WO2013170536A1 - Method for synthesizing aqueous solution of homopolymer n-vinyl butyrolactam (k60) with low residual monomer and middle-high molecular weight - Google Patents

Description

 Method for synthesizing high molecular weight homopolymerized N-vinyl butyrolactam K60 aqueous solution in low residue

 The invention relates to the technical field of compound synthesis, in particular to the technical field of homopolymerization of N-vinyl butyrolactam, in particular to a method for synthesizing a high-molecular-weight homopolymerized N-vinyl butyrolactam K60 aqueous solution in a low residual single. Background technique

 Homopolymerized N-vinyl butyrolactam is a very important water-soluble polymer which is polymerized by N-vinyl butyrolactone under certain conditions (Yan Ruizhen. Water-soluble polymer 2nd Edition [M]. Beijing: Chemical Industry Press, 2010, 217). Among them, K60 is a medium-high molecular weight N-vinyl butyrolactam polymer, which combines the properties of low molecular weight homopolymeric N-vinyl butyrolactam with high molecular weight homopolymerized N-vinyl butyrolactam. prospect.

 Homopolymerized N-vinyl butyrolactam is widely used due to its unique properties. It not only has excellent solubility, chemical stability, film formation, physiological inertness, bonding ability and protective rubber action, but also It is combined with many inorganic and organic compounds. Therefore, homopolymerized N-vinyl butyrolactam has been widely used in medicine, cosmetics, food, brewing, coatings, adhesives, printing and dyeing auxiliaries, separation membranes, and sensitization. Materials and other fields. With the development of science and technology, the application of homopolymerized N-vinyl butyrolactam has become more and more widely used in high-tech fields such as photo-curable resins, optical fibers, laser discs, and drag reducing materials. YANG Zhenhua, et al. Effects of PVP on the characteristics of dye-sensitized solar cells[J]. Journal of Solar Energy, 2010, 31(8): 979-982 ) Lactam is used in the field of dye sensitized batteries that are now very popular.

 K60 is a medium-high molecular weight N-vinyl butyrolactam polymer, which combines the properties of low molecular weight homopolymeric N-vinyl butyrolactam with high molecular weight homopolymeric N-vinyl butyrolactam, while medium and high molecular weight is difficult to produce. The reasons are as follows: (1) The polymerization of N-vinyl butyrolactam is a chain reaction, and it is difficult to terminate once the reaction starts, and the K value is difficult to control; (2) There is also inhibition in the N-vinyl butyrolactam monomer. The agent causes the residual monomer to be too high; (3) Reducing the residual unreacted raw material content increases the cost, and the additional operation is difficult. Therefore, this technology is only mastered by BASF in Germany, and there is no report on K60 products in China.

 According to USP32, the content of unreacted monomeric N-vinyl butyrolactam in pharmaceutical or food grade homopolymerized N-vinyl butyrolactam is less than 10 ppm. Currently, homopolymerized N-vinylbutene Amide industrial production of multi-polymer polymer post-treatment processes such as activated carbon adsorption, solvent extraction or ultrafiltration, radiation, etc. (Nuber, Dr. Adolf, Sanner,

Dr. Axel, Urban, Dr. Dieter. Use of an adsorbent for the removal of vinylpyrrolidon from vinylpyrrolidon polymer solutions[P]. EP 0258854, 1991-3-13; Juergen Detering, Limburgerhof,

Hartwig Voss, Frankenthal. Preparation of ultrapure N-vinylpyrrolidone polymers [P]. US 5354945, 1994-10-11;. INDUSTRY AND polymers residual monomer method for eliminating N- [P] vinylpyrrolidone CN 1712432, 2005-12-28) _0..

