A method for determining the primary amine value in a high molecular polymer using potentiometric titration

Abstract

A method for determining the primary amine value in a high molecular polymer by using a potential titration method, comprising the following steps: (1) preparing a sodium methoxide-methanol solution; (2) preparing a salicylaldehyde-DMF solution; (3) titrating the salicylaldehyde-DMF solution with the sodium methoxide-methanol solution to a mutation point; (4) weighing a high molecular polymer sample to be measured and adding it to the salicylaldehyde-DMF solution prepared in step (2) to obtain a sample to be measured solution; (5) titrating the salicylaldehyde-DMF solution blank and the sample to be measured solution obtained in step (4) with the sodium methoxide-methanol solution prepared in step (1) by using a potential titration method, and calculating the primary amine value in the high molecular polymer. The present application does not use strong acid, strong base and high carcinogenic reagents, is safe and environmentally friendly, and can directly determine the primary amine value in the high molecular polymer at one time.

Description

TECHNICAL FIELD

[0001] The present application relates to a method for determining the amine value in a high molecular polymer, in particular to a method for determining the primary amine value in a high molecular polymer using potentiometric titration. BACKGROUND

[0002] Amine curing agent is an organic polyamine polymer widely used as an epoxy resin curing agent, which includes single polyamine, mixed polyamine, modified polyamine and eutectic mixed polyamine. The characteristic of amine curing agent polymer is that the system contains primary amine groups (-NH2). Primary amines can react with aldehydes / ketones to form Schiff bases and water at room temperature, while secondary and tertiary amines do not undergo this reaction. Therefore, by determining the amount of water generated or the content of consumed aldehyde or ketone, the content of primary amine groups in the polymer can be calculated.

[0003] At present, the primary amine value of most mixed amine polymers is determined by manual titration method according to the relevant national standards. Strong acids such as perchloric acid and hydrochloric acid are usually used as titration reagents, and strong carcinogenic solutions such as pyridine and dioxane are used as solvents. This titration method uses an external indicator to determine the end point of titration. A slightly excessive alkaline solvent is used to make the methyl orange-bromophenol blue reagent turn yellow when the end point of titration is reached. However, the end point indication sensitivity of this method is poor, especially for samples with poor solubility and color. The parallelism and accuracy of the measured results are difficult to control. If other national standard methods are used, the total amine value, secondary amine value and tertiary amine value of the polymer need to be determined manually, and then the primary amine value can be calculated. This method is time-consuming and has poor repeatability.

[0004] CN 110726803 A discloses a method for determining the amino value by full-automatic potentiometric titration. This method uses the principle of diazotization reaction of aromatic primary amine compounds and nitrite salt. Sodium nitrite standard solution is used as the titrant, and Pt electrode is used as the indicating electrode. The end point of titration is determined by the maximum value of the first derivative of the titration curve. However, this method uses strong acids such as hydrochloric acid and hydrobromic acid, which are not environmentally friendly. In addition, the reagents are difficult to obtain and operate, and the primary amine value in the high molecular polymer cannot be determined at one time. SUMMARY

[0005] The technical problem to be solved by the present application is to overcome the above-mentioned defects in the prior art, and to provide a method for determining the primary amine value in a high molecular polymer using potentiometric titration, which does not use strong acids, strong bases and high carcinogenic reagents, has high sensitivity, is simple to operate, is safe and environmentally friendly, and can directly determine the primary amine value in a high molecular polymer at one time.

[0006] The technical scheme adopted by the present application to solve its technical problems is a method for determining the primary amine value in a high polymer by using a potentiometric titration method, wherein a high polymer sample to be measured is added to a salicylaldehyde-DMF solution, a methanol-sodium methoxide solution is used as a titrant, and a composite electrode is used as an indicating electrode.

