High-efficiency polymerization inhibitor, preparation method and application thereof

Abstract

The application provides a high-efficiency polymerization inhibitor and a preparation method and application thereof, and the method comprises the following steps: dispersing demethylated lignin, a mercapto carboxylic acid compound, a phenothiazine carboxylic acid derivative, a carbodiimide coupling agent and a carboxyl activating agent in anhydrous aprotic solvent, and performing esterification reaction between alcohol hydroxyl groups of the demethylated lignin and carboxyl groups of the mercapto carboxylic acid compound and the phenothiazine carboxylic acid derivative to obtain the high-efficiency polymerization inhibitor. The polymerization inhibitor is suitable for storage and transportation of acrylate monomers, and can significantly improve the storage stability and heat resistance of polymers.

Description

TECHNICAL FIELD

[0001] The present application relates to polymerization inhibitors or stabilizers, in particular to a high-efficiency polymerization inhibitor and its preparation method and application. BACKGROUND

[0002] The traditional polymerization inhibitor system has a single action mechanism, lacks multi-functional group synergistic effect, and mostly relies on free radical capture or oxidation-reduction, which is difficult to effectively deal with various polymerization inducers; the thermal stability is poor, and the inhibitor is easy to fail under high-temperature or long-time storage conditions; the small-molecule polymerization inhibitor can reduce the effective concentration and affect the performance of the final product due to volatilization or migration during storage or processing, and it is difficult to achieve long-term stability; some amine or phenolic polymerization inhibitors can cause coloring or generate byproducts, which affect the appearance and performance of downstream polymers.

[0003] Therefore, there is a need to provide a high-efficiency polymerization inhibitor with multi-functional group synergistic effect, thermal stability, and long-term stability. SUMMARY

[0004] The present application provides a preparation method of a high-efficiency polymerization inhibitor, and the high-efficiency polymerization inhibitor obtained by the method has multi-functional group synergistic effect, high thermal stability, and long-term stability.

[0005] In a first aspect, the present application provides a method for preparing a high-efficiency polymerization inhibitor, comprising:

[0006] The demethylated lignin, mercapto carboxylic acid compound, phenothiazine carboxylic acid derivative, carbodiimide coupling agent, and carboxyl activator are dispersed in anhydrous aprotic solvent, the alcohol hydroxyl group of the demethylated lignin is subjected to esterification reaction with the carboxyl group of the mercapto carboxylic acid compound and the phenothiazine carboxylic acid derivative, and a high-efficiency polymerization inhibitor is obtained.

[0007] Through the above technical solution, the structural integrity of the organic raw materials such as demethylated lignin, mercapto carboxylic acid compound, and phenothiazine carboxylic acid derivative is ensured at high temperature; the method uses carbodiimide coupling agent and carboxyl activator to synergistically activate the carboxyl group, so that it rapidly reacts with the lignin alcohol hydroxyl group, realizes high-density grafting of the mercapto group and the phenothiazine group, the introduction of the carboxyl activator improves the selectivity with the alcohol hydroxyl group, and also inhibits the rearrangement and other side reactions of the carbodiimide coupling agent, reduces byproducts, and retains the phenolic hydroxyl group on the lignin which has polymerization inhibition activity, thereby realizing functional superposition; the whole process is carried out in anhydrous aprotic solvent, ensuring the chemical activity of the mercapto group and the phenothiazine group; by covalently introducing the phenothiazine group with free radical capture function and the mercapto group with chain transfer and auxiliary stabilization function on the lignin macromolecular skeleton, a molecular structure with multiple polymerization inhibition mechanisms is constructed, the synergistic effect is realized, and the obtained polymerization inhibitor has more excellent comprehensive polymerization inhibition performance than single component or physical mixing system.

[0008] In some embodiments, the demethylated lignin comprises the following preparation method:

[0009] dispersing the low-ash kraft lignin in an organic solvent to obtain a dispersion liquid; the content of the low-ash kraft lignin in the dispersion liquid is 10-20 mg / mL;

[0010] adding a boron tribromide solution to the dispersion liquid at -20-0°C, the amount of the boron tribromide being 1.5-3.0 times the molar amount of the methoxyl groups of the lignin, and the reaction is carried out at 0-10°C for 12-18 hours to obtain the demethylated lignin.

[0011] In the above embodiments, the selective demethylation of the methoxyl groups in the lignin molecules is carried out by using boron tribromide at -20-0°C to generate phenolic hydroxyl groups and alcoholic hydroxyl groups, thereby increasing the density of the hydroxyl groups and the number of reactive sites, and providing more available alcoholic hydroxyl groups for subsequent esterification coupling; the low-temperature reaction condition can effectively inhibit the degradation and condensation side reactions of the lignin main chain, avoid the aromatic ring cracking or crosslinking caused by excessively high temperature, and ensure the integrity of the lignin macromolecular skeleton and its mechanical properties; the alcoholic hydroxyl groups generated by demethylation can improve the esterification coupling efficiency under the action of the carbodiimide coupling agent and the activator system, and realize the high-density covalent grafting of the mercapto group and the phenothiazine group on the lignin skeleton; the phenolic hydroxyl groups have a certain free radical capturing ability, and after the modification of multiple functional groups, the functional superposition can be realized, and the thermal stability, long-acting property and multi-mechanism synergistic polymerization inhibition performance of the obtained polymerization inhibitor can be improved.

