A hyperbranched polyvinylidene fluoride resin synthesized controllably by using a chain transfer agent and preparation and application thereof

Abstract

The present application relates to a kind of hyperbranched polyvinyl fluoride resin and its preparation and application using chain transfer agent controllable synthesis.The method includes: under the condition of using at least one initiator, at least one chain transfer agent, at least one emulsifier, polyvinyl fluoride is polymerized;The chain transfer agent is at least one chain transfer agent with multiple chain transfer sites (≥2) or the combination of liquid phase transfer agent and gas phase transfer agent forms multiple chain transfer sites.Compared with prior art, the polyvinyl fluoride resin prepared in the present application has hyperbranched configuration, and has higher molecular weight and wider molecular weight distribution, and has high mechanical strength and excellent processing performance.

Description

Technical Field

[0001] This invention relates to the field of polymers, and in particular to a hyperbranched polyvinylidene fluoride resin that can be synthesized in a controlled manner using a chain transfer agent, as well as its preparation and application. Background Technology

[0002] Traditional linear polyvinylidene fluoride (PVDF) holds a significant position in petrochemical, new energy, and specialty functional materials fields due to its superior comprehensive properties. However, there is an irreconcilable contradiction between its performance advantages and processing performance. PVDF's high performance relies on its high molecular weight (>600,000 g / mol). While increasing the molecular weight can enhance its mechanical properties, it leads to an exponential increase in melt viscosity, with the melt index (MFI) dropping as low as 0.2-3 g / 10 min, creating a serious processing bottleneck. Extrusion / injection molding requires high temperatures (250-265 ℃) and high pressures, and is prone to surface defects such as "sharkskin." During blow molding, insufficient melt strength can lead to significant deviations in preform wall thickness. Rapid cooling generates internal stress, making the processed products prone to cracking, requiring complex annealing processes for repair, which extends the production cycle and reduces production efficiency.

[0003] To address the high viscosity processing challenges of traditional linear PVDF, the industry primarily employs methods such as additive-assisted processing, blending modification, and molecular weight reduction. Additive-assisted processing involves incorporating plasticizers or lubricants to improve melt flow properties. However, small-molecule plasticizers are prone to migration and precipitation, leading to reduced toughness, embrittlement, media contamination, and decreased chemical resistance in long-term use. This results in dimensional changes in the molded product, poor joint sealing, and pipe leaks, failing to meet the requirements of dynamic flexible risers in complex operating conditions. Blending modification involves blending organic polymers or inorganic nanoparticles with PVDF to improve processing flowability. For example, when PMMA is blended with PVDF, the carbonyl groups in PMMA's molecular chain form hydrogen bonds with the fluorine atoms of PVDF, disrupting the PVDF's crystalline structure and reducing melt viscosity by 30%–40%, increasing the melt viscosity (MFI) to 10–15 g / 10 min. However, this method suffers from poor compatibility and is prone to phase separation. When inorganic nanoparticles such as Al2O3 are blended with PVDF, the nano-Al2O3 acts as a heterogeneous nucleation point to refine the grains and reduce the size of the crystalline region, which can reduce the melt viscosity by 30%. However, inorganic nanoparticles are prone to agglomeration, which leads to an increase in viscosity and can clog processing equipment. Adding a large amount of chain transfer agent can reduce the molecular weight of PVDF to improve the molecular weight fraction (MFI) and significantly improve processing performance, but this will severely sacrifice the mechanical properties of the material and produce a large amount of low molecular weight PVDF, which will lead to changes in the material's heat resistance and accelerated aging at high temperatures.

[0004] Patent application CN119080980A discloses a polyvinylidene fluoride (PVDF) resin with a broad bimodal molecular weight distribution, its preparation method, and its applications. The method involves polymerizing PVDF using a compound initiator, at least one chain transfer agent, and at least one emulsifier. The PVDF resin prepared by this invention not only possesses excellent mechanical properties but also good processability, a wide operating temperature range, and good corrosion and permeation resistance. However, the method in this patent can only control the molecular weight distribution of PVDF but does not change the linear topology of the polymer. Essentially, it still improves processability by introducing low molecular weight components, which may result in a sacrifice of mechanical properties and long-term stability.

[0005] Therefore, in order to overcome the contradiction between performance and processing of traditional linear PVDF, a solution based on molecular structure innovation is urgently needed. Summary of the Invention

[0006] The purpose of this invention is to provide a method for the controlled synthesis of hyperbranched polyvinylidene fluoride resin using a chain transfer agent to solve at least one of the above problems. This method can overcome the contradiction between performance and processing of traditional linear PVDF, realize the controlled synthesis of hyperbranched PVDF, and the obtained PVDF has good mechanical properties as well as being easy to process.

[0007] The objective of this invention can be achieved through the following technical solutions: In one aspect, the present invention provides a method for the controlled synthesis of hyperbranched polyvinylidene fluoride resin using a chain transfer agent. In a polymerization reaction system containing an initiator, a chain transfer agent, and an emulsifier, polyvinylidene fluoride is polymerized. The chain transfer agent is a chain transfer agent containing multiple chain transfer sites, or a compound chain transfer agent formed by combining it with at least one of a liquid-phase transfer agent and a gas-phase transfer agent.

