Method for accurately and quantitatively determining content of monomer and oligomer in nylon polymer and application

Abstract

The invention discloses a method for accurately and quantitatively determining the content of monomers and oligomers in a nylon polymer and application, and belongs to the technical field of nylon polymer detection. According to the method, GC-TOF and MALDI-TOF are combined for use, and the monomer content and the oligomer content of the nylon polymer are accurately obtained through formula calculation. Compared with the traditional method, the method provided by the invention has the advantages of more accurate determination result, wider range of tested molecular weight and more efficient and simpler operation. According to the method, the current situation that the nylon polymer cannot be accurately quantified is changed, whether the nylon polymer is synthesized by adopting an anionic polymerization method or an industrial hydrolysis ring-opening method can be known by accurately analyzing and accurately judging the monomer and oligomer content of the nylon polymer, and the result can be used for performance improvement and reverse analysis of the nylon polymer.

Description

Technical Field

[0001] The invention relates to the technical field of nylon polymer detection, and in particular to a method and application for accurately and quantitatively determining the content of monomers and oligomers in nylon polymers. Background Art

[0002] Polyamide 6 (Nylon 6) is a nylon polymer, commonly known as nylon 6, and is an important engineering plastic that is widely used in daily production and life. Due to the complex polymerization process and the presence of a large number of reversible reactions or side reactions, a large number of monomers and cyclic and linear oligomers will remain in the product after the polymerization. These residual substances will not only affect its performance, but also have a great impact on the subsequent processing and modification process. Therefore, the quantitative determination of monomers and oligomers in polyamide 6 products is of great significance.

[0003] At present, the quantitative analysis of monomers and oligomers in polyamide 6 in industry mostly adopts the solution extraction-density conversion method, that is, firstly extract the monomers and oligomers in polyamide 6 by solvent, then test the density of the extract, and then compare it with the standard curve between the concentration and density of polyamide 6 monomer solution to calculate the extractable content in the product. However, the standard curve in this method is only based on polyamide 6 monomer, and in reality, the extractable components of polyamide 6 are complex. The above method can only roughly obtain the extractable content in polyamide 6, and cannot accurately obtain the content of monomers and oligomers. In addition, for samples with low extractable content, this method has a large error.

[0004] Compared with the above-mentioned polyamide 6 monomer solution concentration and density standard curve method, the use of time-of-flight mass spectrometry (TOF / MS) is more advantageous for accurate analysis of low-content, complex oligomer components. The time it takes for each component in the sample to arrive at the receiver is different according to its mass. Based on this principle, components of different masses can be separated. Time-of-flight mass spectrometry has a wide detection range, fast speed, and is more efficient and convenient. The paper "Effect of Monomer and Oligomer Content on the Properties of Polyamide 6 Chips" (DOI: 10.3969 / j.issn.1673-3851(n).2024.02.004) used the dissolution / precipitation method to extract the monomers and oligomers in polyamide 6 (PA6), and used liquid chromatography / time-of-flight mass spectrometry / diode array detector (LC-TOF-MS-PDA) and polymer chromatography / multi-angle laser scattering / differential refractometer (APC-MALLS-RID) combined methods to determine the composition of monomers, cyclic dimers to cyclic nonamers (C1~C9) in PA6. However, this method can only detect oligomers such as C1 to C9. When there are many types of test substances, such as more than a dozen high molecular weight oligomers, and different copolymers and end groups, it is not only complicated in terms of sample dissolution and preparation operations, but also very demanding in terms of the selection of test conditions such as solvent, temperature and polarity of the chromatographic column. Even if the above conditions are met, it is impossible to achieve complete separation, so it is impossible to achieve accurate quantification. In addition, nylon polymers are mainly synthesized by two methods, namely anionic polymerization and industrial hydrolysis ring opening. Different synthesis methods also affect the performance of nylon polymers. It is impossible to distinguish the synthesis method simply by the appearance of the finished nylon polymer. Its specific judgment also depends on the accurate quantitative analysis of the components of nylon polymers. Different monomer and oligomer components and proportions have a great influence on the performance of the final product. Only by obtaining the accurate composition of the product can the performance be further improved and reversed. Therefore, it is necessary to find a method with more accurate results, wider molecular weight range of testing, and more efficient and simple operation to determine the content of monomers and oligomers in nylon polymers. Summary of the invention