 Therefore, if it is possible to study the effect of different polymerization processes on the residual monomer content in the solution polymerization process of homopolymerized N-vinyl butyrolactam K60, this is for homopolymeric N-vinylbutylene. The use of amide K60 for food grade or pharmaceutical grade development and production is of great significance. Summary of the invention

 SUMMARY OF THE INVENTION The object of the present invention is to overcome the above-mentioned shortcomings of the prior art and to provide a method for synthesizing a high-molecular-weight homopolymeric N-vinyl butyrolactam K60 aqueous solution in a low-residue single-molecular high-molecular-weight homopolymer N-vinyl group. The synthesis method of butyrolactam K60 aqueous solution is ingeniously designed to prepare a single sheet, and the residual residue of the high-molecular-weight homopolymer N-vinyl butyrolactam K60 aqueous solution prepared in the low residual single is below 10 ppm, K value is 58-65, suitable for large Scale promotion application.

 In order to achieve the above object, a method for synthesizing a low-residue high-molecular-weight homopolymerized N-vinyl butyrolactam K60 aqueous solution of the present invention is characterized in that, in the presence of an inert gas, 20 to 50% by weight of N-vinyl is used. The aqueous solution of butyrolactam monomer is used as a raw material. Under the polymerization temperature of 57 ° C to 72 ° C, the reaction is stirred for 4-6 hours, and the initiator is added stepwise, and the initiator is azobisisoheptanenitrile. The amount of the initiator is 0.01~2% of the mass of the N-vinyl butyrolactam monomer, and the K value of the system is 58~65, and the H is added to the sulfuric acid to adjust the H to 4.2~4.5 at a temperature of 90-140 °C. The residue is eliminated over a period of time to obtain a 20 to 50% by weight aqueous solution of a high molecular weight homopolymeric N-vinyl butyrolactam K60 having a residual color of less than 10 ppm and a K value of 58 to 65.

 The step of raising and decreasing the addition of the initiator may be carried out by any suitable step. Preferably, the step of raising and decreasing the addition of the initiator is specifically carried out by the following steps: first adding 40% of the total weight of the initiator at 57 ° C ~60%, start polymerization, after 2h, add 10~30% of the total weight of the initiator at 62 °C, continue to react for 1h, add 10-30% of the total weight of the initiator at 72 °C, continue the reaction -3h.

 The sulfuric acid may be added in any suitable manner, and preferably, the sulfuric acid is added as a 50% sulfuric acid solution. The temperature of the heat-insulated stirring elimination residue can be selected as needed. Preferably, the temperature of the heat-insulated stirring elimination residue is 90 ° C, 120 ° C or 140 ° C.

The incubation time is generally 4 hours or longer. Preferably, the incubation time is 4-12 hours. The beneficial effects of the present invention are specifically as follows: the method for synthesizing the high-molecular-weight homopolymerized N-vinyl butyrolactam K60 aqueous solution in the low residual single sheet of the present invention is 20-50% by weight of N-vinyl in the presence of an inert gas. The aqueous solution of butyrolactam monomer is used as a raw material. The polymerization temperature is 57 ° C -72 ° C, the reaction is stirred for 4-6 hours, the temperature is increased in stages, and the initiator is added. The initiator is azobisisoheptonitrile, and the total is added. The amount of the initiator is 0.01 to 2% of the mass of the N-vinyl butyrolactam monomer. The K value of the system reaches 58~65, and the sulfuric acid is adjusted to 4.2~4.5. The temperature is stirred at 90-140 °C for 4 hours or more to eliminate the residual, so that 20~50% of the residuals are below lOppm and the K value is obtained. It is a colorless and transparent low-residue single-color high-molecular-weight homopolymerized N-vinyl butyrolactam K60 aqueous solution of 58~65. It is designed in a simple way to prepare a low residual single medium and high molecular weight homopolymerized N-vinyl butyrolactam. The residual residue of K60 7J solution is below lOppm and K value is 58-65, which is suitable for large-scale popularization and application. detailed description

 In order to more clearly understand the technical content of the present invention, the following embodiments are specifically described.

 1.1 Main raw materials

 Table 1 Main raw materials

 Name Specifications Manufacturer

 N-vinyl butyrolactam Industrial grade (decompression distillation) Shanghai Yuang Chemical Technology Development Co., Ltd. Azobisisobutyronitrile (AIBN) Chemically pure Shanghai Test Sihewei Chemical Co., Ltd.