[0008] In a second aspect, the present invention provides a hyperbranched polyvinylidene fluoride resin, prepared by the method described in the first aspect above, having a weight-average molecular weight of 500,000 to 2,200,000, a branching factor of 0.3 to 0.8, a molecular weight distribution index of 2 to 12, a melt index of 0.1 to 10 g / 10 min (230°C, 10 kg load), and a melting point of 150 to 175°C. o C, tensile strength 40.0~60.0 MPa.

[0009] In a third aspect, the present invention provides the application of hyperbranched polyvinylidene fluoride resin in the preparation of an internal pressure sealing layer material for marine flexible risers under high temperature and high pressure conditions.

[0010] Compared with the prior art, the present invention has the following beneficial effects: (1) By using chain transfer agents with multiple chain transfer sites alone or by combining chain transfer agents with single and multiple sites, the chain transfer activity and the growth path of branching points in the free radical reaction process can be precisely controlled, thereby preparing hyperbranched PVDF resin with a highly branched topology.

[0011] (2) The polyvinylidene fluoride resin prepared by the present invention has both high mechanical strength and excellent processing performance, and is particularly suitable for manufacturing the inner lining of marine dynamic flexible risers. It can meet the stringent requirements for material weather resistance, permeability resistance and long-term reliability in deep-sea oil and gas extraction. Detailed Implementation

[0012] The present invention will now be described in detail with reference to specific embodiments. These embodiments are based on the technical solution of the present invention and provide detailed implementation methods and specific operating procedures. However, the scope of protection of the present invention is not limited to the following embodiments.

[0013] For simplicity, this application only explicitly discloses some numerical ranges. However, any lower limit can be combined with any upper limit to form a range not explicitly stated; and any lower limit can be combined with other lower limits to form a range not explicitly stated, just as any upper limit can be combined with any other upper limit to form a range not explicitly stated. Furthermore, although not explicitly stated, each point or individual value between the endpoints of a range is included within that range. Therefore, each point or individual value can be used as its own lower or upper limit and combined with any other point or individual value, or combined with other lower or upper limits, to form a range not explicitly stated. In the description of this application, it should be noted that, unless otherwise stated, "above" includes the stated number, and "multiple" in "one or more" means two or more.

[0014] The foregoing description of this application is not intended to describe every disclosed implementation or method. Instead, the following description provides more specific examples of exemplary embodiments. Throughout the application, guidance is provided through a series of embodiments that can be used in various combinations. The examples listed are representative only and should not be construed as exhaustive.

[0015] Numerous details are explored in the following description to provide a more thorough explanation of embodiments of this application; however, it will be apparent to those skilled in the art that embodiments of this application may be practiced without these specific details.

[0016] The purpose of this invention is to provide a controllable synthesis method for hyperbranched polyvinylidene fluoride (PVDF) resin. This method is based on an emulsion polymerization system and precisely controls the chain transfer activity and the growth path of branching points during the free radical reaction process by using a chain transfer agent with multiple chain transfer sites alone or by combining a combination of single-site and multi-site chain transfer agents. This results in the preparation of a hyperbranched PVDF resin with a highly branched topology, which possesses both high mechanical strength and excellent processing performance.

[0017] To further understand the present invention, the following embodiments are provided. It is worth noting that, unless otherwise specified, all raw materials used in the present invention are commercially available; and all methods and equipment employed are common in the art.

[0018] To overcome the contradiction between performance and processing of traditional linear PVDF, some embodiments provide a method for the controlled synthesis of hyperbranched polyvinylidene fluoride resin using a chain transfer agent. In a polymerization reaction system containing an initiator, a chain transfer agent, and an emulsifier, vinylidene fluoride is polymerized. The chain transfer agent is a chain transfer agent containing multiple chain transfer sites (≥2), or a compound chain transfer agent formed by combining it with at least one of a liquid-phase transfer agent and a gas-phase transfer agent.

[0019] In some other specific embodiments, the amount of the initiator is 0.01 to 1% of the mass of vinylidene fluoride, and for example, it can be any value within the range of 0.01%, 0.05%, 0.1%, 0.5%, 1%, etc.; the amount of the chain transfer agent is 0.01 to 1% of the mass of vinylidene fluoride, and for example, it can be any value within the range of 0.01%, 0.05%, 0.1%, 0.5%, 1%, etc.; the amount of the emulsifier is 0.1 to 3% of the mass of vinylidene fluoride, and for example, it can be any value within the range of 0.1%, 0.5%, 1%, 2%, 3%, etc.

[0020] In other specific embodiments, the chain transfer agent containing multiple chain transfer sites is selected from one or more of pentaerythritol tetrakis(3-mercaptopropionic acid), trimethylolpropane tris(3-mercaptopropionate), mercaptoethanol, 1,4-butanedithiol, 1,6-hexanedithiol, tris(2-mercaptoethyl)amine, glycerol trimercaptopropionate, 1,3,5-benzenetrithiol, 4,4'-thiodiphenylthiol, pentaerythritol tetrakis(3-mercaptobutyrate), pentaerythritol tetrakis(2-(dithiobenzoyl)thiopropionate), glucose pentathiopropionate, and tetrakis(dimethylsiloxy)silane glucose thiopropionate.