[0005] In view of the above-mentioned prior art, the purpose of the present invention is to provide a method and application for accurately and quantitatively determining the content of monomers and oligomers in nylon polymers. The present invention aims to solve the problem that the conventional test method used in the prior art cannot accurately and conveniently quantitatively determine the content of monomers and oligomers in polyamide 6, and proposes a method for quantitatively determining the content of monomers and oligomers in polyamide 6 based on GC-TOF and MALDI-TOF. Since the time-of-flight mass spectrometry detection object used in the present invention is ions, it is necessary to first ionize the sample molecules or atoms into ions, so it is used in series with the ion source device. MALDI-TOF / MS uses laser irradiation to form a co-crystallized film formed by the sample and the matrix, and charge transfer occurs between the matrix and the sample, so that the sample molecules are ionized. It is a soft ionization technology; while GC-TOF / MS uses collision-induced dissociation to cause the parent ion to crack and form daughter ions, and then analyzes the secondary mass analyzer to obtain a secondary mass spectrum. The two methods have different detection ranges. MALDI-TOF / MS has a wider detection range, but it is limited by the matrix, and it is difficult to analyze and detect the lower molecular weight components in the sample, while GC-TOF / MS has higher accuracy for low molecular weight component detection. In the present invention, the two are used together to accurately and quantitatively determine the content of monomers and oligomers in nylon polymers such as polyamide 6.

[0006] To achieve the above object, the present invention adopts the following technical solution:

[0007] The first aspect of the present invention provides a method for accurately and quantitatively determining the content of monomers and oligomers in nylon polymers, comprising the following steps:

[0008] (1) extracting a nylon polymer sample in a solvent, filtering the extract to obtain the extract, measuring the extractable content and then randomly dividing it into two portions;

[0009] (2) taking a portion of the extract obtained in step (1) and performing GC-TOF / MS measurement to obtain the masses of monomers, dimers to pentamers;

[0010] (3) taking the extract obtained in step (1) and performing MALDI-TOF / MS measurement to obtain the peak value or peak area ratio of the pentamer and other oligomers;

[0011] (4) using the mass of the pentamer in the extract in step (2) as a standard, calibrating the mass of the other oligomers in step (3) to obtain the content of monomers and oligomers in the nylon polymer;

[0012] In step (4), the calibration method is to quantify other oligomers based on the mass of the pentamer in the extract in step (2) and the peak value or peak area of ​​the pentamer obtained by MALDI-TOF in step (3). The quantitative formula is as follows:

[0013] mj =P j / (P 5聚体 / m 5聚体 )

[0014] Among them, m j is the mass of the oligomer to be measured, P j is the MALDI-TOF / MS mass spectrum peak value or peak area of ​​the oligomer to be detected, P 5聚体 is the MALDI-TOF / MS mass spectrum peak or peak area of ​​the pentamer, m 5聚体 is the mass of the pentamer in the extract measured in step (2).

[0015] In some embodiments, the extract is taken, diluted a certain multiple, transferred to a sample injection bottle after filtering through an organic filter membrane, and GC-TOF / MS is performed to obtain a gas chromatographic analysis diagram. At the same time, caprolactam monomer is used as a monomer standard, and a relationship curve between the concentration and peak area of ​​the standard is drawn by the GC chromatographic external standard method. The content of caprolactam monomer in the extract can be obtained by calculating the standard relationship curve. In GC-TOF / MS quantitative analysis, the content of specific molecules in the sample can be inferred by measuring the intensity of the ion signal. The intensity of the ion signal is proportional to the number of molecules, so the content of specific molecules in the sample can be quantitatively analyzed by measuring the intensity of the ion signal. Therefore, by the corresponding relationship between the content of caprolactam monomer and the ion signal intensity, the dimer to pentamer content can be obtained according to the corresponding ratio.

[0016] Similarly, the intensity of the ion signal is proportional to the number of molecules, so the content of a specific molecule in a sample can be quantitatively analyzed by measuring the intensity of the ion signal. Therefore, the corresponding relationship between the content of the pentamer and the ion signal intensity can be obtained by gas chromatography, and the content of the pentamer to the 18-mer can be calculated according to the corresponding ratio.

[0017] Furthermore, the nylon polymer is prepared by hydrolysis ring-opening polymerization, anionic polymerization or cationic polymerization.