[0007] Further, the method for determining the primary amine value in a high polymer by using the potentiometric titration method specifically comprises the following steps:

[0008] (1) A sodium methoxide-methanol solution is prepared, and anhydrous benzoic acid is used for calibration, or a certified sodium methoxide-methanol solution is directly purchased, and the specific concentration of the sodium methoxide-methanol solution is recorded;

[0009] The calculation method is: the specific concentration C of the sodium methoxide-methanol solution = the weight (g) of benzoic acid / 0.1221*(the volume (ml) of consumed sodium methoxide - the volume (ml) of consumed sodium methoxide in the blank);

[0010] (2) Salicylaldehyde is weighed and dissolved in a DMF solution to prepare a salicylaldehyde-DMF solution;

[0011] (3) The salicylaldehyde-DMF solution prepared in step (2) is taken as a blank sample, and the sodium methoxide-methanol solution prepared in step (1) is used to titrate the blank sample to a mutation point, and the volume of the sodium methoxide-methanol solution consumed for titrating the blank sample is recorded;

[0012] (4) The high polymer sample to be measured is weighed and added to the salicylaldehyde-DMF solution prepared in step (2), and stirred uniformly to obtain a sample to be measured;

[0013] (5) The blank salicylaldehyde-DMF solution prepared in step (3) and the sample to be measured prepared in step (4) are sealed and stored, and then the sodium methoxide-methanol solution prepared in step (1) is used to titrate them by using a potentiometric titration method, the volume of the sodium methoxide-methanol standard solution consumed when the first derivative of the titration curve reaches a maximum value is recorded, and the primary amine value in the high polymer is calculated.

[0014] Further, in step (5), the formula used for calculating the primary amine value in the high polymer is:

[0015]

[0016]

[0017] In the formula, X is the primary amine value, and the unit is mol / 100g;

[0018] V 实 is the correction of mass deviation, and the unit is mL;

[0019] V0 is the volume of sodium methoxide-methanol solution consumed in titrating the blank sample in step (3), unit: mL;

[0020] V1 is the volume of sodium methoxide-methanol solution consumed in titrating the sample solution in step (5), unit: mL;

[0021] S0 is the mass of the blank sample DMF-salicylaldehyde solution in step (3), unit: g;

[0022] S1 is the mass of the sample solution salicylaldehyde-DMF solution in step (4), unit: g;

[0023] C is the specific concentration of sodium methoxide-methanol solution in step (1), unit: mol / L;

[0024] m is the mass of the high molecular polymer sample in step (4), unit: g.

[0025] Further, in step (1), the molar concentration of the sodium methoxide-methanol solution is 0.01-0.50 mol / L, preferably 0.1-1.0 mol / L, further preferably 0.20-0.50 mol / L, and more preferably 0.27 mol / L.

[0026] Further, in step (2), the molar concentration of the salicylaldehyde-DMF solution is 0.025-0.5 mol / L, preferably 0.05-0.20 mol / L, and more preferably 0.10 mol / L.

[0027] Further, in step (3), the mass of the salicylaldehyde-DMF solution is 15-100 g, preferably 20-30 g.

[0028] Further, in step (4), the mass of the high molecular polymer sample is 0.1-1.0 g.

[0029] Further, in step (4), the molecular weight of the high molecular polymer sample is 100-4000, preferably 500-2500.

[0030] Further, in step (5), the time of closed storage is 20-1440 min, preferably 20-40 min. Too short time of closed storage will affect the titration result, and too long time (≥24 hours) will cause solvent to absorb water, resulting in errors. 20-40 min is the best.

[0031] Further, in step (5), the instrument used in the potentiometric titration is an automatic potentiometric titrator.

[0032] Further, in step (5), the instrument parameters used in the potentiometric titration are: titration mode DETU: pre-addition volume 0 mL; pause 30 s; signal drift 20 Mv / min; minimum waiting time 0 s; maximum waiting time 1-60 s, preferably 15 s; minimum increment 20-30 μL, preferably 29 μL; addition speed: maximum; stop volume: 10-40 mL, preferably 25 mL; stop equivalence point 1; post-equivalence addition volume 5 mL; suction speed: maximum; equivalence point recognition criterion 20-60 mV, preferably 40 mV; equivalence point recognition: maximum.

[0033] Further, the composite electrode is a smart non-aqueous electrode.

