A rapid analysis method for high-density polyethylene structures

Abstract

The application relates to the field of organic structure characterization, in particular to a rapid analysis method of high-density polyethylene structure. 13 Compared with the C NMR spectrum, the application has the following three advantages: (1) by using the method and the corrected branching rate calculation formula, the high-density polyethylene branching rate content test accuracy is equivalent to that of quantitative carbon spectrum; (2) under the condition of the same sample concentration, the experiment time is greatly saved while ensuring the quantitative accuracy, and the application has certain guiding significance for production process quality monitoring and new product development; (3) the application can greatly reduce the damage of high temperature to the instrument and the demand for nitrogen, and has high economic value; (4) the solubility of the sample and the sensitivity requirement of the nuclear magnetic hardware are greatly reduced, the sample with poor solubility can be more widely applied, and the range of detection and characterization objects is greatly expanded.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of structure characterization of organic matter, and particularly relates to a rapid analysis method of high-density polyethylene structure. BACKGROUND

[0002] High-density polyethylene (HDPE) is an important class of polymer materials, which is widely used in manufacturing bottles, barrels, fuel tanks and other containers. Its characteristic is that the density ranges from 0.945 to 0.965 / cm 3 , and it exhibits very low levels of short-chain branching (SCB <1%). It is mainly prepared by copolymerization of ethylene with butene or hexene, or obtained by isomerization reaction in the process of ethylene polymerization. These branches form structural defects in the crystallization process, thereby affecting the crystallization rate, final crystallinity, other physical properties and bulk mechanical properties. Therefore, the branching type and branching rate must be concerned.

[0003] At present, people mainly use high-temperature quantitative 13 C NMR spectrum for such characterization analysis, and the quantitative 13 C NMR spectrum is a one-dimensional NMR technique for detecting 13 C nuclei. By means of inhibiting the NOE gain of various carbon nuclei and adjusting the sampling time interval, the signal integral area in the carbon spectrum is proportional to the number of signals corresponding to the carbon, so as to achieve the quantitative effect. In the quantitative 13 C NMR spectrum, D1 (Delay) is the time for waiting for the balance of the detected nucleus before sampling each scan. NS (number of scans) is the number of scans. SW is the spectrum width. o1p is the central chemical shift. INEPT (Insensitive Nuclei Enhanced by Polarization Transfer) is the polarization transfer technology of insensitive nuclei. DEPT (Distortionless Enhancement by Polarization Transfer) is the polarization transfer enhancement without distortion. The principle of the quantitative 13 C NMR spectrum is that the signal intensity and phase are different according to the deflection angle of the hydrogen magnetization vector, and when the deflection angle is 135 degrees, the methyl and methylene groups are positive peaks, the methylene group is a negative peak, and the carbon without hydrogen does not have a signal, so it is often used to judge the type of carbon atom.

[0004] However, the quantitative 13 C NMR spectrum has some problems: (1) the natural abundance of the detected nucleus 13 C is only 1.1%, and the sensitivity is only about 1 1 / 5700 of that of 1 H, compared with 13C NMR experiments require much more sample volume and require a significant increase in the number of sampling times and sampling time to obtain spectra with a relatively high signal-to-noise ratio; (2) Some 13 The relaxation time of C nuclei is long, and it takes a long time (about 40 seconds or more) to wait for them to return to equilibrium before each scan. This means that the same number of sampling times requires more experimental time. (3) The branching rate of HDPE is extremely low, which further increases the difficulty of scanning peaks. For example, in one report, using 500 MHz to characterize 0.03% of branches in low-density polyethylene required an average of more than 28 hours of experimental time and more than 2 million scans. It can be seen that the experimental time required to characterize high-density polyethylene is very long and difficult.

