阅读说明：本技术 一种共聚序列均匀的聚丙烯腈树脂制备方法 (Preparation method of polyacrylonitrile resin with uniform copolymerization sequence ) 是由 宋文迪 黄翔宇 吴嵩义 袁玉红 季春晓 辛美音 于 2019-10-17 设计创作，主要内容包括：本发明公开了一种共聚序列均匀的聚丙烯腈树脂制备方法。本发明通过水相沉淀聚合工艺,以丙烯腈为主单体,结合两种共聚单体,选用水溶性偶氮为引发剂,在60～80℃下进行连续聚合反应,反应停留时间为60～120分钟。反应结束后,在真空状态下脱除未反应单体,将所得的聚合体依次进行水洗、抽滤和干燥处理,得到聚丙烯腈树脂。本发明获得的聚丙烯腈树脂的共聚组成与单体投料比接近,共聚序列分布均匀,具有良好的亲水性和氧化环化反应活性。(The invention discloses a preparation method of polyacrylonitrile resin with uniform copolymerization sequence. According to the invention, through a water-phase precipitation polymerization process, acrylonitrile is used as a main monomer, two comonomers are combined, and water-soluble azo is used as an initiator to perform continuous polymerization reaction at the temperature of 60-80 ℃, wherein the reaction retention time is 60-120 minutes. After the reaction is finished, removing unreacted monomers in a vacuum state, and sequentially carrying out water washing, suction filtration and drying treatment on the obtained polymer to obtain the polyacrylonitrile resin. The polyacrylonitrile resin obtained by the invention has the advantages of approximate copolymerization composition to monomer charge ratio, uniform distribution of copolymerization sequences, good hydrophilicity and oxidative cyclization reaction activity.)

1. The preparation method of the polyacrylonitrile resin with uniform copolymerization sequence is characterized by comprising the following steps:

introducing acrylonitrile and a comonomer thereof, an initiator and pure water into a continuous stirring polymerization kettle, and carrying out polymerization reaction at the temperature of 60-80 ℃ for 60-120 minutes;

after the reaction is finished, removing unreacted monomers in a vacuum state, and sequentially carrying out water washing, suction filtration and drying treatment on the obtained polymer to obtain polyacrylonitrile resin with uniform copolymerization sequences;

wherein: the initiator is a water-soluble azo initiator; taking the weight of the whole polymerization system as a reference, the total input amount of the acrylonitrile and the comonomer is 15-35 wt%; based on the total monomer weight, the adding amount of the initiator is 0.05 to 0.3 weight percent; the balance is the pure water adding amount.

2. The method according to claim 1, wherein the initiator is a water-soluble azo initiator selected from any one of azobiscyanovaleric acid (ACVA), azobisisobutyramidine hydrochloride (AIBA), azobisisobutyrimidazoline hydrochloride (AIBI), azobisethylimidazolinylpropane hydrochloride (VA-060), and azobisisobutyrimidazoline sulfate (VA-046B).

3. The method according to claim 1, wherein the polymerization temperature in the step (one) is 65 to 75 ℃ and the reaction residence time is 80 to 100 minutes.

4. The process according to claim 1, wherein the total amount of acrylonitrile and comonomer is 20 to 30 wt% based on the weight of the whole polymerization system.

5. The preparation method of claim 1, wherein the comonomer comprises a second comonomer and a third comonomer, and the second comonomer is selected from any one of methyl acrylate, ethyl acrylate, methyl methacrylate, ethyl methacrylate or vinyl acetate; the third comonomer is selected from any one of methacrylic acid, acrylic acid, itaconic acid, acrylamide or methacrylamide.

6. The method of claim 1, wherein the second comonomer is present in an amount of 3.0 to 3.5 wt% and the third comonomer is present in an amount of 1.0 to 1.5 wt% based on the total monomer weight.

7. The method according to claim 1, wherein the amount of the initiator is 0.08 to 0.15 wt% based on the total weight of the monomers.

8. The polyacrylonitrile resin with uniform copolymerization sequences obtained by the preparation method of claims 1-7 is characterized in that the copolymerization composition of the polyacrylonitrile resin is close to the monomer charge ratio, the weight average molecular weight is 8-20 ten thousand, the molecular weight distribution is 2.6-2.9, the hydrophilicity is good, and the contact angle with water is 38-42 degrees.