 Azobisisoheptanenitrile (AVBN) chemical purity Hubei Chengyu Pharmaceutical Co., Ltd.

 Hydrogen peroxide chemical purity Jiangsu Qiangsheng Chemical Co., Ltd.

 Benzoyl peroxide chemical purity China National Pharmaceutical Group Chemical Reagent Co., Ltd.

 Distilled water

 Ammonium Persulfate Chemically Pure Sinopharm Chemical Reagent Co., Ltd.

 Sodium sulfite hydrogen hydride chemical pure Sinopharm Chemical Reagent Co., Ltd.

 Nitrogen 99% Shanghai Hukang Gas

1.2 Experimental instruments

 2XZ-2 rotary vane vacuum pump, RE52CS rotary evaporator, 250ml three-necked flask, HH-WO constant temperature oil bath, Φ0.5 U-viscometer, 100°C thermometer, S312 electric mixer , a syringe, a FA2004 analytical balance, a dropping funnel, a condenser tube, a conical flask, a 10 ml pipette, and a basic burette.

1.3 Aggregation

In this experiment, 20~50% N-vinyl butyrolactam monomer aqueous solution was used, water and N-vinyl butyrolactam monomer were first added to a three-necked flask, placed in a constant temperature oil bath, and protected by N ₂ Under the polymerization temperature of 57 °C -72 °C, the reaction is stirred for 4-6 hours, and the initiator is added in increments of 0.01~2%, and the K value of the system is 58~65. Add Shikic acid to adjust the pH to 4.2-4.5, terminate the reaction, heat up to 90-140 ° C, keep warm for more than 4 hours, and cool to room temperature to obtain a colorless and clarified viscous solution, ie low-molecular weight, high molecular weight homopolymerized N-ethylene An aqueous solution of butylbutyrolamide K60, K value 58-65, residual residue below 10 ppm.

 1.4 Characterization

 1.4.1 Determination of K value

Usually we use the K value of the Fikentscher formula to characterize the molecular weight of homopolymeric N-vinyl butyrolactam, which is a parameter that is only related to molecular weight and does not change with the concentration of homopolymeric N-vinyl butyrolactam. A commonly used method for determining the K value is a viscosity method. The Ubbel viscometer measures the relative viscosity r) _r of the solution against water at a water bath temperature of 25 ± 0.2 °C.

 According to the Fikentscher formula 1_value: 3⁄4 mouth (H. Fikentscher, Die Messung der Viskositat solvatisierter

Sole. Morden Plastics [J], 1945, 23(3): 157 ):

_K = [300Clg^ _r + (C + 1.51g^) ² ] ^1/2 +1.5Clg^-C

~ 0.15C + 0.003C ²

 Where: K is the Fikentscher constant;

 C is the number of grams of homopolymerized N-vinyl butyrolactam dissolved in 0.1 L solution

η _Γ is the relative viscosity (the ratio of solution effluent time to pure solvent efflux time Τ / Τ ₀ )

1.4.2 Residual monomer content

 The determination of the residual monomer content in the homopolymerized fluorene-vinyl butyrolactam is based on the method specified in the 26th edition of the United States Pharmacopoeia. Take 10g of homopolyindole-vinyl butyrolactam (accurate to 0.002g, based on anhydrous matter), dissolve in 80ml of distilled water, add lg sodium acetate, titrate with 0.1 mol/L iodine solution until the solution no longer fades, then Add 3 ml of 0.1mol/L iodine solution for 10 minutes, then titrate excess iodine with 0.1 mol/L sodium thiosulfate. Add 3 ml of starch indicator when approaching the end point, continue titration until the solution color disappears. At the same time, compared with the blank experiment.

