A method for preparing a low molecular weight acrylate polymer

Abstract

The application belongs to the technical field of high polymer materials, and particularly relates to a preparation method of low molecular weight acrylic ester polymer. The macromolecule prepared by the reverse Markovnikov addition reaction of end alkenyl polyethylene glycol and hydrogen bromide is used as an initiator, so that the acrylic ester polymer prepared has low molecular weight, narrow molecular weight distribution, and the acrylic ester polymer prepared can improve the uniformity of PVC foaming; the molar ratio of reaction monomers, initiators, catalysts and pentamethyl diethylene triamine is adjusted to control the molecular weight and molecular weight distribution of the acrylic ester polymer prepared; by controlling process parameters such as reaction temperature and reaction time, the initiation efficiency is effectively improved, the molecular weight distribution width is reduced, and after the reaction is completed, the impurity removal step is carried out to improve the purity of the product.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of high polymer materials, and particularly relates to a preparation method of low molecular weight acrylate polymer. BACKGROUND

[0002] Foamed polyvinyl chloride plastic (PVC) has characteristics similar to natural wood, and has the characteristics of low density, good weather resistance, good chemical stability, high impact strength, high toughness and the like. The acrylate polymer as a foaming regulating additive for regulating the foaming performance of foamed polyvinyl chloride has an important influence on the application of foamed polyvinyl chloride.

[0003] Polyacrylate polymer is a kind of high molecular polymer synthesized by acrylate or methacrylate as the main raw material. This kind of polymer has good electrical insulation, mechanical properties, weather resistance and acid and alkali resistance. At the same time, the copolymer of acrylate monomer also has good transparency, plasticity, weather resistance, good water resistance and chemical resistance. The molecular weight of acrylate polymer is an important index affecting its performance. Low molecular weight acrylate polymer has low viscosity and flowability, high reactivity, good compatibility, film forming property and adhesion. The molecular chain of low molecular weight PVC foaming regulating acrylate polymer can move between the PVC molecular chains, reduce the van der Waals force between the PVC molecules, improve the heat and shear force transmission efficiency, speed up the plasticizing process of PVC resin, reduce the plasticizing time, and make the PVC plasticizing more uniform.

[0004] However, there are still the following problems in the preparation process of low molecular weight acrylate polymer at present: 1. The amount error of chain transfer agent or the instability of initiator decomposition leads to the high or low molecular weight of acrylate polymer, the wide molecular weight distribution, and the difficulty in precise control; 2. The residual of polymerization inhibitor in the polymerization process inhibits the polymerization reaction, or the inert gas protection is insufficient, which leads to the combination of oxygen and free radicals to form peroxide radicals, resulting in low monomer conversion rate.

[0005] The Chinese patent application file with the publication number CN117551228A discloses a preparation method of low molecular weight acrylate polymer, comprising the following steps: a) mixing acrylate monomer, initiator and solvent to obtain a mixed solution under inert atmosphere and at a temperature of-10℃-5℃; b) adding the same solvent as in step a) into a reaction bottle under inert atmosphere and heating to reflux state; c) adding the mixed solution of step a) into the reaction bottle of step b) in a dropwise manner, and the reaction obtains low molecular weight acrylate polymer. This method changes the one-pot reaction into adding the reaction solution dropwise into the reaction bottle without changing the concentration and proportion of each substance in the mother liquor, without changing the reaction temperature, without adding any chain transfer agent, and the molecular weight of the acrylate polymer is controlled by changing the dropwise speed, but the low temperature initiator in step a) is added dropwise into step b) under reflux, which may cause explosive decomposition due to sudden temperature rise, a large number of free radicals are generated instantaneously, the local initiator concentration is too high, the molecular weight distribution of the synthesized acrylate polymer is wide and unstable, and the solvent continues to volatilize under reflux, but the low boiling point acrylate monomer is easy to volatilize with the solvent, resulting in low monomer conversion. In addition, no chain transfer agent is added during the polymerization reaction, and only the solvent chain transfer under high temperature is relied on, resulting in high molecular weight of the synthesized acrylate polymer, which cannot be accurately adjusted. SUMMARY

[0006] In order to solve the technical problems of wide molecular weight distribution and low monomer conversion in the related art, the present application provides a preparation method of low molecular weight acrylate polymer.