[0018] Furthermore, the oligomer includes linear polyamide and cyclic polyamide, and the oligomer is a dimer to an octadecamer.

[0019] Furthermore, the solvent in step (1) is at least one of methanol, trifluoroethanol, ethanol, benzene, toluene or a phenolic compound.

[0020] Furthermore, in step (1), the mass ratio of nylon polymer to extractant is 1:(1-1000).

[0021] Furthermore, in step (1), the mass ratio of nylon polymer to extractant is 1:50.

[0022] Furthermore, in step (1), the method for measuring the extractable content is to determine the density of the extract and calculate the extractable content in the nylon polymer sample.

[0023] Furthermore, in step (2), the measurement conditions of GC-TOF / MS are as follows: the chromatographic column is a polar, weakly polar or non-polar chromatographic column; the carrier gas is nitrogen, argon or helium; the mass spectrometry scanning range is 50-600 m / z, the scanning rate is 10-50 times / s, and the solvent delay time is 1-50 min.

[0024] In some embodiments, the measurement conditions of GC-TOF / MS are as follows: DB-5 chromatographic column, 30μm×250μm, 0.25μm; carrier gas is helium; the flow rate through the column is 10-50mL / min; the injection volume is 0.5-5μL; the injection port, ion source interface, and ion source temperature are 240-300°C; the mass spectrometry scanning range is 50-600m / z, the scanning rate is 10-50 times / s, and the solvent delay time is 1-10min.

[0025] In some embodiments, MALDI-TOF / MS testing is performed on an LDI-1700 laser desorption ionization time-of-flight mass spectrometer, and MALDI-MS analysis is performed using an UltrafleXtreme mass spectrometer equipped with a modified laser (λ=355 nm, 2000 Hz), recording MALDI-TOF mass spectra in reflectron mode.

[0026] The second aspect of the present invention provides an application of the method described in determining the synthesis method of nylon polymers, by determining the mass of the repeating units of the oligomers, determining whether the oligomers contain metal salts and initiator groups, and judging their synthesis method.

[0027] Furthermore, if the oligomer contains a metal salt and an initiator group, its synthesis method is anionic polymerization, otherwise its synthesis method is hydrolysis ring-opening synthesis.

[0028] Beneficial effects of the present invention:

[0029] The present invention combines GC-TOF and MALDI-TOF and calculates the monomer and oligomer content of nylon polymers accurately through formula calculation. Compared with the traditional method, the method of the present invention has more accurate measurement results, a wider molecular weight range, and more efficient and simple operation. During the test process, for the GC-TOF / MS step, the monomer test concentration is as low as 5μg ml -1; For the MALDI-TOF / MS step, the measurement concentration is as low as 1 mg / ml, and the sample mass is as low as 5 mg, which is suitable for the determination of low molecular weight polymers with a molecular weight of less than 5 kDa. The present invention changes the current situation where nylon polymers cannot be accurately quantified. Through precise analysis and accurate judgment of the monomer and oligomer content, it can be known whether the nylon polymer is synthesized by anionic polymerization or industrial hydrolysis ring-opening method. The result can be used for performance improvement and reverse analysis of nylon polymers. The present invention shows important potential application value in the field of product performance analysis and quality inspection of polyamide 6, and provides an innovative solution for the development of related technologies and quality control of polyamide 6. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 This is the MALDI-TOF / MS spectrum of nylon 6 synthesized by industrial hydrolysis ring-opening method.

[0031] Figure 2 This is the LC-TOF / MS mass spectrum of the extract of anionic polymerized nylon 6. DETAILED DESCRIPTION

[0032] It should be noted that the following detailed descriptions are illustrative and are intended to provide further explanation of the present application. Unless otherwise specified, all technical and scientific terms used herein have the same meanings as those commonly understood by those skilled in the art to which the present application belongs.

[0033] In order to enable those skilled in the art to more clearly understand the technical solution of the present application, the technical solution of the present application will be described in detail below in conjunction with specific embodiments.

