application, the ratio of the total weight of all dispersants added to the reaction system during the entire polymerization reaction to the total weight of the vinylidene fluoride monomer added to the reaction system during the entire polymerization reaction is 0.01:100 to 5:100, for example, 0.02:100 to 3:100, or 0.04:100 to 1:100, or within the numerical range obtained by combining any two of the above end values.

[0075] According to one embodiment of the present application, the dispersant is added into the polymerization reaction system at one time at the start of the polymerization reaction.

[0076] According to one embodiment of the present application, the polymerization reaction temperature is 30-70°C, preferably 40-60°C, and more preferably 50-55°C.

[0077] According to another embodiment of the present application, the polymerization reaction is carried out under anaerobic conditions, for example, the oxygen content in the reactor for carrying out the polymerization reaction is less than 50 ppm.

[0078] According to another embodiment of the present application, the vinylidene fluoride monomer in gaseous form is charged into the reactor until the pressure in the reactor reaches 6.0-8.0 MPa, preferably 6.5-7.5 MPa, and more preferably 6.8-7.2 MPa.

[0079] According to an exemplary embodiment of the present application, the method of the present invention is carried out in the following manner:

[0080] 1. Add a dispersant and water (e.g., deionized water) into a polymerization reactor, seal the polymerization reactor and then evacuate it until the oxygen content in the reactor is lower than a preset standard value, e.g., the oxygen content is less than 50 ppm;

[0081] 2. Raise the temperature in the reactor to the reaction temperature mentioned above under stirring, and charge the VDF monomer in supercritical state into the reactor until the pressure mentioned above is reached; (at a pressure higher than 4.5 MPa, the VDF monomer is in a supercritical state)

[0082] 3. At the beginning of the reaction, the initiator is added to the reactor in the manner described above, and at the beginning of the reaction, a portion of the chain transfer agent or no chain transfer agent is added to the reactor as described above;

[0083] 4. During the polymerization reaction, VDF monomer is continuously / intermittently added to keep the pressure in the reactor within the range of ±0.3 MPa of the pressure level mentioned above; and the remaining initiator and chain transfer agent (if no chain transfer agent is added at the beginning of the reaction, all the chain transfer agent) are added to the reactor in an intermittent or continuous manner as described above;

[0084] 5. After the reaction is completed, the obtained polyvinylidene fluoride suspension is washed, dried and granulated to obtain the polyvinylidene fluoride product of the present invention.

[0085] The polyvinylidene fluoride of the present invention has a wide molecular weight distribution, for example, its polydispersity index (PDI, which is the ratio of weight average molecular weight Mw to Mn, the larger the PDI, the wider the molecular weight distribution) is 3-20, preferably 5-15, and more preferably 5.5-10. The molecular weight distribution of the polyvinylidene fluoride of the present invention includes two peaks, one of which is 2 million to 4 million, preferably 2.5 million to 3.5 million; the other peak is 900,000 to 1.8 million, preferably 1 million to 1.7 million, and more preferably 1.1 million to 1.5 million.

[0086] The polyvinylidene fluoride of the present invention has a relatively high molecular weight, and its Mw is 1 million to 4 million, preferably 1.2 million to 3.5 million.

[0087] According to one embodiment of the present application, the melting point of the polyvinylidene fluoride of the present invention is 168-175°C, preferably 170-172°C; the melt index of the polyvinylidene fluoride measured at 230°C and 12.5 kg load is 0.1-4 g / 10 min, preferably 0.5-2.5 g / 10 min.

[0088] As described above, the polyvinylidene fluoride resins in the prior art (polyvinylidene fluoride resins prepared by the existing emulsion polymerization method or suspension polymerization method) cannot achieve the above-mentioned combination of properties.

[0089] The advantages of the present invention are:

[0090] 1. The present invention successfully synthesizes polyvinylidene fluoride resin with ultra-high molecular weight, wide molecular weight distribution and bimodal molecular weight distribution by specially designing the synthesis process. The polyvinylidene fluoride resin has excellent processing performance, mechanical properties, thermal stability, aging resistance, corrosion resistance and permeability resistance, and is suitable for use as the inner lining of flexible risers in deeper oceans;

[0091] 2. The process technology of the present invention is simple and efficient, and all the reagents used are conventional reagents widely used in the art, which can be conveniently used to improve and upgrade existing production lines and processes on an industrial scale.