[0007] In order to achieve the above purpose, the technical scheme of the present application is as follows:

[0008] A preparation method of low molecular weight acrylate polymer, comprising the following steps:

[0009] S1: anhydrous ethanol, reaction monomer and initiator are added into a reaction kettle, stirred uniformly, deoxygenated, and a mixed solution A is obtained;

[0010] S2: under the protection of inert gas, catalyst and pentamethyl diethylene triamine are continuously added to the mixed solution A prepared in step S1, stirred uniformly, heated to 70-80℃ in water bath, and stirred for 2-4h to obtain a primary product;

[0011] S3: oxygen is introduced into the primary product prepared in step S2, washed, separated, the organic phase is dropped into methanol, placed for 1-2h, filtered, dried, and a low molecular weight acrylate polymer is obtained;

[0012] The initiator is prepared by anti-Markovnikov addition reaction of terminal alkenyl polyethylene glycol and hydrogen bromide.

[0013] The present application can prepare the acrylic ester polymer with low molecular weight and narrow molecular weight distribution, the macromolecule prepared by the reverse Markov addition reaction of allyl polyethylene glycol and hydrogen bromide is used as the initiator, the polymerization process can be accurately controlled, the molecular weight is controllable, the molecular weight distribution is narrow, the prepared acrylic ester polymer chain segment has the polar end group, is more uniform in the PVC, and the uniformity of the PVC foaming can be improved. In addition, the reaction temperature and the reaction time in the reaction process are matched with the active system of the initiator, the initiation efficiency can be ensured, the initiation lag can be avoided, the side reaction caused by the chain transfer is inhibited, and the distribution of the acrylic ester polymer caused by the high conversion rate is avoided. After the reaction is completed, the water-soluble impurities are removed by washing and liquid separation, then the unreacted monomer and small molecules are further removed by methanol precipitation, and the purity of the low molecular weight acrylic ester polymer is improved.

[0014] Further, the preparation method of the initiator is as follows: under the protection of inert gas, allyl polyethylene glycol and dichloromethane are mixed, stirred and dissolved, azobisisobutyronitrile is added, stirred and dissolved, the water bath is warmed to 50-60 DEG C, the hydrogen bromide aqueous solution is added dropwise under stirring, the reaction is preserved for 4-6 h, it is cooled, saturated sodium bicarbonate solution is added until the pH value is 6.8-7.5, stirring is carried out for 10-15 min, it is statically layered, the organic phase is collected, dried with anhydrous magnesium sulfate, dropped into ether, stirred to generate white precipitate, filtered, dried, and the initiator is obtained.

[0015] The present application uses the reverse Markov addition reaction of allyl polyethylene glycol and hydrogen bromide under the initiation of azobisisobutyronitrile to prepare the end bromine polyethylene glycol as the initiator, the bromine atom is directly connected with the methylene, the end group has high activity, can efficiently initiate the chain growth of the acrylic ester monomer, and has high initiation efficiency. The molecular main chain of the initiator has strong hydrophilicity, the end group bromine atom and the polyacrylate segment formed after initiation are hydrophobic, so the initiator has amphiphilicity, has good compatibility with the acrylic ester monomer, and can avoid the local initiation uneven problem caused by phase separation in the polymerization process.

[0016] Further, the molar ratio of the allyl polyethylene glycol, azobisisobutyronitrile and hydrogen bromide in the preparation method of the initiator is 17-19:1-2:20-25.

[0017] In the present application, the excess hydrogen bromide can ensure that the double bond in the allyl polyethylene glycol is completely reacted, and the excessive amount of azobisisobutyronitrile can cause the free radical polymerization side reaction in the reaction process, and reduce the purity of the initiator.

