Method for measuring water content in polythiol compound

Abstract

The invention discloses a method for determining the water content in a polythiol compound, and belongs to the technical field of analysis and testing. The determination method comprises the following steps: (1) preparing a blank solution; (2) taking a polythiol compound to be detected, and preparing a sample solution; (3) determining the mercaptan sulfur content of the polythiol compound sample; (4) determining the total manifestation moisture (namely the total amount of water and sulfydryl which react with the Karl Fischer reagent) of the sample solution; and (5) calculating to obtain the water content in the polythiol compound. The method has the advantages of high accuracy, low test cost, simple and feasible operation, short analysis time and the like.

Description

Technical Field

[0001] The invention belongs to the technical field of analysis and testing, and particularly relates to a method for determining the water content in a polythiol compound. Background Art

[0002] At present, the optical resins of optical resin lenses on the market are mainly polythiocarbamate resins prepared with polythiol compounds and isocyanates as raw materials. The refractive index of this type of resin is significantly higher than other types of resins on the market; and the higher the refractive index of the resin, the lighter and thinner the prepared optical resin lens can be, thereby giving full play to the advantages of the optical resin lens. When manufacturing resins for optical materials, sometimes cords or white turbidity are generated in the resin or optical material obtained by polymerization. This cord or white turbidity sometimes has an adverse effect on the performance of the optical material. The polymerization rate of the polymerizable composition and the presence or absence of white turbidity or cords in the polyurethane resin lens are closely related to the water content in the polymerizable composition.

[0003] The thiol groups in polythiol compounds are highly chemically active and can easily react with certain reagents in the test process (such as iodine in Karl Fischer reagent), which can interfere with the normal determination of moisture and lead to inaccurate measurement results.

[0004] In order to overcome the interference of thiol groups on the test, a masking agent is usually added. However, the selection of masking agents and the optimization of reaction conditions are a complicated process, and thiol groups usually react with masking agents to generate water, which interferes with the detection of polythiol compounds.

[0005] CN202011322418.6 discloses a method for analyzing the water content in a polyvalent thiol compound, which uses a gas chromatography sample test with a static headspace sampling device and a thermal conductivity detector and an external standard method for detection. It can quickly and accurately perform quantitative analysis on the water content in the polyvalent thiol compound. Summary of the invention

[0006] The present invention provides a method for determining the water content in a polythiol compound in order to solve the technical problem that the thiol group of the thiol compound interferes with the Karl Fischer reagent when the Karl Fischer method is used to measure the water content, resulting in a high test result and low detection accuracy.

[0007] In order to achieve the above object, the present invention adopts the following technical solutions:

[0008] (1) Prepare blank solution;

[0009] (2) taking a polythiol compound to be tested and preparing a sample solution;

[0010] (3) Determine the mercaptan sulfur content of the sample;

[0011] (4) Determine the total apparent water content of the sample solution;

[0012] (5) The water content in the polythiol compound to be tested is obtained by calculation.

[0013] The inventors of the present invention have found that the test using a Karl Fischer reagent containing pyridine is more accurate than the Karl Fischer reagent without pyridine. The present invention first tests the total apparent moisture of the sample solution, then tests the mercaptan sulfur content of the sample, and through formula deduction, the true moisture of the sample can be accurately calculated, which significantly improves the accuracy of the test.

[0014] Furthermore, the blank solution in step (1) includes N,N-dimethylformamide.

[0015] Furthermore, in the sample solution preparation process of step (2), polythiol sample (weight) / blank solution (volume) = 0.5 g / L to 5 g / L.

[0016] The polythiol compound is selected from tetrakis(3-mercaptobutyric acid) pentaerythritol ester, trimethylolpropane tris(2-mercaptoacetate), trimethylolpropane tris(3-mercaptopropionate), trimethylolbutane tris(3-mercaptopropionate), tris(3-mercaptopropionate), tetrakis(3-mercaptopropionate), 2,3-dimercapto-1-propanol (2-mercaptoacetate), hexa(3-mercaptobutyric acid) dipentaerythritol, ethylene glycol di(3-mercaptopropionate), ... A mixture of one or more of tris(mercaptopropionate), ethoxylated trimethylolpropane tris(3-mercaptopropionate), pentaerythritol tetra(thioglycolate), dipentaerythritol hexa(3-mercaptopropionate), diethylene glycol-di(mercaptopropionate), butanediol-di(mercaptopropionate), tris(2-hydroxyethyl)isocyanurate-tris(mercaptopropionate), and 4,8-bis(mercaptomethyl)-3,6,9-trithia-1,11-undecanedithiol.

[0017] Furthermore, the test of the mercaptan sulfur content in step (3) is performed by manual titration; the titration reagent comprises isopropanol, silver nitrate solution, pyridine, an indicator and sodium hydroxide solution.

