Method for measuring content of isocyanate groups in polyurethane prepolymer

Abstract

The invention discloses a method for measuring the content of isocyanate groups in a polyurethane prepolymer. The method comprises the following steps: measuring dry xylene for later use; weighing a proper amount of polyurethane prepolymer, dissolving the polyurethane prepolymer in xylene, adding a di-n-butylamine-xylene solution, uniformly mixing, and standing; adding isopropanol and standard hydrochloric acid into the mixed solution for mutual dissolution; adding a bromocresol blue indicator and fully oscillating; titrating with a hydrochloric acid standard solution until the terminal color turns yellow from blue, and meanwhile, carrying out a blank experiment; finally, the content of isocyanate groups in the polyurethane prepolymer is obtained through a calculation formula. The mass ratio of the polyurethane prepolymer to the xylene is (0.1-1): (8-12), the mass ratio of the polyurethane prepolymer to the di-n-butylamine-xylene solution is (0.1-1): (9-12), and the mass ratio of the polyurethane prepolymer to the isopropanol is (0.1-1): (18-22). The method is easy and convenient to operate, accurate in measurement, high in reliability and suitable for quality control in the production and application process of the polyurethane prepolymer.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of polyurethane analysis testing, in particular to a method for determining the isocyanate group content in polyurethane prepolymer. BACKGROUND

[0002] Polyurethane prepolymer is an important polymer intermediate, widely used in coatings, adhesives, sealants, elastomers and other fields. In the production and application process of polyurethane prepolymer, the isocyanate group content (NCO%) is a key quality control index, which directly affects the performance and quality of the final product. Accurate determination of the isocyanate group content in polyurethane prepolymer is of great significance for controlling the reaction process and ensuring product quality.

[0003] Currently, the methods for determining the isocyanate group content in polyurethane prepolymer mainly include titration method and high performance liquid chromatography. Among them, the titration method is widely used due to its simple operation and low cost. The traditional titration method usually uses di-n-butylamine to react with isocyanate groups, and then uses hydrochloric acid standard solution to titrate the remaining di-n-butylamine to indirectly determine the isocyanate group content. For example, CN118566414A discloses a method for determining the isocyanate group content in water-based polyurethane prepolymer, which uses di-n-butylamine / n-butyl acetate solution to react with the prepolymer, and then uses HCl standard titration solution for titration, and calculates the NCO value.

[0004] High performance liquid chromatography is also an important method for determining the isocyanate group content in polyurethane prepolymer, especially suitable for the determination of low content of isocyanate. For example, CN106198772B discloses a method for determining the low free toluene diisocyanate content in polyurethane prepolymer, which uses high performance liquid chromatograph, detects at a wavelength of 220nm to 237nm, directly dissolves and determines by gradient elution, and uses peak area external standard method for quantification.

[0005] In the preparation process of polyurethane prepolymer, the control of isocyanate group content is crucial. CN115677971A discloses a preparation method of polyurethane prepolymer, in which the molar ratio of isocyanate to hydroxyl in polyol is controlled within a certain range to solve the problem of high content of free isocyanate monomer in polyurethane prepolymer. CN105713168B discloses a polyurethane prepolymer with a mass percentage of isocyanate group MNCO of 4% to 10%, which has the advantages of low viscosity, high NCO content, high stability and long storage period.

[0006] In addition, CN117686571A discloses a method for rapidly and accurately determining the hydroxyl value of resin polyol by automatic potentiometric titration, which indirectly controls the quality of polyurethane prepolymer by determining the hydroxyl value.

[0007] However, the existing polyurethane prepolymer isocyanate group content determination method has the following problems:

[0008] Firstly, the traditional titration method usually needs to use a large amount of titration reagent, which not only causes raw material waste, increases the test cost, but also causes great burden to the environment. Especially in batch detection, the reagent consumption is large, which does not meet the current green chemistry development concept.

[0009] Secondly, toluene is generally used as a solvent in the existing method, but toluene has been listed in the control range by the state, and its acquisition and use are strictly limited, which brings inconvenience to the normal production and quality control of enterprises. At the same time, toluene has high toxicity and volatility, and long-term contact poses a threat to the health of the detection personnel.

[0010] Thirdly, the operation process of the existing method is complex, and the technical requirements for the operator are high, which is easy to introduce human error and affect the accuracy and reliability of the determination results.

[0011] Therefore, developing an environmentally friendly, efficient and accurate polyurethane prepolymer isocyanate group content determination method can not only reduce the use of harmful reagents, but also ensure the accuracy of the determination results, which is of great significance to the sustainable development of the polyurethane industry. SUMMARY

[0012] The technical problem to be solved by the present application is to provide an environmentally friendly and efficient polyurethane-NCO detection method to overcome the defects of the existing polyurethane-NCO detection method, such as excessive use of titration reagent causing raw material waste, causing great threat to the environment, and using toluene which is listed in the control range by the state and cannot be easily obtained.