[0012] In some embodiments, the mercapto carboxylic acid compound has a general formula: HS-R-COOH; wherein R is selected from C1-C6 linear or branched alkylene, C6-C 11 arylene.

[0013] By the above technical solution, two types of highly reactive functional groups, i.e., mercapto group and carboxyl group, are introduced and connected to a divalent hydrocarbon group structure composed of only carbon and hydrogen elements, which can significantly improve the specificity and coupling efficiency of the reaction system, and enhance the esterification reaction rate and yield between the carboxyl group and the alcoholic hydroxyl group in the demethylated lignin; the structural diversity of the R group helps to improve the dispersibility and thermal stability of the polymerization inhibitor.

[0014] In some embodiments, the phenothiazine carboxylic acid derivative comprises the following preparation method:

[0015] condensing phenothiazine and N,N-dimethylformamide under the catalysis of phosphorus oxychloride and then hydrolyzing to introduce formyl groups on the phenothiazine ring to obtain an intermediate mixture of monoformylated product and diformylated product;

[0016] oxidizing the intermediate mixture using potassium permanganate to oxidize the formyl groups to carboxyl groups to obtain the phenothiazine carboxylic acid derivative.

[0017] By the above technical solution, the electrophilic reaction system constructed by phosphorus oxychloride and N,N-dimethylformamide can efficiently introduce formyl groups on the phenothiazine ring system to generate a mixture of mono-formylated and di-formylated intermediates, simplifying the process flow and improving the selectivity and reaction efficiency of functional group introduction; further, the formyl groups are oxidized to carboxyl groups under alkaline conditions using potassium permanganate as the oxidant, and the oxidation process is mild and highly selective, which helps to maintain the integrity of the phenothiazine parent structure and effectively endows the phenothiazine molecule with carboxyl functional groups, providing reaction sites for subsequent esterification coupling with the alcohol hydroxyl groups of demethylated lignin, enhancing the intermolecular construction ability; the obtained phenothiazine carboxylic acid derivative is a mixture of polycarboxyl structures, which can form multiple esterification connections with demethylated lignin with multiple hydroxyl groups to construct a stable and efficient polymerization inhibitor molecular network, realizing the synergistic effect of free radical capture and inhibition; the phenothiazine ring system has excellent electron transfer performance and thermal stability, which endows the obtained polymerization inhibitor with good free radical inhibition ability in the polymerization system, and makes it maintain thermal stability, long-term stability and polymerization inhibition activity in high-temperature or complex environments such as coatings and composites.

[0018] In some embodiments, the oxidation treatment is carried out in an alkaline aqueous solution with a pH of 9-11, and the molar ratio of potassium permanganate to phenothiazine is 2:1-3:1; the pH of the system is adjusted to 2-3 by adding dilute acid to obtain the phenothiazine carboxylic acid derivative.

[0019] Through the above embodiments, the oxidation treatment step is carried out by reacting in an alkaline aqueous solution with a pH of 9-11, which can promote the hydration of the aldehyde group in the phenothiazine formylated intermediate to form a geminal diol structure, which is efficiently and selectively oxidized to carboxylate by potassium permanganate; the molar ratio of potassium permanganate to phenothiazine is controlled at 2:1-3:1, which ensures complete oxidation while avoiding excessive oxidation that damages the phenothiazine parent nucleus and sulfur and nitrogen heterocyclic structures, thereby improving the yield and purity of the product; after the reaction is completed, the pH of the system is adjusted to 2-3 by adding dilute acid, which quantitatively converts the carboxylate to free carboxylic acid and precipitates, facilitating separation and purification, and finally obtaining a phenothiazine carboxylic acid derivative with complete structure, sufficient carboxyl group introduction and high purity, which provides a stable and active reaction site for subsequent efficient esterification coupling with demethylated lignin.

[0020] In some embodiments, the method satisfies at least one of the following conditions:

[0021] 1) the carbodiimide coupling agent includes at least one of 1,3-dicyclohexyl carbodiimide, 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride, and 1,3-diisopropyl carbodiimide;

[0022] 2) the anhydrous aprotic solvent includes at least one of dichloromethane, tetrahydrofuran, acetonitrile, N,N-dimethylformamide, 1,4-dioxane, N,N-dimethylacetamide, dimethyl sulfoxide;

[0023] 3) the carboxyl activating agent includes at least one of 1-hydroxybenzotriazole, N-hydroxysuccinimide.