 Result calculation:

W曙= fc^ ^ _xl00

 m

 Where: Vi_ titration of the iodine solution consumed by the blank sample (ml)

V ₂ ― Iodine standard solution (ml) consumed by titrating the sample

 N-iodine standard concentration (mol/L)

 Quality of 0.106-1 mmol/L N-vinyl butyrolactam (g)

M—the mass of the sample (g) 2.1 Effect of different initiator systems on the content of residual unreacted raw materials

This experiment mainly studies solution polymerization, using different initiators for polymerization, using a variety of initiator systems, such as: hydrogen peroxide (3⁄40 ₂ ), t-butyl hydroperoxide, benzoyl peroxide; Redox system, such as: ammonium tetrahydrogenate monosodium hydride; azo, such as: azobisisobutyronitrile, azobisisoheptanenitrile. The effect of these systems on the content of residual unreacted raw materials was tested separately.

2.1.1 Peroxide system

 The mechanism of peroxide polymerization is as follows:

 Chain trigger:

 ROOR——► 2RO-

 Wherein ROOR represents a peroxide, R represents an organic group, and 0 is an oxygen atom.

 Table 2 Experimental scheme of peroxide as initiator

 Inducing period residual unreacted experiment number initiator initiator force input K value

 (min) raw material content

1 3⁄40 ₂ 1ml 30% solution did not trigger one by one

 2 t-butyl hydroperoxide 1ml 65% solution did not trigger one

3⁄40 ₂ 1ml 30% solution

 3 did not trigger one

 +NaOH 0.2043 NaOH

4 H ₂ 0 ₂ 1ml 30% solution 2 58.3 1.72% + ammonia water 1ml 25% ammonia water

 Tert-butyl hydroperoxide 1ml 65% solution

 5 10 57.5 2.07%

+CuS0 ₄ 0.0446g CuS0 ₄

 6 benzoyl peroxide 0.2061g 23

Note: The reaction conditions are: temperature 75 ° C, 50 ml N-vinyl butyrolactam (NVP) monomer, 200 ml water meter 2 shows that neither 3⁄40 ₂ nor t-butyl hydroperoxide can initiate polymerization, 3⁄40 ₂ in alkali Under the action of decomposition into a series of intermediates such as hydrogen peroxy anion, hydroxyl radical, hydroxy anion, etc., compared with experiments No. 3 and No. 4, it can be found that different alkalis have a great influence on the initiation efficiency of 3⁄40 ₂ , in the presence of NaOH. 3⁄40 ₂ still does not initiate, and ammonia can quickly cause 3⁄40 _{2 to} initiate, therefore, the choice of 3⁄40 ₂ activator plays an important role in its initiation. Similarly, in comparison with No. 5 and No. 5, t-butyl hydroperoxide has a high initiation efficiency in the presence of Cu ²⁺ . Therefore, t-butyl hydroperoxide also needs to find a suitable activator. For benzoyl peroxide, it can be initiated without the need for an activator, but the residual unreacted raw material obtained is relatively high in content and the reaction time is relatively long.

2.1.2 Redox system

 Using ammonium persulfate-sodium bisulfite redox system, when the mass ratio of ammonium persulfate: sodium bisulfite is 2.0216: 0.8796 (molar ratio is greater than 1), the reaction viscosity is unchanged for 24 hours, the system fails to trigger When the mass ratio of o is 4.6142: 0.5125 (molar ratio is about 4:1), the color of the system is red, and the system fails to be triggered in 24 hours.

2.1.3 Azo

 Fikentscher first developed an aqueous solution polymerization method for N-vinyl butyrolactam. When it was initiated with an azo initiator, the polymerization mechanism was as follows:

 Chain trigger:

RN≡NR R + N.

Chain delivery:

 Stop:

 Wherein RN≡NR represents an azo initiator, R represents an organic group, and N is a nitrogen atom.

 Table 3 Experimental scheme of azo as initiator

 Residual unreacted polymerization temperature

 Experiment No. Initiator Adding amount (g) Polymerization time (h) K value

 Degree (°C)

 the amount (%)

 1 AIBN 0.0304 74 2.5 63.4 0.23

 2 ABVN 0.0231 60 1.5 65.3 0.062 Note: The above residual unreacted raw materials are all after the end of the reaction, add citric acid to adjust the PH value to 3-5, stir for 12 hours. From the above data, it can be found that the azo initiator can be obtained. A homopolymeric N-vinyl butyrolactam having a low residual unreacted raw material content. Compared with AVBN, AIBN has a lower reaction temperature and higher efficiency. The toxicity of ABVN is lower. The homopolymerized N-vinyl butyrolactam studied in this invention is pharmaceutical grade and food grade, and has low toxicity. The requirements are higher.

