Polyacrylonitrile spinning solution with adjustable molecular sequence and preparation method thereof

Abstract

The invention relates to the field of free radical solution polymerization programmed monomer supplementation, in particular to a polyacrylonitrile spinning solution with an adjustable molecular sequence and a preparation method thereof.The preparation method comprises the steps that polymerization solution formula components and dosage ranges are determined, and the components comprise acrylonitrile, itaconic acid, methyl methacrylate or fumaramide and the like; the thermodynamic reaction temperature ranges from 60 DEG C to 66 DEG C, the total monomer concentration ranges from 18 wt% to 26 wt%, and the initiator concentration ranges from 0.072 wt% to 0.103 wt%. When preparation is started, all components except for partial itaconic acid are added, then itaconic acid is supplemented in batches, and the supplementing time and the proportion range interval can be calculated according to a specific formula. The itaconic acid is supplemented in a manner of body nitrogen blowing or metered addition after dissolution, and the solution concentration is less than or equal to 55wt%. According to the method, the molecular sequence can be accurately regulated and controlled, the homogeneity of the copolymer is improved, heat release in the polymerization process is uniform, a stable environment is provided for industrial production, meanwhile, a reaction system is optimized, and the reaction efficiency and the product yield are improved.

Description

Technical Field

[0001] The invention relates to the field of programmed monomer addition in free radical solution polymerization, and in particular to a polyacrylonitrile spinning solution with adjustable molecular sequence and a preparation method thereof. Background Art

[0002] Carbon fiber is an inorganic non-metallic material with multiple excellent properties. It has excellent mechanical properties and chemical stability. It is the fiber with the highest specific strength and the highest specific modulus among the high-performance fibers currently produced. It is widely used in sports and leisure, pressure vessels, aerospace and other fields. The technical bottleneck of carbon fiber materials is mainly in the preparation of precursors, and the key to determining the quality of precursors is the precursor polymer solution. The macromolecular chain structure of uniformly polymerized acrylonitrile (first monomer) is relatively regular and has high crystallinity, but its molecular cohesive energy is large, which makes the fiber poor in softness, rigid and not resistant to folding, and the peak temperature is high during pre-oxidation, and the heat release is concentrated. In order to improve spinnability and reduce the cyclization temperature, itaconic acid is usually added as the second monomer for copolymerization. However, due to the difference in the reactivity of the two monomers, that is, their respective activities in the reaction are different, resulting in uneven heat release during the polymerization reaction, especially in a certain stage where a large amount of concentrated heat release will occur. This phenomenon not only increases the difficulty of reaction control, but may also damage the reaction equipment due to local overheating, and is also not conducive to the stability of the product, safety and production efficiency during industrial production.

[0003] In the prior art, due to the difference in the reactivity ratio of itaconic acid and acrylonitrile, the heat release in the polymerization process is uneven, especially in a certain stage, a large amount of concentrated heat release will occur. This uneven heat release increases the difficulty of reaction control and may also cause damage to the reaction equipment due to local overheating. It is also not conducive to the stability of the product and the safety and production efficiency during industrial production. In addition, the traditional method may not be able to accurately control the addition method and proportion of the comonomer, and it is difficult to achieve effective regulation of the molecular sequence, resulting in uneven distribution of the molecular sequence of the polymerization product, affecting the quality and performance of the product, and failing to meet the high quality requirements of the precursor polymer solution for the preparation of high-performance carbon fibers.

[0004] Therefore, it is necessary to propose a polyacrylonitrile spinning solution with controllable molecular sequence and a preparation method thereof to solve the above problems. Summary of the invention

[0005] The purpose of the present invention is to provide a polyacrylonitrile spinning solution with adjustable molecular sequence and a preparation method thereof, so as to solve the problems that (1) uneven heat release increases the difficulty of reaction control and is not conducive to product stability, safety and production efficiency during industrial production; and (2) the molecular sequence of the polymerization product is unevenly distributed, affecting the quality and performance of the product.

[0006] To achieve the above object, the present invention provides the following technical solutions:

[0007] A method for preparing a polyacrylonitrile spinning solution with adjustable molecular sequence comprises the following steps: the first monomer, the third monomer, the solvent, the initiator and the chain transfer agent in the polymerization solution formula are all added before the reaction starts, and the second comonomer is partially added, the solvent is dimethyl sulfoxide or N,N-dimethylformamide, the initiator is azobisisobutyronitrile, azobisisovaleronitrile, azobisisoheptanenitrile, the first monomer is acrylonitrile, the chain transfer agent is n-dodecyl mercaptan or isopropanol, the second comonomer is itaconic acid, and the third monomer is methyl methacrylate or fumaric acid, and then the itaconic acid is added in batches or continuously during the reaction.