[0018] Furthermore, the device used for the total apparent moisture determination in step (4) is a Karl Fischer titrator; the instrument model is Mettler C10S; the titration rate is 80 μL / min to 5 mL / min; the polarization current is 0 to 50.0 μA; the titration endpoint is 90 to 110 mV; and the Karl Fischer reagent type is a pyridine-containing Karl Fischer reagent (reagent brand is damas-beta, model is 96204E).

[0019] Furthermore, the formula in step (5) is Where W2 is the total apparent moisture of the sample solution (ppm), W k is the water content of blank solution (ppm), C1 is the concentration of sample solution (g / L), W1 is the thiol sulfur content of sample (%), M1 is the relative molecular mass of water (g / mol), and M2 is the relative atomic mass of sulfur (g / mol).

[0020] In some preferred cases, the method for determining the water content in the polythiol compound comprises the following steps:

[0021] (1) Prepare blank solution: exhaust analytically pure N,N-dimethylformamide with nitrogen to saturate it with nitrogen;

[0022] (2) preparing a sample solution: dissolving 0.5 to 5 g of a polythiol compound sample in a blank solution and adjusting the volume to 1 L to obtain a sample solution. The concentration of the sample solution is recorded as C1 in g / L.

[0023] (3) Determination of the mercaptan sulfur content of the sample: weigh 0.1 g to 0.25 g of the polythiol compound sample with a weighing bottle, add it to 50 mL of isopropanol, add 10 mL of pyridine and 10 mL to 15 mL of silver nitrate solution, add 10 drops of mixed indicator, and titrate with sodium hydroxide standard titration solution; take water and make a blank test; repeat the titration N times, and calculate the mercaptan sulfur content W1 of the sample, in %;

[0024] (4) Determination of total apparent moisture of sample solution: Use Karl Fischer titrator to measure the moisture of blank solution M times in parallel to obtain the moisture of blank solution W. k , then measure the water content of the sample solution R times in parallel to obtain the total apparent water content of the sample solution W2, in ppm;

[0025] (5) Through the formula The water content of the polythiol compound sample is calculated; wherein M1 is the relative molecular mass of water (g / mol), and M2 is the relative atomic mass of sulfur (g / mol);

[0026] Preferably, N, M, and R are all ≥3.

[0027] The technical solution provided in the embodiments of the present application has at least the following beneficial effects:

[0028] The problem of high moisture test value caused by the reaction between iodine in Karl Fischer reagent and thiol in polythiol compounds can be effectively avoided, thereby improving the accuracy of the test results of the moisture content of polythiol compounds. DETAILED DESCRIPTION

[0029] For the convenience of understanding the present invention, the present invention lists the following embodiments. It should be understood by those skilled in the art that the embodiments are only to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0030] It should be noted that the experimental methods described in the following examples are conventional methods unless otherwise specified; the reagents, materials and equipment described are all commercially available unless otherwise specified.

[0031] In this embodiment, the weighing is accurate to 0.0001g.

[0032] Example 1

[0033] This embodiment provides a method for determining the water content in a polythiol compound, the method comprising the following steps:

[0034] (1) 500 mL of analytical pure N,N-dimethylformamide was subjected to nitrogen exhaust treatment for 20 min to achieve nitrogen saturation, and then sealed for standby use;

[0035] (2) Weigh 0.9020 g of a sample whose main component is 4,8-di(mercaptomethyl)-3,6,9-trithia-1,11-undecanedithiol into a 250 mL volumetric flask, add the blank solution of step (1) to dissolve and dilute to 250 mL, the sample solution concentration C1 is 3.608 g / L, shake evenly and transfer into a sealed bottle for standby use;

[0036] (3) Weigh 0.15 g of the polythiol compound sample with a weighing bottle, put it into a conical flask containing 50 mL of isopropanol, add 10 mL of pyridine and 15 mL of silver nitrate solution, add 10 drops of fluorescent yellow indicator, and titrate with c (NaOH) = 0.1 mol / L sodium hydroxide standard titration solution. Titrate to the endpoint and record the volume V1 (mL) of the consumed sodium hydroxide solution; take 35 mL of water for blank titration and record the volume V2 (mL) of the consumed sodium hydroxide solution. According to the formula Wherein C2 is the concentration of sodium hydroxide solution (mol / L), M2 is the relative atomic mass of sulfur (g / mol), and m is the mass of the sample (g). The titration was repeated 5 times. The analysis results are shown in Table 1. The mercaptan sulfur content W1 (%) of the sample was calculated;

[0037] Table 1. Parallel determination results of thiol sulfur content in polythiol samples

[0038]

[0039] It can be seen from Table 1 that the mercaptan sulfur content test of the polythiol sample is stable, the RSD of multiple tests is within 0.51, and the test repeatability is high.