[0013] The purpose of the present application is achieved by the following technical scheme: a method for determining the isocyanate group content in polyurethane prepolymer, comprising the following steps: S1, a certain amount of dried xylene is first measured and prepared; S2, a proper amount of polyurethane prepolymer is weighed and added to the xylene to dissolve completely, then a proper amount of di-n-butylamine-xylene solution is added, stirred and mixed uniformly, sealed, fully shaken, and left to stand to obtain a mixed solution A for standby; S3, isopropanol and standard hydrochloric acid are taken and added to the mixed solution A to be miscible to obtain a mixed solution B for standby; S4, a proper amount of bromocresol blue indicator is added to the mixed solution B and fully shaken and mixed uniformly; S5, a commercial hydrochloric acid standard solution is used for titration until the end point changes from blue to yellow, and a blank experiment is performed at the same time; S6, a standard formula is used to obtain the actual-NCO% of the polyurethane.

[0014] Preferably, the mass ratio of the polyurethane prepolymer to xylene is 0.1-1:8-12.

[0015] Preferably, the mass ratio of the polyurethane prepolymer to the di-n-butylamine-xylene solution is 0.1-1:9-12.

[0016] Preferably, the concentration of the di-n-butylamine-xylene solution is 0.1-0.3 mol / L.

[0017] Preferably, the mass ratio of the polyurethane prepolymer to isopropyl alcohol is 0.1-1:18-22.

[0018] Preferably, the mass ratio of the isopropyl alcohol to standard hydrochloric acid is 0.8-1.2:1.

[0019] Preferably, in step S3, the concentration of the standard hydrochloric acid is 0.1-0.3 mol / L.

[0020] Preferably, in step S4, the concentration of the standard hydrochloric acid solution is 0.1-0.3 mol / L.

[0021] Preferably, in step S6, the standard formula is as follows: the isocyanate salt content (ω NCO ) is in terms of the mass percentage of isocyanate salt, and the value is expressed in % and calculated according to formula (1): ω NCO = [(V0-V) × c × 42.02] / m × 100%. (1) In the formula: V0 - the volume of the standard hydrochloric acid solution consumed by the titration blank, in mL; V - the volume of the standard hydrochloric acid solution consumed by the titration sample, in mL; c - the concentration of the standard hydrochloric acid solution, in mol / L; 42.02 - the numerical value of the molar mass of NCO, in g / mol; and m - the mass of the sample, in g.

[0022] The determination result is expressed as the arithmetic mean value of two parallel samples, and the result is rounded to two decimal places.

[0023] The reaction formula involved in the titration is as follows: Reaction of isocyanate groups with di-n-butylamine: R-NCO + (C4H9)2NH → RNHCON(C4H9)2 Reaction of hydrochloric acid with di-n-butylamine: (C4H9)2NH + HCL → (C4H9)2NH•HCL.

[0024] The beneficial effects of the present application are as follows: 1. Environmental improvement: by reducing the amount of reagents used, raw material waste and environmental pollution are reduced. 2. High test precision: Experimental data show that the actual -NCO% of polyurethane prepolymer measured by this method has high uniformity, and the relative standard deviation RSD is less than 0.03%, indicating that the experimental precision is very high; 3. Excellent repeatability: Test results show that the repeatability of the method is higher than that of the industry standard; 4. Good reagent stability: Xylene has lower volatility and better storage stability than toluene; it is less disturbed under normal test environment (0~40℃); 5. Improved safety: Xylene has a higher flash point and lower flammability, requiring less fire prevention measures during storage; 6. High feasibility: Avoid using toluene, which is listed as a controlled substance, and it is easier to obtain and use. DETAILED DESCRIPTION

[0025] In order to facilitate the understanding of those skilled in the art, the present application will be further described below in conjunction with examples, and the content mentioned in the embodiments is not a limitation of the present application. Example 1

[0026] A method for determining the isocyanate group content in polyurethane prepolymer, comprising the following steps: S1: First, a certain amount of dried xylene is measured and prepared;

[0027] Specifically, 100 mL of dried xylene is taken in a dry volumetric flask, ensuring that the xylene is free of moisture to avoid moisture reacting with the isocyanate group and affecting the test results. The drying method can use molecular sieve drying or anhydrous sodium sulfate drying, and the drying time is not less than 24 hours.