[0021] In some other specific embodiments, when the chain transfer agent is a compound chain transfer agent, the total amount of the liquid-phase chain transfer agent and / or the gas-phase chain transfer agent is used in a mass ratio of 15 to 25:1 to the chain transfer agent containing multiple chain transfer sites. In a more preferred embodiment, the liquid-phase chain transfer agent is selected from at least one of methyl acetate, ethyl acetate, propyl acetate, butyl acetate, dimethyl malonate, diethyl malonate, dipropyl malonate, dibutyl malonate, diethyl carbonate, n-butanethiol, tert-butanethiol, n-octanethiol, dodecyl mercaptan, tert-dodecyl mercaptan, chloroform, and methanol; the gas-phase chain transfer agent is selected from at least one of methane, ethane, propane, butane, and hydrogen.

[0022] In some other specific embodiments, the initiator includes one or more of the following: cyclohexanone peroxide, tert-butyl peroxyacetate, tert-butyl peroxybenzoate, n-butyl 4,4-bis(tert-butylperoxy)valerate, di-tert-butyldisperoxyisophthalate, methyl ethyl ketone peroxide, di-tert-butyl peroxide, di-tert-pentyl peroxide, cumene hydroperoxide, di-cumene peroxide, tert-butyl cumene peroxide, 1,1,3,3-tetramethyl hydroperoxide, tert-butanol peroxide, tert-butyl peroxylaurate, tert-butyl peroxy-3,5,5-trimethylhexanoate, ammonium persulfate, potassium persulfate, isobutyl peroxide, diisopropyl peroxydicarbonate, di-n-propyl peroxydicarbonate, tert-butyl peroxyneodecanate, benzoyl peroxide, tert-butyl peroxyisobutyrate, tert-butyl peroxyneodecanate, succinic acid peroxide, acetyl peroxide, octanoyl peroxide, decanoyl peroxide, and lauroyl peroxide.

[0023] In other specific embodiments, the emulsifier is perfluorohexylacetic acid, perfluoropentylacetic acid, perfluoropentylphenylacetic acid, 4,4,5,5,6,6,6-heptafluoro-3,3-bis(trifluoromethyl)heptanoic acid, 4,4,5,5,6,6,6-heptafluoro-3,3-bis(trifluoromethyl)phenylhexanoic acid, 4-(2,2,3,3,5,5,5-heptafluoro-4,4-bis(trifluoromethyl)pentyl)benzoic acid, perfluorodioxane-heptacarbonate, perfluorotrioxane-heptacarbonate, perfluorodioxane-octacarbonate, branched perfluoropolyether mixtures, linear perfluoropolyether mixtures, sodium dodecyl sulfate, sodium dodecyl sulfate, sodium tetradecyl sulfonate, sodium tetradecylbenzene sulfonate, sodium dodecyl diphenyl ether disulfonate, sodium hexadecyl sulfonate, sodium hexadecyl sulfate, sodium hexadecyl sulfate, sodium hexadecyl sulfate, sodium octyl sulfonate, sodium octyl sulfate, polypropylene glycol (Mn At least one of the following: 200~2000), polyethylene glycol (Mn 200~2000), polyethylene glycol-propylene glycol copolymer (Mn 200~2000), isomeric tridecyl polyoxyethylene ether, octyl polyoxyethylene ether, and dodecyl polyoxyethylene ether.

[0024] In some specific embodiments, the polymerization reaction system also contains a stabilizer, the amount of which is 0-5% of the mass of vinylidene fluoride. Preferably, the amount of stabilizer is not zero; when the amount of stabilizer is zero, it means that no stabilizer needs to be added. In a more preferred embodiment, the stabilizer is at least one of paraffin wax (exemplarily, paraffin wax No. 50, paraffin wax No. 58, paraffin wax No. 60, etc.) and long-chain alkanes, wherein the long-chain alkanes are one or more of dodecyl, hexadecyl, octadecyl, and eicosyl.

[0025] In other specific embodiments, the polymerization reaction is carried out at a temperature of 50~130°C and a pressure of 2.0~5.0 MPa.

[0026] Specifically, the preparation method of the present invention can be as follows: The reaction process includes the following steps: 1. Add deionized water, stabilizer, and emulsifier to the polymerization reactor, evacuate, and remove oxygen until the oxygen content is within acceptable limits; 2. Start stirring, raise the reactor temperature to 50-130℃, add a certain amount of an initiator, and add a certain amount of one or more chain transfer agents; 3. Add VDF monomer and continuously replenish VDF monomer, maintaining the polymerization reaction pressure at 2.0-5.0 MPa; 4. During the reaction, replenish a certain amount of an initiator in a specific manner, and simultaneously replenish a certain amount of one or more chain transfer agents; 5. After the reaction is complete, the obtained polyvinylidene fluoride emulsion is subjected to coagulation and demulsification, washing, drying, and granulation to obtain granular products.

[0027] In other specific embodiments, the initiator is added to the polymerization reaction system all at the beginning of the reaction; or a portion of the initiator is added at the beginning of the reaction, and the remaining initiator is added to the polymerization reaction system intermittently or continuously during the polymerization reaction. Similarly, one of the chain transfer agents can be added to the polymerization reaction system all at the beginning of the reaction; or a portion of the chain transfer agent is added at the beginning of the reaction, and the remaining chain transfer agent is added to the polymerization reaction system intermittently or continuously during the polymerization reaction; or no chain transfer agent is added at the beginning of the reaction, but only intermittently or continuously during the polymerization reaction.

[0028] Each of the above implementation methods can be implemented individually, or they can be combined in any two or more combinations based on logical consistency.