[0005] To solve these problems, DEPT (Distortionless Enhancement by Polarization Transfer) and INEPT technologies have attracted attention. They mainly use highly sensitive hydrogen nuclei ( 1 H) to carbon nucleus ( 13 C) energy transfer to achieve cross-polarization transfer enhancement of insensitive nuclei. It has the advantages of high sensitivity and signal enhancement, but the various signal enhancements are uneven and the enhancement degree is uncertain. It cannot be directly used for quantitative analysis. DEPT and INEPT technologies are now mainly used to identify carbon atom types. In 2017, Dow Chemical Company obtained the optimal recombination time of 2-ethylhexyl acrylate and the proportional relationship between the enhancement of various carbon signals by comparing the theoretical standard curves and experimental real curves of DEPT and INEPT, and then used it to calculate the branching rate of low-density polyethylene. Its implementation scheme is as follows: (1) Select the small molecule 2-ethylhexyl acrylate for modeling and obtain the curve of its recombination time and the enhancement degree of various carbon signals. (2) Select the appropriate recombination time and calculate the signal enhancement degree at the recombination time. (3) Under similar conditions, the carbon spectrum of ethylene / 1-octene copolymer was tested, and it was found that the nuclear magnetic spectrometer equipped with a 10 mm ordinary probe could obtain a spectrum with a flat baseline, saving about 50 times the experimental time. Dow Chemical confirmed that the developed QA-INEPT is a method suitable for characterizing the structure of linear low-density polyethylene (ethylene / 1-octene copolymer). However, this method of Dow has the following disadvantages: (1) It is not used for the characterization of high-density polyethylene and polymers with extremely low branching rates; (2) The branching rate of the characterized polyolefin samples is narrow (8.8-12.7 mol%), and the characterization range is limited; (3) Although the low-temperature probe can further improve the signal-to-noise ratio and sensitivity of the spectrum and save experimental time, the spectrum obtained by the low-temperature probe is severely phase-distorted; (4) It is not applicable to 5 mm probes, has low accuracy, and has a quantitative error rate of more than 20%. At present, more than 95% of the nuclear magnetic resonance spectrometers in China are equipped with ordinary 5 mm probes, and these instruments cannot be used for quantitative characterization using this method.

[0006] It can be seen that high temperature quantification 13 C is the most conventional method for characterizing the branching rate of high-density polyethylene, but due to 13 C nucleus inherent low natural abundance and low magnetic spin ratio, quantitative 13 The C NMR technology has the disadvantages of low sensitivity and long experimental time. At present, there is no report on other nuclear magnetic methods for characterizing the branching rate of high-density polyethylene. There are only some reports on other nuclear magnetic methods for characterizing the branching rate of low-density polyethylene, and these other nuclear magnetic methods for characterizing the branching rate of low-density polyethylene also have problems.

[0007] In addition, although the above problems can also be solved by greatly improving the hardware conditions of the nuclear magnetic instrument, such as replacing the 400 MHZ instrument with an 800 or 900 MHZ instrument, and using a more sensitive probe, the economic cost will be 10 times or even dozens of times, and the cost will be greatly increased. At present, there are very few users of such instruments in the world, and they do not have wide applicability. Therefore, it is particularly important for the polyolefin industry to develop a time-saving and rapid method for characterizing the branching degree of HDPE based on carbon nucleus as the detection object. SUMMARY

[0008] Therefore, the technical problem to be solved by the present application is to provide a rapid analysis method for the structure of high-density polyethylene. The method provided by the present application can rapidly characterize the monomer content and branching rate of high-density polyethylene based on existing instruments with high retention rate, and provides accurate characterization results.

[0009] The present application provides a rapid analysis method for the structure of high-density polyethylene, comprising the following steps:

[0010] S1) obtaining the INEPT spectrum of the pretreated high-density polyethylene and defining the integral interval, then attributing and integrating the spectral peaks of the INEPT spectrum according to the integral interval, and obtaining the monomer content formula and branching rate formula of high-density polyethylene according to the integral interval;

[0011] When the high-density polyethylene contains only one branch, the integral interval is:

[0012] A: δ 38.5-41.5 ppm;

[0013] B: δ 33.8-34.8 ppm;

[0014] C: δ 29.5-31.0 ppm;

[0015] D: δ 26.2-27.3 ppm;

[0016] E: δ 24.2-24.6 ppm;

[0017] F: δ 10.5-11.7 ppm;

[0018] When the high density polyethylene contains two or more branches, the integral interval is:

[0019] G: δ 23.3-23.5 ppm;

[0020] H: δ 26.6-26.8 ppm;

[0021] I: δ 29.4-29.6 ppm;

[0022] J: δ 29.9-30.1 ppm;

[0023] K: δ 30.4-30.6 ppm;

[0024] L: δ 34.0-34.1 ppm;

[0025] M: δ 34.2-34.3 ppm;

[0026] N: δ 39.6-39.8 ppm;

[0027] S2) correcting the monomer content formula according to the results attributed in step S1) to obtain a monomer content correction formula, and obtaining the monomer content of the high density polyethylene according to the monomer content correction formula and the results of the integral in step S1);

[0028] S3) correcting the branching rate formula according to the results attributed in step S1) to obtain a branching rate correction formula, and obtaining the branching rate of the high density polyethylene according to the branching rate correction formula and the results of the integral in step S1).

