Analysis method of copolymer sequence structure and application thereof

Abstract

The invention relates to the technical field of high polymer material detection, in particular to an analysis method of a copolymer sequence structure and application thereof. According to the method, copolymer powder is subjected to high-temperature cracking under the action of a cracking catalyst, and a cracking product is subjected to gas chromatography-mass spectrometry, so that the sequence structure of the copolymer is obtained. According to the invention, by optimizing the separation conditions of gas chromatography, the determination and good separation of multiple sequence structures in the copolymer are realized. According to the method, 26 sequence structures after polyformaldehyde cracking and six sequence structures after styrene-acrylonitrile copolymer cracking can be measured and separated, the measured sequence structures are comprehensive in variety and high in separation degree, and the accuracy of sequence distribution analysis is effectively improved.

Description

Technical Field

[0001] This invention relates to the field of polymer material detection technology, specifically to an analytical method for copolymer sequence structure and its application. Background Technology

[0002] Resins such as polyoxymethylene (POM), styrene-acrylonitrile copolymer (SAN), acrylonitrile-butadiene-styrene copolymer (ABS), and styrene-butadiene-styrene copolymer (SBS) possess excellent physicochemical properties and are widely used in electronics, electrical engineering, machinery, instrumentation, daily consumer goods, automotive, building materials, and agriculture. These resins typically involve the polymerization of two or more monomers, resulting in copolymers containing two or more monomer units. Based on the arrangement of the monomers in the copolymer molecular chain, they can be classified as random copolymers, alternating copolymers, block copolymers, and graft copolymers. The distribution of the copolymer unit structure in the copolymer has a significant impact on the resin's density, crystallinity, thermal stability, and other properties.

[0003] Taking POM as an example, POM resin possesses high rigidity and hardness, excellent fatigue and wear resistance, low creep and water absorption, good dimensional stability and chemical stability, making it a versatile engineering plastic with excellent comprehensive properties. The POM backbone is mainly composed of methyl oxysulfate segments (-CH2O-), with molecular weights typically ranging from tens of thousands to hundreds of thousands. Due to the absence of side chains and its regular and symmetrical molecular structure, it exhibits high density and crystallinity. However, when the POM backbone consists solely of pure (-CH2O-) segments, its thermal stability is extremely poor. It often undergoes a rapid formaldehyde depolymerization chain reaction under the influence of light, heat, oxygen, and strong acids, leading to complete depolymerization of the entire polymer chain and a significant decrease in product performance. Therefore, during the polymerization of POM, ethyl oxysulfate segments (-CH2CH2O-) are typically introduced into the backbone to improve its thermal stability. Thus, in polyacetal copolymers, studying their analytical sequence structure and distribution, and estimating the content and distribution of -CH2CH2O- units, is crucial for understanding the various properties of polyacetal copolymers.

[0004] Currently, the main methods for studying the sequence structure of copolymers include nuclear magnetic resonance (NMR), hydrolysis, chemical decomposition, and thermal decomposition.

[0005] Patent CN114486974A discloses an analytical method for the sequence structure distribution of atactic ethylene-propylene copolymers. This method first dissolves the atactic ethylene-propylene copolymer to be tested in deuterated o-dichlorobenzene solvent and adds it to an NMR tube. A conventional 13C NMR spectroscopy mode is used to obtain the quantitative carbon spectrum of the atactic ethylene-propylene copolymer. Secondly, using the quantitative carbon spectrum of the atactic ethylene-propylene copolymer, the integral peak regions are divided, and the types of carbon-containing functional groups corresponding to different integral peaks are correlated to determine the type of carbon corresponding to the integral peak. Finally, based on the relationship between each integral peak and its associated functional group, a calculation formula for the sequence structure distribution is derived, and the unary and ternary sequence structure distributions of the atactic ethylene-propylene copolymer to be tested are calculated using this formula.

