Modified polyvinyl alcohol, preparation method and application thereof, and water-based paint

Abstract

The invention relates to the technical field of paint chemical industry, in particular to modified polyvinyl alcohol, a preparation method and application thereof and water-based paint. The modified polyvinyl alcohol comprises a main chain and end sealing structures at the two ends of the main chain; wherein the main chain contains a structural unit A, a structural unit B and a structural unit C; the weight ratio of the (structural unit A + structural unit B) to the structural unit C is 100: (0.5-3.5); the alcoholysis degree of the modified polyvinyl alcohol is 65 to 90 mol percent. The modified polyvinyl alcohol has the comprehensive effects of excellent dispersion stability, good wettability, good fluidity and good normal-temperature solubility, and as a dispersing agent, the modified polyvinyl alcohol can make the high-solid-content water-based paint have better fluidity and higher stability.

Description

Technical Field

[0001] The present invention relates to the technical field of coating chemicals, and particularly relates to a modified polyvinyl alcohol, a preparation method and application thereof, and an aqueous coating. Background Art

[0002] A coating refers to a fine chemical product that can form a continuous protective film with a certain strength or a film with a certain special function on the surface of an object after being coated on the surface of the object by a specific construction method and cured. Coatings generally consist of a film-forming substance, a solvent, pigments, and additives. Among them, the film-forming substance, also known as the binder, is the main substance that enables the coating to firmly adhere to the surface of the coated object and form a continuous film; the solvent is a volatile component, which can be mainly divided into organic solvents and water; pigments are insoluble fine particles dispersed in the paint, which can be divided into coloring pigments and extender pigments, and are mainly used for coloring, providing protection, decoration, and reducing costs; additives account for a very small proportion in the coating components, but play the most important role in the storage, construction, film formation, and tolerance performance of the coating. Common additives in coatings include leveling agents, thickeners, surfactants, pigment dispersants, plasticizers, driers, curing agents, fungicides, and mildew inhibitors.

[0003] Pigment dispersants, also known as wetting dispersants, commonly used pigment dispersants mainly include inorganic types, surfactant types, and polymer types. The polymer types have better effects, so polymer dispersants are often called superdispersants. Polymer dispersants include natural polymers and synthetic polymers. Natural polymers are mainly used in solvent-based coatings. Synthetic polymers include polyacrylates, polyether derivatives, maleic acid-isobutene (or styrene) copolymer salts, polyvinylpyrrolidone, ethers, etc. However, in actual use, synthetic polymer dispersants have problems such as adaptability and stability. The most commonly used polyacrylate dispersants at present have excellent dispersion ability, but due to the large ion concentration, the stability of the dispersion is poor, the initial wettability of the pigment is poor, a wetting agent needs to be used in combination, the compatibility with the color paste of the coating is poor, and color matching problems are likely to occur, and it is not suitable for the preparation of base color coatings; polyether / polyethylene oxide (PEO) dispersants have a relatively low molecular weight, and the aggregated state is easy to flow, but there are problems such as easy to free from the coating film and damage to the physical and chemical properties of the coating; maleic acid-isobutene (or styrene) copolymer salt dispersants are mainly used in industrial on-line coatings and are not suitable for compounding with anionic additives.

[0004] Therefore, it is urgent to develop a dispersant with excellent dispersion stability, good initial wettability for pigments, easy to flow, and good compatibility with other coating additives to meet the needs of different pigment dispersions, excellent color development and stability of pigment slurries. Summary of the Invention

[0005] The present invention aims at the problems of unsatisfactory dispersion stability and poor wettability existing in the existing dispersants for waterborne coatings, and provides a modified polyvinyl alcohol, a preparation method and application thereof, and a waterborne coating.

[0006] To achieve the above object, in the first aspect of the present invention, a modified polyvinyl alcohol is provided, which includes a main chain and end-capping structures at both ends of the main chain; wherein,

[0007] the main chain contains structural unit A, structural unit B and structural unit C;

[0008] the structural unit A has the structure shown in formula (1); the structural unit B has the structure shown in formula (2); the structural unit C has the structure shown in formula (3) and / or formula (4);

[0009]

[0010] wherein, R 1 is selected from an alkyl group of C 1- C 8 ; R 2 , R 3 , R 4 , R 5 , R 6 , R 7 , R 8 , R 9 are each independently selected from -H or an alkyl group of C 1- C 5 ; Z and Q are each independently selected from K + , Na + or NH 4 + ;

[0011] the molar ratio of (structural unit A + structural unit B) to structural unit C is 100:(0.5 - 3.5);

[0012] the end-capping structure has the structure shown in formula (5);

[0013]

[0014] wherein, R 10 is selected from -H, an alkyl group of C 1- C 5 , propenyl, -CH 2 CH 2 CH 2 CHO or

[0015] the degree of alcoholysis of the modified polyvinyl alcohol is 65 - 90 mol%.

[0016] The second aspect of the present invention provides a method for preparing a modified polyvinyl alcohol, comprising:

[0017] (1) In the presence of an initiator and a solvent, polymerize monomer A', monomer B' and monomer C' to obtain an intermediate polymerization product;

[0018] (2) Alcoholize the intermediate polymerization product in the presence of a base to obtain a modified polyvinyl alcohol;

[0019] Wherein, the monomer A' has the structure shown in formula (6); the monomer B' has the structure shown in formula (7) and / or formula (8); the monomer C' has the structure shown in formula (9);

[0020]

[0021] Wherein, R 1 is selected from C 1- C 8 alkyl; R 2 , R 3 , R 4 , R 5 , R 6 , R 7 , R 8 , R 9 are each independently selected from -H or C 1- C 5 alkyl; Z and Q are each independently selected from H + , K + , Na + or NH 4 + ; R 10 is selected from -H, C 1- C 5 alkyl, propenyl, -CH 2 CH 2 CH 2 CHO or

[0022] The weight ratio of the monomer A': monomer B': monomer C' is 100: (1 - 4.9): (0.8 - 6).

[0023] The third aspect of the present invention provides a modified polyvinyl alcohol prepared by the preparation method described in the second aspect above.

[0024] The fourth aspect of the present invention provides the application of the modified polyvinyl alcohol described in the first aspect or the third aspect above as a dispersant in an aqueous coating.

[0025] The fifth aspect of the present invention provides an aqueous coating containing the modified polyvinyl alcohol described in the first aspect or the third aspect above.