[0024] Through the above embodiments, the carbodiimide coupling agent generates a highly active acyl intermediate by activating the carboxyl group, thereby effectively promoting the esterification reaction with the alcohol hydroxyl group; in the present application, the above coupling agent can improve the esterification efficiency of the mercapto carboxylic acid compound and the phenothiazine carboxylic acid derivative with the alcohol hydroxyl group in the demethylated lignin molecule, shorten the reaction time and improve the yield of the target product; under anhydrous and aprotic solvent conditions, the above carbodiimide coupling agent exhibits excellent activation ability and can achieve efficient esterification at multiple sites, thereby constructing a polymerization inhibitor molecule with a spatial network structure and giving it synergistic effect and long-term stability; the anhydrous aprotic solvent maintains a stable anhydrous reaction environment to avoid side reactions between water and the carbodiimide coupling agent and reduce the hydrolysis of the carboxylic acid end; no protons that can react with the activated carboxylic acid are provided, thereby preventing the functional groups such as mercapto and hydroxyl groups from being protonated, improving their nucleophilicity and the selectivity of esterification coupling; the demethylated lignin, mercapto carboxylic acid compound and phenothiazine carboxylic acid derivative all have good solubility or dispersibility, and a uniform reaction system can be formed by flexible matching of the above anhydrous aprotic solvent, thereby improving the reaction efficiency; the synergistic effect of the carboxyl activating agent and the carbodiimide coupling agent can efficiently convert the carboxyl group into a more reactive esterification intermediate, improve the condensation rate with the alcohol hydroxyl group, and complete the reaction under mild conditions, thereby avoiding damage to sensitive functional groups caused by high temperature or long time treatment; the activating agent can synergize with the carbodiimide to stabilize the O-acyl isourea activated intermediate, reduce the tendency of intramolecular acyl migration to generate N-acyl urea byproducts during the coupling reaction, thereby inhibiting side reactions and improving the yield of the target product; and because it has good solubility in the above anhydrous aprotic solvent, it can be compatible with multifunctional substrates such as demethylated lignin, mercapto compounds and phenothiazine derivatives under mild conditions, ensuring the structural integrity and obtaining high-purity and high-stability target products.

[0025] In some embodiments, the molar ratio of the total carboxyl groups of the mercapto carboxylic acid compound and the phenothiazine carboxylic acid derivative to the alcohol hydroxyl group of the demethylated lignin is 1:1~1.1:1, the molar ratio of the carbodiimide coupling agent to the total carboxyl groups is 1:1~1.2:1, and the molar ratio of the carboxyl activating agent to the total carboxylic acid groups is 1:1~1.2:1.

[0026] By the technical scheme, the molar ratio of total carboxyl and alcohol hydroxyl is controlled at 1:1-1.1:1, which ensures that the number of carboxylic acid groups is sufficient to achieve complete coupling, while avoiding self-condensation or excessive crosslinking caused by excessive carboxylic acid groups, thereby realizing sufficient and controllable functional modification of alcohol hydroxyl in demethylated lignin molecules; the molar ratio of carbodiimide coupling agent to total carboxylic acid groups is controlled at 1:1-1.2:1, which ensures that under the action of the carbodiimide coupling agent, the carboxylic acid groups are activated to form a highly active O-acyl urea intermediate, while reducing the generation of urea by-products and the burden of post-processing caused by excessive coupling agent, thereby improving the economy of the reaction and the purity of the product; the molar ratio of carboxyl activating agent to total carboxyl is controlled at 1:1-1.2:1, which can effectively stabilize the O-acyl urea intermediate, inhibit its rearrangement or hydrolysis, and significantly improve the rate and selectivity of the esterification coupling reaction; the synergistic setting of the above three ratio parameters enables the mercapto carboxylic acid compound and the phenothiazine carboxylic acid derivative to achieve high-density and uniform distribution of multi-functional groups on the demethylated lignin skeleton, enhancing the free radical capture ability, thermal stability and long-term stability of the obtained high-efficiency polymerization inhibitor.

[0027] In some embodiments, the molar ratio of the mercapto carboxylic acid compound to the phenothiazine carboxylic acid derivative is 40:60-60:40.

[0028] By the above technical scheme, the molar ratio of the mercapto carboxylic acid compound to the phenothiazine carboxylic acid derivative is accurately controlled, achieving synergistic effect in function; the specific ratio enables the mercapto group with rapid free radical capture ability to synergize with the phenothiazine functional group with long-term free radical inhibition effect, thereby ensuring that in the polymerization system, the instantaneously generated free radicals can be rapidly terminated to prevent polymerization from running out of control, and a sustained inhibition effect can be provided to ensure the stability of the system during long-term storage or high-temperature processing; the optimization of the ratio utilizes the different steric hindrance and reactivity of the two functional monomers, achieving balanced esterification modification of alcohol hydroxyl sites in different chemical environments in the demethylated lignin molecule, so that various types of hydroxyl groups can participate in coupling with close reaction degree, thereby obtaining a functionalized product with uniform substitution distribution, maximizing the synergistic effect.