 The choice of initiator can be found. First, the redox system is not suitable for the preparation of homopolymeric N-vinyl butyrolactam K60, while the peroxide should consider the choice of activator, the system is more complicated, and azo, The system is simple, the reaction temperature is low, the initiation efficiency is high, and the residual unreacted raw material content is low. ABVN has more advantages than AIBN, so our initiator uses ABVN.

 2.2 Effect of product post-treatment on the content of residual unreacted raw materials

By studying the solubility characteristics of N-vinyl butyrolactam and homopoly N-vinyl butyrolactam, it was found that in dichloromethane, N-vinyl butyrolactam was dissolved in dichloromethane, and homopolymerized N- Vinyl butyrolactam is insoluble and is extracted by liquid separation. Table 4 Experimental protocol for samples used for product post-treatment

 Residue is not reversed

 Polymerization temperature polymerization time

 Initiator Adding amount (g) K value

 Degree (°C) ( ) ^

 the amount (%)

 ΑΙΒΝ 0.0304 74 2.5 63.4 0.23 Based on this experiment, the sample was cooled to room temperature, 30 ml of dichloromethane was added, and the mixture was stirred for 20 minutes to fully disperse the dichloromethane. The dispersed sample was transferred to a separatory funnel and allowed to stand until the next day. Layered, liquid separation, the lower layer is carbon tetrachloride in which N-vinyl butyrolactam monomer is dissolved, and the upper layer is an aqueous solution of homopolymerized N-vinyl butyrolactam, and the residual unreacted raw material content is determined to be 0.058%. Then, 30 ml of carbon dichloride was added to the upper aqueous solution of homopolymerized N-vinylbutyrolactam, shaken and shaken, and allowed to stand still. After stratification for the next day, the liquid was separated, and the residual unreacted raw material content was determined to be 0.027%.

 This method has a significant effect on the low content of residual unreacted raw materials, and methylene chloride can be removed by heating the sample to about 40 ° C; methylene chloride is also less toxic. However, it has been found in experiments that the viscosity of K60 is moderate and the method of liquid separation is feasible. However, if the viscosity of the system is relatively large, such as K90, K120, etc., this method is not applicable because the viscosity of K90 and K120 systems is very large, and the intermolecular The force is very large, the dispensing speed is very slow, the time required for liquid separation is very long, and some even take one to two weeks, which is not applicable in the actual production process.

 2.3 Effect of polymerization process on the content of residual unreacted raw materials

 2.3.1 Special polymerization process

 The initiator is added in multiple stages, and the polymerization temperature is increased in the later stage of polymerization.

 Table 5 Experimental scheme under special process conditions

 Start first, second, residue, not the first time, add the second

 Agglomeration polymerization

 Adding amount of polymerization temperature

 Agent temperature combined with time value

(g), quantity (g) degree (° ^C ),

 (C) between (h) (h) (%)

 ABVN 0.0304 ~~ 54 Ϊ 0.0092 ~~ 75 Ϊ 62.3 0.013

It can be seen from Table 5 that as the viscosity of the system increases, by increasing the temperature and decreasing the additional initiator, the active radicals in the system can be kept at a higher concentration, and the collision probability of the free radicals with the remaining monomers is increased. , to achieve the purpose of reducing the concentration of residual unreacted raw materials. It can also be seen from the data in the table that the use of the stepwise heating and decrementing of the additional initiator has a significant effect on reducing the residual unreacted raw materials. 2.3.2 Acid treatment under high temperature conditions

 The purpose of acid addition is because studies have shown (J. Ferguson, V. SunderRajan. Polymer Joural [J], 1979, (15): 627) that monomeric N-vinyl butyrolactam readily undergoes hydrolysis under acidic conditions. The hydrolysis mechanism is as follows:

The previous experiment used citric acid, and the acid is now modified to use sulfuric acid (H ₂ S0 ₄ ), nitric acid (HN0 ₃ ).