[0029] The above implementation methods will be described in more detail below with reference to specific embodiments.

[0030] The properties of the hyperbranched polyvinylidene fluoride (PVDF) resin synthesized in this invention were tested and characterized by the following methods: (1) Molecular weight and molecular weight distribution Molecular weight and molecular weight distribution were determined using the methods described in ISO 16014-1, -2, -4 via high-temperature gel permeation chromatography (GPC, Waters, Styragel HR5, Waters Technologies, Milford, Massachusetts). Specific details are as follows: a PVDF sample solution with a concentration of 5 mg / mL was prepared, using DMF (containing 50 mmol / L lithium bromide) as the mobile phase at a flow rate of 1.0 mL / min and a column temperature of 50 °C. Detection was performed using a GPC system calibrated with narrow-distribution polystyrene standards via a differential refractive index detector. The relative weight-average molecular weight (Mb) of the polymer was calculated based on the elution volume versus calibration curve. w Number-average molecular weight (M) n ) and molecular weight distribution index (PDI).

[0031] (2) Branching factor (g') The radius of gyration of each fraction eluted from gel permeation chromatography (GPC, as described above) was determined by analyzing light scattering at different angles using multi-angle laser light scattering (MALLS, Waytt, Down 8 detector, Wyatt Technologies, Santa Barbara, California). The laser source used had a wavelength of 658 nm and a power of 120 mW. A specific refractive index was taken as 0.104 ml / g. Data were evaluated using WyattASTRA 4.7.3 and CORONA 1.4 software. The branching factor was determined as described below.

[0032] The parameter g' is the ratio of the mean square radius of gyration of the measured sample to that of a linear polymer with the same molecular weight. A linear molecule shows a g' of 1, while a value less than 1 indicates the presence of branched structures. The value of g' as a function of molecular weight M is calculated from the equation: g'(M) = <Rg 2 > 样品，M / <Rg 2 > 线性参考，M in, <Rg 2 > is the mean square radius of gyration of the fraction with molecular weight M. <Rg 2 > 线性参考，M The linear PVDF reference can be measured using the same apparatus and method described above to confirm this.

[0033] (3) Melt index The test was conducted according to ISO 1133 standard using a fully automated plastic melt index tester (GT-7200-MIA, High-Speed ​​Rail Testing Instruments (Dongguan) Co., Ltd.). Test conditions were: temperature 230 ℃, load 10.0 kg. Preheating time was 5 minutes, followed by automatic cutting and weighing of the polymer extruded within the specified time. Results are expressed in g / 10 min.

[0034] (4) Melting point The test was performed using a differential scanning calorimeter (DSC 250, TA Instruments, USA). Approximately 5-8 mg of sample was weighed and placed in a DSC crucible. Under a nitrogen atmosphere, the temperature was increased from room temperature to 220°C at a rate of 5°C / min and held at this temperature for 3 minutes to eliminate thermal history. The temperature was then decreased to room temperature at a rate of 10°C / min, and finally increased again to 220°C at a rate of 10°C / min. The second heating curve was recorded, and the peak temperature of the endothermic peak was determined as the melting point of the polymer. T m (5) Mechanical properties Tests were performed using a universal testing machine (68TM-5, Instron, Norwood, Massachusetts) according to ISO 527-1 standard. Polymer samples were prepared into Type 1A standard tensile specimens by compression molding or injection molding and tested at a tensile rate of 50 mm / min at room temperature until the specimen broke. Stress-strain curves were recorded, and the tensile strength (in MPa) was reported.

[0035] Example 1 Diisopropyl peroxide (initiator) was initially added, followed by continuous replenishment; pentaerythritol tetrakis(3-mercaptopropionic acid) (a chain transfer agent containing multiple chain transfer sites) and diethyl malonate (a liquid-phase chain transfer agent) were initially added, followed by replenishment in stages, 75 o C reaction.

[0036] Add 35 kg of deionized water, 100 g of No. 50 solid paraffin (stabilizer), and 150 g of a 30 wt% aqueous solution of perfluorohexylacetic acid (emulsifier) ​​to a 50 L horizontal reactor. Perform vacuum deoxygenation on the reaction system until the oxygen content is below 30 ppm. Start stirring and raise the reactor temperature to 75°C. o C. Add vinylidene fluoride monomer, raise the reactor pressure to 4.4 MPa, add 12 g of diisopropyl peroxide dicarbonate, 3 g of diethyl malonate, and 0.2 g of pentaerythritol tetrakis(3-mercaptopropionic acid) ester, and begin the polymerization reaction. Continue to add VDF monomer to maintain the polymerization pressure at 4.4 MPa. During polymerization, add 6 g of diethyl malonate, 3 g of diisopropyl peroxide dicarbonate, and 0.4 g of pentaerythritol tetrakis(3-mercaptopropionic acid) ester every 20 minutes until the total VDF feed reaches 8 kg. After the reaction is complete, release the pressure and discharge the material. The resulting polyvinylidene fluoride emulsion is then subjected to coagulation and demulsification, washing, drying, and granulation to obtain granular products. The vinylidene fluoride resin is analyzed and tested; the results are shown in Table 1 below.

[0037] Example 2 Diisopropyl peroxide dicarbonate was initially added, followed by continuous replenishment; pentaerythritol tetrakis(3-mercaptopropionic acid) ethyl acetate was initially added, followed by replenishment in stages, and the reaction was carried out at 75 °C.