[0028] S2: Weigh an appropriate amount of polyurethane prepolymer, add the polyurethane prepolymer to the xylene and dissolve until completely dissolved, then add an appropriate amount of di-n-butylamine-xylene solution, stir and mix evenly, seal and shake thoroughly, and then stand to obtain a mixed solution A for standby; Specifically, 0.5 g of polyurethane prepolymer is weighed into a 250 mL conical flask, 10 g of dried xylene is added, and the mass ratio of polyurethane prepolymer to xylene is 0.5:10, i.e. 1:20. Stir at room temperature until the polyurethane prepolymer is completely dissolved, which takes about 10-15 min. Then add 10 g of 0.2 mol / L di-n-butylamine-xylene solution, and the mass ratio of polyurethane prepolymer to di-n-butylamine-xylene solution is 0.5:10, i.e. 1:20. Use a magnetic stirrer to stir for 5 min to ensure uniform mixing. After sealing the conical flask, shake on a shaker for 10 min at a frequency of 200 rpm. Stand for 30 min to obtain a mixed solution A.

[0029] S3: Take isopropyl alcohol and standard hydrochloric acid, add isopropyl alcohol and standard hydrochloric acid to the mixed solution A to make them mutually soluble, and obtain a mixed solution B for standby; Specifically, take 20 g of isopropyl alcohol and 20 g of standard hydrochloric acid with a concentration of 0.2 mol / L, the mass ratio of isopropyl alcohol to standard hydrochloric acid is 1:1. Add isopropyl alcohol and standard hydrochloric acid to mixed solution A in turn, stir for 5 min to make them fully miscible, and obtain mixed solution B. The mass ratio of polyurethane prepolymer to isopropyl alcohol is 0.5:20, i.e. 1:40.

[0030] S4: Take an appropriate amount of bromocresol blue indicator and add it to mixed solution B and shake it well; Specifically, take 3-5 drops of bromocresol blue indicator (0.1% aqueous solution) and add it to mixed solution B, shake it on a shaker for 3 min, and the shaking frequency is 200 rpm, so that the indicator is uniformly dispersed in the mixed solution.

[0031] S5: Titrate to the end point from blue to yellow with a commercial hydrochloric acid standard solution, and perform a blank experiment at the same time; Specifically, titrate mixed solution B with a commercial hydrochloric acid standard solution with a concentration of 0.2 mol / L, and control the titration speed at 1-2 drops per second, and slow down the titration speed when approaching the end point. When the solution color changes from blue to yellow and does not fade within 30 seconds, it is the titration end point, and record the volume V of the hydrochloric acid standard solution consumed. At the same time, a blank experiment is performed according to the same procedure, i.e. without adding polyurethane prepolymer, and the rest of the steps are the same, and the volume V0 of the hydrochloric acid standard solution consumed in the blank experiment is recorded.

[0032] S6: Bring in the standard formula to get the actual –NCO% of polyurethane.

[0033] Specifically, the data measured in the above steps are brought into the following formula to calculate the isocyanate group content in the polyurethane prepolymer: Isocyanate group content (ω NCO ) is expressed in mass percent of isocyanate salt, and the value is expressed in %, calculated according to formula (1): ω NCO = [(V0-V) × c × 42.02] / m × 100% (1) In the formula: V0 - the volume of hydrochloric acid standard solution consumed in titration, in mL; V - the volume of hydrochloric acid standard solution consumed in titration, in mL; c - the concentration of hydrochloric acid standard solution, in mol / L; 42.02 - the numerical value of NCO molar mass, in g / mol; m - the mass of the sample, in g.

[0034] For example, if V0=25.6 mL, V=15.2 mL, c=0.2 mol / L, and m=0.5 g, then: ω NCO = [(25.6-15.2) × 0.2 × 42.02] / 0.5 × 100% = 8.74% The determination results are expressed as the arithmetic mean of two parallel samples, and the results are rounded to two decimal places. If two parallel determinations are performed, 8.74% and 8.78% are obtained respectively, and the final result is 8.76%.

[0035] Example 2 A method for determining the isocyanate group content in a polyurethane prepolymer, comprising the following steps: S1: First, a certain amount of dried xylene is measured and prepared; Specifically, 100 mL of dried xylene is taken in a dry volumetric flask, ensuring that the xylene is free of moisture to avoid moisture reacting with the isocyanate group and affecting the determination results.

[0036] S2: Weigh an appropriate amount of polyurethane prepolymer, add the polyurethane prepolymer to the xylene and dissolve it completely, then add an appropriate amount of di-n-butylamine-xylene solution, stir and mix evenly, seal and shake thoroughly, and let stand to obtain a mixed solution A for standby; Specifically, 0.2 g of polyurethane prepolymer is weighed into a 250 mL conical flask, 2 g of dried xylene is added, and the mass ratio of polyurethane prepolymer to xylene is 0.2:2, i.e. 1:10. Stir at room temperature until the polyurethane prepolymer is completely dissolved, which takes about 10-15 min. Then add 2 g of 0.1 mol / L di-n-butylamine-xylene solution, and the mass ratio of polyurethane prepolymer to di-n-butylamine-xylene solution is 0.2:2, i.e. 1:10. Use a magnetic stirrer to stir for 5 min to ensure uniform mixing. Seal the conical flask and shake on a shaker for 10 min at a frequency of 200 rpm. Let stand for 30 min to obtain a mixed solution A.