[0026] Through the above technical solutions, the present invention has the following beneficial effects:

[0027] (1) The modified polyvinyl alcohol provided by the present invention introduces a structural unit containing a sulfonic acid group into the main chain structure, and the end-capping structure contains a carbonyl group, making the modified polyvinyl alcohol have excellent dispersion stability (manifested as high surface activity and low surface tension), good wettability (manifested as low surface tension), good fluidity (manifested as low viscosity, and the viscosity of an aqueous solution of this modified polyvinyl alcohol at a concentration of 4 wt% is 2 - 5.5 mPa·s at 25°C), and good solubility at room temperature;

[0028] (2) The waterborne coating using the modified polyvinyl alcohol provided by the present invention as a dispersant has the characteristics of high solid content, good fluidity, high stability, and bright color, and can be used at a lower temperature;

[0029] (3) The preparation process is simple and the raw materials are easily available, which is conducive to industrial promotion. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 It is the infrared spectrum diagram of the modified polyvinyl alcohol prepared in Example 1 of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0031] In the ranges disclosed herein, the endpoints and any values are not limited to the exact ranges or values, and these ranges or values should be understood to include values close to these ranges or values. For numerical ranges, between the endpoint values of each range, between the endpoint values of each range and individual point values, and between individual point values, they can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be regarded as specifically disclosed herein.

[0032] The following details the specific embodiments of the present invention. It should be understood that the specific embodiments described herein are only for explaining and illustrating the present invention, and are not used to limit the present invention.

[0033] The first aspect of the present invention provides a modified polyvinyl alcohol, including a main chain and end-capping structures at both ends of the main chain; wherein,

[0034] The main chain contains structural unit A, structural unit B, and structural unit C;

[0035] The structural unit A has the structure shown in formula (1); the structural unit B has the structure shown in formula (2); the structural unit C has the structure shown in formula (3) and / or formula (4);

[0036]

[0037] Wherein, R1 Selected from C 1- C 8 alkyl; R 2 、R 3 、R 4 、R 5 、R 6 、R 7 、R 8 、R 9 are each independently selected from -H or C 1- C 5 alkyl; Z and Q are each independently selected from K + 、Na + or NH 4 + ;

[0038] The molar ratio of said (structural unit A + structural unit B) to structural unit C is 100:(0.5 - 3.5);

[0039] The end-capping structure has the structure shown in formula (5);

[0040]

[0041] wherein, R 10 is selected from -H, C 1- C 5 alkyl, propenyl, -CH 2 CH 2 CH 2 CHO or

[0042] The degree of alcoholysis of the modified polyvinyl alcohol is 65 - 90 mol%.

[0043] According to the present invention, in the main chain structure of the modified polyvinyl alcohol, in structural unit B, preferably, R 1 is selected from C 1- C 4 alkyl, more preferably -CH 3 , and further has a smaller steric hindrance, which can make the modified polyvinyl alcohol have better solubility.

[0044] According to the present invention, by introducing a modified structural unit C containing a sulfonic acid group into the main chain structure of the modified polyvinyl alcohol, the modified structural unit C can provide free ions (-SO 3 2- and cations), and the structural unit C has a certain steric hindrance, which can make the modified polyvinyl alcohol have good water solubility and dispersion stability, and is beneficial to improving the dispersion efficiency.

[0045] According to the present invention, in the main chain structure of the modified polyvinyl alcohol, in structural unit C, preferably, R 2 、R 3 、R 4 、R 5 、R 6 、R 7 、R 8 、R 9 are each independently selected from -H or an alkyl group of C 1- C 3 . This can make the steric hindrance around the sulfonic acid group lower, facilitating the ordered arrangement of hydrophobic molecules, and enabling the modified polyvinyl alcohol to have higher dispersion stability and lower surface tension.

[0046] According to the present invention, the structural unit C may only have the structure shown in formula (3) or formula (4), or may contain both the structures shown in formula (3) and formula (4). In some preferred embodiments of the invention, the structural unit C is a structural unit having the structure shown in formula (4), and the sulfonic acid group with relatively large steric hindrance is on the side chain, which is more beneficial for increasing the content of the structural unit C in the main chain. Further preferably, the structural unit C is and / or

[0047] According to the present invention, in the main chain structure of the modified polyvinyl alcohol, on the basis that the structural unit A, structural unit B, and structural unit C satisfy the above ratios, preferably, the molar ratio of (structural unit A + structural unit B) to structural unit C is 100:(1 - 3), which can enable the modified polyvinyl alcohol to have better dispersion stability, wettability, fluidity, and better water solubility.

[0048] According to the present invention, both ends of the main chain structure of the modified polyvinyl alcohol are capped with a capping structure containing a carbonyl group, which can make the modified polyvinyl alcohol have better fluidity, and further enable the modified polyvinyl alcohol to better combine with the coating as a dispersant, enhancing the color fastness of the coating.

[0049] According to the present invention, in the capping structure of the modified polyvinyl alcohol shown in formula (5), preferably, R 10 is selected from -H or an alkyl group of C 1- C 3 , which can make the modified polyvinyl alcohol have better fluidity.

[0050] According to the present invention, in the capping structure of the modified polyvinyl alcohol shown in formula (5), represents the connection position of the capping structure to the main chain.

[0051] According to the present invention, the end-capping structures at both ends of the main chain structure of the modified polyvinyl alcohol may be the same or different, preferably the same.

[0052] According to the present invention, preferably, the degree of alcoholysis of the modified polyvinyl alcohol is 75 mol% - 89 mol%, which has both hydrophilic and lipophilic properties and is beneficial to maintaining good dispersibility.

[0053] According to the present invention, the weight-average molecular weight of the modified polyvinyl alcohol is 50 - 75 g / mol, preferably 55 - 65 g / mol.

[0054] The modified polyvinyl alcohol provided by the present invention introduces a modified structural unit containing a sulfonic acid group in a specific proportion in the main chain. The sulfonic acid group has a large steric hindrance and good polarity, and the end-capping structure of the modified polyvinyl alcohol contains a carbonyl modified functional group. Under the synergistic action of the above-mentioned modified structural unit and the carbonyl modified functional group, the modified polyvinyl alcohol has excellent dispersion stability (manifested as high surface activity and low surface tension), good wettability (manifested as low surface tension), good fluidity (manifested as low viscosity, and the viscosity of an aqueous solution of this modified polyvinyl alcohol with a concentration of 4 wt% is 2 - 5.5 mPa·s at 25 °C), and good solubility at room temperature. The modified polyvinyl alcohol provided by the present invention, as a dispersant, especially as a dispersant for high-solid-content waterborne coatings (the solid content of the waterborne coating ≥ 50 wt%), can make the coating have better fluidity, higher stability, bright color, and can be used at a lower temperature.

[0055] According to a most preferred embodiment of the present invention, the main chain of the modified polyvinyl alcohol contains structural unit A Structural unit B And structural unit C Among them, the molar ratio of (structural unit A + structural unit B) to structural unit C is 100:(1.8 - 2.5); the end-capping structure is The degree of alcoholysis of the modified polyvinyl alcohol is 85 - 90 mol%, and the weight-average molecular weight is 55 - 65 g / mol. The modified polyvinyl alcohol of the above most preferred embodiment has more excellent dispersion stability, wettability, fluidity and solubility at room temperature.