[0038] Add 35 kg of deionized water, 100 g of No. 50 solid paraffin, and 150 g of a 30 wt% perfluorohexylacetic acid ammonium solution to a 50 L horizontal reactor. Perform vacuum deoxygenation on the reaction system until the oxygen content is below 30 ppm. Start stirring and raise the reactor temperature to 75 °C. o C. Add vinylidene fluoride monomer, raise the reactor pressure to 4.4 MPa, add 12 g of diisopropyl peroxide dicarbonate, 5 g of ethyl acetate, and 0.2 g of pentaerythritol tetrakis(3-mercaptopropionic acid) ester, and begin the polymerization reaction. Continue to add VDF monomer to maintain the polymerization pressure at 4.4 MPa. During polymerization, add 8 g of ethyl acetate, 3 g of diisopropyl peroxide dicarbonate, and 0.4 g of pentaerythritol tetrakis(3-mercaptopropionic acid) ester every 20 minutes until the total VDF feed reaches 8 kg. After the reaction, release the pressure and discharge the material. The resulting polyvinylidene fluoride emulsion is then subjected to coagulation and demulsification, washing, drying, and granulation to obtain granular products. The vinylidene fluoride resin is analyzed and tested; the results are shown in Table 1 below.

[0039] Example 3 Diisopropyl peroxide was initially added, followed by continuous additions; propane and pentaerythritol tetrakis(3-mercaptopropionic acid) were initially added, followed by staged additions, and the reaction was carried out at 75 °C. Add 35 kg of deionized water, 100 g of No. 50 solid paraffin, and 150 g of a 30 wt% perfluorohexylacetic acid ammonium solution to a 50 L horizontal reactor. Perform vacuum deoxygenation on the reaction system until the oxygen content is below 30 ppm. Start stirring and raise the reactor temperature to 75 °C. o C. Add vinylidene fluoride monomer, raise the reactor pressure to 4.4 MPa, add 12 g of diisopropyl peroxide dicarbonate, 3 g of propane, and 0.2 g of pentaerythritol tetrakis(3-mercaptopropionic acid) ester, and begin the polymerization reaction. Continue to add VDF monomer to maintain the polymerization pressure at 4.4 MPa. During polymerization, add 2 g of propane, 3 g of diisopropyl peroxide dicarbonate, and 0.4 g of pentaerythritol tetrakis(3-mercaptopropionic acid) ester every 20 minutes until the total VDF feed reaches 8 kg. After the reaction is complete, release the pressure and discharge the material. The resulting polyvinylidene fluoride emulsion is then subjected to coagulation and demulsification, washing, drying, and granulation to obtain granular products. The vinylidene fluoride resin is analyzed and tested; the results are shown in Table 1 below.

[0040] Example 4 Potassium persulfate was initially added, followed by supplementary additions in stages; pentaerythritol tetrakis(3-mercaptopropionic acid) and diethyl malonate were initially added, followed by supplementary additions in stages, and the reaction was carried out at 80 °C.

[0041] Add 35 kg of deionized water, 100 g of hexadecyl acetate, and 150 g of a 30 wt% perfluorohexylacetic acid ammonia solution to a 50 L horizontal reactor. Vacuum deoxygenation of the reaction system is performed until the oxygen content is below 30 ppm. Stirring is started, and the reactor temperature is raised to 80°C. Vinylidene fluoride monomer is added, and the reactor pressure is increased to 4.4 MPa. 2 g of potassium persulfate, 3 g of diethyl malonate, and 0.2 g of pentaerythritol tetrakis(3-mercaptopropionic acid) are added, and VDF monomer is continuously added to maintain the polymerization pressure at 4.4 MPa. During polymerization, 0.2 g of potassium persulfate, 6 g of diethyl malonate, and 0.4 g of pentaerythritol tetrakis(3-mercaptopropionic acid) are added every 20 minutes until the total VDF feed reaches 8 kg. After the reaction was completed, the pressure was released and the material was discharged. The obtained polyvinylidene fluoride emulsion was then subjected to coagulation and demulsification, washing, drying, and granulation to obtain granular products. The polyvinylidene fluoride resin was analyzed and tested, and the analysis results are shown in Table 1 below.

[0042] Example 5 Potassium persulfate was initially added, followed by additional additions in stages; pentaerythritol tetrakis(3-mercaptopropionic acid) and ethyl acetate were initially added, followed by additional additions in stages, and the reaction was carried out at 80 °C. Add 35 kg of deionized water, 100 g of hexadecyl acetate, and 150 g of a 30 wt% perfluorohexylacetic acid ammonia solution to a 50 L horizontal reactor. Vacuum deoxygenation of the reaction system is performed until the oxygen content is below 30 ppm. Stirring is started, and the reactor temperature is raised to 80 °C. Vinylidene fluoride monomer is added, and the reactor pressure is increased to 4.4 MPa. 2 g of potassium persulfate, 5 g of ethyl acetate, and 0.2 g of pentaerythritol tetrakis(3-mercaptopropionic acid) are added, and VDF monomer is continuously added to maintain the polymerization pressure at 4.4 MPa. During polymerization, 0.2 g of potassium persulfate, 8 g of ethyl acetate, and 0.4 g of pentaerythritol tetrakis(3-mercaptopropionic acid) are added every 20 minutes until the total VDF feed reaches 8 kg. After the reaction was completed, the pressure was released and the material was discharged. The obtained polyvinylidene fluoride emulsion was then subjected to coagulation and demulsification, washing, drying, and granulation to obtain granular products. The polyvinylidene fluoride resin was analyzed and tested, and the analysis results are shown in Table 1 below.

