Preparation method of carboxyl-terminated polyether

Abstract

The invention relates to a preparation method of carboxyl-terminated polyether, which comprises the following steps: sequentially adding hydroxyl-terminated polyether, deionized water and a catalyst into a reactor, reacting at 60-90 DEG C, continuously introducing oxygen to maintain the reaction pressure at 0.05-0.2 MPa, and maintaining the pH value of materials in a reaction kettle at 9-10; when the reaction system stops absorbing oxygen, maintaining the pH value of the material in the reaction kettle at 11-12, continuously introducing oxygen, and when the reaction system stops absorbing oxygen, ending the reaction; filtering to remove the catalyst; adding hydrochloric acid to obtain an aqueous solution of crude carboxyl-terminated polyether; carrying out reduced pressure distillation on the aqueous solution of the crude carboxyl-terminated polyether; adding the crude carboxyl-terminated polyether into absolute ethyl alcohol for dissolving, filtering to remove inorganic salt, and crystallizing to obtain the carboxyl-terminated polyether. Water is used as a solvent in the reaction process, the reaction condition is mild, dangerous chemicals such as chlorocarboxylic acid and sodium ethoxide are avoided, and the prepared carboxyl-terminated polyether is high in purity and can be used for synthesizing polyether amide elastomers.

Description

Technical Field

[0001] The invention relates to a method for preparing a carboxyl-terminated polyether, in particular to a method for preparing a carboxyl-terminated polyether by catalytically oxidizing a hydroxyl-terminated polyether using a modified catalyst loaded with cerium oxide and platinum metal. Background Art

[0002] Polyether refers to a compound containing an epoxy structure that undergoes a ring-opening polymerization reaction with an organic compound containing active hydrogen to generate a high molecular weight polymer containing an ether bond in the main molecular chain. Among them, compounds containing an epoxy structure are usually ethylene oxide (EO), propylene oxide (PO), tetrahydrofuran (THF), etc.

[0003] Polyethers are widely used. In the field of polymers, they are mostly used as copolymer units of elastomers. For example, in polyamide elastomers, polyethers are copolymerized with polyamide as soft segments to obtain polyetheramide elastomers. In the synthesis of polyetheramide elastomers, the properties of the polyether end groups directly affect the activity of the reaction and the performance of the product. When hydroxyl-terminated polyethers, such as polyethylene glycol (PEG), polypropylene glycol (PPG) and polytetrahydrofuran diol (PTMG), are used in the synthesis, the polyether and polyamide need to be connected through an esterification reaction. Since the equilibrium constant of the esterification reaction is small, the requirements for the reaction apparatus and vacuum conditions are high, and the reaction requires the addition of a highly active catalyst, which is prone to side reactions, resulting in poor product appearance and performance. When carboxyl-terminated polyethers react with polyamides, they are connected through an amidation reaction. The reaction equilibrium constant is large and the reaction is easy to proceed. Compared with hydroxyl-terminated polyethers, carboxyl-terminated polyethers have obvious advantages as synthetic monomers for polyetheramide elastomers.

[0004] Invention patent CN113861412B discloses a method for synthesizing carboxyl-terminated polyether and using it to prepare polyetheramide elastomer. Carboxyl-terminated polyether can be prepared by reacting hydroxyl polyether with acid anhydride. The preparation method of carboxyl-terminated polyether includes: dehydrating the hydroxyl polyether at 100-120°C and vacuum (such as -0.1MPa) (the dehydration time can be 3-4h) until the moisture content is less than 100ppm, then adding acid anhydride to react at normal pressure, the molar ratio of acid anhydride to hydroxyl polyether is 2.05-2.2:1, and after reacting for 4-6h, vacuuming to remove low boiling to obtain carboxyl-terminated polyether. The method for preparing a polyetheramide elastomer comprises the following steps: (1) adding a dibasic acid, a diamine, a lactam, a carboxyl-terminated polyether, a carboxyl activator, a catalyst and a stabilizer into a reaction kettle; the ratio of the mass of the carboxyl-terminated polyether to the total mass of the dibasic acid, the diamine and the lactam is 30-150:100; the molar ratio of the total amount of carboxyl groups of the carboxyl-terminated polyether and the dibasic acid to the amino group of the diamine is 1:1; (2) heating to 190-210°C for a pressure-maintaining reaction for 3-6 hours at a pressure of 0.5-1.5 MPa, and during the reaction, the pH of the liquid phase in the reaction kettle is adjusted to neutral by adding dibasic acid and / or diamine, and then heating to 220-230°C, vacuuming for a reaction for 1-4 hours, and discharging the material to obtain a polyetheramide elastomer. The carboxyl-terminated polyether of the invention is prepared by reacting a polyether polyol with an acid anhydride. Since the terminal carboxyl group of this type of carboxylic acid-terminated polyether is still connected to the polyether chain segment by an ester bond, it is still possible to hydrolyze and break during the polymerization reaction, resulting in reduced polymer viscosity and difficult reactions. In addition, a large number of additives such as carboxyl activators and catalysts are required during the reaction, which affects the appearance and performance of the final product.