[0018] Further, the mass percentage of the hydrogen bromide aqueous solution in the preparation method of the initiator is 40%-45%.

[0019] Further, the catalyst in step S2 is cuprous bromide or cuprous chloride.

[0020] Further, the oxygen removal in step S1 is specifically: freezing the mixed solution to solid state with liquid nitrogen, vacuumizing for 10-15 min, introducing nitrogen to thaw, and repeating for 3-5 times.

[0021] In the present application, the oxygen in the mixed solution of anhydrous ethanol, reaction monomer and initiator can be removed by the process of freezing with liquid nitrogen and thawing by introducing nitrogen, and the oxygen in the mixed solution can be effectively removed in the repeated process, thereby avoiding the oxidation of the catalyst in the reaction process, causing the catalyst to be deactivated, and affecting the molecular weight distribution of the reaction product.

[0022] Further, the reaction monomer in step S1 is composed of methyl acrylate, methyl methacrylate and methacrylic acid according to a mass ratio of 3-7:5-9:1-3.

[0023] Further, the molar ratio of the reaction monomer, initiator in step S1, catalyst and pentamethyldiethylene triamine in step S2 is 48-52:5-7:1:1.

[0024] In the present application, the molecular weight of the prepared acrylate polymer is controlled by adjusting the molar ratio of the reaction monomer, initiator, catalyst and pentamethyldiethylene triamine, wherein the molar ratio of the reaction monomer and initiator is the key to determine the molecular weight of the acrylate polymer. If the reaction monomer is excessive, the chain growth is sufficient, which can cause the molecular weight of the product to increase, and the viscosity of the system increases in the later reaction stage, causing the molecular weight distribution to be wide. If the initiator is excessive, the chain growth is insufficient, the initiation efficiency decreases, and the probability of biradical termination between short chain radicals increases, causing the molecular weight distribution to be wide. The ratio of the catalyst, initiator and pentamethyldiethylene triamine is the key to affect the catalytic performance of the catalyst. Excessive catalyst and pentamethyldiethylene triamine can cause the polymerization rate to decrease, reducing the catalytic activity of the catalyst. Insufficient amount can cause the monomer conversion rate to decrease, biradical termination, chain transfer and other side reactions to intensify, and the molecular weight distribution of the product to be wide.

[0025] Further, the molar ratio of the reaction monomer, initiator in step S1, catalyst and pentamethyldiethylene triamine in step S2 is 51:6:1:1.

[0026] Further, the washing in step S3 is dilute hydrochloric acid washing, the washing number is 3-5 times, the concentration of dilute hydrochloric acid is 0.8-1.2 mol / L, the drying temperature is 40-45℃, and the drying time is 24-30 h.

[0027] Compared with the prior art, the preparation method of the low molecular weight acrylate polymer provided by the present application has the following technical advantages:

[0028] (1) The macromolecule prepared by the anti-Markovnikov addition reaction of end-alkenyl polyethylene glycol and hydrogen bromide is used as an initiator, so that the molecular weight of the prepared acrylic ester polymer is low, the molecular weight distribution is narrow, and the prepared acrylic ester polymer can improve the uniformity of PVC foaming;

[0029] (2) The molecular weight and the molecular weight distribution of the prepared acrylic ester polymer are controlled by adjusting the molar ratio of the reaction monomer, the initiator, the catalyst and the pentamethyl diethylene triamine;

[0030] (3) The present application effectively improves the initiation efficiency and reduces the molecular weight distribution width by controlling the reaction temperature, the reaction time and other process parameters, and the purity of the product is improved after the impurity removal step. BRIEF DESCRIPTION OF DRAWINGS

[0031] Figure 1 The SEC spectrum of the acrylic ester polymer prepared in Example 1;

[0032] Figure 2 The SEC spectrum of the acrylic ester polymer prepared in Example 2;