[0037] S3: Take isopropyl alcohol and standard hydrochloric acid, and add isopropyl alcohol and standard hydrochloric acid to the mixed solution A to make them mutually soluble to obtain a mixed solution B for standby; Specifically, 4 g of isopropyl alcohol and 4 g of 0.1 mol / L standard hydrochloric acid are taken, and the mass ratio of isopropyl alcohol to standard hydrochloric acid is 1:1. Add isopropyl alcohol and standard hydrochloric acid to mixed solution A in turn, stir for 5 min to make them fully miscible, and obtain a mixed solution B. The mass ratio of polyurethane prepolymer to isopropyl alcohol is 0.2:4, i.e. 1:20.

[0038] S4: Take an appropriate amount of bromocresol blue indicator and add it to the mixed solution B and shake thoroughly to make it uniform; Specifically, take 3-5 drops of bromocresol blue indicator (0.1% aqueous solution) into the mixed solution B, and shake on the shaker for 3 min at a shaking frequency of 200 rpm to make the indicator uniformly dispersed in the mixed solution.

[0039] S5: Titrate to the end point where the color changes from blue to yellow, and perform a blank test at the same time; Specifically, titrate the mixed solution B with a commercially available hydrochloric acid standard solution with a concentration of 0.1 mol / L, and control the titration speed at 1-2 drops per second. Slow down the titration speed when approaching the end point. When the solution color changes from blue to yellow and does not fade within 30 seconds, it is the titration end point, and record the volume V of hydrochloric acid standard solution consumed. At the same time, perform a blank test according to the same procedure, i.e. do not add polyurethane prepolymer, and the rest of the steps are the same, and record the volume V0 of hydrochloric acid standard solution consumed in the blank test.

[0040] S6: Bring in the standard formula to get the actual -NCO% of polyurethane.

[0041] Specifically, the data measured in the above steps are brought into the following formula to calculate the isocyanate group content in the polyurethane prepolymer: Isocyanate group content (ω NCO ) is expressed in mass percent of isocyanate salt, and the value is expressed in %, calculated according to formula (1): ω NCO = [(V0-V) × c × 42.02] / m × 100% (1) In the formula: V0 - the volume of hydrochloric acid standard solution consumed in the titration blank, in mL; V - the volume of hydrochloric acid standard solution consumed in the titration of the sample, in mL; c - the concentration of the hydrochloric acid standard solution, in mol / L; 42.02 - the numerical value of the molar mass of NCO, in g / mol; m - the mass of the sample, in g.

[0042] For example, if V0 = 20.5 mL, V = 12.3 mL, c = 0.1 mol / L, and m = 0.2 g, then: ω NCO = [(20.5-12.3) × 0.1 × 42.02] / 0.2 × 100% = 8.62% The test results are expressed as the arithmetic mean of two parallel samples, and the results are rounded to two decimal places.

[0043] Example 3 A method for determining the isocyanate group content in a polyurethane prepolymer, comprising the following steps: S1: First take a certain amount of dried xylene, ready for use; Specifically, 100 mL of dried xylene was taken in a dry volumetric flask, ensuring that the xylene was free of moisture to avoid moisture reacting with the isocyanate group and affecting the test results. The drying method used molecular sieve drying, and the drying time was 48 hours.

[0044] S2: Take an appropriate amount of polyurethane prepolymer, add the polyurethane prepolymer to the xylene and dissolve until completely dissolved, then add an appropriate amount of di-n-butylamine-xylene solution, stir and mix evenly, seal and shake thoroughly, stand, get mixed liquid A, ready for use; Specifically, 0.1 g of polyurethane prepolymer was weighed into a 250 mL conical flask, 1 g of dried xylene was added, and the mass ratio of polyurethane prepolymer to xylene was 0.1:1, i.e. 1:10. Stir at room temperature until the polyurethane prepolymer is completely dissolved, the dissolution time is about 10 min. Then add 1.2 g of di-n-butylamine-xylene solution with a concentration of 0.3 mol / L, the mass ratio of polyurethane prepolymer to di-n-butylamine-xylene solution is 0.1:1.2, i.e. 1:12. Use a magnetic stirrer to stir for 5 min to ensure uniform mixing. After sealing the conical flask, shake on a shaker for 15 min at a shaking frequency of 180 rpm. Stand for 40 min to get mixed liquid A.