9. The polyacrylonitrile resin according to claim 8, wherein the weight average molecular weight of the polyacrylonitrile resin is 10-15 ten thousand, and the molecular weight distribution is 2.6-2.7.

Technical Field

The invention relates to the technical field of textile chemicals and high-performance fibers, in particular to a method for preparing polyacrylonitrile resin with uniform copolymerization sequence by adopting aqueous phase precipitation polymerization reaction.

Background

Due to the properties of high specific strength, high specific modulus, good chemical stability, low thermal expansion coefficient and the like, the carbon fiber is widely applied to different fields of aerospace, satellite rockets, automobile industry, wind power, sports and leisure articles and the like, and the global demand is increased year by year. Among the three organic fiber precursors, polyacrylonitrile is the one with the highest use ratio and the best product quality.

The polyacrylonitrile resin for the carbon fibers usually contains 2-5 wt% of a second comonomer and a third comonomer, and a certain amount of ester groups and carboxyl functional groups are introduced to a macromolecular chain to improve the flexibility and the thermal oxidation stabilization reaction activity of polyacrylonitrile molecules. The second monomer is selected from any one of methyl acrylate, ethyl acrylate, methyl methacrylate, ethyl methacrylate or vinyl acetate, and methyl acrylate is most commonly used; the third monomer is selected from any one of methacrylic acid, acrylic acid, itaconic acid, acrylamide or methacrylamide, with itaconic acid being most commonly used. Because the aqueous phase precipitation polymerization temperature is lower, the reaction heat is easy to remove, the chain transfer reaction of the solvent is very little, and the polypropylene with high molecular weight and narrow distribution can be obtainedOlefinic nitrile resins are widely used in the industrial production of carbon fibers. In the prior art, an oxidation-reduction initiator (such as sodium chlorate-sodium metabisulfite) is mostly adopted, and in order to keep the activity of the initiator, the pH value of a reaction system needs to be controlled to be 2.0 +/-0.2. However, under the pH condition, reactivity ratios of acrylonitrile and itaconic acid are greatly different (r)_AN＝0.25，r_IA1.57), which is expressed by the reaction tendency of preferential copolymerization of itaconic acid in the system, causes uneven distribution of IA units on a macromolecular chain (a plurality of IA units are polymerized together, and the rest is an acrylonitrile long chain segment), and a large amount of 'ineffective' carboxyl units exist, so that the function of improving the thermal oxidation stabilization reaction activity cannot be achieved, the polyacrylonitrile macromolecular chain also contains excessive chemical structure defects, and finally the 'heredity' is the structural defects of carbon fibers.

Although the polymerization of itaconic acid to PAN macromolecular chains can be regulated and controlled at different polymerization stages by improving polymerization reaction equipment and optimizing process conditions (CN104371060A and CN104372431A), the difference of reactivity among comonomers is not fundamentally solved, and thus the sequence junction uniformity of acrylonitrile copolymers is still greatly limited.

Disclosure of Invention

In order to overcome the defects in the prior art, the invention aims to provide a preparation method of polyacrylonitrile resin with uniform copolymerization sequence, wherein a water-soluble azo initiator with a carboxyl functional group is used, and the pH value of a reaction system is controlled to be 5.5-6.5, so that the reactivity ratio of main monomer acrylonitrile and comonomer itaconic acid is approximate (r is r_AN≈r_IA0.6) to prepare a polyacrylonitrile resin having a uniform copolymerization sequence. The copolymerization composition of the resin is close to the monomer feed ratio, the chain structure regularity of the acrylonitrile copolymer can be effectively controlled, the weight average molecular weight (Mw) can reach 80000-200000, the molecular weight distribution (Mw/Mn) is 2.6-2.9, the hydrophilicity is good, and the contact angle with water is 38-42 degrees.

The technical scheme of the invention is as follows:

the invention provides a preparation method of polyacrylonitrile resin with uniform copolymerization sequence, which mainly comprises the following steps:

adding acrylonitrile and a comonomer thereof, an initiator and pure water into a continuous stirring polymerization kettle, and carrying out polymerization reaction at the temperature of 60-80 ℃ for 60-120 minutes;

and (II) after the reaction is finished, removing unreacted monomers in a vacuum state, and sequentially carrying out water washing, suction filtration and drying treatment on the obtained polymer to obtain the polyacrylonitrile resin with uniform copolymerization sequences.