[0033] Figure 3 The SEC spectrum of the acrylic ester polymer prepared in Example 3;

[0034] Figure 4 The SEC spectrum of the acrylic ester polymer prepared in Example 4;

[0035] Figure 5 The SEC spectrum of the acrylic ester polymer prepared in Comparative Example 1;

[0036] Figure 6 The SEC spectrum of the acrylic ester polymer prepared in Comparative Example 2;

[0037] Figure 7 The SEC spectrum of the acrylic ester polymer prepared in Comparative Example 3;

[0038] Figure 8 The SEC spectrum of the acrylic ester polymer prepared in Comparative Example 4;

[0039] Figure 9 The nuclear magnetic spectrum of the initiator prepared in Preparation Example 4. DETAILED DESCRIPTION

[0040] The present application will be further described below in conjunction with specific embodiments, but the present application is not limited to the following embodiments. Those skilled in the art can make various modifications according to the basic idea of the present application, as long as they do not deviate from the basic idea of the present application, and they are within the scope of the present application.

[0041] In the present embodiment, before the preparation of the initiator, the allyl polyethylene glycol is precipitated with diethyl ether for 2.5 h, and then placed in a vacuum drying oven and dried at 40°C for 24 h; the hydrogen bromide aqueous solution and dichloromethane are dried with anhydrous sodium sulfate and deoxygenated with nitrogen for 30 min.

[0042] Preparation Example 1

[0043] The preparation method of the initiator is as follows: under nitrogen protection, 17 mmol of allyl polyethylene glycol and 100 mL of dichloromethane are added to a three-necked flask, stirred until completely dissolved, 1 mmol of azobisisobutyronitrile is added, and stirring is continued until completely dissolved; the water bath is warmed to 50°C, and 40% hydrogen bromide aqueous solution (hydrogen bromide dosage is 20 mmol) is added dropwise under stirring at a rotation speed of 300 rpm; the reaction is kept at temperature for 4 h, cooled to room temperature, and saturated sodium bicarbonate solution is slowly added until the pH value is 6.8; stirring is performed for 10 min, and the layers are separated after standing; the organic phase is collected, the aqueous phase is extracted twice with 30 mL of dichloromethane, the organic phases obtained by extraction are combined, dried with anhydrous magnesium sulfate for 2 h, and dropped into excess diethyl ether; white precipitate is produced by stirring, and the solid is collected by filtration and placed in a vacuum drying oven and dried at 40°C for 24 h to obtain the initiator.

[0044] Preparation Example 2

[0045] The preparation method of the initiator is as follows: under nitrogen protection, 19 mmol of allyl polyethylene glycol and 100 mL of dichloromethane are added to a three-necked flask, stirred until completely dissolved, 2 mmol of azobisisobutyronitrile is added, and stirring is continued until completely dissolved; the water bath is warmed to 60°C, and 45% hydrogen bromide aqueous solution (hydrogen bromide dosage is 25 mmol) is added dropwise under stirring at a rotation speed of 500 rpm; the reaction is kept at temperature for 6 h, cooled to room temperature, and saturated sodium bicarbonate solution is slowly added until the pH value is 7.5; stirring is performed for 15 min, and the layers are separated after standing; the organic phase is collected, the aqueous phase is extracted twice with 40 mL of dichloromethane, the organic phases obtained by extraction are combined, dried with anhydrous magnesium sulfate for 3 h, and dropped into excess diethyl ether; white precipitate is produced by stirring, and the solid is collected by filtration and placed in a vacuum drying oven and dried at 45°C for 24 h to obtain the initiator.