[0008] Preferably, the total monomer concentration c M The range is 18%-26wt%, wt% is weight percentage, the monomers include the first monomer, the second monomer and the third monomer, the initiator concentration c I The range is 0.072-0.103wt%.

[0009] Preferably, the thermodynamic reaction temperature T ranges from 60°C to 66°C.

[0010] Preferably, during the preparation, it is specified that the amount of itaconic acid added for the first time accounts for x1% of the total amount used, and x1%≤48.6wt%.

[0011] Preferably, the comonomer is added with itaconic acid in batches, characterized in that: the time t2 for the second addition of itaconic acid and the proportion of the amount of itaconic acid added in the second addition to the total amount of itaconic acid are specified as x2%,

[0012] When to join:

[0013]

[0014] Add Amount:

[0015]

[0016] Wherein, x1 is the ratio of the amount of itaconic acid added for the first time to the total amount used, cI is the initiator concentration range, cM is the total monomer concentration range, and T is the thermodynamic reaction temperature.

[0017] Preferably, the comonomer is added with itaconic acid in batches, and the time tn of adding itaconic acid for the nth time and the proportion of the amount of itaconic acid added for the nth time to the total amount of itaconic acid are specified as xn%.

[0018] The nth joining time:

[0019]

[0020] The amount added for the n-1th time:

[0021]

[0022] The amount added for the nth time:

[0023]

[0024] Wherein, cI is the initiator concentration range, cM is the total monomer concentration range, and T is the thermodynamic reaction temperature.

[0025] Preferably, the comonomer is added with itaconic acid in batches, and the time tf for the completion of all the itaconic acid addition is specified.

[0026]

[0027] Wherein, cI is the initiator concentration range, cM is the total monomer concentration range, and T is the thermodynamic reaction temperature.

[0028] Preferably, the continuous acceleration rate V is as follows:

[0029]

[0030] Wherein, tf is the time when all itaconic acid addition is completed, x1 is the ratio of the amount of itaconic acid added for the first time to the total amount, I m is the total amount of itaconic acid used.

[0031] Preferably, the comonomer can be added in batches by blowing nitrogen into the itaconic acid bulk, or adding it in a metered manner after dissolving itaconic acid, and the concentration of the itaconic acid solution is ≤55wt%.

[0032] Preferably, a polyacrylonitrile spinning stock solution with adjustable molecular sequence is prepared by the method for preparing a polyacrylonitrile spinning stock solution with adjustable molecular sequence according to any one of claims 1 to 9.

[0033] Technical effects and advantages of the present invention:

[0034] 1. By adding itaconic acid in batches, the molecular sequence of polyacrylonitrile spinning solution can be precisely controlled. The addition time and proportion range are calculated according to a specific formula, so that itaconic acid can be gradually added according to a predetermined rule and sequence, thereby achieving fine control of the molecular sequence of the polymerization product and improving the uniformity of the copolymer;

[0035] 2. By adjusting the proportion of itaconic acid in the polymerization process, the heat release in the entire polymerization process becomes smoother and more uniform. The programmed addition of itaconic acid can not only reduce the concentrated release of heat in the polymerization process, reduce the temperature fluctuation of the reaction system, and provide a more stable and controllable environment for industrial production, but also promote the uniform distribution of copolymer segments and improve the homogeneity of the copolymer;

[0036] 3. The thermodynamic reaction temperature was determined to be in the range of 60°C to 66°C, which is conducive to controlling the reaction rate and product quality. Within this temperature range, the reaction can proceed more stably, reduce the occurrence of side reactions, and improve the purity and performance of the product. The total monomer concentration range is 18%-26wt% and the initiator concentration range is 0.072-0.103wt%. The determination of these parameters helps to optimize the reaction system, so that the reaction can proceed under appropriate concentration conditions, and improve the reaction efficiency and product yield. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 The present invention is a schematic diagram of a process for preparing a polyacrylonitrile spinning solution with controllable molecular sequence. DETAILED DESCRIPTION

[0038] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0039] The present invention provides Figure 1 A method for preparing a polyacrylonitrile spinning solution with adjustable molecular sequence is shown, wherein the first monomer, the third monomer, the solvent, the initiator and the chain transfer agent in the polymerization solution formula are all added before the reaction starts, and the second comonomer is partially added, the solvent is dimethyl sulfoxide or N,N-dimethylformamide, the initiator is azobisisobutyronitrile, azobisisovaleronitrile, azobisisoheptanenitrile, the first monomer is acrylonitrile, the chain transfer agent is n-dodecyl mercaptan or isopropanol, the second comonomer is itaconic acid, and the third monomer is methyl methacrylate or fumaramide, and then itaconic acid is added in batches or continuously during the reaction;