[0092] The method of the present application is specifically described in the following examples, the purpose of which is to better understand the content of the present application. It should be understood that these examples are merely illustrative and not restrictive. The water used in the examples is deionized water, and the reagents used are all purchased from the market and used directly without further purification.

[0093] Example

[0094] Example 1

[0095] This embodiment uses a vertical reactor with a capacity of 50 L and equipped with a stirring device, a vacuum device, a heating and temperature control device, and a gas / liquid / solid feeding device to carry out the polymerization reaction.

[0096] 30 kg of deionized water and 10 g of hydroxymethyl cellulose were added to a 50 L vertical reactor, and the reactor was sealed and evacuated to remove oxygen therein until the oxygen content therein was less than 50 ppm. At this time, the stirring device was started, and the heating device was started to raise the temperature in the reactor to 50° C. and maintain this temperature throughout the polymerization reaction process.

[0097] The reactor was charged with vinylidene fluoride (VDF) monomer until the pressure in the reactor reached 7 MPa. 40 g of tert-amyl peroxypivalate and 10 g of diisopropyl peroxydicarbonate were added to the reactor at one time, and 40 g of diethyl carbonate was added to start the polymerization reaction.

[0098] During the polymerization reaction, VDF monomer is continuously added to the reactor to keep the pressure in the polymerization reactor at 6.8-7.2 MPa.

[0099] When the cumulative amount of VDF charged into the reactor has reached 5 kg, 20 g of diethyl carbonate is added to the reactor. When the cumulative amount of VDF charged into the reactor has reached 10 kg, 20 g of diethyl carbonate is added to the reactor. When the cumulative amount of VDF charged into the reactor has reached 15 kg, 20 g of diethyl carbonate is added to the reactor. At the same time, after the polymerization reaction starts, 2 g of diisopropyl peroxydicarbonate is added to the reactor every 15 minutes until the reaction ends. A total of 20 kg of VDF monomer is input into the reactor during the entire reaction process.

[0100] After the reaction is completed, the reactor is cooled to room temperature, the pressure is released and the material is discharged into the washing bucket.

[0101] The polyvinylidene fluoride suspension obtained by the polymerization reaction is washed in a washing bucket. Specifically, deionized water twice the weight of the PVDF suspension is added to the washing bucket, the temperature is raised to 70°C, and the PVDF solid material is washed under stirring conditions, and solid-liquid separation is performed after washing. The above washing / separation steps are repeated at least three times, and then the washed PVDF powder is transferred to an oven and dried at 110°C for 4 hours. Finally, the PVDF powder is granulated by a twin-screw extruder and a pelletizer to form a pellet product.

[0102] The molecular weight and distribution of the polyvinylidene fluoride resin product were measured by gel permeation chromatography (GPC). The gel permeation chromatography curve is shown in FIG. Figure 1 As shown; the melt index of the polyvinylidene fluoride resin under a load of 12.5 kg and a temperature of 230°C was measured using an automatic melt indexer, and its melting point was tested using differential scanning calorimetry (DSC); the tensile strength was measured using a universal tensile testing machine; the analysis results are shown in Table 1 below.

[0103] Example 2

[0104] In this example, the same reactor as in Example 1 was used to carry out the suspension polymerization reaction.

[0105] 30 kg of deionized water and 10 g of hydroxymethyl cellulose were added to a 50 L vertical reactor, and the reactor was sealed and evacuated to remove oxygen therein until the oxygen content therein was less than 50 ppm. At this time, the stirring device was started, and the heating device was started to raise the temperature in the reactor to 50° C. and maintain this temperature throughout the polymerization reaction process.

[0106] The reactor was charged with vinylidene fluoride (VDF) monomer until the pressure in the reactor reached 7 MPa. 40 g of tert-amyl peroxypivalate and 10 g of diisopropyl peroxydicarbonate were added to the reactor at one time, and 3 g of propane and 12 g of diethyl malonate were added to start the polymerization reaction.

[0107] During the polymerization reaction, VDF monomer is continuously added to the reactor to keep the pressure in the polymerization reactor at 6.8-7.2 MPa.