[0006] Patent CN111978449A discloses a method for studying the sequence structure of acrylate-ethylene copolymers. This method uses deuterated chloroform to dissolve the copolymer, characterizes its copolymer unit composition using 1H NMR spectroscopy, and calculates the composition of methyl acrylate units and 1-octene units separately. Furthermore, 1C NMR spectroscopy characterizes the copolymer unit sequence structure, revealing that the copolymer structure is a fully alternating methyl acrylate-methyl acrylate structure.

[0007] While NMR analysis of copolymer sequence structures is simple to operate and highly accurate, it requires expensive NMR equipment. Furthermore, the copolymer units and sequence structures of different copolymers vary considerably, making it unsuitable for analyzing all copolymer sequence structures. The testing cost is high, and it can typically only analyze the distribution of mono- to ternary sequence structures of copolymers, not multi-component sequence structures. Summary of the Invention

[0008] To address the aforementioned technical problems in the prior art, this invention provides a method for analyzing the sequence structure of copolymers.

[0009] Another object of the present invention is to provide an application of the above-described method.

[0010] To achieve the above-mentioned objectives, the present invention adopts the following technical solution:

[0011] This invention protects a method for analyzing the sequence structure of copolymers, comprising the following steps:

[0012] S1. Mix the copolymer powder to be tested with the pyrolysis catalyst to obtain the sample to be tested;

[0013] S2. The sample to be tested is analyzed by pyrolysis-gas chromatography-mass spectrometry to obtain the sequence structure of the copolymer;

[0014] The stationary phase of the gas chromatograph is selected from a nonpolar phenyl aryl polymer, and the heating program is as follows: the temperature is increased to 280-300℃ at a heating rate of 5℃ / min and held for 5-10min.

[0015] This invention provides a method for analyzing the sequence structure of copolymers. The copolymer powder is subjected to high-temperature pyrolysis using a pyrolysis catalyst, and the pyrolysis products are then analyzed by gas chromatography-mass spectrometry to obtain the sequence structure of the copolymer. This invention achieves the determination and effective separation of multiple sequence structures in copolymers by optimizing the separation conditions of gas chromatography.

[0016] Specifically, the cracking catalyst is selected from acidic catalysts or basic catalysts. More specifically, the cracking catalyst is selected from at least one of cobalt sulfate heptahydrate, cobalt nitrate hexahydrate, zinc oxide, and ferric oxide.

[0017] Specifically, the amount of the pyrolysis catalyst is 15wt%-30wt% of the total mass of the pyrolysis catalyst and the polyoxymethylene powder, preferably 18wt%-22wt%.

[0018] Specifically, the amount of copolymer powder fed is 0.1-0.3 mg.

[0019] Specifically, the pyrolysis temperature is 400-450℃.

[0020] Specifically, the stationary phase of the gas chromatograph is phenyl silicone oil.

[0021] Preferably, the gas chromatographic column is an Agilent DB-5MS gas chromatographic column.

[0022] Specifically, the split flow rate of the gas chromatograph is 1.0-1.2 mL / min.

[0023] Specifically, the purge flow rate of the gas chromatograph is 1.0-1.2 mL / min.

[0024] Specifically, the ion source temperature of the mass spectrometer is 280°C.

[0025] Specifically, the mass number acquisition range of the mass spectrometer is 29-1000.

[0026] Specifically, the copolymer powder is obtained by pulverizing the copolymer.

[0027] Specifically, the mixing method includes grinding.

[0028] Preferably, the copolymer is polyoxymethylene or styrene-acrylonitrile copolymer.

[0029] When the copolymer is polyoxymethylene, the copolymer sequence structure includes at least one of F, EF, F3, EF2, F4, EF3, E2F, F5, EF4, F6, EF5, F7, EF6, F8, EF7, F9, EF8, F10, EF9, F11, EF10, F12, EF11, F13, (EF2)4, and (EF2)5, wherein in the copolymer sequence structure, F is an oxymethyl unit, E is an oxyethyl unit, and the numbers represent the number of repeating units of each unit.