[0034] The present invention is designed and implemented based on the following principles: For monomers and oligomers in polyamide 6 (in the present invention, oligomers are dimers to 18-mers), they can be obtained by solvent extraction, wherein the information of each component can be quantitatively analyzed by a time-of-flight mass spectrometer. MALDI-TOF / MS uses a strong ionization matrix to desorb and ionize the sample to obtain ion fragments, which are analyzed by a tandem time-of-flight mass spectrometer to obtain the distribution information of oligomers in the product. However, affected by the matrix, low molecular weight components are difficult to form ion fragments, so the information extraction is insufficient. GC-TOF / MS is a gas chromatography tandem time-of-flight mass spectrometer, which obtains an ion source by gasifying the sample, and extracts relatively low molecular weight components more fully. The results obtained by the above two methods are combined to obtain the overall distribution of oligomers in the extractables. Combined with the extractable content, the composition and distribution of monomers and oligomers in polyamide 6 can be calculated.

[0035] This method is not only applicable to the determination of the content of each monomer and oligomer in nylon 6 and the determination of the synthesis method, but also to various other nylon polymers (including nylon 66, nylon 6T, and nylon 10T) products.

[0036] Further, based on the above-mentioned precise measurement results, the present invention can also be used to determine the synthesis method of nylon polymers, as follows: the repeating unit mass of PA6 oligomer is 113 Daltons (Da), therefore, the corresponding mass-to-charge ratio can accurately correspond to different oligomer types, such as the following categories: cyclic oligomer peak with initiator group, whose mass-to-charge ratio is (113n+m); cyclic oligomer sodium salt peak with initiator group, whose mass-to-charge ratio is (113n+23+m); linear oligomer sodium salt peak with initiator group, whose mass-to-charge ratio is (113n+38+m); cyclic oligomer peak without initiator group, whose mass-to-charge ratio is (113n); cyclic oligomer sodium salt peak without initiator group, whose mass-to-charge ratio is (113n+23); and linear oligomer sodium salt peak without initiator group, whose mass-to-charge ratio is (113n+38). Where n represents the degree of polymerization of the oligomer, and m is the molecular weight of the initiator group. Generally, nylon 6 oligomers synthesized by anionic polymerization contain metal salts and initiator groups, while nylon 6 synthesized by hydrolysis ring opening generally does not contain initiator groups. Therefore, this method can not only identify the monomers and various oligomer contents in an unknown PA6 sample, but also know its synthesis method and determine whether it is polymerized by anionic polymerization or synthesized by industrial hydrolysis ring opening.

[0037] The experimental materials used in the examples of the present invention but not specifically described are all conventional experimental materials in the art and can be purchased through commercial channels.

[0038] Example 1

[0039] Determination of monomer and oligomer content in nylon 6 synthesized by anionic polymerization

[0040] (1) Determination of extractable content in samples

[0041] A 10g sample of anionic polymerized polyamide 6 (nylon 6) was placed in 500mL of methanol, extracted and refluxed at 65°C for 12h, cooled to room temperature, filtered and separated to obtain a methanol extract. The density ρ of the methanol extract at 20°C was measured using a density meter, and the proportion w of the extractable components in the original polyamide 6 sample was calculated using the following formula:

[0042]

[0043] where ρ 0 =0.7918g / cm 3 , m 0is the mass of nylon 6 sample, and ρ is the density of sample extract.

[0044] The same sample was measured three times and the average value was taken.

[0045] The measurement and calculation data are shown in Table 1:

[0046] Table 1 Extractable content of samples in Example 1

[0047] Sample name Sample weight / g <![CDATA[ρ / g·cm 3 ]]> w / ％ An-PA-1 31.60 0.7942 3.72 An-PA-2 30.09 0.7940 3.7 An-PA-3 29.81 0.7940 3.63

[0048] Taking the average of three measurements, the extractable rate was 3.67%.

[0049] (2) GC-TOF / MS method to measure the content of monomers and oligomers below pentamer

[0050] GC-TOF uses Agilent 7890 gas chromatograph-7000B tandem mass spectrometer. Take 1mL of the above methanol extract, dilute it 500 times, filter it through an organic filter membrane, and transfer it to an injection bottle for GC-TOF / MS mass spectrometry analysis. The specific conditions of GC-TOF / MS mass spectrometry analysis are: DB-5 chromatographic column (30m×250μm, 0.25μm), helium carrier gas, column flow rate of 20mL / min, injection volume of 1μL; injection port, ion source interface, ion source temperature are 280, 280 and 250℃ respectively; mass spectrometry scanning range is 50-600m / z, scanning rate is 20 times / s, and solvent delay time is set to 6min.