[0040] (4) Turn on the moisture meter and stabilize the drift value below 10μg / min. Use a syringe with a needle to draw 1±0.1000g of a standard water sample containing 0.01% water, inject it from the fluororubber sealed inlet, and start the moisture meter to record the change of the drift value. Enter the sample mass. After the instrument test is completed, record the water content of the sample injected into the moisture meter. Test three times in parallel, and the deviation should not exceed 0.1%; before testing the next sample, the drift value should be stabilized below 10ug / min; add 0.2g of blank solution to the moisture meter in the same way, enter the mass, start the moisture test, and record the moisture value output by the instrument. Repeat the test 5 times, which is the moisture value W of the blank solution. k (ppm), the test results are shown in Table 2; then 0.1g of sample solution was added, and the test was repeated 5 times to obtain the total apparent moisture W2 (ppm) of the sample solution. The analysis results are shown in Table 3:

[0041] Table 2. Parallel determination results of water content of blank solution:

[0042]

[0043]

[0044] It can be seen from Table 2 that the moisture meter test is stable, the moisture test of the blank solution is repeated many times, the RSD is within 5.22, and the test repeatability is high.

[0045] Table 3. Parallel determination results of total apparent moisture of polythiol sample solutions:

[0046]

[0047] It can be seen from Table 3 that the moisture test of the polythiol sample solution was repeated many times, and the RSD was within 5.34, and the test repeatability was high.

[0048] (5) Through the formula The water content of the polythiol compound sample is calculated; wherein W2 is the total apparent water content of the sample solution (ppm), W k is the water content of the blank solution (ppm), C1 is the sample solution concentration (g / L), W1 is the sample thiol sulfur content (%), M1 is the relative molecular mass of water (g / mol), and M2 is the relative atomic mass of sulfur (g / mol); According to the average value of the above table, the water content W of the polythiol compound sample is w It is 383.48ppm.

[0049] Example 2

[0050] This embodiment provides a method for determining the water content in a polythiol compound. The method is the same as that in Example 1 except that another batch of the polythiol samples is selected, the sample solution concentration is 3.534 g / L, and the method is repeated three times. The test results are shown in Table 4:

[0051] Table 4

[0052]

[0053]

[0054] After calculation, the water content W of the polythiol compound in this batch w It is 292.53ppm.

[0055] Example 3

[0056] This embodiment provides a method for determining the water content in a polythiol compound. The method is the same as that in Example 1 except that the sample whose main component is pentaerythritol tetrakis(3-mercaptobutyrate) is selected, the sample solution concentration is 3.778 g / L, and the method is repeated three times. The test results are shown in Table 5:

[0057] Table 5

[0058]

[0059] After calculation, the water content W of the polythiol compound is w It is 545.84ppm.

[0060] Example 4

[0061] This embodiment provides a method for determining the water content in a polythiol compound. The method is the same as that in Example 1 except that the sample whose main component is trimethylolpropane tris(2-thioglycolate) is selected, the sample solution concentration is 3.212 g / L, and the method is repeated three times. The test results are shown in Table 6:

[0062] Table 6

[0063]

[0064] After calculation, the water content W of the polythiol compound is w It is 332.15ppm.

[0065] Spike recovery experiment

[0066] The method of Example 1 was used to perform a spike recovery experiment on polythiol compounds, that is, a known amount of water standard was added to three batches of polythiol sample solutions with known water content (1.0000g (accurate to 0.0001g) polythiol samples were weighed in three different 250mL volumetric flasks), and the water content was determined according to the above method. The spike recovery rate of the water content was calculated respectively, and the data is shown in Table 7. The result is an average spike recovery rate of water of 101.28. It can be seen from Table 7 that the measured values ​​of the target recovery rate are all between 95% and 105%, which meets the requirements of daily analysis and detection.

[0067] Table 7

[0068]

[0069] The above-mentioned embodiments only express several implementation methods of the present invention, and the description thereof is relatively specific and detailed, but it cannot be understood as limiting the scope of the patent of the present invention. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present invention, which all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the attached claims.

Claims

1. A method for determining the water content in a polythiol compound, characterized in that: The steps include: (1) Prepare blank solution; (2) Take the polythiol compound to be tested, dissolve it in the blank solution, and prepare the sample solution. The concentration of the sample solution is recorded as C1, in g / L; (3) Determine the thiol sulfur content of the polythiol compound sample and calculate the thiol sulfur content W1 of the sample, in units of %; (4) Determine the total apparent water content of the sample solution to obtain the total apparent water content W2 of the sample solution, in units of ppm; The water content of the blank solution was measured M times in parallel using a Karl Fischer titrator to obtain the water content of the blank solution W. k , the unit is ppm; (5) Through the formula W w (ppm) = W2-W k - , the water content of the polythiol compound sample is calculated; where M1 is the relative molecular mass of water (g / mol), and M2 is the relative atomic mass of sulfur (g / mol).