 The polymerization process was as follows: Using AVBN at 54 ° C, the reaction was first carried out for 1 hour, then AVBN was added, the temperature was raised to 75 ° C, and the reaction was observed at 75 ° C to observe the viscosity change. When the K value was about 60, the acid was adjusted to pH. Between 3-5, the temperature was raised to 80 ° C, and the mixture was stirred for 12 hours.

 Table 6 Experimental protocols for the use of different acids

 After lh, the residue is not reversed.

 Experiment No. Initiator Adding amount (g) Adding amount Acid K value

 (g) Quantity (%)

"1 AVBN ~~ 0.0212 0.0120 H ₂ S0 ₄ ~ 67 0

2 AVBN 0.0198 0.0118 HN0 ₃ 65.8 0.022

As can be seen in Table 6, the effect of H ₂ S0 ₄ is the best, and the concentration of residual unreacted raw materials can reach almost zero, which is completely within the range specified by the United States Pharmacopoeia (USP 32). In order to meet the requirements of the US Pharmacopoeia USP 32, appropriate initiators, special processes, and adjustment of relevant process parameters, it is possible to obtain homopolymeric N-vinyl butyrolactam with a low residual unreacted raw material content.

 The best initiator for the homopolymerization of N-vinyl butyrolactam K60, which has a very low residual unreacted raw material content, is azobisisoheptanenitrile (ABVN). The polymerization process uses a special segmental high temperature, which increases with temperature. The method of reducing the dosage of the additional dosage is carried out by using sulfuric acid to adjust the pH 4.2-4.5 at a high temperature of 90-140 ° C for more than 4 hours, so that the residue can be effectively reduced even if the residual residue treatment process such as methylene chloride precipitation is not used. The amount of residual unreacted raw materials is less than 0.001% as specified in USP 32. The invention will be more specifically illustrated by the following examples, but the invention is not limited by these examples. In the following, unless otherwise stated, "parts by weight" is only expressed as "parts", and "% by weight" is only expressed as "%".

 Example 1

 200 parts of water and 50 parts of N-vinyl butyrolactam were added to a reaction vessel equipped with a gas inlet and a thermometer, and nitrogen gas was introduced while stirring, and the air in the reaction vessel was drained to form a nitrogen atmosphere. Next, after heating using an oil bath to bring the internal temperature of the reaction vessel to 57 ° C, 0.003 parts of azobisisoheptanenitrile was added. After the reaction was carried out for 2 hours, 0.001 parts of azobisisoheptanenitrile was added, and the temperature was raised to 62 ° C. The reaction was further continued for 1 hour, and 0.001 parts of azobisisoheptanenitrile was further added, and the temperature was raised to The reaction was maintained at 72 ° C for 1 hour at 72 ° C. Immediately thereafter, a 50% sulfuric acid solution was added to the reaction solution, the pH was adjusted to 4.2, the temperature of the oil bath was raised to 90 ° C, the temperature was maintained, and after stirring for 4 hours, it was cooled. As a result, a medium-high molecular weight homopolymeric N-vinyl butyrolactam K60 polymer solution having a solid content of 19.7% and being colorless and transparent was obtained. The K value of the product (measured as a 1% by weight aqueous solution) was 58.7, and the residual unreacted N-vinyl butyrolactam content was below 10 ppm. Example 2

 The difference from Example 1 is as follows: After the addition of azobisisoheptanenitrile, the reaction is maintained at 72 ° C for 2 hours; the temperature of the oil bath is raised to 140 ° C, the temperature is maintained, and after stirring for 12 hours, the solid content is obtained. 20.3% of a colorless, transparent medium to high molecular weight homopoly N-vinyl butyrolactam K60 polymer solution. The K value of the product (measured as a 1% by weight aqueous solution) was 62.1, and the residual unreacted monomer N-vinyl butyrolactam content was below 10 ppm. Example 3