[0040] The total monomer concentration ranges from 18% to 26wt%, where wt% is weight percentage. The monomers include a first monomer, a second monomer and a third monomer. The initiator concentration ranges from 0.072 to 0.103wt%. The thermodynamic reaction temperature T ranges from 60°C to 66°C. During preparation, the amount of itaconic acid added for the first time accounts for x1% of the total amount, and x1%≤48.6wt%. The copolymerization monomer can be added in batches by blowing nitrogen into the itaconic acid bulk, or by metering after dissolution. The concentration of the itaconic acid solution is ≤55wt%.

[0041] The time t2 for the second addition of itaconic acid and the proportion of the amount of itaconic acid added the second time to the total amount of itaconic acid x2% are specified.

[0042] When to join:

[0043]

[0044] Add Amount:

[0045]

[0046] Wherein, x1 is the ratio of the amount of itaconic acid added for the first time to the total amount, cI is the initiator concentration range, cM is the total monomer concentration range, and T is the thermodynamic reaction temperature;

[0047] The time tn of adding itaconic acid for the nth time and the proportion xn% of the amount of itaconic acid added for the nth time to the total amount of itaconic acid are specified.

[0048] The nth joining time:

[0049]

[0050] The amount added for the n-1th time:

[0051]

[0052] The amount added for the nth time:

[0053]

[0054] Wherein, cI is the initiator concentration range, cM is the total monomer concentration range, and T is the thermodynamic reaction temperature;

[0055] The time tf for the completion of all itaconic acid addition is specified.

[0056]

[0057] Wherein, cI is the initiator concentration range, cM is the total monomer concentration range, and T is the thermodynamic reaction temperature;

[0058] The continuous acceleration rate V is as follows:

[0059]

[0060] Wherein, tf is the time for the completion of all itaconic acid addition, x1 is the ratio of the amount of itaconic acid added for the first time to the total amount, I m is the total amount of itaconic acid used.

[0061] A polyacrylonitrile spinning stock solution with adjustable molecular sequence can be prepared by the method for preparing the polyacrylonitrile spinning stock solution with adjustable molecular sequence.

[0062] Embodiment 1

[0063] A blank group with one-time feeding was set up, with the total reaction system mass fixed at 1500g, the total monomer mass at 360g (accounting for 24% of the total system mass), the mass of itaconic acid at 3.6g (accounting for 1.0% of the total monomer mass), the mass of initiator azobisisobutyronitrile at 2.16g (accounting for 0.6% of the total monomer mass), and no chain transfer agent. The polymerization experiment temperature was 64°C, the stirring rate was 600r / min, and the polymerization was carried out under the protection of a nitrogen atmosphere for 18h. Itaconic acid was dissolved in the solvent dimethyl sulfoxide before polymerization and fed once. After the reaction was completed, about 1g of PAN stock solution was taken and placed in a vacuum oven at 65°C for 3 days. The sample was then tested by DSC and elemental analysis.

[0064] The results showed that the exothermic peak area of ​​the system was 442.4 J / g, and the peak width was around 5.8°C. Elemental analysis test results showed that in the early stage of polymerization, the mass proportion of itaconic acid in the product was nearly 5%. As the polymerization time increased, the proportion dropped to 1%, which was close to the feed ratio.

[0065] Embodiment 2

[0066] The scheme of itaconic acid supplementation procedure of the present invention is adopted, the total mass of the fixed reaction polymerization system is 50g, the total mass of the monomer is 12g (accounting for 24% of the total mass of the system), the mass of itaconic acid is 0.12g (accounting for 1.0% of the total mass of the monomer), and the mass of the initiator azobisisobutyronitrile is 0.072g (accounting for 0.6% of the total mass of the monomer). The polymerization experiment temperature is 64°C, the stirring rate is 600r / min, and the polymerization is carried out under the protection of nitrogen atmosphere for 10h. The materials are added in three times: ① before polymerization, according to the copolymerization curve, itaconic acid (0.0583g) of acrylonitrile monomer is added; ② at 2h of polymerization reaction, 0.0275g of itaconic acid is added; ③ at 4h of polymerization reaction, the remaining itaconic acid (0.0342g) is added. After the polymerization reaction is completed, about 1g of PAN stock solution is taken and placed in a vacuum oven at 65°C for 3 days. The sample is then subjected to DSC and elemental analysis tests.