[0046] Preparation Example 3

[0047] The preparation method of the initiator is: under the protection of nitrogen, 18 mmol of allyl polyethylene glycol and 100 mL of dichloromethane are added to a three-necked flask, stirred until completely dissolved, 1.4 mmol of azobisisobutyronitrile is added, continue to stir until completely dissolved, the water bath is heated to 55℃, and the stirring speed is 400 rpm. Drop 43% hydrogen bromide aqueous solution (hydrogen bromide dosage is 22 mmol) into the solution, and keep the temperature for 5 hours. Cool to room temperature, slowly add saturated sodium bicarbonate solution to pH 7.0, stir for 12 min, stand for separation, collect the organic phase, extract the aqueous phase with 35 mL of dichloromethane twice, combine the organic phase and the extracted organic phase, dry with anhydrous magnesium sulfate for 2.5 h, drop into excess ether, stir to produce white precipitate, filter, collect the solid, and dry in a vacuum drying oven at 43℃ for 24 h to obtain the initiator.

[0048] Preparation Example 4

[0049] The preparation method of the initiator is: under the protection of nitrogen, 18 mmol of allyl polyethylene glycol and 100 mL of dichloromethane are added to a three-necked flask, stirred until completely dissolved, 1.4 mmol of azobisisobutyronitrile is added, continue to stir until completely dissolved, the water bath is heated to 55℃, and the stirring speed is 400 rpm. Drop 43% hydrogen bromide aqueous solution (hydrogen bromide dosage is 22 mmol) into the solution, and keep the temperature for 5 hours. Cool to room temperature, slowly add saturated sodium bicarbonate solution to pH 7.0, stir for 12 min, stand for separation, collect the organic phase, extract the aqueous phase with 35 mL of dichloromethane twice, combine the organic phase and the extracted organic phase, dry with anhydrous magnesium sulfate for 2.5 h, drop into excess ether, stir to produce white precipitate, filter, collect the solid, and dry in a vacuum drying oven at 43℃ for 24 h to obtain the initiator.

[0050] Example 1

[0051] A preparation method of a low molecular weight acrylate polymer, comprising the following steps:

[0052] S1: anhydrous ethanol, reaction monomer and initiator are added to a reaction kettle, stirred uniformly, frozen with liquid nitrogen to solid state, vacuumized for 10 min, introduced with nitrogen to thaw, and repeated for 3 times to obtain a mixed solution A;

[0053] S2: under the protection of nitrogen, cuprous chloride and pentamethyldiethylene triamine are added to the mixed solution A prepared in step S1, stirred uniformly, heated to 70℃ in a water bath, and stirred at a speed of 300 rpm for 2 h to obtain a primary product;

[0054] S3: oxygen was bubbled into the initial product prepared in step S2 for 5 min, and the initial product was washed with dilute hydrochloric acid with a concentration of 0.8 mol / L for 3 times, and the organic phase was dropped into excessive methanol for precipitation, and the mixture was allowed to stand for 1 h, and then filtered, and the solid was placed into a vacuum drying oven for drying at 40℃ for 24 h to obtain the low molecular weight acrylate polymer.

[0055] The initiator in the example was prepared by Preparation Example 1. The reaction monomers in step S1 were composed of methyl acrylate, methyl methacrylate and methacrylic acid with a mass ratio of 3:5:1; the molar ratio of the reaction monomers in step S1, the initiator, the catalyst in step S2 and pentamethyldiethylene triamine was 48:5:1:1.

[0056] Example 2

[0057] A preparation method of a low molecular weight acrylate polymer, comprising the following steps:

[0058] S1: anhydrous ethanol, reaction monomers and initiator were added into a reaction kettle, and stirred uniformly, and then frozen to solid state by liquid nitrogen, and vacuumized for 15 min, and then nitrogen was introduced to thaw, and the operation was repeated for 5 times to obtain a mixed solution A;

[0059] S2: under the protection of nitrogen, cuprous bromide and pentamethyldiethylene triamine were added into the mixed solution A prepared in step S1, and stirred uniformly, and then heated to 80℃ by water bath, and stirred at a rotation speed of 500 rpm for 4 h to obtain an initial product;

[0060] S3: oxygen was bubbled into the initial product prepared in step S2 for 10 min, and the initial product was washed with dilute hydrochloric acid with a concentration of 1.2 mol / L for 5 times, and the organic phase was dropped into excessive methanol for precipitation, and the mixture was allowed to stand for 2 h, and then filtered, and the solid was placed into a vacuum drying oven for drying at 45℃ for 30 h to obtain the low molecular weight acrylate polymer.