[0029] In a second aspect, the application provides a high-efficiency polymerization inhibitor prepared by the method according to any one of the embodiments of the first aspect.

[0030] In a third aspect, the application provides an application of the high-efficiency polymerization inhibitor, which can prolong the induction period and inhibit spontaneous polymerization of the acrylate monomer during storage and transportation.

[0031] Through the technical solution, based on the free radical polymerization mechanism design, in view of the problem that the monomers containing active carbon-carbon double bond such as acrylate are easy to generate free radicals and occur chain polymerization under the action of heat, light, peroxide or metal ions and have self-accelerating effect, through covalently introducing mercapto and phenothiazine groups on the skeleton of demethyl lignin, the synergistic polymerization inhibition effect of instantaneous capture and long-term stabilization is realized; the mercapto and phenothiazine groups are covalently bonded on the skeleton of demethyl lignin through ester bond, which significantly reduces the migration rate and volatilization loss of the polymerization inhibitor in the monomer, improves the thermal stability and long-term stability during storage and processing.

[0032] Compared with the prior art, the beneficial effects of the present application are at least:

[0033] Compared with the traditional small molecule type polymerization inhibitor, the present application covalently grafts mercapto and phenothiazine groups on the skeleton of demethyl lignin, constructs a polymerization inhibition structure with multi-functional group synergistic effect, prolongs the induction period of polymerization reaction and effectively inhibits spontaneous polymerization; the mercapto and phenothiazine groups are stably fixed on the skeleton of demethyl lignin through ester bond, solving the problem of activity attenuation caused by volatilization or migration of traditional polymerization inhibitors, improving the thermal stability and long-term stability of the polymerization inhibitor under high temperature and storage conditions; in addition, the present application uses bio-based lignin as the skeleton raw material, has the characteristics of renewability and high resource utilization efficiency, has environmental friendliness and sustainable development potential. DETAILED DESCRIPTION

[0034] Each embodiment or embodiment in the present specification is described in a progressive manner, and each embodiment focuses on the difference from other embodiments.

[0035] In the description of the present specification, the description of the terms "one embodiment", "some embodiments", "exemplary embodiment", "example", "specific example", or "some examples" means that the specific features, structures, materials or characteristics described in conjunction with the embodiments or examples are included in at least one embodiment or example of the present application. In the present specification, the exemplary description of the above terms does not necessarily mean the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner.

[0036] In addition, the terms "first", "second" are only for descriptive purposes, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined with "first", "second" can explicitly or implicitly include at least one of the features. In the description of the present application, the meaning of "multiple" is at least two, for example, two, three, etc., unless otherwise specifically limited.

[0037] In the description of the present specification, "parts" means "mass parts" unless otherwise specified.

[0038] Hereinafter, the embodiments of the present application will be described. The embodiments described below are exemplary and are for the purpose of explanation of the present application and cannot be understood as a limitation of the present application. In the embodiments, the specific techniques or conditions not noted are performed in accordance with the techniques or conditions described in the literature in the art or in accordance with the product manual. The reagents or instruments not noted for the manufacturer are all conventional products that can be obtained on the market.

[0039] Low ash Kraft lignin, CAS: 9005-53-2, purity ≥ 95wt%, ash ≤ 1.0wt%, moisture ≤ 2.0wt%, total phenolic hydroxyl content: 1.5~3.0mmol / g, alcohol hydroxyl content ≥ 0.5mmol / g, number average molecular weight: 5000~15000g / mol, total amount of metal ions ≤ 0.5wt%, solubility: good solubility under alkaline conditions, can form a stable dispersion system in anhydrous aprotic solvents such as dichloromethane and tetrahydrofuran.

[0040] Preparation Example 1

[0041] Preparation of demethylated lignin:

[0042] Under nitrogen protection, the low ash Kraft lignin was dispersed in anhydrous dichloromethane to prepare a uniform dispersion liquid with a lignin mass concentration of 20mg / mL;

[0043] Anhydrous solution of boron tribromide in dichloromethane with a concentration of 1.0mol·L -1 was slowly added to the above uniform dispersion liquid at -20℃, and the temperature was controlled at -20~-15℃; the amount of boron tribromide was calculated as 2.2 times the total moles of methoxyl groups in lignin;

[0044] After the drop was completed, the temperature was raised to 5℃ and kept for 16h to fully complete the demethylation reaction; after the reaction was completed, 0℃ ice methanol (10 times the mass of boron tribromide, ml / g) was added at 5℃ and the temperature was controlled at 0~5℃ to completely quench the residual boron tribromide, then it was washed with deionized water for several times until the pH of the washing liquid was 7 to remove inorganic salts and byproducts, and then it was separated to obtain the organic phase;