[0045] S3: Take isopropyl alcohol and standard hydrochloric acid, add isopropyl alcohol and standard hydrochloric acid to mixed liquid A to get mixed liquid B, ready for use; Specifically, take 2 g of isopropyl alcohol and 1.8 g of standard hydrochloric acid with a concentration of 0.3 mol / L, the mass ratio of isopropyl alcohol to standard hydrochloric acid is 2:1.8, i.e. 1.11:1. Add isopropyl alcohol and standard hydrochloric acid to mixed liquid A in turn, stir for 5 min to make them fully miscible, get mixed liquid B. The mass ratio of polyurethane prepolymer to isopropyl alcohol is 0.1:2, i.e. 1:20.

[0046] S4: Take an appropriate amount of bromocresol blue indicator and add it to mixed liquid B and shake thoroughly; Specifically, take 4 drops of bromocresol blue indicator (0.1% aqueous solution) and add it to mixed liquid B, shake on a shaker for 3 min at a shaking frequency of 180 rpm to make the indicator evenly dispersed in the mixed liquid.

[0047] S5: Titrate with commercial hydrochloric acid standard solution to the end point from blue to yellow, and do a blank test at the same time; Specifically, the mixed solution B is titrated with a commercial hydrochloric acid standard solution with a concentration of 0.3 mol / L, the titration speed is controlled at 1 drop per second, and the titration speed is slowed down when approaching the end point. When the color of the solution changes from blue to yellow and does not fade within 30 seconds, it is the end point of titration, and the volume V of the consumed hydrochloric acid standard solution is recorded. At the same time, a blank experiment is carried out according to the same procedure, that is, no polyurethane prepolymer is added, and the rest of the steps are the same, and the volume V0 of the consumed hydrochloric acid standard solution in the blank experiment is recorded.

[0048] S6: The standard formula is brought in to obtain the actual -NCO% of the polyurethane.

[0049] Specifically, the data measured in the above steps are brought into the following formula to calculate the isocyanate group content in the polyurethane prepolymer: The isocyanate group content (ω NCO ) is in terms of mass percentage of isocyanate salt, and the value is expressed in %, which is calculated according to formula (1): ω NCO = [(V0-V) × c × 42.02] / m × 100% (1) In the formula: V0 - the volume of the hydrochloric acid standard solution consumed in the titration of the blank, in mL; V - the volume of the hydrochloric acid standard solution consumed in the titration of the sample, in mL; c - the concentration of the hydrochloric acid standard solution, in mol / L; 42.02 - the value of the molar mass of NCO, in g / mol; m - the mass of the sample, in g.

[0050] For example, if V0 = 15.3 mL, V = 10.2 mL, c = 0.3 mol / L, and m = 0.1 g, then: ω NCO = [(15.3-10.2) × 0.3 × 42.02] / 0.1 × 100% = 6.43% The test results are expressed as the arithmetic mean of two parallel samples, and the results are rounded to two decimal places. If two parallel tests are performed and the results are 6.43% and 6.47% respectively, the final result is 6.45%.

[0051] Example 4 A method for determining the isocyanate group content in a polyurethane prepolymer, comprising the following steps: S1: First, a certain amount of dried xylene is measured and prepared; Specifically, 100 mL of dried xylene was taken in a dry volumetric flask to ensure that the xylene was free of moisture to avoid moisture reacting with the isocyanate group and affecting the test results. The drying method used anhydrous sodium sulfate drying, and the drying time was 36 hours.

[0052] S2: An appropriate amount of polyurethane prepolymer was weighed, the polyurethane prepolymer was added to xylene and dissolved until completely dissolved, then an appropriate amount of di-n-butylamine-xylene solution was added, stirred and mixed uniformly, sealed, fully oscillated, and stood to obtain a mixed solution A for standby;

[0053] Specifically, 1 g of polyurethane prepolymer was weighed in a 250 mL conical flask, 8 g of dried xylene was added, and the mass ratio of polyurethane prepolymer to xylene was 1:8. Stir at room temperature until the polyurethane prepolymer is completely dissolved, and the dissolution time is about 20 min. Then 9 g of di-n-butylamine-xylene solution with a concentration of 0.2 mol / L was added, and the mass ratio of polyurethane prepolymer to di-n-butylamine-xylene solution was 1:9. Stir for 8 min using a magnetic stirrer to ensure uniform mixing. After sealing the conical flask, oscillate on a shaker for 12 min at a frequency of 220 rpm. Stand for 35 min to obtain a mixed solution A.