100 parts of water and 100 parts of N-vinyl butyrolactam were added to a reaction vessel equipped with a gas inlet and a thermometer, and nitrogen gas was introduced while stirring, and the air in the reaction vessel was drained to form a nitrogen atmosphere. Then, use an oil bath to heat it up. After the internal temperature of the vessel reached 57 ° C, 1 part of azobisisoheptanenitrile was added. When the reaction was carried out for 2 hours, the force was applied. 0.5 parts of azobisisoheptanenitrile, and the temperature was raised to 62 ° C, the reaction was further continued for 1 hour, 0.5 parts of azobisisoheptanenitrile was added, and the temperature was raised to 72 ° C, maintained at 72 ° C Reaction for 3 hours. Immediately thereafter, a 50% sulfuric acid solution was added to the reaction liquid, the pH was adjusted to 4.5, the oil bath temperature was raised to 120 ° C, the temperature was maintained, and after stirring for 8 hours, the mixture was cooled. As a result, a medium-high molecular weight homopolymeric N-vinyl butyrolactam K60 polymer solution having a solid content of 49.8% and being colorless and transparent was obtained. The K value of the product (measured as a 1% by weight aqueous solution) was 63.5, and the residual unreacted monomer N-vinyl butyrolactam content was 10 ppm or less. Example 4:

 To the reaction vessel equipped with the gas inlet and the thermometer, 150 parts of water and 50 parts of N-vinyl butyrolactam were added, and nitrogen gas was introduced while stirring, and the air in the reaction vessel was drained to form a nitrogen atmosphere. Next, after heating in an oil bath to bring the internal temperature of the reaction vessel to 57 ° C, 0.3 part of azobisisobutyronitrile was added. When the reaction was carried out for 2 hours, the force was applied. 0.15 parts of azobisisobutyronitrile, and the temperature was raised to 62 ° C, the reaction was further continued for 1 hour, 0.15 parts of azobisisobutyronitrile was added, and the temperature was raised to 72 ° C, maintained at 72 ° C Reaction for 1 hour. Immediately thereafter, a 50% sulfuric acid solution and 50 parts of water were added to the reaction liquid, the pH was adjusted to 4.2, the temperature of the oil bath was raised to 90 ° C, the temperature was maintained, and after stirring for 12 hours, it was cooled. As a result, a homopolymeric N-vinyl butyrolactam K60 polymer solution having a solid content of 24.6% and being colorless and transparent was obtained. The K value of the product (measured as a 1% by weight aqueous solution) was 49.5, and the residual unreacted monomer N-vinyl butyrolamide content was below 10 ppm. Comparative example 1

 Polymerization was carried out in the same manner as in Example 1 except that nitric acid was used instead of sulfuric acid to obtain 19.9% of a colorless transparent homopolymeric N-vinylbutyrolactam K60 polymer solution. The K value of the product (measured as a 1% by weight aqueous solution) was 54.8, and the residual unreacted monomer N-vinyl butyrolactam content was 80 ppm or more. Comparative example 2:

To a reaction vessel equipped with a gas inlet and a thermometer, 200 parts of water and 50 parts of N-vinyl butyrolactam were added, and nitrogen gas was introduced while stirring, and the air in the reaction vessel was drained to form a nitrogen atmosphere. Next, after heating using an oil bath so that the internal temperature of the reaction container reached 57 ° C, 0.3 part of azobisisoheptanenitrile was added. When the reaction was carried out for 2 hours, the force was applied. 0.15 parts of azobisisoheptanenitrile, and the temperature was raised to 62 ° C, the reaction was further continued for 1 hour, and then 0.05 parts of azobisisoheptanenitrile was added, and the temperature was raised to 72 ° C, and maintained at 72 ° C. Reaction for 1 hour. Cool to room temperature, add 200ml of dichloromethane, stir well, let stand for 24h to fully stratify, take the upper layer to measure the K value of 59.1, the measured residue is more than 500ppm, will The upper layer was taken out at night, and then 200 ml of dichloromethane was added to repeat the stirring and stratification process. After standing for 24 hours, the obtained colorless transparent homopolymer N-vinyl butyrolactam K60 polymer solution was found to have a K value of 59.0, It is 70ppm or more. Comparative example 3