[0067] The results showed that the exothermic peak area of ​​the system was 534.7 J / g and the peak width was 3.4°C.

[0068] Embodiment 3

[0069] The scheme of itaconic acid supplementation procedure of the present invention is adopted, the total mass of the fixed reaction polymerization system is 50g, the total mass of the monomer is 12g (accounting for 24% of the total mass of the system), the mass of itaconic acid is 0.12g (accounting for 1.0% of the total mass of the monomer), and the mass of the initiator azobisisobutyronitrile is 0.072g (accounting for 0.6% of the total mass of the monomer). The polymerization experiment temperature is 64°C, the stirring rate is 600r / min, and the polymerization is carried out under the protection of nitrogen atmosphere for 10h. The materials are added in four times: ① before polymerization, according to the copolymerization curve, itaconic acid (0.0583g) of acrylonitrile monomer is added; ② at 1.5h of polymerization reaction, 0.0193g of itaconic acid is added; ③ at 3h of polymerization reaction, 0.0228g of itaconic acid is added. ④ at 4.5h of polymerization reaction, the remaining itaconic acid is added, totaling 0.0196g. After the polymerization reaction is completed, about 1g of PAN stock solution is taken and placed in a vacuum oven at 65°C for 3 days. The samples were then subjected to DSC and elemental analysis tests.

[0070] The results showed that the exothermic peak area of ​​the system was 730.0 J / g and the peak width was 4.6°C. Compared with the system with three-time addition, the area of ​​cyclization heat increased significantly and the width of the exothermic peak was significantly widened, indicating that the more times of batch addition, the more conducive it is to improving the cyclization degree of polyacrylonitrile and alleviating the exothermic phenomenon in the polymerization process.

[0071] Embodiment 4

[0072] The itaconic acid supplementation program of the present invention is adopted, the total reaction system mass is fixed to 1500g, the total monomer mass is 360g (accounting for 24% of the total system mass), the itaconic acid mass is 3.6g (accounting for 1.0% of the total monomer mass), the initiator azobisisobutyronitrile mass is 2.16g (accounting for 0.6% of the monomer mass), and no chain transfer agent is added. The polymerization experiment temperature is 64°C, the stirring rate is 600r / min, and the polymerization is carried out under the protection of nitrogen atmosphere for 10h. Itaconic acid is added in three batches: ① before polymerization, according to the copolymerization curve, 0.2mol% of itaconic acid (1.75g) of acrylonitrile monomer is added; ② at 2h of polymerization reaction, 0.95g of itaconic acid is calculated by empirical formula; ③ at 4h of polymerization reaction, before the viscosity rises, the remaining itaconic acid (0.9g) is added. After the polymerization reaction is completed, about 1g of PAN stock solution is taken and placed in a vacuum oven at 65°C for 3 days. The samples were then subjected to DSC and elemental analysis tests.

[0073] The results showed that the exothermic peak was 761.7 J / g and the peak width was 3.6°C. Before the addition, the proportion of itaconic acid dropped from 4.5% to below 3%. After two additions, the proportion of itaconic acid increased, and as the polymerization time increased, the itaconic acid content gradually decreased. Compared with Example 1, the solution of adding itaconic acid in the present invention can significantly reduce the content of itaconic acid in the early stage of polymerization and achieve a more balanced itaconic acid distribution.

[0074] Embodiment 5

[0075] The scheme of itaconic acid supplementation procedure of the present invention is adopted, the total reaction system mass is fixed to 1500g, the total monomer mass is 360g (accounting for 24% of the total system mass), the mass of itaconic acid is 3.6g (accounting for 1.0% of the total monomer mass), the mass of initiator azobisisobutyronitrile is 2.16g (accounting for 0.6% of the monomer mass), and the mass of chain transfer agent DM is 3g (accounting for 0.2% of the total monomer mass). The polymerization experiment temperature is 64°C, the stirring rate is 600r / min, and the polymerization is carried out under the protection of nitrogen atmosphere for 10h. Itaconic acid is added in three batches: ① before polymerization, according to the copolymerization curve, 0.2mol% of itaconic acid (1.75g) of acrylonitrile monomer is added; ② at 2h of polymerization reaction, 1.46g of itaconic acid is calculated by empirical formula; ③ at 4h of polymerization reaction, before the viscosity rises, the remaining itaconic acid (0.39g) is added. After the polymerization reaction was completed, about 1 g of PAN stock solution was taken and placed in a vacuum oven at 65°C for 3 days. The sample was then subjected to DSC and elemental analysis tests.