[0054] S3: Take isopropyl alcohol and standard hydrochloric acid, and add isopropyl alcohol and standard hydrochloric acid to the mixed solution A to make them mutually soluble to obtain a mixed solution B for standby;

[0055] Specifically, 18 g of isopropyl alcohol and 15 g of standard hydrochloric acid with a concentration of 0.2 mol / L were taken, and the mass ratio of isopropyl alcohol to standard hydrochloric acid was 18:15, i.e. 1.2:1. Isopropyl alcohol and standard hydrochloric acid were added to mixed solution A in turn, stirred for 6 min to make them fully miscible, and a mixed solution B was obtained. The mass ratio of polyurethane prepolymer to isopropyl alcohol was 1:18.

[0056] S4: Take an appropriate amount of bromocresol blue indicator and add it to the mixed solution B and fully oscillate to make it uniform;

[0057] Specifically, 5 drops of bromocresol blue indicator (0.1% aqueous solution) were added to the mixed solution B, oscillated on a shaker for 4 min at a frequency of 220 rpm, and the indicator was uniformly dispersed in the mixed solution.

[0058] S5: Titrate to the end point from blue to yellow with a commercial hydrochloric acid standard solution, and perform a blank test at the same time;

[0059] Specifically, the mixed solution B is titrated with a commercial hydrochloric acid standard solution with a concentration of 0.2 mol / L, the titration speed is controlled at 1-2 drops per second, and the titration speed is slowed down when approaching the end point. When the color of the solution changes from blue to yellow and does not fade within 30 seconds, the titration end point is reached, and the volume V of the consumed hydrochloric acid standard solution is recorded. At the same time, a blank experiment is carried out according to the same procedure, i.e. without adding the polyurethane prepolymer, and the rest of the steps are the same, and the volume V0 of the consumed hydrochloric acid standard solution in the blank experiment is recorded.

[0060] S6: The standard formula is brought in to obtain the actual -NCO% of the polyurethane.

[0061] Specifically, the data measured in the above steps are brought into the following formula to calculate the isocyanate group content in the polyurethane prepolymer: Isocyanate group content (ω NCO ) is expressed in mass percentage of isocyanate salt, and the value is expressed in %, calculated according to formula (1): ω NCO = [(V0-V) × c × 42.02] / m × 100% (1) In the formula: V0 - the volume of the hydrochloric acid standard solution consumed in the titration of the blank, in mL; V - the volume of the hydrochloric acid standard solution consumed in the titration of the sample, in mL; c - the concentration of the hydrochloric acid standard solution, in mol / L; 42.02 - the numerical value of the molar mass of NCO, in g / mol; m - the mass of the sample, in g.

[0062] For example, if V0 = 30.5 mL, V = 18.7 mL, c = 0.2 mol / L, and m = 1 g, then: ω NCO = [(30.5-18.7) × 0.2 × 42.02] / 1 × 100% = 9.88% The test results are expressed as the arithmetic mean of two parallel samples, and the results are rounded to two decimal places. If two parallel tests are performed and the results are 9.88% and 9.92% respectively, the final result is 9.90%.

[0063] Example 5 A method for determining the isocyanate group content in a polyurethane prepolymer, comprising the following steps: S1: First, a certain amount of dried xylene is measured and prepared; Specifically, 100 mL of dried xylene was taken in a dry volumetric flask to ensure that the xylene was free of moisture to avoid the reaction of moisture with the isocyanate group affecting the determination results. The drying method used molecular sieve drying, and the drying time was 24 hours.

[0064] S2: An appropriate amount of polyurethane prepolymer was weighed, the polyurethane prepolymer was added to xylene and dissolved until completely dissolved, then an appropriate amount of di-n-butylamine-xylene solution was added, stirred and mixed uniformly, sealed, fully oscillated, and stood to obtain a mixed solution A for standby;

[0065] Specifically, 0.8 g of polyurethane prepolymer was weighed in a 250 mL conical flask, 9.6 g of dried xylene was added, and the mass ratio of polyurethane prepolymer to xylene was 0.8:9.6, i.e. 1:12. Stir at room temperature until the polyurethane prepolymer is completely dissolved, and the dissolution time is about 15 min. Then 9.6 g of di-n-butylamine-xylene solution with a concentration of 0.15 mol / L was added, and the mass ratio of polyurethane prepolymer to di-n-butylamine-xylene solution was 0.8:9.6, i.e. 1:12. Stir for 6 min using a magnetic stirrer to ensure uniform mixing. After sealing the conical flask, oscillate on a shaker for 10 min at a frequency of 200 rpm. Stand for 30 min to obtain a mixed solution A.