[0005] Invention patent CN117510827A discloses a method for preparing a carboxyl-terminated polyether, which comprises the following steps: (1) adding hydroxyl-terminated polyether and sodium ethoxide to a reactor in sequence, heating to 70-80°C under nitrogen protection, stirring for reaction for 3-5 hours, and then evacuating to an absolute pressure of 50-200 Pa, and reacting for 10-15 hours; (2) adding chlorocarboxylic acid to the reactor, the reaction temperature is 70-80°C, the system absolute pressure is 50-200 Pa, and the reaction is performed for 8-10 hours; (3) cooling the reactor to 50-60°C, adding hydrogen chloride ethanol solution, stirring for 1-2 hours, and then standing for stratification for 3-5 hours, taking out the material in the reactor, filtering, and drying to obtain a crude carboxyl-terminated polyether; (4) further removing water-soluble impurities in the crude carboxyl-terminated polyether; (5) crystallizing the washed crude carboxyl-terminated polyether to obtain a carboxyl-terminated polyether. This method uses hazardous chemicals such as sodium ethoxide and chlorocarboxylic acid, and there are safety and environmental pollution problems in industrial production. Summary of the invention

[0006] The purpose of the present invention is to overcome the shortcomings of the prior art and provide a method for preparing a carboxyl-terminated polyether. The present invention uses a cerium oxide-supported platinum metal modified catalyst to catalyze and oxidize a hydroxyl-terminated polyether to prepare a carboxyl-terminated polyether. The carboxyl-terminated polyether synthesized by the present invention can be used to prepare a polyetheramide elastomer.

[0007] To achieve the above technical objectives, the technical solution adopted in the embodiment of the present invention is: a method for preparing a carboxyl-terminated polyether, comprising the following steps: (1) Adding hydroxyl-terminated polyether, deionized water and catalyst into the reactor in sequence, stirring, introducing oxygen to expel the air in the reactor, raising the temperature to 60-90° C., continuously introducing oxygen, maintaining the reactor pressure at 0.05-0.2 MPa, and continuously introducing sodium hydroxide aqueous solution to maintain the pH of the material in the reactor at 9-10; (2) When the reaction system stops absorbing oxygen, adjust the flow rate of the sodium hydroxide aqueous solution to maintain the pH of the material in the reactor at 11-12, continue to introduce oxygen into the reaction system, and the reaction system continues to absorb oxygen. When the reaction system stops absorbing oxygen, the reaction ends; (3) taking out the material in the reactor in step (2), filtering and removing the catalyst to obtain a salt solution of a crude carboxyl-terminated polyether; (4) adding hydrochloric acid to the salt solution of the crude carboxyl-terminated polyether in step (3) to obtain an aqueous solution of the crude carboxyl-terminated polyether; (5) subjecting the aqueous solution of the crude carboxyl-terminated polyether in step (4) to reduced pressure distillation to remove water, thereby obtaining a crude carboxyl-terminated polyether; (6) Adding anhydrous ethanol to the crude carboxyl-terminated polyether in step (5) to dissolve it, filtering to remove inorganic salts, cooling to 5-10° C., waiting for the carboxyl-terminated polyether to crystallize, filtering, and vacuum drying to remove the solvent to obtain a carboxyl-terminated polyether with a purity greater than> 99%.

[0008] Furthermore, in step (1), the mass ratio of the terminal hydroxyl polyether to deionized water is 1:2-9, and the mass ratio of the catalyst to the terminal hydroxyl polyether is 1:9-100.

[0009] Furthermore, the terminal hydroxyl polyether in step (1) is polyethylene glycol with a number average molecular weight of 400-2000.

[0010] Furthermore, the catalyst in step (1) is a cerium oxide carrier loaded with platinum, lanthanum and strontium. By mass fraction, the catalyst includes 2-6% platinum, 1-3% lanthanum, 1-3% strontium and 88-96% cerium oxide.

[0011] The catalyst is prepared according to a public method, for example, an aqueous solution of chloroplatinic acid, an aqueous solution of lanthanum chloride, an aqueous solution of strontium chloride and an aqueous solution of cerium dioxide are mixed, loaded, and then reduced to obtain the catalyst.