[0045] At 0℃, anhydrous isopropanol (4 times the volume of the organic phase) was added to the washed organic phase and stirred at a speed of 300rpm for 60min, then it was left to stand for 2h to allow the lignin to be analyzed, then it was centrifuged at 6000rpm for 20min at 0℃ to collect the precipitate, and then it was vacuum dried at 55℃ to constant weight to obtain the demethylated lignin;

[0046] The total moles of methoxyl groups in the low-ash Kraft lignin were determined by Zeisel-Vieböck methoxyl determination method, which was 1.8 mmol / g; the total moles of methoxyl groups in the obtained demethylated lignin were determined to be 0.14 mmol / g.

[0047] Preparation Example 2

[0048] Preparation of phenothiazine carboxylic acid derivative:

[0049] Phosphorus oxychloride (1.3 eq) was added dropwise into N,N-dimethylformamide (10 times the mass of phenothiazine, ml / g) at 0°C under nitrogen protection, and the temperature of the system was controlled at 0-5°C, and the stirring rate was 600 rpm; after the dropwise addition was completed, the system was stirred for 1 h to obtain Vilsmeier reagent (chloromethylidene dimethylammonium salt);

[0050] Phenothiazine (1.0 eq) was dissolved in N,N-dimethylformamide (8 times the mass of phenothiazine, ml / g) to prepare a uniform solution; the uniform solution was slowly added dropwise into the Vilsmeier reagent, and the reaction system was kept at 0-10°C; after the addition was completed, the temperature was gradually increased to 80°C, and the reaction was stirred for 12 h;

[0051] After the reaction was completed, the reaction solution was obtained, and the reaction solution was slowly added into 5°C ice water with a volume of 6 times that of the reaction solution to quench and hydrolyze the formylation product to precipitate a solid; saturated sodium bicarbonate solution was added to adjust the pH to 7, and the mixture was stirred for 30 min; the solid was collected by suction filtration, washed with deionized water (15 times the mass of the formylated product solid, ml / g) to remove residual solvents and inorganic salts, and dried at 40-50°C under vacuum to obtain a mixture of formylated and diformylated phenothiazine crude products;

[0052] The formylated phenothiazine crude product was dispersed in a sodium hydroxide aqueous solution (12 times the mass of the formylated phenothiazine crude product, ml / g) with a pH of 10 to obtain an alkaline dispersion, and tert-butyl alcohol (1.2 times the mass of the formylated phenothiazine crude product, ml / g) was added to improve the dispersion;

[0053] The alkaline dispersion was stirred at 0°C at a rate of 600 rpm, and a 0.1 g / ml aqueous solution of potassium permanganate was slowly added dropwise, and the reaction temperature was controlled at 0-5°C; after the addition was completed, the temperature was increased to 25°C, and the reaction was performed for 8 h, during which the purple color faded and a brown manganese dioxide precipitate was formed; the amount of potassium permanganate was calculated based on 2.6 times the molar amount of phenothiazine;

[0054] The filtrate was cooled to 2°C, and 3 mol / L hydrochloric acid was added dropwise to adjust the pH to 2, and the phenothiazine monocarboxylic acid and dicarboxylic acid solid was precipitated; the solid was collected by suction filtration, washed with deionized water (15 times the mass of the phenothiazine monocarboxylic acid and dicarboxylic acid solid, ml / g) to remove inorganic salts, and dried at 45°C under vacuum to obtain the phenothiazine carboxylic acid derivative.

[0055] The N,N-dimethylformamide is both a reactant and a solvent.

[0056] Example 1

[0057] Preparation of a high-efficiency polymerization inhibitor:

[0058] S1: Under nitrogen protection, the desmethyl lignin prepared in Preparation Example 1 was dispersed in anhydrous dichloromethane to prepare a uniform dispersion liquid with a desmethyl lignin mass concentration of 15 mg / mL, and 4-mercapto-1-naphthoic acid and the phenothiazine carboxylic acid derivative prepared in Preparation Example 2 were sequentially added at 0°C to obtain a mixture, so that the molar ratio of total carboxyl to desmethyl lignin alcohol hydroxyl was 1:1, and the molar ratio of the mercapto group of 4-mercapto-1-naphthoic acid to the carboxyl group of the phenothiazine carboxylic acid derivative was 50:50;

[0059] S2: The above mixture was stirred at a rate of 300 rpm, 1,3-dicyclohexyl carbodiimide was added in batches (with a molar ratio of 1:1 to the total carboxylic acid) and the temperature was kept at 0-5°C, after the addition was completed, N-hydroxysuccinimide was added in batches (with a molar ratio of 1:1 to the total carboxylic acid) and the temperature was kept at 0-5°C, after the addition was completed, the temperature was raised to 20°C and the stirring was kept for 24 h, and the coupling reaction was completed;