[0051] The data in Table 2 below are obtained. According to the different oligomer peak areas, the following oligomer proportions are obtained:

[0052] Table 2 GC-TOF / MS measurement results in Example 1

[0053]

[0054] (3) MALDI-TOF / MS determination of pentamer and above oligomer contents

[0055] MALDI-TOF / MS test was performed on LDI-1700 laser desorption ionization time-of-flight mass spectrometer. Take 1 mL of the above methanol extract, dilute it 200 times, filter it through an organic filter membrane and transfer it to a sample injection bottle. The matrix solution was prepared as follows: 10 mL of methanol extract (10 mg of methanol extract dissolved in 1 mL of TFE, final concentration 10 mg / mL) was mixed with 10 mL of 4'-hydroxyazobenzene-2-carboxylic acid (HABA) matrix solution (20 mg of HABA dissolved in 1 mL of TFE, final concentration 20 mg / mL); 1 μL of 0.05N KI solution (solute is KI, solvent is TFE and H) was added to the mixture.2 O, TFE and H 2 O (volume ratio is 1mL:1mL) as a cationized salt; obtain a matrix solution. 1μL of the matrix solution was spotted on a matrix-assisted laser desorption ionization target plate and dried naturally in air at room temperature to produce a thin matrix layer. Then 1μL of the methanol extract was spotted on the matrix layer and dried naturally in air at room temperature. After drying, mass spectrometry analysis was performed. The instrument parameters are as follows: MALDI-TOF / MS test was performed on an LDI-1700 laser desorption ionization time-of-flight mass spectrometer. MALDI-MS analysis used an UltrafleXtreme mass spectrometer equipped with a modified laser (λ=355nm, 2000 Hz), and the reflection mode of the MALDI-TOF mass spectrum was recorded.

[0056] According to the different peak areas corresponding to oligomers, the following oligomer distribution information can be obtained as shown in Table 3:

[0057] Table 3 MALDI-TOF / MS measurement results in Example 1

[0058]

[0059]

[0060] (4) Based on the measurement results of MALDI-TOF / MS and GC-TOF / MS, the contents of monomers and oligomers in the polyamide 6 sample were calculated. Specifically:

[0061] GC-TOF / MS calculates the content of each component by internal standard method:

[0062] m i =f×A i / (A s / m s )

[0063] In the above formula, f is the instrument correction factor, which is obtained by instrument verification test, and A i and A s are the peak areas or peak heights of the test sample and internal standard, m s is the mass of the internal standard added, m i is the mass of the substance being measured in the sample.

[0064] According to the GC-TOF / MS measurement data, the above calculation formula is used to obtain m 5聚体 quality.

[0065] The MALDI-TOF / MS test obtains an ion number peak diagram. Based on the ratio of mass spectrum peaks of different polymers (corresponding to different mass-to-charge ratios), the relative mass ratio of different polymers can be obtained. Since the samples used for GC-TOF / MS and MALDI-TOF / MS tests are the same, the contents of each substance in the two samples are also the same, both from the extract prepared in step (1). Based on the labeled m 5聚体 The content of the polymer and the corresponding peak of MALDI-TOF can be used to absolutely quantify other polymers according to the following formula:

[0066] m j =P j / (P 5聚体 / m 5聚体 )

[0067] Where P j is the MALDI-TOF / MS mass spectrum peak of the polymer being tested, P 5聚体 is the MALDI-TOF / MS mass spectrum peak of the pentamer, m j is the mass of the polymer being tested.

[0068] Based on the pentamer as the basis, the content and distribution of monomers and oligomers in the anionic polymerized polyamide 6 are calculated as shown in Table 4 below:

[0069] Table 4 Measurement results of anionic polymerization of polyamide 6 in Example 1

[0070]

[0071]

[0072] Furthermore, the labeled amount can be converted into a percentage based on the dilution multiple, the sampling amount and the labeled amount, or converted into a percentage based on the dilution multiple and the sampling amount.