[0056] In the present invention, the degree of alcoholysis and viscosity of polyvinyl alcohol are measured according to the methods specified in "GB / T 12010.2 - 2010 Plastics - Polyvinyl Alcohol Materials (PVAL) - Part 2: Determination of Properties".

[0057] The second aspect of the present invention provides a method for preparing a modified polyvinyl alcohol, comprising:

[0058] (1) In the presence of an initiator and a solvent, monomers A', B' and C' are subjected to a polymerization reaction to obtain an intermediate polymerization product;

[0059] (2) In the presence of a base, the intermediate polymerization product is subjected to alcoholysis to obtain a modified polyvinyl alcohol;

[0060] Among them, the monomer A' has the structure shown in formula (6); the monomer B' has the structure shown in formula (7) and / or formula (8); the monomer C' has the structure shown in formula (9);

[0061]

[0062] Among them, R 1 is selected from alkyl groups of C 1- C 8 ; R 2 , R 3 , R 4 , R 5 , R 6 , R 7 , R 8 , R 9 are each independently selected from -H or alkyl groups of C 1- C 5 ; Z and Q are each independently selected from H + , K + , Na + or NH 4 + ; R 10 is selected from -H, alkyl groups of C 1- C 5 , propenyl, -CH 2 CH 2 CH 2 CHO or

[0063] The weight ratio of the monomer A': monomer B': monomer C' is 100:(1 - 4.9):(0.8 - 6).

[0064] According to the present invention, in the preparation method of the modified polyvinyl alcohol, in the monomer A' shown in formula (6), preferably, R 1 is selected from alkyl groups of C 1- C 4 . Further preferably, the monomer A' is selected from at least one of vinyl acetate, vinyl propionate, and vinyl butyrate, and more preferably vinyl acetate.

[0065] According to the present invention, in the preparation method of the modified polyvinyl alcohol, in the monomer B' shown in formula (7) or formula (8), R 2 , R 3 , R4 , R 5 , R 6 , R 7 , R 8 , R 9 are each independently selected from -H or C 1- C 3 alkyl. Further preferably, the monomer B' is selected from at least one of vinylsulfonic acid and / or its salts, allylsulfonic acid and / or its salts, and methallylsulfonic acid and / or its salts, more preferably methallylsulfonic acid and / or its salts, allylsulfonic acid and / or its salts, or a mixture of the two.

[0066] In the present invention, when the monomer B' is an organic salt, sodium salt is preferably used.

[0067] According to the present invention, in the preparation method of the modified polyvinyl alcohol, in the capping agent monomer C' represented by formula (9), preferably, R 10 is selected from -H or C 1- C 3 alkyl. Further preferably, the monomer C' is selected from n-butyraldehyde and / or acetaldehyde.

[0068] According to the present invention, in the preparation method of the modified polyvinyl alcohol, on the basis that the monomer A', monomer B' and monomer C' satisfy the above feeding ratio relationship, preferably, the weight ratio of monomer A': monomer B': monomer C' is 100: (1.5 - 4): (1 - 5.5). By using the above preferred feeding ratio, the prepared modified polyvinyl alcohol can have better dispersion stability, wettability, fluidity and better water solubility.

[0069] According to the present invention, in the preparation method of the modified polyvinyl alcohol, in step (1), the solvent can be any solvent that can be used for the polymerization reaction of vinyl esters, and the present invention has no particular limitation thereto. Preferably, the solvent can be selected from at least one of methanol, ethanol, isopropanol and tert-butanol, and further preferably methanol.

[0070] According to the present invention, in the preparation method of the modified polyvinyl alcohol, in step (1), the initiator can be selected from peroxide initiators or azo initiators.

[0071] In the present invention, preferably, the peroxide initiator can be selected from at least one of tert-butyl peroxyneodecanoate, diisopropyl diperoxy dicarbonate, bis(4-tert-butylcyclohexyl) peroxydicarbonate, tert-amyl peroxyneodecanoate, bis(2-ethylhexyl) peroxydicarbonate, bis(3,5,5-trimethylhexanoyl) peroxide and dipropyl peroxydicarbonate, and further preferably tert-butyl peroxyneodecanoate and / or diisopropyl diperoxy dicarbonate.

[0072] In the present invention, preferably, the azo initiator can be selected from azodiisobutyronitrile and / or azodiisooctanenitrile.

[0073] According to the present invention, the initiator is preferably fed in the form of an initiator solution. For example, the initiator and an alcohol can be mixed to form a solution, wherein, preferably, the weight ratio of the initiator to the alcohol is (0.5 - 5.5):100. The alcohol is preferably methanol.

[0074] According to the present invention, in step (1) of the method for preparing the modified polyvinyl alcohol, preferably, the weight ratio of the initiator to monomer A' is (0.05 - 0.3):100.

[0075] According to the present invention, in step (1) of the method for preparing the modified polyvinyl alcohol, preferably, the weight ratio of the solvent to monomer A' is (15 - 35):100.

[0076] According to the present invention, in step (1) of the method for preparing the modified polyvinyl alcohol, preferably, the conditions for the polymerization reaction include: a temperature of 62 - 65 °C and a time of 4.5 - 9.5 h.

[0077] According to a preferred embodiment of the present invention, the polymerization reaction can be carried out as follows: in the presence of an initiator and a solvent, monomers A' and B' are subjected to a first polymerization, and then monomer C' is added for a second polymerization to obtain the intermediate polymerization product. Among them, the types and feeding ratios of the initiator, solvent, monomer A', monomer B' and the capping agent monomer C' satisfy the above limitations; the conditions for the first polymerization include: a temperature of 62 - 65 °C and a time of 1.5 - 4 h; the conditions for the second polymerization include: a temperature of 62 - 65 °C and a time of 3 - 5.5 h.

[0078] According to the present invention, in step (1) of the method for preparing the modified polyvinyl alcohol, it further includes separating and removing the unreacted monomers in the product system after the polymerization reaction. For example, the product system can be mixed with an alcohol and heated to 75 - 90 °C, so that the unreacted monomers are distilled out together with the alcohol to achieve the removal of the unreacted monomers.

[0079] According to the present invention, in step (2) of the method for preparing the modified polyvinyl alcohol, the alcoholysis can be carried out with reference to the well-known alcoholysis method of polyvinyl acetate in the art. Preferably, the intermediate polymerization product can be diluted with methanol to obtain an intermediate polymerization product - methanol solution with a concentration of 25 - 55 wt%, and then mixed with an alkali - methanol solution for alcoholysis. After reaching the predetermined alcoholysis time, glacial acetic acid equimolar to the alkali is added to terminate the alcoholysis reaction. The obtained alcoholysis product is filtered and dried to obtain the modified polyvinyl alcohol.