[0060] S3: After the reaction was completed, filtration was performed, the filter cake was washed with a mixed solution of dichloromethane:methanol=1:1 (the volume of the mixed solution was 15 times the mass of the filter cake, g / ml), and vacuum drying was performed at 40°C for 12 h until the constant weight was reached, to obtain a high-efficiency polymerization inhibitor;

[0061] The detection of the phenolic hydroxyl and alcohol hydroxyl groups of the desmethyl lignin was determined by acetylation-saponification method, the detection of the carboxylic acid of the phenothiazine carboxylic acid derivative was determined by sodium bicarbonate back titration method, and the detection of the mercapto group was determined by Ellman method.

[0062] Example 2

[0063] Preparation of a high-efficiency polymerization inhibitor:

[0064] The preparation was substantially the same as that in Example 1, except that the 4-mercapto-1-naphthoic acid in step S1 was replaced by 4-mercaptobenzoic acid.

[0065] Example 3

[0066] Preparation of a high-efficiency polymerization inhibitor:

[0067] The preparation was substantially the same as that in Example 1, except that the 4-mercapto-1-naphthoic acid in step S1 was replaced by 3-mercaptopropionic acid.

[0068] Example 4

[0069] Preparation of a high-efficiency polymerization inhibitor:

[0070] The same as example 1, the only difference is that 4-mercapto-1-naphthoic acid in step S1 is replaced by mercaptoacetic acid.

[0071] Example 5

[0072] Preparation of a highly efficient polymerization inhibitor:

[0073] The same as example 1, the only difference is that the molar ratio of 4-mercapto-1-naphthoic acid to phenothiazine carboxylic acid derivative in step S1 is 30:70.

[0074] Example 6

[0075] Preparation of a highly efficient polymerization inhibitor:

[0076] The same as example 1, the only difference is that the molar ratio of 4-mercapto-1-naphthoic acid to phenothiazine carboxylic acid derivative in step S1 is 40:60.

[0077] Example 7

[0078] Preparation of a highly efficient polymerization inhibitor:

[0079] The same as example 1, the only difference is that the molar ratio of 4-mercapto-1-naphthoic acid to phenothiazine carboxylic acid derivative in step S1 is 60:40.

[0080] Example 8

[0081] Preparation of a highly efficient polymerization inhibitor:

[0082] The same as example 1, the only difference is that the molar ratio of 4-mercapto-1-naphthoic acid to phenothiazine carboxylic acid derivative in step S1 is 70:30.

[0083] Comparative Example 1

[0084] Comparative Example 1 uses non-demethylated low-ash Kraft lignin instead of demethylated lignin in Preparation Example 1, and the rest of the conditions are the same as in Example 1.

[0085] Comparative Example 2

[0086] Comparative Example 2 only physically mixes an equivalent amount of 4-mercapto-1-naphthoic acid and phenothiazine carboxylic acid derivative in Example 1 and demethylated lignin in Preparation Example 1.

[0087] Comparative Example 3

[0088] Comparative Example 3 only uses phenothiazine as a polymerization inhibitor compared to Example 1.

[0089] Comparative Example 4

[0090] In comparison with Example 1, only 4-mercapto-1-naphthalene carboxylic acid was used as polymerization inhibitor in Comparative Example 4.

[0091] Test section

[0092] Constant temperature induction period: 10 mg of sample was placed in a sealed high-pressure aluminum crucible, and tested in a differential scanning calorimeter under the conditions of GB / T 19466.6-2009 at 25°C constant temperature, and oxygen flow rate of 50 mL / min. The time from the start of constant temperature to the onset of exothermic reaction was the constant temperature induction period, and the results were the average of three parallel tests.

[0093] Peroxide challenge induction period: the sample was weighed and 0.10wt% of dicumyl peroxide was added. After rapid mixing and uniformity at 25°C, the test was carried out under the procedure of ASTM D2471-99 at 25°C constant temperature. The time from the start of mixing to the appearance of the exothermic peak was recorded, and the resulting value was the peroxide challenge induction period. The results were the average of three parallel tests.

[0094] Accelerated storage polymer content: the sample was stored in a 70°C air oven for 7d under the accelerated aging conditions of ASTM D573-04, and the polymer mass fraction was determined by methanol precipitation-vacuum drying method after removal. The results were the average of three parallel tests, accurate to 0.01wt%.

[0095] Induction period retention rate: the initial constant temperature induction period of the sample was determined according to GB / T 19466.6-2009, and the constant temperature induction period was determined again after the accelerated storage polymer content was treated. The induction period retention rate = the induction period after storage / initial induction period x 100%, and the results were the average of three parallel tests, accurate to 0.1%.