[0066] S3: Take isopropyl alcohol and standard hydrochloric acid, and add isopropyl alcohol and standard hydrochloric acid to mixed solution A to make them mutually soluble to obtain a mixed solution B for standby;

[0067] Specifically, 16 g of isopropyl alcohol and 16 g of standard hydrochloric acid with a concentration of 0.15 mol / L were taken, and the mass ratio of isopropyl alcohol to standard hydrochloric acid was 1:1. Isopropyl alcohol and standard hydrochloric acid were added to mixed solution A in turn, stirred for 5 min to make them fully mutually soluble, and a mixed solution B was obtained. The mass ratio of polyurethane prepolymer to isopropyl alcohol was 0.8:16, i.e. 1:20.

[0068] S4: Take an appropriate amount of bromocresol blue indicator and add it to mixed solution B and fully oscillate to make it uniform; Specifically, 4 drops of bromocresol blue indicator (0.1% aqueous solution) were added to mixed solution B, oscillated on a shaker for 3 min at a frequency of 200 rpm, and the indicator was uniformly dispersed in the mixed solution.

[0069] S5: Titrate with a commercial hydrochloric acid standard solution to the end point from blue to yellow, and perform a blank experiment at the same time; Specifically, the mixed solution B is titrated with a commercial hydrochloric acid standard solution with a concentration of 0.15 mol / L, the titration speed is controlled at 1-2 drops per second, and the titration speed is slowed down when approaching the end point. When the color of the solution changes from blue to yellow and does not fade within 30 seconds, it is the end point of titration, and the volume V of the consumed hydrochloric acid standard solution is recorded. At the same time, a blank experiment is carried out according to the same procedure, i.e. without adding the polyurethane prepolymer, and the rest of the steps are the same, and the volume V0 of the consumed hydrochloric acid standard solution in the blank experiment is recorded.

[0070] S6: The standard formula is brought in to obtain the actual-NCO% of the polyurethane.

[0071] Specifically, the data measured in the above steps are brought into the following formula to calculate the isocyanate group content in the polyurethane prepolymer: The isocyanate group content (ω NCO ) is in terms of mass percentage of isocyanate salt, and the value is expressed in %, calculated according to formula (1): ω NCO = [(V0-V) × c × 42.02] / m × 100% (1) In the formula: V0 - the volume of the hydrochloric acid standard solution consumed in the titration of the blank, in mL; V - the volume of the hydrochloric acid standard solution consumed in the titration of the sample, in mL; c - the concentration of the hydrochloric acid standard solution, in mol / L; 42.02 - the numerical value of the molar mass of NCO, in g / mol; m - the mass of the sample, in g.

[0072] For example, if V0=28.4 mL, V=17.6 mL, c=0.15 mol / L, and m=0.8 g, then: ω NCO = [(28.4-17.6) × 0.15 × 42.02] / 0.8 × 100% = 8.50% The test results are expressed as the arithmetic mean of two parallel samples, and the results are rounded to two decimal places. If two parallel tests are performed and the results are 8.50% and 8.54% respectively, the final result is 8.52%.

[0073] It should be noted that Example 1, Example 2, Example 3, Example 4, and Example 5 are all one kind of method for determining the isocyanate group content in the polyurethane prepolymer.

[0074] Performance Test Section Test environment temperature: standard room temperature 25℃; test environment humidity: 55%; the temperature of each reagent is standard room temperature 25℃; hydrochloric acid standard solution concentration (Shenzhen Bolinda Technology Co., Ltd.): 0.1 mol / L; calibrate the analytical balance before weighing the prepolymer; Synthesis of one-pot polyurethane prepolymer, temperature 124℃, its theoretical -NCO%: 5.9916%; The patent blank control test consumes hydrochloric acid standard solution volume: 12.5 mL; The blank control test consumes hydrochloric acid standard solution volume: 25 mL according to the method described in the chemical industry standard HG / T2409; The polyurethane prepolymer is titrated three times by the method of the patent and the method described in the chemical industry standard HG / T2409 respectively, and the relevant data are shown in Table 1 below; Table 1 It can be seen that the actual -NCO% of the polyurethane prepolymer has high uniformity, and the relative standard deviation RSD is less than 0.03%, indicating that the experimental precision is very high, and it can be seen that the repeatability of the patent method is higher than that of the industry standard.

[0075] Note: The method described in the chemical industry standard HG / T2409-1992: take 1.0000 g of sample, dissolve with 25 mL of toluene, add 25 mL of 0.1 mol / L di-n-butylamine-toluene solution, seal and shake, stand for 15 min, add 100 mL of isopropyl alcohol and 5 drops of bromocresol blue indicator, titrate with 0.1 mol / L hydrochloric acid solution to the end point from blue to yellow, and perform a blank test at the same time.

[0076] Regarding solution stability Except for xylene and the prepared 0.1 mol / L di-n-butylamine-xylene solution, the rest of the reagents are industry standards.