Wherein the initiator is a water-soluble azo initiator; taking the weight of the whole polymerization system as a reference, the total input amount of the acrylonitrile and the comonomer is 15-35 wt%; based on the total monomer weight, the adding amount of the initiator is 0.05 to 0.3 weight percent; the balance is the pure water adding amount.

In the preparation method, the initiator is a water-soluble azo initiator and is selected from any one of azobiscyanovaleric acid (ACVA), azobisisobutyramidine hydrochloride (AIBA), azobisisobutyrimidazoline hydrochloride (AIBI), azobisethylimidazolinyl propane hydrochloride (VA-060) and azobisisobutyrimidazoline sulfate (VA-046B). More preferably, the initiator is azobiscyanovaleric acid (ACVA).

In the preparation method, the polymerization reaction temperature in the step (I) is preferably 65-75 ℃, and the polymerization reaction time is preferably 80-100 minutes.

In the above preparation method, the total amount of acrylonitrile and comonomer is preferably 20 to 30 wt% based on the weight of the whole polymerization system.

In the above preparation method, the comonomer comprises a second comonomer and a third comonomer, the second comonomer is selected from any one of methyl acrylate, ethyl acrylate, methyl methacrylate, ethyl methacrylate or vinyl acetate, preferably methyl acrylate; the third comonomer is selected from any one of methacrylic acid, acrylic acid, itaconic acid, acrylamide or methacrylamide, preferably itaconic acid. Based on the total monomer weight, the mass ratio of the second comonomer is 3.0-3.5 wt%, and the mass ratio of the third comonomer is 1.0-1.5 wt%; the initiator is added in an amount of 0.08 to 0.15 wt% based on the total monomer weight.

The invention also provides the polyacrylonitrile resin with uniform copolymerization sequences, which is prepared by the preparation method, the copolymerization composition of the polyacrylonitrile resin is close to the monomer charge ratio, the weight average molecular weight is 8-20 ten thousand, and the molecular weight distribution is 2.6-2.9. More preferably, the weight average molecular weight of the polyacrylonitrile resin is 10-15 ten thousand, and the molecular weight distribution is 2.6-2.7.

Compared with the prior art, the technical scheme of the invention has the following beneficial effects:

(1) the water-soluble azo initiator is adopted to initiate the water-phase precipitation polymerization reaction of the acrylonitrile and the comonomer thereof, compared with the traditional redox initiator (pH value is 2.0), the pH value of the reaction system is 5.5-6.5, the reactivity ratio of the acrylonitrile and the comonomer itaconic acid is close under the condition, the polyacrylonitrile resin with uniform distribution of copolymerization sequences and controllable chain structure can be obtained, and the polyacrylonitrile resin has better hydrophilicity and preoxidation cyclization reaction activity.

(2) The water-soluble azo initiator does not contain cyano, the decomposed product is non-toxic, meets the requirement of environmental protection, and has high initiation efficiency, higher relative molecular mass of the product, less molecular structure defects, less composition impurities and no alkali metal.

(3) Compared with a solution polymerization process in an organic solvent, the aqueous-phase precipitation polymerization process has no chain transfer reaction, is beneficial to controlling molecular weight and distribution thereof, and the polyacrylonitrile resin obtained after washing, filtering and drying has no residual monomer and small molecular impurities and high purity.

Detailed Description

The present invention will be described in detail with reference to specific examples. The following examples will assist those skilled in the art in further understanding the invention, but are not intended to limit the invention in any way. It should be noted that it would be apparent to those skilled in the art that several modifications and improvements can be made without departing from the inventive concept. All falling within the scope of the present invention.

Examples 1 to 10

Acrylonitrile is used as a first comonomer, a second comonomer is selected from one of methyl acrylate, ethyl acrylate, methyl methacrylate, ethyl methacrylate or vinyl acetate, a third comonomer is selected from one of itaconic acid, acrylic acid, methacrylic acid, acrylamide or methacrylamide, and the composition and the feeding weight ratio of the three monomers are shown in table 1. The total monomer charge is shown in Table 1, based on the weight of the entire polymerization system. The initiator is a water-soluble azo initiator, the types of the initiators are shown in table 1, and the adding amount of the initiators is shown in table 1 based on the total monomer weight. And (3) introducing all the comonomers, the initiator and pure water into a continuous stirring polymerization kettle, carrying out polymerization reaction at the temperature of 60-80 ℃, and controlling the reaction residence time to be 60-120 minutes, wherein the reaction temperature and the reaction time are shown in table 1. After the reaction is finished, removing unreacted monomers in a vacuum state, and sequentially carrying out water washing, suction filtration and drying treatment on the obtained polymer to obtain the polyacrylonitrile resin with uniform copolymerization sequences.