2. The method for determining the water content in a polythiol compound according to claim 1, characterized in that: The polythiol compound is selected from tetrakis(3-mercaptobutyric acid) pentaerythritol ester, trimethylolpropane tris(2-mercaptoacetate), trimethylolpropane tris(3-mercaptopropionate), trimethylolbutane tris(3-mercaptopropionate), tris(3-mercaptopropionate), pentaerythritol tris(3-mercaptopropionate), tetrakis(3-mercaptopropionic acid) pentaerythritol ester, 2,3-dimercapto-1-propanol (2-mercaptoacetate), hexa(3-mercaptobutyric acid) A mixture of one or more of dipentaerythritol, ethylene glycol di(3-mercaptopropionate), ethoxylated trimethylolpropane tri(3-mercaptopropionate), pentaerythritol tetra(mercaptoacetate), dipentaerythritol hexa(3-mercaptopropionate), diethylene glycol-di(mercaptopropionate), butanediol-di(mercaptopropionate), tris(2-hydroxyethyl)isocyanurate-tris(mercaptopropionate), and 4,8-bis(mercaptomethyl)-3,6,9-trithia-1,11-undecanedithiol.

3. The method for determining the water content in a polythiol compound according to claim 1, characterized in that: The blank solution is analytical grade N,N-dimethylformamide, and nitrogen is exhausted for 10 min to 15 min to reach nitrogen saturation.

4. The method for determining the water content in a polythiol compound according to claim 1, characterized in that: The ratio of the sample solution, the polythiol compound and the blank solution is 0.5-5 g:1 L.

5. The method for determining the water content in a polythiol compound according to claim 1, characterized in that: In the measurement of the thiol sulfur content, the mass of the polythiol compound sample is 0.1 g to 0.25 g.

6. The method for determining the water content in a polythiol compound according to claim 1, characterized in that: The mass of the sample solution weighed for the total apparent moisture determination is 0.03 g to 0.3 g.

7. The method for determining the water content in a polythiol compound according to claim 1, characterized in that: During the determination of the mercaptan sulfur content, the sample is processed quickly to reduce the contact time between the sample and the air. After the sample is added to the titration cup, the titration starts immediately, and the titration process is carried out under a nitrogen protection environment.

8. The method for determining the water content in a polythiol compound according to claim 1, characterized in that: The device used for the total apparent moisture determination is a Karl Fischer titrator; the instrument model is Mettler C10S; the titration rate is 80μL / min~5mL / min; the polarization current is 0~50.0μA; the titration endpoint is 90~110mV; the Karl Fischer reagent type is a pyridine-containing Karl Fischer reagent.

9. The method for determining the water content in a polythiol compound according to claim 8, characterized in that: The mercaptan sulfur content is determined by manual titration; the titration reagent includes isopropanol, silver nitrate solution, pyridine, an indicator and a sodium hydroxide standard solution.

10. The method according to any one of claims 1 to 9, characterized in that: The method for determining the water content in the polythiol compound comprises the following steps: (1) Prepare blank solution: exhaust analytically pure N,N-dimethylformamide with nitrogen to saturate it with nitrogen; (2) Prepare sample solution: dissolve 0.5-5 g of polythiol compound sample in blank solution and dilute to 1 L to obtain sample solution. The concentration of sample solution is recorded as C1 in g / L. (3) Determination of the thiol sulfur content of the sample: Weigh 0.1g~0.25g of the polythiol compound sample with a weighing bottle, add it to 50mL of isopropanol, add 10mL of pyridine and 10mL~15mL of silver nitrate solution, add 10 drops of mixed indicator, and titrate with sodium hydroxide standard titration solution; take water and make a blank test; repeat the titration N times and calculate the thiol sulfur content of the sample W1, the unit is %; (4) Determination of total apparent moisture of the sample solution: Use a Karl Fischer titrator to measure the moisture of the blank solution M times in parallel to obtain the moisture of the blank solution W. k , then measure the water content of the sample solution R times in parallel to obtain the total apparent water content of the sample solution W2, in ppm; (5) Through the formula W w (ppm) = W2-W k - The water content of the polythiol compound sample is calculated; wherein M1 is the relative molecular mass of water (g / mol), and M2 is the relative atomic mass of sulfur (g / mol); Preferably, N, M, and R are all ≥3.

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