[0061] The initiator in the example was prepared by Preparation Example 2. The reaction monomers in step S1 were composed of methyl acrylate, methyl methacrylate and methacrylic acid with a mass ratio of 7:9:3; the molar ratio of the reaction monomers in step S1, the initiator, the catalyst in step S2 and pentamethyldiethylene triamine was 52:7:1:1.

[0062] Example 3

[0063] A preparation method of a low molecular weight acrylate polymer, comprising the following steps:

[0064] S1: anhydrous ethanol, reaction monomers and initiator were added into a reaction kettle, and stirred uniformly, and then frozen to solid state by liquid nitrogen, and vacuumized for 13 min, and then nitrogen was introduced to thaw, and the operation was repeated for 4 times to obtain a mixed solution A;

[0065] S2: Under the protection of nitrogen, add cuprous bromide and pentamethyldiethylenetriamine into the mixed solution A prepared in step S1, stir uniformly, heat to 75°C in water bath, stir at the speed of 400 rpm for 3.2 h to obtain the primary product;

[0066] S3: Pass oxygen into the primary product prepared in step S2 for 8 min, wash with dilute hydrochloric acid with the concentration of 1.0 mol / L for 4 times, separate the liquid, drop the organic phase into excessive methanol to precipitate, stand for 1.5 h, filter, put the solid into the vacuum drying oven to dry at 43°C for 28 h to obtain the low molecular weight acrylate polymer.

[0067] The initiator in the example is prepared by the preparation example 3. The reaction monomers in step S1 are composed of methyl acrylate, methyl methacrylate and methacrylic acid according to the mass ratio of 5:8:2; the molar ratio of the reaction monomers in step S1, the initiator, the catalyst in step S2 and pentamethyldiethylenetriamine is 49:6:1:1.

[0068] Example 4

[0069] A preparation method of a low molecular weight acrylate polymer, comprising the following steps:

[0070] S1: Put anhydrous ethanol, reaction monomers and initiator into a reaction kettle, stir uniformly, freeze to solid state with liquid nitrogen, vacuumize for 13 min, introduce nitrogen to thaw, and repeat for 4 times to obtain a mixed solution A;

[0071] S2: Under the protection of nitrogen, add cuprous bromide and pentamethyldiethylenetriamine into the mixed solution A prepared in step S1, stir uniformly, heat to 75°C in water bath, stir at the speed of 400 rpm for 3.2 h to obtain the primary product;

[0072] S3: Pass oxygen into the primary product prepared in step S2 for 8 min, wash with dilute hydrochloric acid with the concentration of 1.0 mol / L for 4 times, separate the liquid, drop the organic phase into excessive methanol to precipitate, stand for 1.5 h, filter, put the solid into the vacuum drying oven to dry at 43°C for 28 h to obtain the low molecular weight acrylate polymer.

[0073] The initiator in the example is prepared by the preparation example 4. The reaction monomers in step S1 are composed of methyl acrylate, methyl methacrylate and methacrylic acid according to the mass ratio of 5:8:2; the molar ratio of the reaction monomers in step S1, the initiator, the catalyst in step S2 and pentamethyldiethylenetriamine is 51:6:1:1.

[0074] Comparative example 1

[0075] The low molecular weight acrylate polymer in the present comparative example is prepared by the preparation method of low molecular weight acrylate polymer disclosed in the Chinese patent publication CN17551228A, and the reaction monomers are composed of methyl acrylate, methyl methacrylate and methacrylic acid in a mass ratio of 5:8:2.