[0034] Compared with the prior art, the present application has the following beneficial effects:

[0035] (1) Using DMF (N,N-dimethylformamide) weak base solvent as a diluent greatly improves the solubility of the high molecular polymer and speeds up the generation of the Schiff base, and the salicylaldehyde-DMF solution system formed by mixing salicylaldehyde and DMF can be stored for a long time and stably;

[0036] (2) Compared with other aldehydes, salicylaldehyde is easy to synthesize, has large production capacity, is inexpensive, has obvious color development effect, and the aldehyde group is located in an ortho position with respect to the hydroxyl group, and can react with the primary amine in the high molecular polymer at room temperature, but appropriately increasing the temperature can effectively speed up the reaction speed, wherein DMF has a high boiling point and excellent water solubility, heating the system will not cause the solvent to volatilize, and will not produce toxic volatile substances, and appropriately increasing the temperature will not affect the accuracy of the titration;

[0037] (3) All the solvent systems used in the present application are weak base and weak acid systems, and no strong acid, strong base or high carcinogenic reagent is used, and there is no problem of difficult acquisition of strong corrosive solvents and reagents;

[0038] (4) In the calculation method of the present application, the error caused by the different weighing masses of salicylaldehyde-DMF is considered, and the error can be eliminated by the calculation formula of the present application to ensure the stability and parallelism of the results, and the amount of salicylaldehyde-DMF can also be adjusted according to the characteristics of the sample itself;

[0039] (5) In the preferred scheme, the automatic potentiometric titrator used in the potentiometric titration method of the present application can automatically determine the titration end point and input the formula to directly calculate the results, avoiding the problem that the end point is difficult to determine due to the indicator, reducing human error, and having better precision and standard recovery rate compared with the manual titration method;

[0040] (6) The present application has low temperature requirement for titration, wide temperature range (0-40℃), can obtain test data faster and more accurately, is safe, environment-friendly, simple, fast, and reliable. BRIEF DESCRIPTION OF DRAWINGS

[0041] Figure 1 is a potential titration primary amine curve graph of Example 2 3,3-dimethyl-4,4-diaminodicyclohexylmethane. DETAILED DESCRIPTION

[0042] The present application is further described below in conjunction with the drawings and specific examples.

[0043] The potential titration method of the present example uses an automatic potential titrator 916Ti-Touch potential titrator.

[0044] The theoretical value of the primary amine in the high molecular polymer 3,3-dimethyl-4,4-diaminodicyclohexylmethane used in the present example is 0.8264 moL / 100g.

[0045] Example 1

[0046] The method of the present example for determining the primary amine value in the high molecular polymer using the potential titration method comprises the following steps:

[0047] (1) 19.4g of 30% sodium methoxide solution is dissolved in 379.2g of methanol, shaken well, and left to stand for half an hour to prepare a 0.27mol / L sodium methoxide-methanol solution; 0.4g of benzoic acid is weighed to 0.001g, 25g of anhydrous methanol is added to dissolve it, anhydrous benzoic acid is used to calibrate the sodium methoxide-methanol solution, and the titration result is corrected by a 25g anhydrous methanol blank experiment, and the specific concentration C of the sodium methoxide-methanol solution is calculated to be 0.2708mol / L;

[0048] (2) 1.2212g of salicylaldehyde is dissolved in 94g of DMF to prepare a 0.1mol / L salicylaldehyde-DMF solution;

[0049] (3) 24.9200g of the salicylaldehyde-DMF solution obtained in step (2) is taken as a blank sample, and the sodium methoxide-methanol solution obtained in step (1) is used to titrate the blank sample to the mutation point, and the volume of the sodium methoxide-methanol solution consumed for titrating the blank sample is recorded as 10.9477mL;

[0050] (4) 0.1012g of 3,3-dimethyl-4,4-diaminodicyclohexylmethane sample is added to 24.2232g of the salicylaldehyde-DMF solution obtained in step (2), stirred uniformly, and left to stand at room temperature for 20-40min to obtain a sample to be tested;

[0051] (5) The blank sample salicylaldehyde-DMF solution obtained in step (3) and the sample to be tested solution obtained in step (4) are sealed and stored, and then titrated with the methanolic sodium-methanol solution obtained in step (1) by using the potentiometric titration method. The titration volume is taken as the abscissa, and the electric potential is taken as the ordinate. The titration curve is recorded. The volume of the methanolic sodium-methanol standard solution consumed when the first derivative of the titration curve reaches the maximum is 7.5882 mL. The primary amine value in the high molecular polymer is calculated to be 0.8172 mol / 100g, which deviates from the theoretical value by 1.117%.