[0030] This invention enables the determination and separation of twenty-six sequence structures after the cleavage of polyoxymethylene (POM), allowing for the study of POM sequence structures from various grades and copolymer compositions. The determined sequence structures are comprehensive, with high resolution, improving the accuracy of sequence distribution. The sequence structures obtained after POM cleavage are mainly chemical compositions composed of two structural units: methyl oxyoxide (-CH2O-, denoted by F) and ethyl oxyoxide (-CH2CH2O-, denoted by E). The POM cleavage sequence structures determined by this invention are shown in the table below:

[0031] Table 1. Sequence structure obtained from the cleavage of polyoxymethylene.

[0032]

[0033]

[0034] The analytical method of the present invention can also be used for sequence structure analysis of styrene-acrylonitrile copolymers, and can also separate multiple sequence structures in styrene-acrylonitrile copolymers, thereby realizing the analysis of sequence distribution.

[0035] Further, when the copolymer is a styrene-acrylonitrile copolymer, the copolymer sequence structure includes at least one of A, BA, B2A, A2, and A3, wherein A is a styrene unit, B is an acrylonitrile unit, and the number represents the number of repeating units of each unit.

[0036] The analytical method of this invention can also separate the five sequence structures after the pyrolysis of styrene-acrylonitrile copolymer. The sequence structures obtained after the pyrolysis of styrene-acrylonitrile copolymer are mainly chemical compositions composed of two structural units: styrene (represented by A) and acrylonitrile (represented by B). The sequence structures of styrene-acrylonitrile copolymer after pyrolysis determined by this invention are shown in the table below:

[0037] Table 2. Sequence structures obtained from the pyrolysis of styrene-acrylonitrile copolymers.

[0038] sequence structure Retention time (min) A 8.5 BA 22.0 B2A 32.3 A2 38.4 A3 43.4

[0039] This invention also protects the application of the above-described analytical method.

[0040] Compared with the prior art, the present invention has the following beneficial effects:

[0041] This invention provides a method for analyzing the sequence structure of copolymers. The copolymer powder is pyrolyzed at high temperature using a pyrolysis catalyst, and the pyrolysis products are then analyzed by gas chromatography-mass spectrometry to obtain the sequence structure of the copolymer. The pyrolysis-gas chromatography-mass spectrometry separation conditions of this invention can achieve the determination and complete separation of multiple sequence structures in polyoxymethylene and styrene-acrylonitrile copolymers.

[0042] In particular, the analytical method of the present invention enables the determination and complete separation of twenty-six sequence structures after the cleavage of polyoxymethylene. The determined sequence structures are comprehensive and have high separation, thus improving the accuracy of sequence distribution. Attached Figure Description

[0043] Figure 1 Total ion chromatogram of Example 1;

[0044] Figure 2 Total ion chromatogram of Example 2;

[0045] Figure 3 Total ion chromatogram of Example 3;

[0046] Figure 4 : Total ion chromatogram of Comparative Example 1;

[0047] Figure 5 : Total ion chromatogram of Comparative Example 2;

[0048] Figure 6 : Total ion chromatogram of Comparative Example 3. Detailed Implementation

[0049] The present invention is further illustrated below with reference to specific embodiments. These embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Experimental methods in the following embodiments that do not specify specific conditions are generally performed under conventional conditions in the art or as recommended by the manufacturer; the raw materials and reagents used, unless otherwise specified, are all commercially available from the conventional market. Any non-substantial changes and substitutions made by those skilled in the art based on the present invention are within the scope of protection claimed by the present invention.

[0050] Example 1

[0051] A method for analyzing the sequence structure of copolymers includes the following steps:

[0052] The test sample was a copolymer POM resin raw material 1 with the grade M25 from Yuntianhua, which was purchased from the market.

[0053] Step 1: Sample Preparation

[0054] First, the copolymer POM resin raw material 1 was crushed into small particles using a crusher, and the crushed sample was sieved through a 60-mesh sieve to remove the fine particles.