[0096] Thermal stability: the sample was placed in a rotary viscometer (shear rate of 10s -1 , sealed measurement system) with a constant temperature control accuracy of ±0.1°C. The viscosity-time curve was continuously recorded under the isothermal condition of 90°C according to the rotary method clause of GB / T 10247-2008. The time from the start of constant temperature to the viscosity increasing by 2 times of the initial viscosity was defined as the thermal stability index, and the results were the average of three parallel tests.

[0097] The effective active groups of the polymerization inhibitors used in Examples 1-8 and Comparative Examples 1-4 were calculated according to the total molar amount of phenothiazine group, mercapto group and phenolic hydroxyl group in the molecule, and the concentration of such effective active groups in the monomer was 2.5 mmol / kg.

[0098] The test results of monomer methyl acrylate are shown in Table 1:

[0099] Table 1

[0100]

[0101] According to Table 1, the constant temperature induction period and the peroxide challenge induction period of each example are higher than those of the comparative examples in the methyl acrylate and other free radical polymerization type easy self-polymerization monomer system, the accelerated storage polymer content is reduced, the induction period retention rate and thermal stability are more excellent; this shows that the efficient inhibitor of the application has excellent inhibition and heat resistance to the spontaneous polymerization of methyl acrylate and other free radical polymerization type easy self-polymerization monomer; the reason may be that the phenothiazine group has high efficient capture and inactivation ability to long-lived free radicals, thereby inhibiting the occurrence of chain growth process and branching reaction; the mercapto group is easy to transfer hydrogen atoms to the newly generated free radicals due to its low S-H bond dissociation energy, realizing rapid chain transfer termination and blocking the further growth of active chains; the phenolic hydroxyl group on the lignin skeleton can be used as an efficient hydrogen donor, and the hydrogen transfer reaction occurs with active free radicals to quench and terminate the growth of polymer chains; the three functional groups are covalently bonded to the demethylated lignin skeleton, thereby significantly reducing the volatility and migration of the lignin in the system, ensuring the long-term maintenance of the effective concentration of the monomer.

[0102] According to Examples 1-4 in Table 1, the structure difference of the selected mercapto carboxylic acid compound in the efficient inhibitor of the application will affect the inhibition performance, the stronger the aromaticity and the larger the conjugated system, the higher the resonance stabilization ability of the obtained mercapto group, thereby improving the capture efficiency of the chain growth free radical; the increase of the carbon chain length can give the molecule more flexible spatial orientation, reduce the steric hindrance, and be conducive to the effective contact of the mercapto group with the free radical; on the contrary, when the aromaticity is weakened and the carbon chain is shortened, the rapid termination ability of the mercapto group to the newly generated free radical chain is reduced, and the synergistic inhibition effect is weakened; as a result, the constant temperature induction period, the peroxide challenge induction period and the thermal stability and other indicators gradually decrease with the decrease of aromaticity and the shortening of carbon chain; therefore, the efficient inhibitor described in the application can significantly prolong the induction period of the polymerization reaction and effectively inhibit the spontaneous polymerization during the storage and transportation of the monomer.

[0103] According to Table 1, Examples 1, 5-8, the insufficient content of mercapto group weakens the ability of rapid termination of short-lived free radicals, resulting in that the free radical reaction in the initial stage of chain growth cannot be effectively inhibited; the insufficient content of phenothiazine group reduces the efficiency of complexation and deactivation of long-lived free radicals generated in the polymerization process, resulting in that these free radicals accumulate in the reaction system and continuously participate in the chain growth reaction, so that the induction period of the polymerization reaction is shortened, the storage stability is decreased, the induction period retention rate is reduced, the active chain termination is limited, and the polymerization side reaction is intensified; controlling the molar ratio of carboxylic acid of mercapto carboxylic acid compound and phenothiazine carboxylic acid derivative to be 40:60-60:40 can take into account the synergistic effect of initial rapid chain truncation and long-term inhibition in the middle and late stages, so as to ensure that the polymerization inhibitor has excellent and stable polymerization inhibition performance under storage and high temperature conditions; therefore, the high-efficiency polymerization inhibitor described in the application can significantly prolong the induction period of the polymerization reaction and effectively inhibit the occurrence of spontaneous polymerization during the storage and transportation of monomers.

[0104] According to Table 1, Examples 1, Comparative Example 1, the methoxyl group on the low-ash Kraft lignin occupies the active site on the aromatic ring, reducing the number and reactivity of phenolic hydroxyl and alcoholic hydroxyl, thereby limiting the grafting density and distribution uniformity of mercapto carboxylic acid compound and phenothiazine carboxylic acid derivative; after demethylation treatment, more phenolic hydroxyl and alcoholic hydroxyl sites are exposed, which not only improves the esterification reaction efficiency with activated carboxyl to form a higher density of multifunctional covalent structure, but also enhances the free radical quenching ability of phenolic hydroxyl as a hydrogen donor; therefore, the high-efficiency polymerization inhibitor described in the application can significantly prolong the induction period of the polymerization reaction and effectively inhibit the occurrence of spontaneous polymerization during the storage and transportation of monomers.