[0080] According to the present invention, in the preparation method of the modified polyvinyl alcohol, in step (2), NaOH is preferably used as the base.

[0081] According to the present invention, in the preparation method of the modified polyvinyl alcohol, in step (2), preferably, the conditions for alcoholysis include: temperature is 32 - 45 °C, and time is 20 - 40 min.

[0082] The present invention copolymerizes a vinyl ester, an unsaturated monomer capable of providing a sulfonic acid group, and a capping agent aldehyde monomer, and then performs alcoholysis to prepare a modified polyvinyl alcohol having a sulfonic acid group in the main chain structure and a carbonyl group in the capping structure. The modified polyvinyl alcohol prepared by the method of the present invention has excellent dispersion stability (manifested as high surface activity and low surface tension), good wettability (manifested as low surface tension), good fluidity (manifested as low viscosity, the viscosity of an aqueous solution of this modified polyvinyl alcohol at a concentration of 4 wt% is 2 - 5.5 mPa·s at 25 °C), and good solubility at room temperature.

[0083] The third aspect of the present invention provides a modified polyvinyl alcohol prepared by the preparation method described in the second aspect above.

[0084] According to the present invention, the modified polyvinyl alcohol prepared by the method described in the second aspect above has the same structure, parameters, and properties as the modified polyvinyl alcohol described in the first aspect of the present invention above, and will not be elaborated here.

[0085] The fourth aspect of the present invention provides the application of the modified polyvinyl alcohol described in the first aspect or the third aspect above as a dispersant in a waterborne coating.

[0086] The modified polyvinyl alcohol provided by the present invention has the characteristics of low viscosity, high surface activity, and low surface tension, and can be well dissolved in water at room temperature. It has excellent dispersion stability, good wettability, good fluidity, and good solubility at room temperature, and can be used as a dispersant for waterborne coatings with excellent performance, especially as a dispersant for high-solid-content waterborne coatings. Compared with conventional PVA dispersants, it can make the coating have better fluidity, higher stability, bright color, and can be used at a lower temperature.

[0087] The fifth aspect of the present invention provides a waterborne coating containing the modified polyvinyl alcohol described in the first aspect or the third aspect above.

[0088] The present invention will be described in detail below through examples. In the following examples and comparative examples, unless otherwise specified, all are conventional methods; the reagents and materials, unless otherwise specified, can be obtained from commercial channels.

[0089] In the following examples and comparative examples, the molar ratio of the structural units contained in the obtained polyvinyl alcohol product was calculated from the feed amount of the raw materials.

[0090] Example 1

[0091] (1) Monomer A' (vinyl acetate), solvent methanol, monomer B' (sodium allylsulfonate), and a peroxide initiator solution (obtained by mixing tert-butyl peroxyneopentanoate initiator and methanol in a weight ratio of 1.2:100) were added to a polymerization kettle, and a first polymerization reaction was carried out at 63 °C for 2 h. Then, a capping agent monomer C' (acetaldehyde) was added and a second polymerization reaction was carried out at 63 °C for 4.5 h. After the second polymerization reaction ended, methanol was added to the polymerization kettle, and the temperature was raised to 80 °C for the removal treatment of unreacted monomers to obtain an intermediate polymerization product after monomer removal.

[0092] Among them, the weight ratio of monomer A': monomer B': capping agent monomer C' was 100:3.5:1.5; the weight ratio of initiator: monomer A' was 0.25:100; the weight ratio of solvent methanol: monomer A' was 25:100;

[0093] (2) The above intermediate polymerization product after monomer removal was diluted with methanol to obtain an intermediate polymerization product-methanol solution with a concentration of 40 wt%. Then, it was mixed with a NaOH-methanol solution (weight ratio of NaOH:methanol was 4:100) and subjected to alcoholysis (weight ratio of intermediate polymerization product:NaOH was 3000:100, alcoholysis temperature was 37 °C, and alcoholysis time was 22 min). After reaching the predetermined time, glacial acetic acid equimolar to NaOH was added to terminate the alcoholysis reaction. Then, the alcoholysis product was filtered and dried at 85 °C for 3 h to obtain modified polyvinyl alcohol (denoted as P1).

[0094] P1 was subjected to infrared spectroscopy test, and the results were as Figure 1 shown. Among them, at 1143.04 cm -1 and 1037.68 -1 cm were two characteristic peaks of -SO 3 Na. 1143.04 cm -1 was the asymmetric stretching vibration peak of -SO 3 Na; 1037.68 cm -1 was the symmetric stretching vibration peak of -SO 3 Na; 1715 cm -1 was the carbonyl peak; 1650 cm -1 was the stretching vibration peak of C=O in the amide; 2940 cm -1 was the stretching vibration peak of -CH 2 -; the broad peak at 3321 cm -1 was the stretching vibration peak of O-H; 1089 cm-1 is the stretching vibration peak of C-OH; 1329 cm -1 is the in-plane bending vibration peak of -OH. This indicates that vinyl acetate, sodium allylsulfonate, and the capping agent acetaldehyde have undergone copolymerization, indicating successful initiation of polymerization and preparation of the modified polyvinyl alcohol of the present invention.

[0095] In P1, the molar ratio of (structural unit A + structural unit B ) to structural unit C in the main chain is 100:2.23; the capping structure is

[0096] The degree of alcoholysis of P1 is 86.67 mol%, and the weight-average molecular weight is 60.62 g / mol.

[0097] Example 2

[0098] (1) Monomer A' (vinyl acetate), solvent methanol, monomer B' (sodium allylsulfonate), and azobisisobutyronitrile solution (prepared by mixing azobisisobutyronitrile and methanol in a weight ratio of 0.5:100) are added to the polymerization kettle, and the first polymerization reaction is carried out at 64°C for 3 h. Then, the capping agent monomer C' (acetaldehyde) is added and the second polymerization reaction is carried out at 64°C for 4.5 h; after the second polymerization reaction is completed, methanol is added to the polymerization kettle, and the temperature is raised to 80°C for the removal treatment of unreacted monomers to obtain the intermediate polymerization product after monomer removal;

[0099] Among them, the weight ratio of monomer A': monomer B': monomer C' is 100:3:1.5; the weight ratio of initiator to monomer A' is 0.078:100; the weight ratio of solvent methanol to monomer A' is 25:100;

[0100] (2) The above intermediate polymerization product after monomer removal is diluted with methanol to obtain an intermediate polymerization product-methanol solution with a concentration of 40 wt%. Then, it is mixed with a NaOH-methanol solution (the weight ratio of NaOH to methanol is 4:100) and subjected to alcoholysis (the weight ratio of intermediate polymerization product to NaOH is 3000:100, the alcoholysis temperature is 37°C, and the alcoholysis time is 22 min). After reaching the predetermined time, glacial acetic acid equimolar to the base is added to terminate the alcoholysis reaction. Then, the alcoholysis product is filtered and dried at 85°C for 3 h to obtain the modified polyvinyl alcohol (denoted as P2).