[0076] Comparative Example 2

[0077] The preparation method of the acrylate polymer in the present comparative example is similar to that in Example 4, and the difference between the present comparative example and Example 4 is that the molar ratio of allyl polyethylene glycol, azobisisobutyronitrile and hydrogen bromide in the preparation method of the initiator in the present comparative example is 13:10:15.

[0078] Comparative Example 3

[0079] The preparation method of the acrylate polymer in the present comparative example is similar to that in Example 4, and the difference between the present comparative example and Example 4 is that the molar ratio of the reaction monomers, the initiator in step S1 and the catalyst, pentamethyldiethylenetriamine in step S2 in the present comparative example is 35:12:1:1.

[0080] Comparative Example 4

[0081] The preparation method of the acrylate polymer in the present comparative example is similar to that in Example 4, and the difference between the present comparative example and Example 4 is that the molar ratio of the reaction monomers, the initiator in step S1 and the catalyst, pentamethyldiethylenetriamine in step S2 in the present comparative example is 67:5:1:1.

[0082] Test Example

[0083] Monomer conversion rate: The low molecular weight acrylate polymers prepared in Examples 1-4 and Comparative Examples 1-4 are tested by gas chromatograph;

[0084] Molecular weight (Mn) and molecular weight distribution (PDI): The low molecular weight acrylate polymers prepared in Examples 1-4 and Comparative Examples 1-4 are tested for relative molecular mass (Mn), weight average molecular weight (Mw) and molecular weight distribution (Mw / Mn) by size exclusion chromatography (SEC).

[0085] The test results are shown in Table 1 and Figures 1-8 .

[0086] Table 1 Test results of monomer conversion rate, Mn and PDI

[0087]

[0088] From Table 1 and Figures 1-4It can be seen that the monomer conversion rate of the low molecular weight acrylate polymer preparation method provided by the present invention is >99%, the relative molecular mass of the obtained acrylate polymer is about 5000 g / mol, and the SEC curves are all single peaks, which basically conform to the normal distribution law, with a molecular weight distribution ≤1.13 and a relatively narrow molecular weight distribution.

[0089] Compared to Example 4, Comparative Example 1 used a small molecule initiator to prepare acrylate polymers, but the monomer conversion rate decreased, while the relative molecular mass and molecular weight distribution increased. This indicates that the macromolecular initiator used in this invention can better control the molecular mass and molecular weight distribution of the polymerization product compared to the small molecule initiator. Comparative Example 2 changed the molar ratio of allyl polyethylene glycol, azobisisobutyronitrile, and hydrogen bromide in the initiator preparation method, but the relative molecular mass decreased and the molecular weight distribution increased. This indicates that in the initiator preparation process, the molar ratio of allyl polyethylene glycol, azobisisobutyronitrile, and hydrogen bromide... The molar ratio of reactants, initiators, catalysts, and pentamethyldiethylenetriamine has been optimized. Comparative Example 3 changed the molar ratio of reactants, initiators, catalysts, and pentamethyldiethylenetriamine, but the monomer conversion rate and relative molecular mass decreased, while the molecular weight distribution increased. Comparative Example 4 changed the molar ratio of reactants, initiators, catalysts, and pentamethyldiethylenetriamine, but the monomer conversion rate decreased, while the relative molecular mass and molecular weight distribution increased. This indicates that in the synthesis of low molecular weight acrylate polymers, the molar ratio of reactants, initiators, catalysts, and pentamethyldiethylenetriamine is the key factor controlling the molecular weight and molecular weight distribution of the polymer product.

[0090] In addition, the initiator prepared in Example 4 was characterized by NMR, and the test results are shown in [Figure 4]. Figure 9 .Depend on Figure 9 It can be seen that the alkenyl characteristic peak (δ 5.0-5.2 ppm, -CH=CH2) disappears, the chemical shift δ of 5.4 ppm corresponds to the characteristic peak of -OH, the chemical shift δ of 4.2 ppm corresponds to the characteristic peak of -CH2-, the chemical shift δ of 3.5-3.70 ppm corresponds to the characteristic peak of -CH2-CH2-, and the chemical shift δ of 1.88 ppm corresponds to the characteristic peak of the methylene group in -CH2-CH2-Br. This proves that the anti-Markovnikov addition reaction was successful.