 To a reaction vessel equipped with a gas inlet and a thermometer, 200 parts of water and 50 parts of N-vinyl butyrolactam were added, and nitrogen gas was introduced while stirring, and the air in the reaction vessel was drained to form a nitrogen atmosphere. Next, after heating in an oil bath to bring the internal temperature of the reaction vessel to 57 ° C, 0.5 part of azobisisoheptanenitrile was added, and after reacting for 4 hours, a 50% sulfuric acid solution was immediately added to the reaction liquid to adjust the pH to 4.2, the temperature of the system was raised to 140 ° C, and kept for 4 hours, and the K value of the colorless transparent homopolymer N-vinyl butyrolactam K60 polymer solution was 37.9, and the residual amount was 500 ppm or more.

 Therefore, the present invention adjusts the homopolymerization of N-vinyl butyl by studying the effect of different initiation systems and different polymerization processes on the residual monomer content in the solution polymerization process of homopolymerized N-vinyl butyrolactam K60. The polymerization process of lactam K60 gave a low residual single homopolymer N-vinyl butyrolactam K60.

 In summary, the method for synthesizing the high-molecular-weight homopoly-vinylbutyrolactam Κ60 aqueous solution in the low-residue single-book of the present invention is ingeniously designed, and the prepared low-single medium-high molecular weight homopoly-vinyl butyrolactam Κ60 is prepared. The residue of the aqueous solution is below 10 ppm and the K value is 58-65, which is suitable for large-scale popularization and application.

 In this specification, the invention has been described with reference to specific embodiments thereof. However, it will be apparent that various modifications and changes can be made without departing from the spirit and scope of the invention. Accordingly, the description is to be considered as illustrative and not restrictive.

Claims

Rights request 1 . A method for synthesizing a high-molecular-weight homopolymerized N-vinyl butyrolactam K60 aqueous solution in a low residual single product, characterized in that, in the presence of an inert gas, 20 to 50% by weight of N-vinyl butyrolactam The aqueous solution is used as a raw material. Under the polymerization temperature of 57 ° C to 72 ° C, the reaction is stirred for 4-6 hours, and the initiator is added in a stepwise manner. The initiator is azobisisoheptonitrile, and the total amount of the initiator is added. It is 0.01-2% of the mass of N-vinyl butyrolactam monomer, the K value of the system is 58-65, the pH of the sulfuric acid is adjusted to 4.2~4.5, and the temperature is stirred for more than 4 hours at 90-140 temperature to eliminate the residual. Thus, 20 to 50% by weight of a high-molecular-weight homogeneous N-vinyl butyrolactam K60 aqueous solution having a residual color of 10 ppm or less and a K value of 58 to 65 in a colorless and transparent low residual single sheet is obtained.  2 . The method for synthesizing a high-molecular-weight homopolymerized N-vinyl butyrolactam K60 aqueous solution according to claim 1 , wherein the step of heating and decreasing the addition of the initiator comprises the following steps: Adding 40~60% of the total weight of the initiator at 57 °C, starting the polymerization. After 2 hours, add 10~30% of the total weight of the initiator at 62 °C. After the reaction is continued for 1 hour, the total weight of the initiator is added at 72. 10~30%, continue to react for 1-3h.  The method for synthesizing a low-residue medium-high molecular weight homopolymeric N-vinyl butyrolactam K60 aqueous solution according to claim 1, wherein the sulfuric acid is added as a 50% sulfuric acid solution.  The method for synthesizing a high-molecular-weight homopolymerized N-vinyl butyrolactam K60 aqueous solution according to claim 1, wherein the temperature of the heat-dissipating stirring elimination residue is 90 ° C and 120 ° C. Or 140 ° C.  The method for synthesizing a high-molecular-weight homopolymerized N-vinyl butyrolactam K60 aqueous solution according to claim 1, wherein the incubation time is 4-12 hours.