[0101] In P2, the molar ratio of (structural unit A + structural unit B ) to structural unit C in the main chain is 100:1.93; the capping structure is

[0102] The degree of alcoholysis of P2 is 87.6 mol%, and the weight-average molecular weight is 59.22 g / mol.

[0103] Example 3

[0104] (1) Monomer A' (vinyl acetate), solvent methanol, monomer B' (sodium 2-methylallylsulfonate), and azobisisobutyronitrile solution (prepared by mixing azobisisobutyronitrile and methanol in a weight ratio of 0.5:100) were added to a polymerization kettle, and the first polymerization reaction was carried out at 63 °C for 3 h. Then, capping agent monomer C' (acetaldehyde) was added and the second polymerization reaction was carried out at 63 °C for 3.5 h. After the second polymerization reaction ended, methanol was added to the polymerization kettle, and the temperature was raised to 80 °C for the removal of unreacted monomers to obtain an intermediate polymerization product after monomer removal.

[0105] Among them, the weight ratio of monomer A': monomer B': monomer C' is 100:3:2; the weight ratio of initiator: monomer A' is 0.080:100; the weight ratio of solvent methanol: monomer A' is 30:100.

[0106] (2) The intermediate polymerization product after monomer removal was diluted with methanol to obtain an intermediate polymerization product-methanol solution with a concentration of 40 wt%. Then, it was mixed with a NaOH-methanol solution (weight ratio of NaOH:methanol is 4:100) and subjected to alcoholysis (weight ratio of intermediate polymerization product:NaOH is 3000:100, alcoholysis temperature is 37 °C, and alcoholysis time is 22 min). After reaching the predetermined time, glacial acetic acid equimolar to the alkali was added to terminate the alcoholysis reaction. Then, the alcoholysis product was filtered and dried at 85 °C for 3 h to obtain modified polyvinyl alcohol (denoted as P3).

[0107] In P3, the molar ratio of (structural unit A + structural unit B ) : structural unit C is 100:1.41; the capping structure is

[0108] The degree of alcoholysis of P3 is 88.02 mol%, and the weight-average molecular weight is 57.40 g / mol.

[0109] Example 4

[0110] (1) Add monomer A' (vinyl acetate), solvent methanol, monomer B' (sodium 2-methylallylsulfonate), and azobisisobutyronitrile solution (prepared by mixing azobisisobutyronitrile and methanol at a weight ratio of 0.5:100) into a polymerization kettle, carry out the first polymerization reaction at 64 °C for 3 h, then add capping agent monomer C' (n-butanal) and carry out the second polymerization reaction at 64 °C for 3.5 h; after the second polymerization reaction ends, add methanol to the polymerization kettle, raise the temperature to 80 °C for unreacted monomer removal treatment to obtain the intermediate polymerization product after monomer removal;

[0111] Among them, the weight ratio of monomer A': monomer B': monomer C' is 100:2.5:4.5; the weight ratio of initiator: monomer A' is 0.076:100; the weight ratio of solvent methanol: monomer A' is 25:100;

[0112] (2) Dilute the above intermediate polymerization product after monomer removal with methanol to obtain an intermediate polymerization product-methanol solution with a concentration of 40 wt%, then mix it with NaOH-methanol solution (weight ratio of NaOH:methanol is 4:100) and carry out alcoholysis (weight ratio of intermediate polymerization product:NaOH is 3000:100, alcoholysis temperature is 37 °C, alcoholysis time is 22 min), after reaching the predetermined time, add glacial acetic acid equimolar to the alkali to terminate the alcoholysis reaction, then filter the alcoholysis product and dry it at 85 °C for 3 h to obtain modified polyvinyl alcohol (denoted as P4).

[0113] In P4, the molar ratio of (structural unit A + structural unit B ) in the main chain: structural unit C is 100:1.23; the capping structure is

[0114] The alcoholysis degree of P4 is 87.7 mol%, and the weight-average molecular weight is 57.03 g / mol.

[0115] Example 5

[0116] (1) Add monomer A' (vinyl acetate), solvent methanol, monomer B' (sodium 2-methylallylsulfonate), and azobisisobutyronitrile solution (prepared by mixing azobisisobutyronitrile and methanol at a weight ratio of 0.5:100) into a polymerization kettle, carry out the first polymerization reaction at 64 °C for 3 h, then add capping agent monomer C' (n-butanal) and carry out the second polymerization reaction at 64 °C for 3.5 h; after the second polymerization reaction ends, add methanol to the polymerization kettle, raise the temperature to 80 °C for unreacted monomer removal treatment to obtain the intermediate polymerization product after monomer removal;

[0117] Among them, the weight ratio of monomer A': monomer B': monomer C' is 100:2.5:2.5; the weight ratio of initiator to monomer A' is 0.076:100; the weight ratio of solvent methanol to monomer A' is 25:100;

[0118] (2) Dilute the above-mentioned monomer-removed intermediate polymerization product with methanol to obtain an intermediate polymerization product-methanol solution with a concentration of 40 wt%, and then mix it with a NaOH-methanol solution (the weight ratio of NaOH to methanol is 4:100) and carry out alcoholysis (the weight ratio of intermediate polymerization product to NaOH is 3000:100, the alcoholysis temperature is 37 °C, and the alcoholysis time is 22 min). After reaching the predetermined time, add glacial acetic acid equimolar to the base to terminate the alcoholysis reaction, and then filter the alcoholysis product and dry it at 85 °C for 3 h to obtain modified polyvinyl alcohol (denoted as P5).

[0119] In P5, the molar ratio of (structural unit A + structural unit B ) to structural unit C is 100:1.07; the end-capping structure is

[0120] The alcoholysis degree of P5 is 89.1 mol%, and the weight-average molecular weight is 55.34 g / mol.

[0121] Example 6

[0122] (1) Add monomer A' (vinyl acetate), solvent methanol, monomer B' (sodium methyl vinyl sulfonate), and azobisisobutyronitrile solution (prepared by mixing azobisisobutyronitrile and methanol according to a weight ratio of 0.5:100) into the polymerization kettle, carry out the first polymerization reaction at 64 °C for 3 h, then add the end-capping agent monomer C' (n-butanal) and carry out the second polymerization reaction at 64 °C for 3.5 h; after the second polymerization reaction ends, add methanol to the polymerization kettle, raise the temperature to 80 °C to carry out the treatment for removing unreacted monomers, and obtain the monomer-removed intermediate polymerization product;

[0123] Among them, the weight ratio of monomer A': monomer B': monomer C' is 100:3.5:4.5; the weight ratio of initiator to monomer A' is 0.082:100; the weight ratio of solvent methanol to monomer A' is 25:100;

[0124] (2) Dilute the above-mentioned intermediate polymerization product after removing monomers with methanol to obtain an intermediate polymerization product-methanol solution with a concentration of 40 wt%, and then mix it with a NaOH-methanol solution (weight ratio of NaOH to methanol is 4:100) and carry out alcoholysis (weight ratio of intermediate polymerization product to NaOH is 3000:100, alcoholysis temperature is 37 °C, and alcoholysis time is 22 min). After reaching the predetermined time, add glacial acetic acid equimolar to the base to terminate the alcoholysis reaction. Then filter the alcoholysis product and dry it at 85 °C for 3 h to obtain modified polyvinyl alcohol (denoted as P6).