[0108] When the cumulative amount of VDF charged into the reactor has reached 5 kg, 6 g of diethyl malonate is added to the reactor. When the cumulative amount of VDF charged into the reactor has reached 10 kg, 6 g of diethyl malonate is added to the reactor. When the cumulative amount of VDF charged into the reactor has reached 15 kg, 6 g of diethyl malonate is added to the reactor. At the same time, after the polymerization reaction starts, 2 g of diisopropyl peroxydicarbonate is added to the reactor every 15 minutes until the reaction ends. A total of 20 kg of VDF monomer is input into the reactor during the entire reaction process.

[0109] After the reaction is completed, the reactor is cooled to room temperature, and the pressure is released to discharge the materials.

[0110] The polyvinylidene fluoride suspension obtained by the polymerization reaction was washed, dried and granulated in the same manner as in Example 1 to obtain a granular product. The various properties of the granular product were characterized as described in Example 1, and the analysis results are shown in Table 1 below.

[0111] Example 3

[0112] In this example, the same reactor as in Example 1 was used to carry out the suspension polymerization reaction.

[0113] 30 kg of deionized water and 10 g of hydroxymethyl cellulose were added to a 50 L vertical reactor, and the reactor was sealed and evacuated to remove oxygen therein until the oxygen content therein was less than 50 ppm. At this time, the stirring device was started, and the heating device was started to raise the temperature in the reactor to 50° C. and maintain this temperature throughout the polymerization reaction process.

[0114] The reactor was charged with vinylidene fluoride (VDF) monomer until the pressure in the reactor reached 7 MPa. 2 g of ammonium persulfate and 1.5 g of sodium trifluoromethylsulfinate were added to the reactor at one time, and 20 g of ethyl acetate was added to start the polymerization reaction.

[0115] During the polymerization reaction, VDF monomer is continuously added to the reactor to keep the pressure in the polymerization reactor at 6.8-7.2 MPa.

[0116] When the cumulative amount of VDF charged into the reactor has reached 5 kg, 10 grams of ethyl acetate is added to the reactor. When the cumulative amount of VDF charged into the reactor has reached 10 kg, 10 grams of ethyl acetate is added to the reactor. When the cumulative amount of VDF charged into the reactor has reached 15 kg, 10 grams of ethyl acetate is added to the reactor. At the same time, after the polymerization reaction begins, 2 grams of diisopropyl peroxydicarbonate are added to the reactor every 15 minutes until the reaction ends. A total of 20 kg of VDF monomer is input into the reactor during the entire reaction process.

[0117] After the reaction is completed, the reactor is cooled to room temperature, and the pressure is released to discharge the materials.

[0118] The polyvinylidene fluoride suspension obtained by the polymerization reaction was washed, dried and granulated in the same manner as in Example 1 to obtain a granular product. The various properties of the granular product were characterized as described in Example 1, and the analysis results are shown in Table 1 below.

[0119] Example 4

[0120] In this example, the same reactor as in Example 1 was used to carry out the suspension polymerization reaction.

[0121] 30 kg of deionized water and 10 g of hydroxymethyl cellulose were added to a 50 L vertical reactor, and the reactor was sealed and evacuated to remove oxygen therein until the oxygen content therein was less than 50 ppm. At this time, the stirring device was started, and the heating device was started to raise the temperature in the reactor to 50° C. and maintain this temperature throughout the polymerization reaction process.

[0122] The reactor was charged with vinylidene fluoride (VDF) monomer until the pressure in the reactor reached 7 MPa. 2 g of ammonium persulfate and 1.5 g of sodium trifluoromethylsulfinate were added to the reactor at one time, and 20 g of ethyl acetate and 3 g of propane were added to start the polymerization reaction.

[0123] During the polymerization reaction, VDF monomer is continuously added to the reactor to keep the pressure in the polymerization reactor at 6.8-7.2 MPa.

[0124] When the cumulative amount of VDF charged into the reactor has reached 5 kg, 10 grams of ethyl acetate is added to the reactor. When the cumulative amount of VDF charged into the reactor has reached 10 kg, 10 grams of ethyl acetate is added to the reactor. When the cumulative amount of VDF charged into the reactor has reached 15 kg, 10 grams of ethyl acetate is added to the reactor. At the same time, after the polymerization reaction begins, 2 grams of diisopropyl peroxydicarbonate are added to the reactor every 15 minutes until the reaction ends. A total of 20 kg of VDF monomer is input into the reactor during the entire reaction process.