[0012] Adding an alkaline solution during the reaction to convert the terminal carboxyl group generated by the oxidation reaction into the corresponding carboxylate helps the oxidation reaction proceed toward the product. If the pH of the reaction system is too low, the reaction rate is low and the reaction is incomplete. If the pH of the reaction system is too high, the alkoxy group in the hydroxy polyether may break, resulting in a decrease in the product molecular weight and a higher acid value. The inventors of the present invention unexpectedly discovered that the above-mentioned problem can be effectively solved by using a two-stage reaction. The reaction is first carried out at a lower pH. When the reaction stops, the pH of the reaction system is increased to continue the reaction, which can increase the reaction conversion rate and avoid side reactions.

[0013] Compared with the prior art, the technical solution provided by the embodiment of the present invention has the following beneficial effects: The invention adopts a highly active catalyst to heterogeneously catalyze and oxidize a hydroxy-terminated polyether to prepare a carboxyl-terminated polyether. Water is used as a solvent in the reaction. The reaction conditions are mild and the use of hazardous chemicals such as chlorocarboxylic acid and sodium ethoxide is avoided. The purity of the prepared carboxyl-terminated polyether is greater than 99%, and the polyether can be used to synthesize a polyether amide elastomer. DETAILED DESCRIPTION

[0014] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0015] The evaluation methods used in Examples 1-3 and Comparative Example 1 are as follows: 1) Acid value and purity of carboxyl-terminated polyether Accurately weigh 0.4 g of the carboxyl-terminated polyether sample and dissolve it in 40 mL of a mixed reagent of ethylene glycol / isopropanol (volume ratio 1:1), add 3-5 drops of 0.05% alcohol solution of methyl red or methyl orange, and titrate with 0.2 mol / L sodium hydroxide in ethylene glycol / isopropanol standard solution until the pink color turns to yellow, and perform a blank test.

[0016] Purity of the product = acid value obtained by titration / theoretical acid value.

[0017] Example 1 A method for preparing a carboxyl-terminated polyether comprises the following steps: (1) 500 g of polyethylene glycol with a number average molecular weight of 600, 3000 g of deionized water and 25 g of catalyst (including CeO by mass fraction) were added to the reactor in sequence. 293%, Pt 5%, La 1% and Sr 1%), start stirring, introduce oxygen into the reactor to replace the air in the reactor, raise the reactor temperature to 65°C and maintain it, continuously introduce oxygen to maintain the reactor pressure at 0.08MPa, and simultaneously continuously introduce 25% by mass sodium hydroxide aqueous solution into the reactor to maintain the pH of the reaction system at 9-10; (2) After 3 hours of reaction, the reaction system stops absorbing oxygen. The amount of sodium hydroxide aqueous solution added is adjusted to maintain the pH of the reaction system at 11-12. The reaction system continues to absorb oxygen. After 3 hours of reaction, the reaction system stops absorbing oxygen and the reaction ends. Since the reaction process is a constant pressure reaction, the oxygen supply valve is automatically adjusted. When the opening of the oxygen supply valve is zero, it means that the pressure can be maintained without oxygen supply, and oxygen absorption stops at this time. (3) The reaction material in the reactor in step (2) is taken out, filtered to remove the catalyst, and then 620 g of 10% by mass hydrochloric acid is added to the reaction material to obtain an aqueous solution of a crude carboxyl-terminated polyether; (4) subjecting the aqueous solution of the crude carboxyl-terminated polyether obtained in step (3) to reduced pressure distillation to remove water, thereby obtaining 620 g of crude carboxyl-terminated polyether; (5) Add 2500 g of anhydrous ethanol to the crude carboxyl-terminated polyether of step (4), stir and dissolve, filter to remove inorganic salts, cool to 8°C, wait for crystals to precipitate, filter, and vacuum dry to remove the solvent to obtain 510 g of carboxyl-terminated polyether.

[0018] According to the hydroxyl value of raw material PEG600 of 183.3 (mgKOH / g), the theoretical acid value of the terminal carboxyl polyether is 3.130 mmol / g, the acid value of the terminal carboxyl polyether is detected to be 3.106 mmol / g, and the purity is calculated to be 99.2%.