Table 1 examples raw material composition and polymerization conditions

Comparative examples 1 to 3

Acrylonitrile is used as a first comonomer, the second comonomer and the third comonomer are shown in table 2, and the monomer feeding weight ratio is shown in table 2. The total monomer charge, based on the weight of the entire polymerization system, is shown in Table 2. Sodium chlorate-sodium metabisulfite (oxidation-reduction system) is used as an initiator, and the dosage of the initiator is shown in table 2 based on the weight of total monomers. The polymerization time and temperature are shown in Table 2.

TABLE 2 comparative examples raw material composition and polymerization conditions

Test instruments and conditions:

gel Permeation Chromatography (GPC) determination of molecular weights and their distribution: a Waters 1525/2414 gel permeation chromatograph was used. PMMA is used as a standard sample, 0.065mol/L NaNO₃DMF as the mobile sample, flow rate 1.5ml/min, temperature 40 ℃.

Copolymerization composition by infrared spectroscopy (FTIR): fully dissolving polymer sample, standing for defoaming, taking appropriate amount of stock solution, drawing into film with moderate thickness and uniform thickness, cleaning, oven drying at 105 deg.C, scanning with Nicolet 6500 infrared spectrophotometer to obtain cyano (-CN), ester (-COO-), carboxyl (-COOH) or amide (-CONH)₂) Calculating the percentage of acrylonitrile and the second and third comonomers in the polymer.

Testing polyacrylonitrile resin contact angle by A20 contact angle tester: fully and uniformly dissolving a polymer sample, standing for defoaming, taking a proper amount of stock solution, drawing the stock solution into a film with moderate thickness and uniform thickness, cleaning, drying in an oven at 105 ℃, and measuring a contact angle by taking water as titration liquid.

Differential Scanning Calorimetry (DSC) to determine polymer thermal properties: a differential scanning calorimeter from the company METTLER, Switzerland was used. And washing a sample to be detected by acetone, putting the sample to be detected in an oven, drying the sample for 2 hours at 110 ℃, taking the sample out, and cooling the sample in a dryer for 15 min. About 1.50mg of the polymer sample was pressed into a sheet of a certain shape in an aluminum crucible and subjected to DSC measurement. The scanning range is 100-400 ℃, the heating rate is 5 ℃/min, the ambient atmosphere is air, and the atmosphere flow is 20 ml/min. Data were obtained from the DSC exotherm: exothermic peak onset temperature (Ti), exothermic peak (Tpi), termination temperature (Tf), exothermic peak width (Δ T ═ Tf-Ti), and exotherm (Δ H).

The weight average molecular weight and the molecular weight distribution of the polyacrylonitrile resin are shown in Table 3, the copolymerization composition is shown in Table 3, the test result of the contact angle with water is shown in Table 3, and the test result of the DSC thermal property is shown in Table 4.

TABLE 3 contact Angle with Water test results

TABLE 4DSC thermal Property test results

The test results in tables 3 and 4 show that: in examples 1 to 10, the radical copolymerization of acrylonitrile and the second and third comonomers was carried out by aqueous precipitation polymerization using a water-soluble azo initiator, and the resulting polyacrylonitrile resin had a copolymer composition close to the monomer charge ratio, and had designability and controllability of the copolymer chain structure, higher regularity of the chain structure, and narrower molecular weight distribution, as compared with the oxidation-reduction initiator system (comparative examples 1 to 3), where the former was Mw/Mn of 2.6 to 2.9, and the latter was 3.1 to 3.6. Meanwhile, as the distribution uniformity of the copolymerization sequence is improved, the number of effective carboxyl groups capable of initiating oxidative cyclization through an anion reaction mechanism is increased, which is represented by that the DSC heat release starting temperature is reduced and the heat release width is increased. The uniform distribution of the hydrophilic groups also improves the hydrophilicity of the resin, and the contact angle with water is obviously reduced.