[0077] Compared with toluene (boiling point about 110.6℃), xylene (boiling point about 138.4℃) has lower volatility and better storage stability; On the other hand, under high temperature and light conditions, the molecular structure of toluene (single methyl substitution benzene ring) is more prone to oxidation or other side reactions than xylene (double methyl substitution); Finally, toluene has lower flash point (about 4.4℃) and higher flammability, and stricter fire prevention measures are required during storage.

[0078] In addition, the titration of polyurethane prepolymer is affected by the presence of blank control test. Except for the operation of frequent titration, as long as the blank test is performed before titration, the deterioration of the solution has no effect on the actual -NCO%.

[0079] But in order to test the stability of the solution system, high and low temperature test was designed to test the actual effect of storage environment on xylene and configured 0.1 mol / L di-n-butylamine-xylene solution.

[0080] Xylene and configured 0.1 mol / L di-n-butylamine-xylene solution were stored in a 40℃ blast drying oven and a 0℃ refrigerator for three days, and then were placed at standard room temperature (25℃) for one day to recover the temperature, so as to avoid accidental errors caused by volatilization and crystallization phenomenon due to immediate opening. Then titration test was carried out, and the test conditions were the same as before, and the relevant data are shown in Table 2 below; Table 2 It can be seen that the actual -NCO% of the polyurethane prepolymer has high uniformity, and is basically the same after two decimal places, indicating that the reagent stability used in the present application is good and is less disturbed in the commonly used test environment (0~40℃).

[0081] Finally, it should be pointed out that: the above examples are only used to illustrate the technical solutions of the present application, but not to limit it; although the present application has been described in detail with reference to the foregoing examples, those skilled in the art should understand that: it can still modify the technical solutions recorded in the foregoing examples, or make equivalent replacement for part of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present application.

Claims

1. A method for determining the isocyanate group content in a polyurethane prepolymer, characterized by: It comprises the following steps: S1, first take a certain amount of dry xylene, ready for use; S2, take a certain amount of polyurethane prepolymer, add the polyurethane prepolymer to the xylene to dissolve completely, then add a certain amount of di-n-butylamine-xylene solution, stir and mix evenly, seal and fully oscillate, stand, get mixed liquid A, ready for use; S3, take isopropyl alcohol and standard hydrochloric acid, add isopropyl alcohol and standard hydrochloric acid to mixed liquid A to make them mutually soluble, get mixed liquid B, ready for use; S4, take a certain amount of bromocresol blue indicator and add it to mixed liquid B and fully oscillate evenly; S5, use commercial hydrochloric acid standard solution to titrate to the end point from blue to yellow, and do a blank experiment at the same time; S6, get the actual-NCO% of polyurethane by using the standard formula.

2. A method of determining the isocyanate group content of a polyurethane prepolymer according to claim 1, characterised in that: The mass ratio of the polyurethane prepolymer to xylene is 0.1-1:8-12.

3. A method of determining the isocyanate group content of a polyurethane prepolymer according to claim 1 or 2, characterised in that: The mass ratio of the polyurethane prepolymer to di-n-butylamine-xylene solution is 0.1-1:9-12.

4. A method of determining the isocyanate group content of a polyurethane prepolymer according to claim 3, characterised in that: The concentration of the di-n-butylamine-xylene solution is 0.1-0.3 mol / L.

5. A method of determining the isocyanate group content of a polyurethane prepolymer according to claim 1, characterized in that: The mass ratio of the polyurethane prepolymer to isopropyl alcohol is 0.1-1:18-22.

6. A method of determining the isocyanate group content of a polyurethane prepolymer according to claim 1 or 5, characterised in that: The mass ratio of the isopropyl alcohol to standard hydrochloric acid is 0.8-1.2:

1.

7. A method of determining the isocyanate group content of a polyurethane prepolymer according to claim 6, characterised in that: In step S3, the concentration of the standard hydrochloric acid is 0.1-0.3 mol / L.

8. A method of determining the isocyanate group content of a polyurethane prepolymer according to claim 1, characterized in that: In step S4, the concentration of the hydrochloric acid standard solution is 0.1-0.3 mol / L.

9. A method of determining the isocyanate group content of a polyurethane prepolymer according to claim 1, characterized in that: In step S6, the standard formula is as follows: Isocyanate salt content (ω NCO ) in mass-%, values in %, calculated according to formula (1): ω NCO = [(V0-V) x c x 42.02] / m x 100% (1) In the formula, V0 is the volume of hydrochloric acid standard solution consumed for titration of the blank, in mL; V is the volume of hydrochloric acid standard solution consumed for titration of the sample, in mL; c is the concentration of the hydrochloric acid standard solution, in mol / L; 42.02 is the numerical value of the molar mass of NCO, in g / mol; and m is the mass of the sample, in g.

10. The determination result is expressed as the arithmetic mean value of two parallel samples, and the result is retained to two decimal places.

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