[0043] Example 6 Diisopropyl peroxide (initiator) was initially added, followed by continuous replenishment; pentaerythritol tetrakis(3-mercaptopropionic acid) (chain transfer agent with multiple chain transfer sites) was initially added and replenished in stages, 75 o C reaction.

[0044] Add 35 kg of deionized water, 100 g of No. 50 solid paraffin, and 150 g of a 30 wt% aqueous solution of perfluorohexylacetic acid to a 50 L horizontal reactor. Perform vacuum deoxygenation on the reaction system until the oxygen content is below 30 ppm. Turn on the stirrer and raise the reactor temperature to 75 °C. o C. Add vinylidene fluoride monomer, raise the reactor pressure to 4.4 MPa, add 12 g of diisopropyl peroxide and 0.2 g of pentaerythritol tetrakis(3-mercaptopropionic acid) ester, and begin the polymerization reaction. Continue to add VDF monomer to maintain the polymerization pressure at 4.4 MPa. During polymerization, add 3 g of diisopropyl peroxide and 0.4 g of pentaerythritol tetrakis(3-mercaptopropionic acid) ester every 20 minutes until the total VDF feed reaches 8 kg. After the reaction is complete, release the pressure and discharge the material. The resulting polyvinylidene fluoride emulsion is then subjected to coagulation and demulsification, washing, drying, and granulation to obtain granular products. The vinylidene fluoride resin is analyzed and tested; the results are shown in Table 1 below.

[0045] Example 7 Diisopropyl peroxide dicarbonate (initiator) was initially added, followed by continuous replenishment; pentaerythritol tetrakis(3-mercaptopropionic acid) ester (chain transfer agent with multiple chain transfer sites), diethyl malonate (liquid-phase chain transfer agent), and propane (gas-phase chain transfer agent) were initially added and replenished in stages, 75 o C reaction.

[0046] Add 35 kg of deionized water, 100 g of No. 50 solid paraffin, and 150 g of a 30 wt% aqueous solution of perfluorohexylacetic acid to a 50 L horizontal reactor. Perform vacuum deoxygenation on the reaction system until the oxygen content is below 30 ppm. Start stirring and raise the reactor temperature to 75 °C. o C. Add vinylidene fluoride monomer, raise the reactor pressure to 4.4 MPa, add 12 g of diisopropyl peroxide, 3 g of diethyl malonate, 3 g of propane, and 0.2 g of pentaerythritol tetrakis(3-mercaptopropionic acid) ester, and begin the polymerization reaction. Continue to add VDF monomer to maintain the polymerization pressure at 4.4 MPa. During polymerization, add 3 g of diisopropyl peroxide, 4 g of diethyl malonate, 4 g of propane, and 0.4 g of pentaerythritol tetrakis(3-mercaptopropionic acid) ester every 20 minutes until the total VDF feed reaches 8 kg. After the reaction is complete, release the pressure and discharge the material. The resulting polyvinylidene fluoride emulsion is then subjected to coagulation and demulsification, washing, drying, and granulation to obtain granular products. The vinylidene fluoride resin is analyzed and tested; the results are shown in Table 1 below.

[0047] Comparative Example 1 Diisopropyl peroxide was added initially and then gradually added in stages; diethyl malonate was added initially and then gradually added in stages; 75 o C reaction Add 35 kg of deionized water, 100 g of No. 50 solid paraffin, and 150 g of a 30 wt% perfluorohexylacetic acid ammonia solution to a 50 L horizontal reactor. Vacuum the reactor to remove oxygen until the oxygen content is <30 ppm. Start stirring and raise the reactor temperature to 75°C. o C. Add vinylidene fluoride monomer, raise the reactor pressure to 4.4 MPa, add 12 g of diisopropyl peroxide and 3 g of diethyl malonate, and start the polymerization reaction. Continue to add VDF monomer to maintain the polymerization pressure at 4.4 MPa. During polymerization, add 6 g of diethyl malonate and 3 g of diisopropyl peroxide every 20 minutes until the total VDF feed reaches 8 kg. After the reaction is complete, release the pressure and discharge the material. The resulting polyvinylidene fluoride emulsion is then subjected to coagulation and demulsification, washing, drying, and granulation to obtain granular products. The vinylidene fluoride resin is analyzed and tested; the results are shown in Table 1 below.

[0048] Comparative Example 2 Potassium persulfate was added initially, then gradually added in stages; diethyl malonate was added initially, then gradually added in stages, and the reaction was carried out at 80°C. 35 kg of deionized water, 100 g of hexadecyl acetate, and 150 g of a 30 wt% perfluorohexylacetic acid ammonia solution were added to a 50 L horizontal reactor. The reactor was evacuated to remove oxygen until the oxygen content was <30 ppm. Stirring was started, and the reactor temperature was raised to 80℃. Vinylidene fluoride monomer was added, and the reactor pressure was increased to 4.4 MPa. 2 g of potassium persulfate and 3 g of diethyl malonate were added, and VDF monomer was continuously added to maintain the polymerization pressure at 4.4 MPa. During polymerization, 0.2 g of potassium persulfate and 6 g of diethyl malonate were added every 20 minutes until the total VDF feed reached 8 kg. After the reaction, the pressure was released, and the resulting polyvinylidene fluoride emulsion was subjected to coagulation and demulsification, washing, drying, and granulation to obtain granular products. The polyvinylidene fluoride resin was analyzed, and the results are shown in Table 1 below.