[0105] According to Table 1, Examples 1, Comparative Examples 2-4, in Comparative Example 2, the mercapto group and the phenothiazine group exist in a free state, lacking spatial synergy and uniform distribution on the same macromolecular skeleton, and the diffusion rate, solubility and action timing of the two in the reaction system are not matched; the mercapto group is easily consumed quickly in the initial stage, the phenothiazine group can inhibit free radicals in the middle and late stages, but due to the lack of covalent anchoring, it is easy to migrate, volatilize or be consumed by side reactions, the synergistic effect is unstable, the active components are lost quickly under storage and high temperature conditions, the induction period retention rate and thermal stability are reduced; Comparative Examples 3 and 4 are single small molecule polymerization inhibitors, which have specific action mechanisms, single function, limited action stage and insufficient stability; phenothiazine has long-term free radical quenching ability but insufficient initial free radical capturing ability; 4-mercapto-1-naphthalene carboxylic acid can efficiently truncate active free radical chains in the initial stage of polymerization, but lacks long-term inhibition and is easy to volatilize and be consumed by side reactions; therefore, the high-efficiency polymerization inhibitor described in the application can significantly prolong the induction period of the polymerization reaction and effectively inhibit the occurrence of spontaneous polymerization during the storage and transportation of monomers.

[0106] Finally, it should be noted that: the above embodiments are only used to illustrate the technical solutions of the present application, but not to limit them; although the present application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that: it can still modify the technical solutions recorded in the foregoing embodiments, or make equivalent replacement for part or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present application.

Claims

1. A process for the preparation of a highly efficient polymerization inhibitor, characterized in that, The application relates to a high-efficiency polymerization inhibitor and a preparation method thereof. The preparation method of the phenothiazine carboxylic acid derivative comprises the following steps: The thiol carboxylic acid compound has the general formula: HS-R-COOH; wherein R is selected from C1~C6 straight-chain or branched alkylene, C6~C6... 11 Alpha-aryl; The intermediate mixture is subjected to oxidation treatment by using potassium permanganate to oxidize the formyl groups into carboxyl groups, so that the phenothiazine carboxylic acid derivative is obtained; The molar ratio of the mercapto groups of the mercapto carboxylic acid compound to the carboxyl groups of the phenothiazine carboxylic acid derivative is 40:60-60:40; The molar ratio of the total carboxyl groups of the mercapto carboxylic acid compound and the phenothiazine carboxylic acid derivative to the alcohol hydroxyl groups of the demethyl lignin is 1:1-1.1:1; The molar ratio of the carbodiimide coupling agent to the total carboxyl groups is 1:1-1.2:1; The molar ratio of the carboxyl group activator to the total carboxyl groups is 1:1-1.2:

1. The demethyl lignin comprises the following preparation method: The low-ash Kraft lignin is dispersed in an organic solvent to obtain a dispersion liquid; the content of the low-ash Kraft lignin in the dispersion liquid is 10-20 mg / mL; 2. The method of claim 1, wherein, The boron tribromide solution is added to the dispersion liquid under the condition of-20-0 DEG C, the amount of the boron tribromide is 1.5 times to 3.0 times of the molar number of the methoxyl groups of the lignin, the temperature is increased to 0-10 DEG C, and the demethyl lignin is obtained after 12-18 h of reaction. The oxidation treatment is carried out in an alkaline aqueous solution with a pH of 9-11, the molar ratio of potassium permanganate to phenothiazine is 2:1-3:1, and the pH of the system is adjusted to 2-3 by adding dilute acid to obtain the phenothiazine carboxylic acid derivative. The method satisfies at least one of the following conditions:

3. The method of claim 1, wherein, 1) the carbodiimide coupling agent comprises at least one of 1,3-dicyclohexyl carbodiimide, 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride and 1,3-diisopropyl carbodiimide; 4. The method of claim 1, wherein, 2) the anhydrous aprotic solvent comprises at least one of dichloromethane, tetrahydrofuran, acetonitrile, N,N-dimethylformamide, 1,4-dioxane, N,N-dimethylacetamide and dimethyl sulfoxide; 3) the carboxyl group activator comprises at least one of 1-hydroxybenzotriazole and N-hydroxysuccinimide. The high-efficiency polymerization inhibitor is prepared by the method according to any one of claims 1-4. The high-efficiency polymerization inhibitor can prolong the induction period of polymerization and inhibit spontaneous polymerization in the storage and transportation process of the acrylate free radical polymerization type self-polymerization monomer.

5. A highly efficient polymerization inhibitor, characterized in that, ​ 6. Use of a highly efficient polymerization inhibitor, characterized in that ​

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