[0029] Step S1) of the present application needs to obtain the INEPT spectrum of the pretreated high density polyethylene. The pretreated high density polyethylene is obtained from the high density polyethylene, paramagnetic reagent and deuterated tetrachloroethane, specifically, 5-30 mg of high density polyethylene is weighed and added to a 5 mm or 10 mm NMR tube, then 0.5-20 mg of paramagnetic reagent and 0.3-3.0 mL of deuterated tetrachloroethane are added, and the mixture is heated to fully dissolve to obtain a homogeneous polymer solution of the pretreated high density polyethylene.

[0030] The sampling parameters for obtaining the INEPT spectrum include: d1=1-10s, cnst2=100-200Hz, cnst8=100-150Hz, and the three sampling parameters are important for the test accuracy of the method. Further, the sampling parameters for obtaining the INEPT spectrum include: d1=1-10s, cnst2=100-200Hz, cnst8=100-150Hz, td=16-64k, ns=128-5000, ds=4-16, sw=50-250ppm, d3=0.0005-0.0015s, O1P=10-40ppm. Preferably, d1=1-5s, cnst2=100-150Hz, cnst8=120-130Hz, td=32-64k, ns=500-2000, ds=15-16, sw=100-150ppm, d3=0.0008-0.0013s, O1P=25-35ppm. The experimental temperature for obtaining the INEPT spectrum is 80-150°C, and the experimental time is 0.3-5h. By optimizing the parameters (d1, cnst8, etc.) of the INEPT spectrum, the present application obtains a nuclear magnetic carbon spectrum with clear gain degree and high signal-to-noise, and defines the interval for calculation according to the representative carbon atom chemical shift. After obtaining the INEPT spectrum, the present application also includes baseline correction and phase correction of the INEPT spectrum. The peak position and baseline are corrected to ensure accurate integration of all signals subsequently.

[0031] The step S1) of the present application also needs to define the integration interval, which is defined according to the atomic arrangement structure in the polymer chain. When the high-density polyethylene contains only one branched chain, the integration interval of the present application is:

[0032] A: δ 38.5-41.5ppm;

[0033] B: δ 33.8-34.8ppm;

[0034] C: δ 29.5-31.0ppm;

[0035] D: δ 26.2-27.3ppm;

[0036] E: δ 24.2-24.6ppm;

[0037] F: δ 10.5-11.7ppm;

[0038] When the high-density polyethylene contains two or more branched chains, the integration interval of the present application is:

[0039] G: δ 23.3-23.5ppm;

[0040] H: δ 26.6-26.8 ppm;

[0041] I: δ 29.4-29.6 ppm;

[0042] J: δ 29.9-30.1 ppm;

[0043] K: δ 30.4-30.6 ppm;

[0044] L: δ 34.0-34.1 ppm;

[0045] M: δ 34.2-34.3 ppm;

[0046] N: δ 39.6-39.8 ppm;

[0047] Preferably, the definition integral interval is under the assumption condition, comprising:

[0048] Assumption condition 1: the weight average molecular weight of the high density polyethylene is less than 1 million, that is, the polymer molecular weight is moderate, not super high polyethylene;

[0049] Assumption condition 2: when the polymer molecular weight is small, there will be a terminal end group, if the high density polyethylene has a terminal end group, the end group does not participate in the calculation;

[0050] Assumption condition 3: the INEPT spectrum signal-to-noise is high enough, specifically, the INEPT spectrum signal-to-noise ratio is greater than 400, wherein the smallest signal-to-noise ratio is greater than 10;

[0051] Assumption condition 4: the branch content of the high density polyethylene is less than 1%, and there is no continuous branched chain sequence.

[0052] Due to the difference in gain degree, different types of carbon atoms need to be integrated and calibrated. The present application obtains the attribution result by attributing the peaks of the obtained INEPT spectrum according to the integral interval, and obtains the integral result by integration.