[0055] Secondly, CoSO4·7H2O was ground into powder using a mortar and pestle;

[0056] Finally, the ground CoSO4·7H2O powder was thoroughly mixed with the fine particles of the pulverized and sieved copolymer POM resin raw material 1 sample to obtain a mixed sample, wherein the content of CoSO4·7H2O catalyst was 20wt% of the mixed sample.

[0057] Step 2: On-machine testing

[0058] Weigh 0.2 mg of the mixed sample into the sample boat and pass it through a pyrolysis gas chromatography-mass spectrometer (ISQ). TM The copolymer POM resin raw material 1 was tested using 7000-EGA / PY-3030D to obtain the total ion chromatogram of the pyrolysis gas chromatography-mass spectrometry, as shown below. Figure 1 As shown.

[0059] Test conditions:

[0060] The pyrolysis temperature is 400℃;

[0061] The chromatographic column was DB-5MS, 30m×0.25mm×0.25μm, with a split flow rate of 50mL / min, a purge flow rate of 1mL / min, and a temperature program of 5℃ / min to reach 280℃ and holding for 5min.

[0062] Step 3: Component analysis of pyrolysis products

[0063] The chemical structures of the pyrolysis products of copolymer POM resin raw material 1 were analyzed by gas chromatography-mass spectrometry total ion chromatogram analysis, and the sequence structure and other components of copolymer POM resin raw material 1 were studied. The sequence structure of the pyrolysis products of copolymer POM resin raw material 1 is mainly composed of two structural units: oxymethyl (-CH2O-, represented by F) and oxyethyl (-CH2CH2O-, represented by E). Among them, seven sequence structures (F, EF, F3, EF2, F4, EF3, and E2F) with peaks in the retention time range of 1 min to 13.5 min were qualitatively identified by database search, and other sequence structures (F...) with peaks in the retention time range of 14 min to 60 min were also identified. n and EF n Qualitative characterization is based on derivation from characteristic fragment peaks and retention times. For example, when the characteristic fragment peaks in the mass spectrum are 31, 61, and 89, the sequence structure is characterized as F. nWhen the characteristic fragment peaks in the mass spectrum are 31, 44, and 73, the sequence structure is characterized as EF. n Simultaneously, a comprehensive analysis was performed based on the peak retention time and molecular weight of each structure. The sequence structure of the chemical composition of the pyrolysis products of copolymer POM resin raw material 1 is shown in Table 3.

[0064] Table 3. Pyrolysis products of Example 1

[0065]

[0066]

[0067] Step 4: Calculate the ternary structure sequence distribution of copolymer POM resin raw material 1

[0068] Based on the relationship between the mass spectrometry peaks and the assigned ternary sequence structures, the calculation formula for the distribution of ternary sequence structures is derived (see Formulas 1 to 5, refer to Macromolecules 1995, 28, 6528-6532). The calculation formula is then used to calculate the distribution of ternary structure sequences and the mole fractions of E and F structural units in copolymer POM resin raw material 1 (see Table 4).

[0069]

[0070] Where, n x The mole fraction of the corresponding ternary structure sequence in Table 3 can be obtained through testing software. F and L E These represent the average sequence lengths of the ternary structures centered at F and E in Table 3, respectively, where R is the copolymer randomness, and n... E and n F These are the mole fractions of structural units E and F in Table 3, respectively.

[0071] Table 4. Sequence distribution and mole fraction of structural units in Example 1

[0072]

[0073] Step 5: Calculate the E-unit sequence structure distribution of copolymer POM resin raw material 1

[0074] Based on the relationship between the mass spectrometry peaks and the assigned E-unit-containing sequence structures, the calculation formula for the sequence structure distribution is derived (see Formulas 6 to 10, refer to J. Anal. Appl. Pyrolysis 71 (2004) 83-106). The E-unit-containing sequence structure distribution of copolymer POM resin raw material 1 is calculated using the calculation formula (see Table 5).