[0019] Example 2 A method for preparing a carboxyl-terminated polyether comprises the following steps: (1) 500 g of polyethylene glycol with a number average molecular weight of 1000, 3500 g of deionized water and 32 g of catalyst (including CeO by mass fraction) were added to the reactor in sequence. 2 93%, Pt 5%, La 1% and Sr 1%), start stirring, introduce oxygen into the reactor to replace the air in the reactor, raise the reactor temperature to and maintain it at 75°C, continuously introduce oxygen to maintain the reactor pressure at 0.09MPa, and simultaneously continuously introduce 25% by mass sodium hydroxide aqueous solution into the reactor to maintain the pH of the reaction system at 9-10; (2) After 4 hours of reaction, the reaction system stops absorbing oxygen. The amount of sodium hydroxide aqueous solution added is adjusted to maintain the pH of the reaction system at 11-12. The reaction system continues to absorb oxygen. After 4 hours of reaction, the reaction system stops absorbing oxygen and the reaction is terminated. (3) After filtering the reaction material in the reactor in step (2) to remove the catalyst, 410 g of 10% hydrochloric acid was added to the reaction material to obtain an aqueous solution of a crude carboxyl-terminated polyether; (4) subjecting the aqueous solution of the crude carboxyl-terminated polyether obtained in step (3) to reduced pressure distillation to remove water, thereby obtaining 580 g of crude carboxyl-terminated polyether; (5) Add 2500 g of anhydrous ethanol to the crude carboxyl-terminated polyether of step (4), stir and dissolve, filter to remove inorganic salts, cool to 10° C., wait for crystals to precipitate, filter, and vacuum dry to remove the solvent to obtain 500 g of carboxyl-terminated polyether.

[0020] According to the hydroxyl value of raw material PEG1000 of 114.2 (mgKOH / g), the theoretical acid value of the terminal carboxyl polyether is 1.984 mmol / g. The acid value of the terminal carboxyl polyether is detected to be 1.966 mmol / g, and the purity is calculated to be 99.1%.

[0021] Example 3 A method for preparing a carboxyl-terminated polyether comprises the following steps: (1) Add 500 g of polyethylene glycol with a number average molecular weight of 2000, 4000 g of deionized water and 40 g of catalyst (including CeO 2 93%, Pt 5%, La 1% and Sr 1%), start stirring, introduce oxygen into the reactor to replace the air in the reactor, raise the reactor temperature to and maintain it at 85°C, continuously introduce oxygen to maintain the reactor pressure at 0.12MPa, and simultaneously continuously introduce 25% by mass sodium hydroxide aqueous solution into the reactor to maintain the pH of the reaction system at 9-10; (2) After 4.5 hours of reaction, the reaction system stopped absorbing oxygen. The amount of sodium hydroxide aqueous solution added was adjusted to maintain the pH of the reaction system at 11-12. The reaction system continued to absorb oxygen. After 5 hours of reaction, the reaction system stopped absorbing oxygen and the reaction was terminated. (3) After filtering the reaction material in the reactor in step (2) to remove the catalyst, 230 g of 10% hydrochloric acid was added to the reaction material to obtain an aqueous solution of a crude carboxyl-terminated polyether; (4) subjecting the aqueous solution of the crude carboxyl-terminated polyether obtained in step (3) to reduced pressure distillation to remove water, thereby obtaining 540 g of crude carboxyl-terminated polyether; (5) Add 2500 g of anhydrous ethanol to the crude carboxyl-terminated polyether of step (4), stir and dissolve, filter to remove inorganic salts, cool to 10° C., wait for crystals to precipitate, filter, and vacuum dry to remove the solvent to obtain 482 g of carboxyl-terminated polyether.

[0022] According to the hydroxyl value of 57.4 (mgKOH / g) of the raw material PEG2000, the theoretical acid value of the terminal carboxyl polyether is 1.011 mmol / g. The acid value of the terminal carboxyl polyether is detected to be 0.992 mmol / g, and the purity is calculated to be 99.1%.

[0023] Comparative Example 1 A method for preparing a carboxyl-terminated polyether comprises the following steps: (1) 500 g of polyethylene glycol with a number average molecular weight of 1000, 3500 g of deionized water and 32 g of catalyst (including CeO by mass fraction) were added to the reactor in sequence. 2 93%, Pt 5%, La 1% and Sr 1%), start stirring, introduce oxygen into the reactor to replace the air in the reactor, raise the reactor temperature to and maintain it at 75°C, continuously introduce oxygen to maintain the reactor pressure at 0.09MPa, and simultaneously continuously introduce 25% by mass sodium hydroxide aqueous solution into the reactor to maintain the pH of the reaction system at 11-12; (2) After 6 hours of reaction, the reaction system stops absorbing oxygen and the reaction ends; (3) After filtering the reaction material in the reactor in step (2) to remove the catalyst, 410 g of 10% by mass hydrochloric acid was added to the reaction material to obtain an aqueous solution of a crude carboxyl-terminated polyether; (4) subjecting the aqueous solution of the crude carboxyl-terminated polyether obtained in step (3) to reduced pressure distillation to remove water, thereby obtaining 590 g of crude carboxyl-terminated polyether; (5) Add 2500 g of anhydrous ethanol to the crude carboxyl-terminated polyether of step (4), stir and dissolve, filter to remove inorganic salts, cool to 10° C., wait for crystals to precipitate, filter, and vacuum dry to remove the solvent to obtain 510 g of carboxyl-terminated polyether.