[0052] In step (5), the formula used to calculate the primary amine value in the high molecular polymer is:

[0053]

[0054]

[0055] In step (5), the instrument parameters used in the potentiometric titration method are as follows: titration mode DET U: pre-adding volume 0 mL; pause 30 s; signal drift 20 Mv / min; minimum waiting time 0 s; maximum waiting time 15 s; minimum increment 29 μL; liquid adding speed: maximum; stop volume: 25 mL; stop equivalence point 1; liquid adding volume after the equivalence point 5 mL; liquid absorbing speed: maximum; equivalence point identification standard: 40 mV; equivalence point identification: maximum.

[0056] Example 2

[0057] The method for determining the primary amine value in the high molecular polymer by using the potentiometric titration method in this example includes the following steps:

[0058] (1) 19.4 g of 30% sodium methoxide solution is dissolved in 379.2 g of methanol, shaken well, and left to stand for half an hour to prepare a 0.27 mol / L sodium methoxide-methanol solution. 0.4 g of benzoic acid is accurately weighed to 0.001 g, and 25 g of anhydrous methanol is added to dissolve it to obtain anhydrous benzoic acid. The sodium methoxide-methanol solution is calibrated with the anhydrous benzoic acid, and the titration result is corrected with a 25 g anhydrous methanol blank experiment. The specific concentration C of the sodium methoxide-methanol solution is calculated to be 0.2708 mol / L;

[0059] (2) 1.2212 g of salicylaldehyde is dissolved in 94 g of DMF to prepare a 0.1 mol / L salicylaldehyde-DMF solution;

[0060] (3) 24.9200 g of the salicylaldehyde-DMF solution obtained in step (2) is taken as a blank sample, and the blank sample is titrated to the mutation point with the sodium methoxide-methanol solution obtained in step (1). The volume of the sodium methoxide-methanol solution consumed for titrating the blank sample is recorded to be 10.9477 mL;

[0061] (4) Weigh 0.1117g of 3,3-dimethyl-4,4-diaminodicyclohexylmethane sample and add it to the 31.5816g of salicylaldehyde-DMF solution obtained in step (2). Stir well and let stand at room temperature for 20-40 minutes to obtain the sample test solution.

[0062] (5) Seal and store the blank salicylaldehyde-DMF solution obtained in step (3) and the sample test solution obtained in step (4). Then, titrate them separately using the sodium methoxide-methanol solution obtained in step (1) by potentiometric titration. With the titration volume as the abscissa and the electric position as the ordinate, record the volume of sodium methoxide-methanol standard solution consumed when the first derivative of the titration curve reaches its maximum value. The volume is 10.516 mL. According to the calculation formula:

[0063]

[0064]

[0065] The primary amine value in the polymer of this embodiment was calculated to be 0.8143 mol / 100g, which deviates from the theoretical value by 1.478%.

[0066] In step (5), the instrument parameters used in the potentiometric titration method are as follows: titration mode DET U: pre-addition volume 0 mL; pause 30 s; signal drift 20 Mv / min; minimum waiting time 0 s; maximum waiting time 15 s; minimum increment 29 μL; addition rate: maximum value; stop volume: 25 mL; stop equivalence point 1; addition volume after equivalence point 5 mL; aspiration rate: maximum value; equivalence point identification standard: 40 mV; equivalence point identification: maximum.

[0067] (6) Nine identical samples of 3,3-dimethyl-4,4-diaminodicyclohexylmethane were taken and subjected to different reaction temperatures, different masses of DMF-salicylaldehyde solution (S1), different masses of test substance (m), and different reaction times of test substance and DMF-salicylaldehyde solution. The primary amine content of 3,3-dimethyl-4,4-diaminodicyclohexylmethane was determined by L9(3) 4 Orthogonal tests, orthogonal arrays and results are shown in Tables 1-3.