[0125] In P6, the content of (structural unit A + structural unit B ) in the main chain: structural unit C The molar ratio is 100:1.21; the end-capping structure is

[0126] The alcoholysis degree of P6 is 89.96 mol%, and the weight-average molecular weight is 57.66 g / mol.

[0127] Example 7

[0128] (1) Add monomer A' (vinyl acetate), solvent methanol, monomer B' (sodium 2-methylallylsulfonate), and a peroxide initiator solution (obtained by mixing tert-butyl peroxyneopentanoate initiator and methanol in a weight ratio of 1.2:100) into a polymerization kettle, carry out the first polymerization reaction at 64 °C for 3 h, then add end-capping agent monomer C' (phenylacetaldehyde) and carry out the second polymerization reaction at 64 °C for 3.5 h; after the second polymerization reaction ends, add methanol to the polymerization kettle, raise the temperature to 80 °C for the treatment of removing unreacted monomers to obtain an intermediate polymerization product after removing monomers;

[0129] Among them, the weight ratio of monomer A': monomer B': monomer C' is 100:4:5.5; the weight ratio of initiator to monomer A' is 0.088:100; the weight ratio of solvent methanol to monomer A' is 25:100;

[0130] (2) Dilute the above-mentioned intermediate polymerization product after removing monomers with methanol to obtain an intermediate polymerization product-methanol solution with a concentration of 40 wt%, and then mix it with a NaOH-methanol solution (weight ratio of NaOH to methanol is 4:100) and carry out alcoholysis (weight ratio of intermediate polymerization product to NaOH is 3000:100, alcoholysis temperature is 37 °C, and alcoholysis time is 22 min). After reaching the predetermined time, add glacial acetic acid equimolar to the base to terminate the alcoholysis reaction. Then filter the alcoholysis product and dry it at 85 °C for 3 h to obtain modified polyvinyl alcohol (denoted as P7).

[0131] In P7, the content of (structural unit A + Structural unit B ): Structural unit C The molar ratio is 100:1.23; the end-capping structure is

[0132] The degree of alcoholysis of P7 is 88.95 mol%, and the weight-average molecular weight is 54.59 g / mol.

[0133] Example 8

[0134] (1) Monomer A' (vinyl acetate), solvent methanol, monomer B' (sodium 2-methylallylsulfonate), and a peroxide initiator solution (prepared by mixing tert-butyl peroxyneopentanoate initiator and methanol in a weight ratio of 1.2:100) were added to a polymerization kettle, and the first polymerization reaction was carried out at 64 °C for 3 h. Then, the end-capping agent monomer C' (crotonaldehyde) was added and the second polymerization reaction was carried out at 64 °C for 3.5 h. After the second polymerization reaction ended, methanol was added to the polymerization kettle, and the temperature was raised to 80 °C for the removal treatment of unreacted monomers, obtaining an intermediate polymerization product after monomer removal;

[0135] Among them, the weight ratio of monomer A': monomer B': monomer C' is 100:4.5:4; the weight ratio of initiator: monomer A' is 0.086:100; the weight ratio of solvent methanol: monomer A' is 25:100;

[0136] (2) The above intermediate polymerization product after monomer removal was diluted with methanol to obtain an intermediate polymerization product-methanol solution with a concentration of 40 wt%. Then, it was mixed with a NaOH-methanol solution (the weight ratio of NaOH: methanol is 4:100) and subjected to alcoholysis (the weight ratio of intermediate polymerization product: NaOH is 3000:100, the alcoholysis temperature is 37 °C, and the alcoholysis time is 22 min). After reaching the predetermined time, glacial acetic acid equimolar to the base was added to terminate the alcoholysis reaction. Then, the alcoholysis product was filtered and dried at 85 °C for 3 h to obtain modified polyvinyl alcohol (denoted as P8).

[0137] In P8, the content of (structural unit A + structural unit B ): structural unit C The molar ratio is 100:1.22; the end-capping structure is

[0138] The degree of alcoholysis of P8 is 89.7 mol%, and the weight-average molecular weight is 53.73 g / mol.

[0139] Comparative Example 1

[0140] (1) Monomer A' (vinyl acetate), solvent methanol, monomer C' (acetaldehyde), and a peroxide initiator solution (prepared by mixing tert-butyl peroxyneodecanoate initiator and methanol in a weight ratio of 1.2:100) are added to a polymerization kettle, and a polymerization reaction is carried out at 64 °C for 6.5 h; after the polymerization reaction is completed, methanol is added to the polymerization kettle, and the temperature is raised to 80 °C for the removal of unreacted monomers to obtain an intermediate polymerization product after monomer removal;

[0141] Among them, the weight ratio of monomer A' to monomer C' is 100:1.5; the weight ratio of the initiator to monomer A' is 0.198:100; the weight ratio of solvent methanol to monomer A' is 25:100;

[0142] (2) The above intermediate polymerization product after monomer removal is diluted with methanol to obtain an intermediate polymerization product-methanol solution with a concentration of 40 wt%, and then mixed with a NaOH-methanol solution (the weight ratio of NaOH to methanol is 4:100) and subjected to alcoholysis (the weight ratio of the intermediate polymerization product to NaOH is 3000:100, the alcoholysis temperature is 37 °C, and the alcoholysis time is 22 min). After reaching the predetermined time, glacial acetic acid equimolar to the base is added to terminate the alcoholysis reaction, and then the alcoholysis product is filtered and dried at 85 °C for 3 h to obtain polyvinyl alcohol (denoted as D1).

[0143] In D1, the main chain contains structural unit A and structural unit B The end-capping structure is

[0144] The alcoholysis degree of D1 is 91.37 mol%, and the weight-average molecular weight is 50.54 g / mol.