[0073] From the test results in Table 4, it can be seen that for dimers to nonamers, there are two values ​​for their molecular weight, one of which conforms to the calculation formula of 113n+23, and the other conforms to the calculation formula of 113n+23+m; the molecular weight values ​​of nonamers (cyclic) to 18amers (cyclic) conform to the calculation formula of 113 or 113n+2m. In the above calculation formula, n is the degree of polymerization and m is the molecular weight of the initiator group. According to this test result, the molecular weight of the initiator group is 174. Based on the value of m, it can be determined that the synthesis process of nylon 6 uses anionic polymerization synthesis using toluene diisocyanate (Toluene diisocyanate, TDI, molecular weight 174.156) as an initiator.

[0074] During the test, for GC-TOF / MS, caprolactam was in the range of 5 to 400 μg ml -1 (correlation coefficient r = 0.9999) shows a good linear relationship within the concentration range; for MALDI-TOF / MS, in reflection mode, it is suitable for the determination of low molecular weight polymers with a molecular weight less than 5kDa, the lowest measurement concentration is 1mg / ml, and the minimum sample mass is 5mg.

[0075] Example 2

[0076] Determination of monomer and oligomer content in nylon 6 synthesized by industrial hydrolysis ring opening method

[0077] The results were obtained by measuring according to the method of Example 1:

[0078] (1) Determination of extractable content in samples

[0079] The measurement and calculation data are shown in Table 5 below:

[0080] Table 5 Extractable content of samples in Example 2

[0081] Sample name Sample weight / g <![CDATA[ρ / g·cm 3 ]]> w / ％ An-PA-1 31.95 0.7993 11.76 An-PA-2 30.99 0.7990 11.58 An-PA-3 29.85 0.7988 11.66

[0082] Taking the average of three measurements, the extractable rate was 11.68%.

[0083] (2) GC-TOF / MS method to measure the content of monomers and oligomers below pentamer

[0084] Through testing, we can obtain Figure 1 Spectrum shown.

[0085] The data in Table 6 below were obtained. According to the different oligomer peak areas, the following oligomer proportions were obtained:

[0086] Table 6 GC-TOF / MS measurement results in Example 2

[0087]

[0088] (3) MALDI-TOF / MS determination of pentamer and above oligomer contents

[0089] Through testing, according to the different peak areas corresponding to oligomers, the following oligomer distribution information can be obtained as shown in Table 7:

[0090] Table 7 MALDI-TOF / MS measurement results in Example 2

[0091]

[0092] (4) Combining the results of the two flight mass spectrometers, the content and distribution of monomers and oligomers in the polyamide 6 synthesized by the industrial hydrolysis ring-opening method were calculated based on the pentamer, as shown in Table 8 below:

[0093] Table 8 Measurement results of polyamide 6 synthesized by industrial hydrolysis ring-opening method in Example 2

[0094]

[0095]

[0096] Furthermore, the labeled amount can be converted into a percentage based on the dilution multiple, the sampling amount and the labeled amount, or converted into a percentage based on the dilution multiple and the sampling amount.

[0097] It can be seen from the test results that although the molecular weights of hexamer to nonamer have two values, after calculation, the molecular weights of each oligomer generally conform to the calculation formula of 113n+23 (where n is the degree of polymerization), which is consistent with the molecular weight characteristics of oligomers without initiator groups. Therefore, it can be determined that the nylon 6 is prepared by the industrial hydrolysis ring-opening method.

[0098] Comparative Example 1

[0099] Liquid chromatography / time of flight mass spectrometry (LC-TOF / MS) was used to measure the content of monomers and oligomers in nylon 6 synthesized by anionic polymerization.

[0100] (1) Determination of extractable content in samples

[0101] The same sample as used in Example 1 was taken and the extractable content was determined according to the method of Example 1. The measured and calculated data are shown in Table 9 below:

[0102] Table 9 Extractable content in samples in Example 3

[0103] Sample name Sample weight / g <![CDATA[ρ / g·cm 3 ]]> w / ％ An-PA-1 32.10 0.7942 3.68 An-PA-2 31.05 0.7941 3.73 An-PA-3 30.13 0.7940 3.63

[0104] Taking the average of three measurements, the extractable rate was 3.68%.

[0105] (2) LC-TOF / MS method for measuring monomer and other oligomer content

[0106] Liquid chromatography / time-of-flight mass spectrometry / diode array detector (instrument model: Agilent 6545) was used to analyze the content of monomers and oligomers in PA6 products. The injection volume was 0.2uL and the mobile phase was 100% methanol. ESI source and positive ion scanning mode were used. The mass spectrometry scanning range was 25-3200.