[0049] Comparative Example 3 It is largely the same as Example 1, except that pentaerythritol tetrakis(3-mercaptopropionic acid) is replaced with an equal mass of diethyl malonate.

[0050] Add 35 kg of deionized water, 100 g of No. 50 solid paraffin, and 150 g of a 30 wt% perfluorohexylacetic acid ammonia solution to a 50 L horizontal reactor. Vacuum the reactor to remove oxygen until the oxygen content is <30 ppm. Start stirring and raise the reactor temperature to 75°C. oC. Add vinylidene fluoride monomer, raise the reactor pressure to 4.4 MPa, add 12 g of diisopropyl peroxide and 3.2 g of diethyl malonate, and start the polymerization reaction. Continue to add VDF monomer to maintain the polymerization pressure at 4.4 MPa. During polymerization, add 6.4 g of diethyl malonate and 3 g of diisopropyl peroxide every 20 minutes until the total VDF feed reaches 8 kg. After the reaction is complete, release the pressure and discharge the material. The resulting polyvinylidene fluoride emulsion is then subjected to coagulation and demulsification, washing, drying, and granulation to obtain granular products. The vinylidene fluoride resin is analyzed and tested; the results are shown in Table 1 below.

[0051] Comparative Example 4 It is largely the same as Example 1, except that pentaerythritol tetrakis(3-mercaptopropionic acid) is replaced with an equal mass of carbon tetrachloride.

[0052] Add 35 kg of deionized water, 100 g of No. 50 solid paraffin, and 150 g of a 30 wt% perfluorohexylacetic acid ammonia solution to a 50 L horizontal reactor. Vacuum the reactor to remove oxygen until the oxygen content is <30 ppm. Start stirring and raise the reactor temperature to 75°C. o C. Add vinylidene fluoride monomer, raise the reactor pressure to 4.4 MPa, add 12 g of diisopropyl peroxide, 3 g of diethyl malonate, and 0.2 g of carbon tetrachloride to start the polymerization reaction, and continuously add VDF monomer to maintain the polymerization reaction pressure at 4.4 MPa. During the polymerization process, add 6 g of diethyl malonate, 0.4 g of carbon tetrachloride, and 3 g of diisopropyl peroxide every 20 minutes until the total VDF feed reaches 8 kg. After the reaction is completed, release the pressure and discharge the material. The obtained polyvinylidene fluoride emulsion is coagulated, demulsified, washed, dried, and granulated to obtain granular products. The vinylidene fluoride resin is analyzed and tested, and the analysis results are shown in Table 1 below.

[0053] The vinylidene fluoride resin products obtained in Examples 1-5 and Comparative Examples 1-2 were tested and characterized. The test and analysis results are shown in Table 1 below: Table 1 Performance test data of polyvinylidene fluoride resin Table 1 shows that, compared to the comparative example without added or with a changed type of chain transfer agent, the example with added chain transfer agent containing multiple chain transfer sites effectively formed a hyperbranched topology with multi-site chain transfer as branching sites, while maintaining a high weight-average molecular weight. This significantly reduced the branching factor g' of the PVDF resin. Furthermore, this structure significantly improved the melt flow index and processing fluidity. Due to the presence of the hyperbranched structure, the PVDF molecular chains were highly entangled, resulting in a tensile strength significantly higher than the comparative example. This achieved the preparation of a PVDF resin that combines easy processing and high strength at a high molecular weight.

[0054] The above description of the embodiments is provided to enable those skilled in the art to understand and use the invention. It will be apparent to those skilled in the art that various modifications can be made to these embodiments, and the general principles described herein can be applied to other embodiments without inventive effort. Therefore, the present invention is not limited to the above embodiments, and any improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the invention should be within the protection scope of the present invention.

Claims

1. A method for the controlled synthesis of hyperbranched polyvinylidene fluoride resin using a chain transfer agent, characterized in that, In a polymerization reaction system containing an initiator, a chain transfer agent, and an emulsifier, vinylidene fluoride is polymerized, wherein the chain transfer agent is a chain transfer agent containing multiple chain transfer sites, or a compound chain transfer agent formed by combining it with at least one of a liquid-phase transfer agent and a gas-phase transfer agent.

2. The method for controllably synthesizing hyperbranched polyvinylidene fluoride resin using a chain transfer agent according to claim 1, characterized in that, The amount of the initiator used is 0.01~1% of the mass of vinylidene fluoride; The amount of the chain transfer agent used is 0.01~1% of the mass of vinylidene fluoride; The amount of the emulsifier used is 0.1-3% of the mass of vinylidene fluoride.