[0125] After the reaction is completed, the reactor is cooled to room temperature, and the pressure is released to discharge the materials.

[0126] The polyvinylidene fluoride suspension obtained by the polymerization reaction was washed, dried and granulated in the same manner as in Example 1 to obtain a granular product. The various properties of the granular product were characterized as described in Example 1, and the analysis results are shown in Table 1 below.

[0127] Example 5

[0128] In this example, the same reactor as in Example 1 was used to carry out the suspension polymerization reaction.

[0129] 30 kg of deionized water and 10 g of hydroxymethyl cellulose were added to a 50 L vertical reactor, and the reactor was sealed and evacuated to remove oxygen therein until the oxygen content therein was less than 50 ppm. At this time, the stirring device was started, and the heating device was started to raise the temperature in the reactor to 50° C. and maintain this temperature throughout the polymerization reaction process.

[0130] The reactor was charged with vinylidene fluoride (VDF) monomer until the pressure in the reactor reached 7 MPa. 40 g of tert-amyl peroxypivalate and 10 g of diisopropyl peroxydicarbonate were added into the reactor at one time to start the polymerization reaction.

[0131] During the polymerization reaction, VDF monomer is continuously added to the reactor to keep the pressure in the polymerization reactor at 6.8-7.2 MPa.

[0132] When the cumulative amount of VDF charged into the reactor has reached 5 kg, 20 g of diethyl carbonate is added to the reactor. When the cumulative amount of VDF charged into the reactor has reached 10 kg, 20 g of diethyl carbonate is added to the reactor. When the cumulative amount of VDF charged into the reactor has reached 15 kg, 20 g of diethyl carbonate is added to the reactor. At the same time, after the polymerization reaction starts, 2 g of diisopropyl peroxydicarbonate is added to the reactor every 15 minutes until the reaction ends. A total of 20 kg of VDF monomer is input into the reactor during the entire reaction process.

[0133] After the reaction is completed, the reactor is cooled to room temperature, and the pressure is released to discharge the materials.

[0134] The polyvinylidene fluoride suspension obtained by the polymerization reaction was washed, dried and granulated in the same manner as in Example 1 to obtain a granular product. The various properties of the granular product were characterized as described in Example 1, and the analysis results are shown in Table 1 below.

[0135] Comparative Example 1

[0136] In this comparative example, the suspension polymerization reaction was carried out using the same reactor as in Example 1 and only one initiator.

[0137] 30 kg of deionized water and 10 g of hydroxymethyl cellulose were added to a 50 L vertical reactor, and the reactor was sealed and evacuated to remove oxygen therein until the oxygen content therein was less than 50 ppm. At this time, the stirring device was started, and the heating device was started to raise the temperature in the reactor to 50° C. and maintain this temperature throughout the polymerization reaction process.

[0138] The reactor was charged with vinylidene fluoride (VDF) monomer until the pressure in the reactor reached 7 MPa. 10 g of diisopropyl peroxydicarbonate and 40 g of diethyl carbonate were added into the reactor at one time to start the polymerization reaction.

[0139] During the polymerization reaction, VDF monomer is continuously added to the reactor to keep the pressure in the polymerization reactor at 6.8-7.2 MPa.

[0140] When the cumulative amount of VDF charged into the reactor has reached 5 kg, 20 g of diethyl carbonate is added to the reactor. When the cumulative amount of VDF charged into the reactor has reached 10 kg, 20 g of diethyl carbonate is added to the reactor. When the cumulative amount of VDF charged into the reactor has reached 15 kg, 20 g of diethyl carbonate is added to the reactor. At the same time, after the polymerization reaction starts, 2 g of diisopropyl peroxydicarbonate is added to the reactor every 15 minutes until the reaction ends. A total of 20 kg of VDF monomer is input into the reactor during the entire reaction process.

[0141] After the reaction is completed, the reactor is cooled to room temperature, and the pressure is released to discharge the materials.

[0142] The polyvinylidene fluoride suspension obtained by the polymerization reaction was washed, dried and granulated in the same manner as in Example 1 to obtain a granular product. The various properties of the granular product were characterized as described in Example 1, and the analysis results are shown in Table 1 below.