[0145] Comparative Example 2

[0146] (1) Monomer A' (vinyl acetate), solvent methanol, monomer B' (sodium allylsulfonate), and a peroxide initiator solution (prepared by mixing tert-butyl peroxyneodecanoate initiator and methanol in a weight ratio of 1.2:100) are added to a polymerization kettle, and a polymerization reaction is carried out at 64 °C for 6.5 h; after the polymerization reaction is completed, methanol is added to the polymerization kettle, and the temperature is raised to 80 °C for the removal of unreacted monomers to obtain an intermediate polymerization product after monomer removal;

[0147] Among them, the weight ratio of monomer A' to monomer B' is 100:3.5; the weight ratio of the initiator to monomer A' is 0.17:100; the weight ratio of solvent methanol to monomer A' is 25:100;

[0148] (2) Dilute the above-mentioned intermediate polymerization product after the removal of unreacted monomers with methanol to obtain an intermediate polymerization product - methanol solution with a concentration of 40 wt%, and then mix it with a NaOH - methanol solution (weight ratio of NaOH to methanol is 4:100) and carry out alcoholysis (weight ratio of intermediate polymerization product to NaOH is 3000:100, alcoholysis temperature is 37 °C, and alcoholysis time is 22 min). After reaching the predetermined time, add glacial acetic acid in an amount equimolar to the base to terminate the alcoholysis reaction. Then filter the alcoholysis product and dry it at 85 °C for 3 h to obtain polyvinyl alcohol (denoted as D2).

[0149] In D2, the content of (structural unit A + structural unit B ) in the main chain: structural unit C The molar ratio is 100:1.71;

[0150] The alcoholysis degree of D2 is 85.97 mol%, and the weight-average molecular weight is 60.95 g / mol.

[0151] Comparative Example 3

[0152] (1) Add monomer A' (vinyl acetate), solvent methanol, monomer B' (sodium allylsulfonate), and a peroxide initiator solution (obtained by mixing tert-butyl peroxyneopentanoate initiator and methanol in a weight ratio of 1.2:100) into a polymerization kettle, carry out the first polymerization reaction at 64 °C for 2 h, then add the capping agent monomer D' (propyl mercaptan) and carry out the second polymerization reaction at 64 °C for 4.5 h; after the second polymerization reaction ends, add methanol to the polymerization kettle, raise the temperature to 80 °C to carry out the treatment for removing unreacted monomers, and obtain an intermediate polymerization product after the removal of unreacted monomers;

[0153] Among them, the weight ratio of monomer A': monomer B': monomer D' is 100:3.5:8.5; the weight ratio of initiator: monomer A' is 0.27:100; the weight ratio of solvent methanol: monomer A' is 25:100;

[0154] (2) Dilute the above-mentioned intermediate polymerization product after the removal of unreacted monomers with methanol to obtain an intermediate polymerization product - methanol solution with a concentration of 40 wt%, and then mix it with a NaOH - methanol solution (weight ratio of NaOH to methanol is 4:100) and carry out alcoholysis (weight ratio of intermediate polymerization product to NaOH is 3000:100, alcoholysis temperature is 37 °C, and alcoholysis time is 22 min). After reaching the predetermined time, add glacial acetic acid in an amount equimolar to the base to terminate the alcoholysis reaction. Then filter the alcoholysis product and dry it at 85 °C for 3 h to obtain modified polyvinyl alcohol (denoted as D3).

[0155] In D3, the content of (structural unit A + structural unit B ): Structural unit C The molar ratio is 100:2.23; the end-capping structure is

[0156] The degree of alcoholysis of D3 is 87.31 mol%, and the weight-average molecular weight is 56.73 g / mol.

[0157] Comparative Example 4

[0158] (1) Monomer A' (vinyl acetate), solvent methanol, monomer B' (sodium allylsulfonate), and a peroxide initiator solution (prepared by mixing tert-butyl peroxyneopentanoate initiator and methanol in a weight ratio of 1.2:100) were added to a polymerization kettle, and the first polymerization reaction was carried out at 64 °C for 2 h. Then, end-capping agent monomer C' (acetaldehyde) was added and the second polymerization reaction was carried out at 64 °C for 4.5 h. After the second polymerization reaction ended, methanol was added to the polymerization kettle, and the temperature was raised to 80 °C for unreacted monomer removal treatment to obtain an intermediate polymerization product after monomer removal;

[0159] Among them, the weight ratio of monomer A': monomer B': monomer C' is 100:5:1.5; the weight ratio of initiator: monomer A' is 0.25:100; the weight ratio of solvent methanol: monomer A' is 25:100;

[0160] (2) The above intermediate polymerization product after monomer removal was diluted with methanol to obtain an intermediate polymerization product-methanol solution with a concentration of 40 wt%. Then, it was mixed with a NaOH-methanol solution (the weight ratio of NaOH: methanol is 4:100) and subjected to alcoholysis (the weight ratio of intermediate polymerization product: NaOH is 3000:100, the alcoholysis temperature is 37 °C, and the alcoholysis time is 22 min). After reaching the predetermined time, glacial acetic acid equimolar to the base was added to terminate the alcoholysis reaction. Then, the alcoholysis product was filtered and dried at 85 °C for 3 h to obtain modified polyvinyl alcohol (denoted as D4).

[0161] In D4, the content of (structural unit A + structural unit B ) in the main chain: structural unit C The molar ratio is 100:3.61; the end-capping structure is

[0162] The degree of alcoholysis of D4 is 76.03 mol%, and the weight-average molecular weight is 69.36 g / mol.

[0163] Comparative Example 5

[0164] (1) Monomer A' (vinyl acetate), solvent methanol, and azobisisobutyronitrile solution (prepared by mixing azobisisobutyronitrile and methanol in a weight ratio of 0.5:100) were added to a polymerization kettle, and a polymerization reaction was carried out at 64 °C for 6.5 h. After the polymerization reaction ended, methanol was added to the polymerization kettle, and the temperature was raised to 80 °C for the removal of unreacted monomers, obtaining an intermediate polymerization product after monomer removal.

[0165] Among them, the weight ratio of the initiator to monomer A' was 0.049:100; the weight ratio of solvent methanol to monomer A' was 25:100.

[0166] (2) The above intermediate polymerization product after monomer removal was diluted with methanol to obtain an intermediate polymerization product - methanol solution with a concentration of 40 wt%. Then, it was mixed with a NaOH - methanol solution (weight ratio of NaOH to methanol was 4:100) and subjected to alcoholysis (weight ratio of intermediate polymerization product to NaOH was 3000:100, alcoholysis temperature was 37 °C, and alcoholysis time was 22 min). After reaching the predetermined time, glacial acetic acid equimolar to the base was added to terminate the alcoholysis reaction. Then, the alcoholysis product was filtered and dried at 85 °C for 3 h to obtain modified polyvinyl alcohol (denoted as D5).

[0167] The alcoholysis degree of D5 was 94.7 mol%, and the weight - average molecular weight was 48.14 g / mol.