[0091] The above embodiments are merely illustrative of the present invention and are not intended to limit the invention. Those skilled in the art should not modify the above embodiments without departing from the spirit and scope of the present invention. All equivalent modifications or alterations made by those skilled in the art without departing from the technical concept of the present invention are still within the protection scope of the present invention.

Claims

1. A method for preparing a low molecular weight acrylate polymer, characterized in that, Includes the following steps: S1: Add anhydrous ethanol, reactant monomer and initiator to the reaction vessel, stir evenly, remove oxygen, and obtain mixture A; S2: Under inert gas protection, continue to add catalyst and pentamethyldiethylenetriamine to the mixture A obtained in step S1, stir evenly, heat in a water bath to 70-80℃, stir and react for 2-4 hours to obtain the initial product; S3: Introduce oxygen into the initial product obtained in step S2, wash, separate the liquid and liquid phases, add the organic phase dropwise into methanol, let stand for 1-2 hours, filter, dry, and obtain low molecular weight acrylate polymers. The initiator was prepared by an anti-Markovnikov addition reaction of allyl polyethylene glycol and hydrogen bromide under the initiation of azobisisobutyronitrile; The molar ratio of allyl polyethylene glycol, azobisisobutyronitrile, and hydrogen bromide is 17-19:1-2:20-25; The reactive monomers described in step S1 consist of methyl acrylate, methyl methacrylate, and methacrylic acid in a mass ratio of 3-7:5-9:1-3. The molar ratio of the reaction monomer, initiator, catalyst, and pentamethyldiethylenetriamine mentioned in step S1 is 48-52:5-7:1:

1.

2. The method for preparing the low molecular weight acrylate polymer according to claim 1, characterized in that, The initiator is prepared as follows: Under inert gas protection, allyl polyethylene glycol and dichloromethane are mixed and stirred to dissolve. Azobisisobutyronitrile is added and stirred to dissolve. The mixture is heated to 50-60°C in a water bath. Hydrogen bromide aqueous solution is added dropwise while stirring. The mixture is kept at this temperature for 4-6 hours. After cooling, saturated sodium bicarbonate solution is added to adjust the pH to 6.8-7.

5. The mixture is stirred for 10-15 minutes, allowed to stand for separation, and the organic phase is collected. The organic phase is dried with anhydrous magnesium sulfate and added dropwise to diethyl ether. A white precipitate is produced by stirring. The precipitate is filtered and dried to obtain the initiator.

3. The method for preparing the low molecular weight acrylate polymer according to claim 2, characterized in that, The mass percentage of the hydrogen bromide aqueous solution is 40%-45%.

4. The method for preparing the low molecular weight acrylate polymer according to claim 1, characterized in that, The catalyst mentioned in step S2 is cuprous bromide or cuprous chloride.

5. The method for preparing the low molecular weight acrylate polymer according to claim 1, characterized in that, The deoxygenation process in step S1 specifically involves freezing the mixture to a solid state with liquid nitrogen, evacuating it for 10-15 minutes, thawing it by introducing nitrogen gas, and repeating this process 3-5 times.

6. The method for preparing the low molecular weight acrylate polymer according to claim 1, characterized in that, The molar ratio of the reaction monomer, initiator, catalyst, and pentamethyldiethylenetriamine mentioned in step S1 is 51:6:1:

1.

7. The method for preparing the low molecular weight acrylate polymer according to claim 1, characterized in that, The washing in step S3 is a dilute hydrochloric acid wash, which is performed 3-5 times, and the concentration of the dilute hydrochloric acid is 0.8-1.2 mol / L; the drying temperature is 40-45℃ and the drying time is 24-30 h.

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