[0024] According to the hydroxyl value of 114.2 (mgKOH / g) of the raw material PEG1000, the theoretical acid value of the terminal carboxyl polyether is 1.984 mmol / g. The detected acid value of the terminal carboxyl polyether is 2.145 mmol / g. The acid value of the product is greater than the theoretical acid value, which indicates that the alkoxy group in the raw material hydroxy polyether breaks during the reaction to produce low molecular weight hydroxy polyether, resulting in a decrease in the molecular weight of the product terminal carboxyl polyether, that is, an increase in by-products.

[0025] The catalysts in Examples 1-3 and Comparative Example 1 were prepared by the following method: Add 50g of cerium dioxide to 200mL of deionized water and stir evenly to obtain a carrier slurry. Weigh 8.15g of chloroplatinic acid hexahydrate, 1.91g of lanthanum chloride heptahydrate, and 2.21g of strontium chloride hexahydrate, and dissolve them in 200mL of deionized water to form a solution. Slowly drip the metal chloride solution into the carrier slurry, stir at 30°C for 3h, then adjust the pH value to pH=13 with 10wt% NaOH solution, then slowly drip 40mL of 10wt% formaldehyde solution, and at pH=13, heat to 80°C for reduction for 15 minutes, cool to room temperature and filter, wash the precipitate with deionized water until neutral, filter, and obtain the catalyst (catalyst composition is Pt5%, La 1%, Sr 1%, CeO 2 93%).

[0026] Finally, it should be noted that the above specific implementation methods are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to examples, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the spirit and scope of the technical solution of the present invention, which should be included in the scope of the claims of the present invention.

Claims

1. A method for preparing a carboxyl-terminated polyether, characterized in that: The following steps are involved: (1) Adding hydroxyl-terminated polyether, deionized water and catalyst into the reactor in sequence, stirring, introducing oxygen to expel the air in the reactor, heating to 60-90° C., continuously introducing oxygen, maintaining the reactor pressure at 0.05-0.2 MPa, and continuously introducing sodium hydroxide aqueous solution to maintain the pH of the material in the reactor at 9-10; (2) When the reaction system stops absorbing oxygen, adjust the flow rate of the sodium hydroxide aqueous solution to maintain the pH of the material in the reactor at 11-12, continue to introduce oxygen into the reaction system, and the reaction system continues to absorb oxygen. When the reaction system stops absorbing oxygen, the reaction ends; (3) taking out the material in the reactor in step (2), filtering and removing the catalyst to obtain a salt solution of a crude carboxyl-terminated polyether; (4) adding hydrochloric acid to the salt solution of the crude carboxyl-terminated polyether in step (3) to obtain an aqueous solution of the crude carboxyl-terminated polyether; (5) subjecting the aqueous solution of the crude carboxyl-terminated polyether in step (4) to vacuum distillation to remove water, thereby obtaining a crude carboxyl-terminated polyether; (6) Adding anhydrous ethanol to the crude carboxyl-terminated polyether in step (5) to dissolve it, filtering to remove inorganic salts, cooling to 5-10° C., waiting for the carboxyl-terminated polyether to crystallize, filtering, and vacuum drying to remove the solvent to obtain a carboxyl-terminated polyether with a purity greater than> 99%.

2. The method for preparing a carboxyl-terminated polyether according to claim 1, wherein In step (1), the mass ratio of the terminal hydroxyl polyether to deionized water is 1:2-9, and the mass ratio of the catalyst to the terminal hydroxyl polyether is 1:9-100.

3. The method for preparing a carboxyl-terminated polyether according to claim 1, wherein The hydroxy-terminated polyether in step (1) is polyethylene glycol having a number average molecular weight of 400-2000.

4. The method for preparing a carboxyl-terminated polyether according to claim 1, wherein The catalyst in step (1) is a cerium oxide carrier loaded with platinum, lanthanum and strontium. By mass fraction, the catalyst includes 2-6% platinum, 1-3% lanthanum, 1-3% strontium and 88-96% cerium oxide.