[0143] Comparative Example 2

[0144] In this comparative example, the suspension polymerization reaction was carried out using the same reactor as in Example 1, using only one initiator, and using only a gas chain transfer agent.

[0145] 30 kg of deionized water and 10 g of hydroxymethyl cellulose were added to a 50 L vertical reactor, and the reactor was sealed and evacuated to remove oxygen therein until the oxygen content therein was less than 50 ppm. At this time, the stirring device was started, and the heating device was started to raise the temperature in the reactor to 50° C. and maintain this temperature throughout the polymerization reaction process.

[0146] The reactor was charged with vinylidene fluoride (VDF) monomer until the pressure in the reactor reached 7 MPa. 10 g of diisopropyl peroxydicarbonate and 3 g of propane were added into the reactor at one time to start the polymerization reaction.

[0147] During the polymerization reaction, VDF monomer is continuously added to the reactor to keep the pressure in the polymerization reactor at 6.8-7.2 MPa.

[0148] After the polymerization reaction started, 2 grams of diisopropyl peroxydicarbonate were added to the reactor every 15 minutes until the reaction was completed. During the entire reaction process, a total of 20 kilograms of VDF monomer was added to the reactor.

[0149] After the reaction is completed, the reactor is cooled to room temperature, and the pressure is released to discharge the materials.

[0150] The polyvinylidene fluoride suspension obtained by the polymerization reaction was washed, dried and granulated in the same manner as in Example 1 to obtain a granular product. The various properties of the granular product were characterized as described in Example 1, and the analysis results are shown in Table 1 below.

[0151] Table 1 Performance test results of polyvinylidene fluoride resins prepared in Examples 1-5 and Comparative Examples 1-2

[0152]

[0153] From the contents shown in Table 1 above, it can be seen that the PVDF resin synthesized by the methods of Examples 1-5 exhibits ultra-high molecular weight, wide PDI, and unique bimodal distribution, and the PVDF resins of these Examples have better melt index and tensile strength, and the final pellets have good processing properties and can be made into high-quality pipes by extrusion molding. In sharp contrast, the melt index of the PVDF resin synthesized by Comparative Examples 1-2 is much worse, the tensile strength is lower than that of the Examples, and it is not possible to smoothly form a uniform pipe during extrusion molding, and it is easy to yellow.

Claims

1. A suspension polymerization method for preparing polyvinylidene fluoride, the method comprising: In a polymerization reactor containing a dispersant, an initiator system, at least one chain transfer agent and water, vinylidene fluoride is polymerized to form a polyvinylidene fluoride suspension; The initiator system comprises at least one first initiator and at least one second initiator, wherein the first initiator is selected from one or more of the following: peroxidized C2-C12 carboxylic acid esters, peroxidized C2-C12 carboxylic acids, persulfates, C2-C10 alkyl peroxides, C2-C12 acyl peroxides; The second initiator is a peroxycarbonate.

2. The suspension polymerization method according to claim 1, characterized in that The first initiator is selected from at least one of the following: 3-hydroxy-1,1-dimethylbutyl peroxyneodecanoate, ammonium persulfate, potassium persulfate, isobutyl peroxide, tert-butyl peroxyneodecanoate, benzoyl peroxide, tert-butyl peroxyisobutyrate, tert-butyl peroxypivalate, tert-amyl peroxypivalate, succinic acid peroxide, acetyl peroxide, octanoyl peroxide, decanoyl peroxide, lauroyl peroxide; the first initiator is optionally used together with one or more reducing agents selected from the following: sodium sulfite, sodium bisulfite, sodium trifluoromethylsulfinate, potassium trifluoromethylsulfinate; The second initiator is selected from one or more of the following: diisopropyl peroxydicarbonate and di-n-propyl peroxydicarbonate.

3. The suspension polymerization method according to claim 1, characterized in that Based on the weight of vinylidene fluoride as 100 weight percent, the amount of the initiator system is 0.01-1 weight percent; And the weight ratio of the first initiator to the second initiator is 1:20 to 5:

1.