[0068] Table 1L9(3) 4 Setting parameters for different influencing factors in orthogonal arrays

[0069]

[0070] Table 2L9(3) 4 Orthogonal arrays for orthogonal experiments

[0071]

[0072] Table 3L9 (3 4 ) Orthogonal test results

[0073]

Claims

1. A method for determining the primary amine value in a high molecular polymer using potentiometric titration, characterized by, The polymer sample to be measured is added to the salicylaldehyde-DMF solution, and methanol-sodium methoxide solution is used as the titrant, and a composite electrode is used as the indicating electrode; Specifically includes the following steps: (1) Prepare sodium methoxide-methanol solution, calibrate with anhydrous benzoic acid, or directly purchase certified sodium methoxide-methanol solution, and record the specific concentration of the sodium methoxide-methanol solution; (2) Weigh salicylaldehyde and dissolve it in DMF solution to prepare salicylaldehyde-DMF solution; (3) Take the salicylaldehyde-DMF solution obtained in step (2) as a blank sample, titrate the blank sample with the sodium methoxide-methanol solution prepared in step (1) to the mutation point, and record the volume of the sodium methoxide-methanol solution consumed in titrating the blank sample; (4) Weigh the polymer sample to be measured and add it to the salicylaldehyde-DMF solution prepared in step (2), stir until uniform, and obtain a sample to be measured; (5) Seal the blank sample salicylaldehyde-DMF solution prepared in step (3) and the sample to be measured obtained in step (4), and then use the sodium methoxide-methanol solution prepared in step (1) to titrate them by potentiometric titration, take the titration volume as the horizontal coordinate and the electric potential as the vertical coordinate, record the volume of the sodium methoxide-methanol standard solution consumed when the first derivative of the titration curve reaches the maximum value, and calculate the primary amine value in the polymer; In step (5), the formula used to calculate the primary amine value in the polymer is: = ； X= ； In the formula, X is the primary amine value, unit: mol / 100g; To correct for mass bias, units: mL; V0 is the volume of the sodium methoxide-methanol solution consumed in titrating the blank sample in step (3), unit: mL; V1 is the volume of the sodium methoxide-methanol solution consumed in titrating the sample to be measured in step (5), unit: mL; S0 is the mass of the blank sample DMF-salicylaldehyde solution in step (3), unit: g; S1 is the mass of the salicylaldehyde-DMF solution in the sample to be measured in step (4), unit: g; C is the specific concentration of the sodium methoxide-methanol solution in step (1), unit: mol / L; m is the mass of the polymer sample to be measured in step (4), unit: g.

2. The method of determining the primary amine value in a high molecular polymer using potentiometric titration according to claim 1, characterized by, In step (1), the molar concentration of the sodium methoxide-methanol solution is 0.01-0.50 mol / L.

3. The method of determining the primary amine value in a high molecular polymer using potentiometric titration according to claim 1 or 2, characterized in that, In step (2), the molar concentration of the salicylaldehyde-DMF solution is 0.025-0.500 mol / L.

4. The method of determining the primary amine value in a high molecular polymer by using potentiometric titration according to any one of claims 1 to 3, characterized in that, In step (3), the mass of the salicylaldehyde-DMF solution is 15-100 g.

5. The method of determining the primary amine value in a high molecular polymer by using potentiometric titration according to any one of claims 1 to 4, characterized in that, In step (4), the molecular weight of the polymer sample to be measured is 100-4000.

6. The method of determining the primary amine value in a high molecular polymer according to any one of claims 1 to 5, characterized in that, In step (5), the sealing time is 20-1440 min.

7. The method of determining the primary amine value in a high molecular polymer according to any one of claims 1 to 6, characterized in that, In step (5), the instrument parameters used in the potentiometric titration are: titration mode DET U: pre-addition volume 0 mL; pause 30 s; signal drift 20 Mv / min; minimum waiting time 0 s; maximum waiting time 1-60 s; minimum increment 20-30 μL; addition speed: maximum; stop volume: 10-40 mL; stop equivalence point 1; post-equivalence addition volume 5 mL; suction speed: maximum; equivalence point recognition standard 20-60 mV; equivalence point recognition: maximum.

8. The method of determining the primary amine value in a high molecular polymer according to any one of claims 1 to 7, characterized in that, In step (5), the instrument used in the potentiometric titration is an automatic potentiometric titrator.

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