[0107] Get Figure 2According to the data in Table 10 below, the following oligomer ratios are obtained based on the different oligomer peak areas:

[0108] Table 10 Oligomer ratio in Example 3

[0109]

[0110]

[0111] It can be seen from the test results in Table 10 that the liquid chromatography / time-of-flight mass spectrometry method in Comparative Example 1 can only measure oligomers with a polymerization degree of heptamer and less, and since it is impossible to measure the confirmed existence of oligomers with a polymerization degree of octamer and above, the measurement is not accurate.

[0112] The above description is only the preferred embodiment of the present application and is not intended to limit the present application. For those skilled in the art, the present application may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A method for accurately and quantitatively determining the content of monomers and oligomers in nylon polymers, characterized in that: The method comprises the following steps: (1) extracting a nylon polymer sample in a solvent, filtering the extract to obtain the extract, measuring the extractable content and then randomly dividing it into two portions; (2) taking a portion of the extract obtained in step (1) and performing GC-TOF / MS measurement to obtain the masses of monomers, dimers to pentamers; (3) taking the extract obtained in step (1) and performing MALDI-TOF / MS measurement to obtain the peak value or peak area ratio of the pentamer and other oligomers; (4) using the mass of the pentamer in the extract in step (2) as a standard, calibrating the mass of the other oligomers in step (3) to obtain the content of monomers and oligomers in the nylon polymer; In step (4), the calibration method is to quantify other oligomers based on the mass of the pentamer in the extract in step (2) and the peak value or peak area of ​​the pentamer obtained by MALDI-TOF in step (3). The quantitative formula is as follows: m j =P j / (P 5聚体 / m 5聚体 ) Among them, m j is the mass of the oligomer to be measured, P j is the MALDI-TOF / MS mass spectrum peak value or peak area of ​​the oligomer to be detected, P 5聚体 is the MALDI-TOF / MS mass spectrum peak or peak area of ​​the pentamer, m 5聚体 is the mass of the pentamer in the extract measured in step (2).

2. The method for accurately and quantitatively determining the content of monomers and oligomers in nylon polymers according to claim 1, characterized in that: The nylon polymer is prepared by hydrolysis ring-opening polymerization, anionic polymerization or cationic polymerization.

3. The method for accurately and quantitatively determining the content of monomers and oligomers in nylon polymers according to claim 1, characterized in that: The oligomer includes linear polyamide and cyclic polyamide, and the oligomer is a dimer to an octadecamer.

4. The method for accurately and quantitatively determining the content of monomers and oligomers in nylon polymers according to claim 1, characterized in that: The solvent in step (1) is at least one of methanol, trifluoroethanol, ethanol, benzene, toluene or a phenolic compound.

5. The method for accurately and quantitatively determining the content of monomers and oligomers in nylon polymers according to claim 1, characterized in that: In step (1), the mass ratio of nylon polymer to extractant is 1:(1-1000).

6. The method for accurately and quantitatively determining the content of monomers and oligomers in nylon polymers according to claim 4, characterized in that: In step (1), the mass ratio of nylon polymer to extractant is 1:

50.

7. The method for accurately and quantitatively determining the content of monomers and oligomers in nylon polymers according to claim 4, characterized in that: In step (1), the method for measuring the extractable content is to determine the density of the extract and calculate the extractable content in the nylon polymer sample.

8. The method for accurately and quantitatively determining the content of monomers and oligomers in nylon polymers according to claim 4, characterized in that: In step (2), the determination conditions of GC-TOF / MS are as follows: the chromatographic column is a polar, weakly polar or non-polar chromatographic column; the carrier gas is nitrogen, argon or helium; the mass spectrometry scanning range is 50 to 600 m / z, the scanning rate is 10 to 50 times / s, and the solvent delay time is 1 to 50 min.

9. Application of the method according to any one of claims 1 to 8 in determining the synthesis mode of nylon polymers, characterized in that: By determining the mass of the repeating unit of the oligomer, whether the oligomer contains metal salts and initiator groups, and judging its synthesis method.

10. The use according to claim 9, characterized in that If the oligomer contains a metal salt and an initiator group, its synthesis method is anionic polymerization, otherwise its synthesis method is hydrolysis ring-opening synthesis.

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