4. The suspension polymerization method according to claim 1, characterized in that The initiator system is added to the reactor in a manner selected from the following: The first initiator is added all at once at the start of the reaction, a portion of the second initiator is added all at once at the start, and the remaining second initiator is added intermittently or continuously during the polymerization reaction; The first initiator is added all at once at the start of the reaction, and all the second initiators are added intermittently or continuously during the polymerization reaction; At least a portion of the first initiator is added all at once at the start, and the remaining first initiator is added intermittently or continuously during the polymerization reaction, and at least a portion of the second initiator is added all at once at the start, and the remaining second initiator is added intermittently or continuously during the polymerization reaction; or All of the first initiator is added intermittently or continuously during the polymerization reaction, and all of the second initiator is added intermittently or continuously during the polymerization reaction.

5. The suspension polymerization method according to claim 1, characterized in that The chain transfer agent is a liquid phase chain transfer agent, or a combination of a liquid phase chain transfer agent and a gas phase chain transfer agent; The liquid phase chain transfer is selected from one or more of the following: methyl acetate, ethyl acetate, propyl acetate, butyl acetate, dimethyl malonate, diethyl malonate, dipropyl malonate, dibutyl malonate, diethyl carbonate, n-butyl mercaptan, tert-butyl mercaptan, isopropanol, methanol, ethanol, n-butyl alcohol, acetone, chloroform, cyclohexane; The gas phase chain transfer agent is selected from one or more of the following: methane, ethane, propane, butane, hydrogen; When the chain transfer agent is a combination of a liquid phase chain transfer agent and a gas phase chain transfer agent, the weight ratio of the liquid phase chain transfer agent to the gas phase chain transfer agent is 30:1 to 6:1; Based on the weight of vinylidene fluoride as 100 weight percent, the amount of the chain transfer agent is 0.01-1 weight percent; The chain transfer agent is added to the reactor in a manner selected from the following: The chain transfer agent only includes a liquid chain transfer agent, which is added once at the start of the reaction; The chain transfer agent comprises only a liquid chain transfer agent, at least a portion of which is added once at the beginning, and the remaining liquid chain transfer agent is added intermittently or continuously during the polymerization reaction; The chain transfer agent only includes liquid chain transfer agent, and all the liquid chain transfer agent is added in an intermittent or continuous manner during the polymerization reaction; The chain transfer agent includes a liquid chain transfer agent and a gas chain transfer agent, at least a portion of the liquid chain transfer agent is added once at the start, and the remaining liquid chain transfer agent is added intermittently or continuously during the polymerization reaction, and the gas chain transfer agent is added once at the start of the reaction; The chain transfer agent includes a liquid chain transfer agent and a gas chain transfer agent, at least a portion of the liquid chain transfer agent is added once at the start, and the remaining liquid chain transfer agent is added intermittently or continuously during the polymerization reaction; at least a portion of the gas chain transfer agent is added once at the start, and the remaining gas chain transfer agent is added intermittently or continuously during the polymerization reaction; The chain transfer agent includes a liquid chain transfer agent and a gas chain transfer agent, and all of the liquid chain transfer agent and the gas chain transfer agent are added at once at the beginning.

6. The suspension polymerization method according to claim 1, characterized in that The dispersant is selected from one or more of the following: hydroxymethyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, hydroxypropyl methyl cellulose, cellulose acetate, cellulose acetate phthalate, cellulose phosphate, polyanionic cellulose, polycationic cellulose, polyvinyl alcohol, polyethylene glycol, polypropylene glycol, polyethylene glycol-propylene glycol copolymer, fatty acid polyethylene glycol ester, polyacrylamide; Based on 100% by weight of vinylidene fluoride, the amount of the dispersant used is 0.01-5% by weight.

7. The method according to claim 1, characterized in that The polymerization reaction temperature is 30-70° C., and the polymerization reaction pressure is 6.0-8.0 MPa.

8. A polyvinylidene fluoride resin having a weight average molecular weight of 1 million to 4 million, a PDI of 3-20, and a molecular weight distribution including at least two peaks; Its melting point is 168-175°C and its melt index is 0.1-4 g / 10 min.

9. The polyvinylidene fluoride according to claim 8, which is prepared by the method according to any one of claims 1 to 7.

10. A marine dynamic flexible riser, wherein the inner lining layer is made of the polyvinylidene fluoride resin according to claim 8 or 9.

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