[0076] The results show that the exothermic peak is 631.1 J / g and the peak width is 21.6°C. Before adding itaconic acid, the proportion of itaconic acid dropped from 2.5% to about 1%, and with the increase in the number of additions, the proportion of itaconic acid fluctuated slightly between 1% and 2%. This shows that the system of adding itaconic acid in batches containing a chain transfer agent has a more balanced distribution of itaconic acid in the polymer than the systems of Examples 1 and 4.

[0077] The above shows and describes the basic principles, main features and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The above embodiments and descriptions only describe the principles of the present invention. The present invention may be subject to various changes and improvements without departing from the spirit and scope of the present invention. These changes and improvements fall within the scope of the present invention. The scope of protection claimed by the present invention is defined by the attached claims and their equivalents.

Claims

1. A method for preparing polyacrylonitrile spinning solution with adjustable molecular sequence, characterized in that: The first monomer, the third monomer, the solvent, the initiator and the chain transfer agent in the polymerization liquid formula are all added before the reaction starts, and the second comonomer is partially added. The solvent is dimethyl sulfoxide or N,N-dimethylformamide, the initiator is azobisisobutyronitrile, azobisisovaleronitrile, azobisisoheptanenitrile, the first monomer is acrylonitrile, the chain transfer agent is n-dodecyl mercaptan or isopropanol, the second comonomer is itaconic acid, and the third monomer is methyl methacrylate or fumaric acid. Then, itaconic acid is added in batches or continuously during the reaction.

2. The method for preparing a polyacrylonitrile spinning solution with adjustable molecular sequence according to claim 1, characterized in that: Total monomer concentration c M The range is 18%-26wt%, wt% is weight percentage, the monomers include the first monomer, the second monomer and the third monomer, the initiator concentration c I The range is 0.072-0.103wt%.

3. The method for preparing a polyacrylonitrile spinning solution with controllable molecular sequence according to claim 1, characterized in that: The thermodynamic reaction temperature T ranges from 60°C to 66°C.

4. The method for preparing a polyacrylonitrile spinning solution with adjustable molecular sequence according to claim 1, characterized in that: During the preparation, it is stipulated that the proportion of the amount of itaconic acid added for the first time to the total amount is x1%, and x1%≤48.6wt%.

5. The method for preparing a polyacrylonitrile spinning solution with adjustable molecular sequence according to claim 1, wherein the comonomer is supplemented with itaconic acid in batches, characterized in that: The time t2 for the second addition of itaconic acid and the proportion of the amount of itaconic acid added the second time to the total amount of itaconic acid x2% are specified. When to join: Add Amount: Wherein, x1 is the ratio of the amount of itaconic acid added for the first time to the total amount used, cI is the initiator concentration range, cM is the total monomer concentration range, and T is the thermodynamic reaction temperature.

6. The method for preparing a polyacrylonitrile spinning solution with adjustable molecular sequence according to claim 1, wherein the comonomer is supplemented with itaconic acid in batches, characterized in that: The time tn of adding itaconic acid for the nth time and the proportion xn% of the amount of itaconic acid added for the nth time to the total amount of itaconic acid are specified. The nth joining time: The amount added for the n-1th time: The amount added for the nth time: Wherein, cI is the initiator concentration range, cM is the total monomer concentration range, and T is the thermodynamic reaction temperature.

7. The method for preparing a polyacrylonitrile spinning solution with adjustable molecular sequence according to claim 1, wherein the comonomer is supplemented with itaconic acid in batches, characterized in that: The time tf for the completion of all itaconic acid addition is specified. Wherein, cI is the initiator concentration range, cM is the total monomer concentration range, and T is the thermodynamic reaction temperature.

8. The method for preparing a polyacrylonitrile spinning solution with adjustable molecular sequence according to claim 1, characterized in that: The continuous acceleration rate V is as follows: Wherein, tf is the time for the completion of all itaconic acid addition, x1 is the ratio of the amount of itaconic acid added for the first time to the total amount, I m is the total dosage of itaconic acid.

9. The method for preparing a polyacrylonitrile spinning solution with adjustable molecular sequence according to claim 1, characterized in that: The comonomer can be added in batches by blowing nitrogen into the itaconic acid bulk, or adding it in a metered manner after dissolving itaconic acid, and the concentration of the itaconic acid solution is ≤55wt%.

10. A polyacrylonitrile spinning solution with adjustable molecular sequence, characterized in that: A polyacrylonitrile spinning stock solution with adjustable molecular sequence is prepared by the method for preparing the polyacrylonitrile spinning stock solution with adjustable molecular sequence according to any one of claims 1 to 9.

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