[0168] Test Examples

[0169] The polyvinyl alcohols P1 - P8 and D1 - D5 prepared in Examples 1 - 8 and Comparative Examples 1 - 5 were subjected to performance tests. Specifically:

[0170] Viscosity test: P1 - P8 and D1 - D5 were respectively formulated with water into aqueous solutions with a polyvinyl alcohol concentration of 4 wt%, and the viscosity values of the aqueous solutions were measured at 25 °C.

[0171] Surface tension test: P1 - P8 and D1 - D5 were respectively formulated with water into aqueous solutions with a polyvinyl alcohol concentration of 0.2 wt%, and the surface tension was measured with a surface tension meter at 25 °C.

[0172] Solubility test: At 25 °C, P1 - P8 and D1 - D5 (both with a particle size of 20 mesh) were respectively mixed with water at a stirring rate of 350 revolutions per minute to prepare aqueous solutions with a polyvinyl alcohol concentration of 4 wt%, and the time required from the start of mixing to the complete dissolution of polyvinyl alcohol was recorded.

[0173] The test results are shown in Table 1.

[0174] Table 1

[0175]

[0176] As can be seen from Table 1, the modified polyvinyl alcohols P1 - P8 provided by the present invention have an ultra - low molecular weight. The viscosity of the aqueous solutions of P1 - P8 with a concentration of 4 wt% is less than 5 mPa·s at 25°C. They have a low viscosity and good fluidity. At the same time, P1 - P8 have an extremely low surface tension, high surface activity, excellent dispersion stability and wettability, and a fast dissolution rate in water at room temperature, showing excellent water solubility at room temperature. Therefore, they can be used as dispersants for water - based coatings with excellent performance, can be used at lower temperatures, and make the coatings have better fluidity and higher stability. In contrast, polyvinyl alcohols D1 - D5 do not have the structure or composition of the modified polyvinyl alcohols of the present invention, and their comprehensive performance is inferior to that of P1 - P8.

[0177] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited thereto. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solutions of the present invention, including any other suitable combination of each technical feature. These simple modifications and combinations should also be regarded as the content disclosed by the present invention and fall within the protection scope of the present invention.

Claims

1. A modified polyvinyl alcohol, characterized in that, it includes a main chain and end-capping structures at both ends of the main chain; wherein, the main chain contains structural unit A, structural unit B and structural unit C; the structural unit A has the structure shown in formula (1); the structural unit B has the structure shown in formula (2); the structural unit C has the structure shown in formula (3) and / or formula (4); Wherein, R 1 is selected from C 1- C 8 alkyl; R 2 , R 3 , R 4 , R 5 , R 6 , R 7 , R 8 , R 9 are each independently selected from -H or C 1- C 5 alkyl; Z and Q are each independently selected from K + , Na + or NH 4 + ; the molar ratio of (structural unit A + structural unit B) : structural unit C is 100 : (0.5 - 3.5); the end-capping structure has the structure shown in formula (5); wherein, R 10 is selected from –H, C 1- C 5 alkyl, propenyl, -CH 2 CH 2 CH 2 CHO or the degree of alcoholysis of the modified polyvinyl alcohol is 65 - 90 mol%.

2. The modified polyvinyl alcohol according to claim 1, wherein, R 1 selected from C 1- C 4 alkyl; R 2 、R 3 、R 4 、R 5 、R 6 、R 7 、R 8 、R 9 each independently selected from -H or C 1- C 3 alkyl; R 10 selected from –H or C 1- C 3 alkyl; and / or, the molar ratio of (structural unit A + structural unit B) : structural unit C is 100 : (1 - 3); and / or, the degree of alcoholysis of the modified polyvinyl alcohol is 75 - 89 mol%.

3. The modified polyvinyl alcohol according to claim 1 or 2, wherein, the weight-average molecular weight of the modified polyvinyl alcohol is 50 - 75 g / mol, preferably 55 - 65 g / mol.

4. A preparation method of a modified polyvinyl alcohol, characterized in that, it includes: (1) In the presence of an initiator and a solvent, polymerize monomer A', monomer B' and monomer C' to obtain an intermediate polymerization product; (2) In the presence of a base, alcoholize the intermediate polymerization product to obtain a modified polyvinyl alcohol; wherein, the monomer A' has the structure shown in formula (6); the monomer B' has the structure shown in formula (7) and / or formula (8); the monomer C' has the structure shown in formula (9); wherein, R 1 is selected from C 1- C 8 alkyl; R 2 , R 3 , R 4 , R 5 , R 6 , R 7 , R 8 , R 9 are each independently selected from -H or C 1- C 5 alkyl; Z and Q are each independently selected from H + , K + , Na + or NH 4 + ; R 10 is selected from –H, C 1- C 5 alkyl, propenyl, -CH 2 CH 2 CH 2 CHO or the weight ratio of monomer A' : monomer B' : monomer C' is 100 : (1 - 4.9) : (0.8 - 6).

5. The method according to claim 4, wherein, R 1 selected from C 1- C 4 alkyl; R 2 、R 3 、R 4 、R 5 、R 6 、R 7 、R 8 、R 9 each independently selected from -H or C 1- C 3 alkyl; R 10 selected from –H or C 1- C 3 alkyl; and / or, the weight ratio of monomer A' : monomer B' : monomer C' is 100 : (1.5 - 4) : (1 - 5.5).

6. The method according to claim 4 or 5, wherein, the solvent is selected from at least one of methanol, ethanol, isopropanol and tert-butanol, preferably methanol; preferably, the initiator is selected from peroxide initiators or azo initiators; preferably, the peroxide initiator is selected from at least one of tert-butyl peroxyneodecanoate, diisopropyl peroxydicarbonate, bis(4-tert-butylcyclohexyl) peroxydicarbonate, tert-amyl peroxyneodecanoate, bis(2-ethylhexyl) peroxydicarbonate, bis(3,5,5-trimethylhexanoyl) peroxide and dipropyl peroxydicarbonate, more preferably tert-butyl peroxyneodecanoate and / or diisopropyl peroxydicarbonate; preferably, the azo initiator is selected from azobisisobutyronitrile and / or azobisisoheptonitrile; preferably, the weight ratio of the initiator : monomer A' is (0.05 - 0.3) : 100; preferably, the weight ratio of the solvent : monomer A' is (15 - 35) :

100.

7. The method according to any one of claims 4 - 6, wherein, The conditions of the polymerization reaction include: the temperature is 62 - 65 °C, and the time is 4.5 - 9.5 h. Preferably, the conditions of the alcoholysis include: the temperature is 32 - 45 °C, and the time is 20 - 40 min.

8. The modified polyvinyl alcohol prepared by the preparation method according to any one of claims 4 - 7.

9. The application of the modified polyvinyl alcohol according to any one of claims 1 - 3, 8 as a dispersant in an aqueous coating.

10. An aqueous coating containing the modified polyvinyl alcohol according to any one of claims 1 - 3, 8.

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