[0075]

[0076] Among them, I x The peak intensities of the sequences containing E-unit structures in Table 3 are given, where W is the sample mass, i and j are the number of E-unit and F-unit structures, respectively, and C is the peak intensity. x The peak intensity is the corrected value, M(total) is the total molar yield, and D(-FE) is the peak intensity. x F-) is the sequence distribution containing E units.

[0077] Table 5. Distribution of E-unit-containing structural sequences in Example 1

[0078] E-unit sequence structure —FEF— <![CDATA[—FE2F—]]> Distribution of E-unit sequence structures 67.15 32.85

[0079] Example 2

[0080] A method for analyzing the sequence structure of copolymers includes the following steps:

[0081] The analysis method in Example 2 is the same as that in Example 1, except that:

[0082] Step 1: The test sample is copolymer POM resin raw material 2 with brand name M90 ​​from Yuntianhua, which was purchased from the market.

[0083] The total ion chromatogram of the pyrolysis gas chromatography-mass spectrometry of copolymer POM resin raw material 2 is shown below. Figure 2 As shown in Table 6, the sequence structure of copolymer POM resin raw material 2 is shown in Table 7, the sequence distribution and mole fraction of structural units are shown in Table 8, and the sequence distribution of E-unit-containing structures is shown in Table 8.

[0084] Table 6. Pyrolysis products of Example 2

[0085]

[0086] Table 7. Sequence distribution and mole fraction of structural units in Example 2

[0087]

[0088] Table 8. Distribution of E-unit-containing structural sequences in Example 2

[0089] E-unit sequence structure —FEF— <![CDATA[—FE2F—]]> Distribution of E-unit sequence structures 98.91 1.09

[0090] Example 3

[0091] A method for analyzing the sequence structure of copolymers includes the following steps:

[0092] The analysis method in Example 3 is the same as that in Example 1, except that:

[0093] Step 1: The test sample was replaced with copolymer SAN resin raw material 3, grade 130B, from Kingfa Science & Technology.

[0094] Step 3: The chemical composition of the pyrolysis products is mainly a sequence structure composed of two structural units: styrene (represented by A) and acrylonitrile (represented by B) (see Table 9);

[0095] Step 4: The formula for calculating the structural distribution of ternary sequences is as follows:

[0096]

[0097] Where, n x The mole fraction of the x ternary structure sequence corresponding to Table 9 can be obtained through testing software. A and L B These represent the average sequence lengths of the ternary structures centered at A and B in Table 9, respectively, where R is the copolymer randomness, and n... A and n B These are the mole fractions of structural units A and B in Table 9, respectively.

[0098] Step 5: The formula for calculating the sequence structure distribution is as follows:

[0099]

[0100] Among them, I x The peak intensities of the sequences containing B units in Table 9 are given, where W is the sample mass, i and j are the number of A and B structural units, respectively, and C is the peak intensity. x The peak intensity is the corrected value, M(total) is the total molar yield, and D(-AB) is the peak intensity. x A-) represents the sequence distribution containing unit B.

[0101] The total ion chromatogram of the pyrolysis gas chromatography-mass spectrometry of copolymer SAN resin raw material 3 is shown below. Figure 3 As shown in Table 10, the sequence distribution and mole fraction of structural units are shown in Table 11, and the sequence distribution of structures containing B units is shown in Table 11.

[0102] Table 9. Pyrolysis products of Example 3

[0103] sequence structure Retention time (min) A 8.5 BA 22.0 B2A 32.3 A2 38.4 A3 43.4

[0104] Table 10 Sequence distribution and mole fraction of structural units in Example 3

[0105]

[0106] Table 11. Distribution of B-unit-containing structural sequences in Example 3

[0107] B-unit sequence structure —ABA— —AB2A— Distribution of sequence structures containing B units 37.84 62.16

[0108] Comparative Example 1

[0109] The analytical method for Comparative Example 1 is the same as that for Example 1, except that:

[0110] Step 1: The content of CoSO4·7H2O catalyst was changed to 10wt%.