3. The method for controllably synthesizing hyperbranched polyvinylidene fluoride resin using a chain transfer agent according to claim 1, characterized in that, The chain transfer agent containing multiple chain transfer sites is selected from one or more of the following: pentaerythritol tetrakis(3-mercaptopropionic acid), trimethylolpropane tris(3-mercaptopropionate), mercaptoethanol, 1,4-butanedithiol, 1,6-hexanedithiol, tris(2-mercaptoethyl)amine, glycerol trimercaptopropionate, 1,3,5-benzenetrithiol, 4,4'-thiodiphenylthiol, pentaerythritol tetrakis(3-mercaptobutyric acid), pentaerythritol tetrakis(2-(dithiobenzoyl)thiopropionate), glucose pentathiopropionate, and tetrakis(dimethylsiloxy)silane glucose thiopropionate.

4. The method for controllably synthesizing hyperbranched polyvinylidene fluoride resin using a chain transfer agent according to claim 1, characterized in that, When the chain transfer agent is a compound chain transfer agent, the total amount of the liquid-phase chain transfer agent and / or gas-phase chain transfer agent is used in a mass ratio of 15 to 25 to 1 to the chain transfer agent containing multiple chain transfer sites. The liquid-phase chain transfer is selected from at least one of methyl acetate, ethyl acetate, propyl acetate, butyl acetate, dimethyl malonate, diethyl malonate, dipropyl malonate, dibutyl malonate, diethyl carbonate, n-butanethiol, tert-butanethiol, n-octanethiol, dodecyl mercaptan, tert-dodecyl mercaptan, chloroform, and methanol. The gas-phase chain transfer agent is selected from at least one of methane, ethane, propane, butane, and hydrogen.

5. The method for controllably synthesizing hyperbranched polyvinylidene fluoride resin using a chain transfer agent according to claim 1, characterized in that, The initiator includes one or more of the following: cyclohexanone peroxide, tert-butyl peroxyacetate, tert-butyl peroxybenzoate, n-butyl 4,4-bis(tert-butylperoxy)valerate, di-tert-butyldisperoxyisophthalate, methyl ethyl ketone peroxide, di-tert-butyl peroxide, di-tert-pentyl peroxide, cumene hydroperoxide, di-isopropylbenzene peroxide, tert-butyl cumene peroxide, 1,1,3,3-tetramethyl hydroperoxide, tert-butanol peroxide, tert-butyl peroxylaurate, tert-butyl peroxy-3,5,5-trimethylhexanoate, ammonium persulfate, potassium persulfate, isobutyl peroxide, diisopropyl peroxydicarbonate, di-n-propyl peroxydicarbonate, tert-butyl peroxyneodecanate, benzoyl peroxide, tert-butyl peroxyisobutyrate, tert-butyl peroxyneodecanate, succinic acid peroxide, acetyl peroxide, octanoyl peroxide, decanoyl peroxide, and lauroyl peroxide.

6. The method for controllably synthesizing hyperbranched polyvinylidene fluoride resin using a chain transfer agent according to claim 1, characterized in that, The emulsifier is perfluorohexylacetic acid amino, perfluoropentylacetic acid, perfluoropentylphenylacetic acid, 4,4,5,5,6,6,6-heptafluoro-3,3-bis(trifluoromethyl)heptanoic acid. At least one of the following: 4,4,5,5,6,6,6-heptafluoro-3,3-bis(trifluoromethyl)benzenehexanoic acid, 4-(2,2,3,3,5,5,5-heptafluoro-4,4-bis(trifluoromethyl)pentyl)benzoic acid, perfluorodioxaneheptacarbonate, perfluorotrioxaneheptacarbonate, perfluorodioxaneoctacarbonate, branched perfluoropolyether mixtures, linear perfluoropolyether mixtures, sodium dodecyl sulfate, sodium dodecyl sulfate, sodium tetradecyl sulfonate, sodium tetradecylbenzene sulfonate, sodium dodecyl diphenyl ether disulfonate, sodium hexadecyl sulfonate, sodium hexadecyl sulfate, sodium hexadecyl sulfate, sodium hexadecyl sulfate, sodium octyl sulfonate, sodium octyl sulfate, polypropylene glycol, polyethylene glycol, polyethylene glycol-propylene glycol copolymer, isomeric tridecyl polyoxyethylene ether, octyl polyoxyethylene ether, and dodecyl polyoxyethylene ether.

7. The method for controllably synthesizing hyperbranched polyvinylidene fluoride resin using a chain transfer agent according to claim 1, characterized in that, The polymerization reaction system also contains a stabilizer, the amount of which is 0-5% of the mass of vinylidene fluoride; The stabilizer is at least one of paraffin wax and long-chain alkanes, wherein the long-chain alkanes are one or more of dodecyl, hexadecyl, octadecyl, and eicosyl.

8. The method for controllably synthesizing hyperbranched polyvinylidene fluoride resin using a chain transfer agent according to claim 1, characterized in that, The polymerization reaction is carried out at a temperature of 50~130℃ and a pressure of 2.0~5.0MPa.

9. A hyperbranched polyvinylidene fluoride resin, characterized in that, Prepared by the method according to any one of claims 1-8, the weight-average molecular weight is 500,000 to 2,200,000, the branching factor is 0.3 to 0.8, the molecular weight distribution index is 2 to 12, the melt index is 0.1 to 10 g / 10 min (230℃, 10 kg load), and the melting point is 150 to 175℃. o C, tensile strength 40.0~60.0 MPa.

10. The application of the hyperbranched polyvinylidene fluoride resin as described in claim 9 in the preparation of the internal pressure sealing layer material for marine flexible risers under high temperature and high pressure conditions.

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