[0111] The total ion chromatogram of the pyrolysis gas chromatography-mass spectrometry of sample 1 of copolymer POM resin raw material is shown below. Figure 4 As shown in Table 12, the sequence structure of POM resin raw material 1 sample is shown in Table 13, the sequence distribution and mole fraction of structural units are shown in Table 14, and the sequence distribution of E-unit-containing structures is shown in Table 15.

[0112] Table 12. Pyrolysis products of Comparative Example 1

[0113]

[0114] Table 13 Sequence distribution and mole fraction of structural units in Comparative Example 1

[0115]

[0116] Table 14 Distribution of E-unit-containing structural sequences in Comparative Example 1

[0117] E-unit sequence structure —FEF— <![CDATA[—FE2F—]]> Distribution of E-unit sequence structures 100.00 0.00

[0118] Comparative Example 2

[0119] The analytical method for Comparative Example 2 is the same as that for Example 1, except that:

[0120] Compared to Example 1, in step 1, the content of the CoSO4·7H2O catalyst was changed to 5 wt%. The total ion chromatogram of the pyrolysis gas chromatography-mass spectrometry of sample 1 of the copolymer POM resin is shown below. Figure 5 As shown, the sequence structure of sample 1, the copolymer POM resin raw material, only has an F unit structure, making sequence structure analysis impossible.

[0121] Comparative Example 3

[0122] The analytical method for Comparative Example 3 is the same as that for Example 1, except that:

[0123] Step 2: Change the heating rate to 10℃ / min.

[0124] The total ion chromatogram of the pyrolysis gas chromatography-mass spectrometry of sample 1 of copolymer POM resin raw material is shown below. Figure 6 As shown, the F and EF structures of the copolymer POM resin raw material 1 sample eluted before 2 minutes were piled up together and could not be separated, which is not conducive to the subsequent study of sequence structure distribution.

[0125] Therefore, the testing method of this invention can determine and separate multiple sequence structures after polyoxymethylene (POM) pyrolysis. The determined sequence structures are comprehensive and have high resolution, improving the accuracy of sequence distribution and facilitating the study of sequence structures of various POM grades and copolymer compositions. However, when the testing conditions specified in this invention are not met, the accuracy of the polymer sequence structure determination will decrease, hindering detailed analysis.

[0126] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A method for analyzing the sequence structure of a copolymer, comprising the following steps: S1. Mix the copolymer powder to be tested with the pyrolysis catalyst to obtain the sample to be tested; S2. The sample to be tested is analyzed by pyrolysis-gas chromatography-mass spectrometry to obtain the sequence structure of the copolymer; The stationary phase of the gas chromatograph is selected from a nonpolar phenyl aryl polymer, and the temperature program is as follows: the temperature is increased to 280-300℃ at a rate of 5℃ / min and held for 5-10min.

2. The analytical method according to claim 1, characterized in that, The pyrolysis catalyst is selected from acidic catalysts or basic catalysts.

3. The analytical method according to claim 2, characterized in that, The pyrolysis catalyst is selected from at least one of cobalt sulfate heptahydrate, cobalt nitrate hexahydrate, zinc oxide, and ferric oxide.

4. The analytical method according to claim 1, characterized in that, The amount of the pyrolysis catalyst is 15 wt% to 30 wt% of the total mass of the pyrolysis catalyst and the polyoxymethylene powder.

5. The analytical method according to claim 1, characterized in that, The pyrolysis temperature is 400-450℃.

6. The analytical method according to claim 1, characterized in that, The gas chromatographic column used was a DB-5MS.

7. The analytical method according to claim 1, characterized in that, The split flow rate of the gas chromatograph is 1.0-1.2 mL / min.

8. The analytical method according to claim 1, characterized in that, The purge flow rate for the gas chromatograph is 1.0-1.2 mL / min.

9. The analytical method according to claim 1, characterized in that, The ion source temperature of the mass spectrometer is 280℃.

10. The analytical method according to claim 1, characterized in that, The copolymer is polyoxymethylene or styrene-acrylonitrile copolymer.

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