[0053] The present application obtains the monomer content formula of high density polyethylene and the branching rate formula of high density polyethylene according to the integral interval, and the obtained monomer content formula of high density polyethylene and the branching rate formula of high density polyethylene are the formulas before correction, as shown in formula a, formula b and formula c:

[0054] Mole fraction of butene:

[0055] B mol%={(I B -I A ) / (I B -I A +0.5I C +0.25ID -0.75I F )}×100%formula a;

[0056] Mole fraction of ethylene:

[0057] E mol% = 100% - B mol% formula b;

[0058] Branching rate of high-density polyethylene:

[0059] C bb ={(5I B -5I A ) / (I B -I A +0.5I C +0.25I D -0.75I F )}×1000‰ formula c;

[0060] Wherein, B mol% represents the molar content of butene monomer in the high-density polyethylene, E mol% represents the molar content of ethylene monomer in the high-density polyethylene, and C bb represents the branching ratio of the high-density polyethylene.

[0061] The present invention also requires appropriate correction of specific types of carbon core signals based on the attribution of different signals in the INEPT spectrum, that is, correcting the monomer content formula according to the result of the attribution in step S1) to obtain a monomer content correction formula, and correcting the branching rate formula according to the result of the attribution in step S1) to obtain a branching rate correction formula. Specifically, the monomer content formula is corrected by multiplying the calibration factor by comparing the results of the high-temperature quantitative carbon spectrum experiment, and the branching rate formula is corrected by multiplying the calibration factor by comparing the results of the high-temperature quantitative carbon spectrum experiment, so that it is suitable for the integral calculation of the INEPT spectrum, optimizing the original sequence structure distribution formula for different types of high-density polyethylene carbon spectra, and obtaining the monomer content correction formula and branching rate correction formula of the present invention. In the present invention, the derivation of the sequence distribution formula and the selection of the correction factor are extremely important for the calculation of the structure and branching rate of high-density polyethylene.

[0062] After obtaining the monomer content correction formula, the present invention obtains the monomer content of the high-density polyethylene based on the monomer content correction formula and the result of the integration in step S1). Specifically, when the high-density polyethylene contains only one type of branched chain, the monomer content calculation formula of the high-density polyethylene includes:

[0063] B mol%={(I B -1.30I A ) / (I B –1.30I A+0.5I C +0.25I E -0.75I F )}x 100% Formula 1

[0064] Emol% = 100% - Bmol% Formula 2

[0065] When the high density polyethylene contains two or more branches, the monomer content calculation formula of the high density polyethylene includes:

[0066] Bmol% = {(0.333I H +0.167I L +0.443I N ) / (0.333I H +0.167I L +0.443I N +

[0067] 0.5I G +0.5I M +0.5I J +0.5I K -0.5I I )}x 100% Formula 3

[0068] Hmol% = {(0.5I G +0.5I M ) / (0.333I H +0.167I L +0.443I N +0.5I G +0.5

[0069] I M +0.5I J +0.5I K -0.5I I}x 100% Formula 4

[0070] Emol% = 100% - Bmol% - Hmol% Formula 5

[0071] Wherein, Bmol% represents the molar content of butene monomer of the high density polyethylene, Hmol% represents the molar content of 1-hexene monomer of the high density polyethylene, Emol% represents the molar content of ethylene monomer of the high density polyethylene, I A , I B , I C , I E , I F , I G , I H , II J K L M N A, B, C, E, F, G, H, I, J, K, L, M and N represent the integral area of the spectral peak in each of the integral intervals A, B, C, E, F, G, H, I, J, K, L, M and N, respectively.

[0072] After obtaining the branching rate correction formula, the branching rate of the high-density polyethylene is obtained according to the branching rate correction formula and the integral result of step S1). Specifically, when the high-density polyethylene contains only one branch, the branching rate calculation formula of the high-density polyethylene comprises:

[0073] C bb = {(5I B -6.5I A ) / (I B -1.30I A +0.5 I C +0.25 I D -0.75 I E )}×1000‰ formula 6

[0074] When the high-density polyethylene contains two or more branches, the branching rate calculation formula of the high-density polyethylene comprises:

[0075] C bb = {(3.33I H +1.67I L +4.43I N +5I G +5I M ) / (0.666I H +0.333I L +0.886I N

[0076] +I G +I M +I J +I K -I I )}×1000% formula 7

[0077] Wherein, C bb represents the branching rate of the high-density polyethylene, I A , I B , I C , I D , I E , I G , I H , I I , I J , I​​​​​K , I L , I M and I N They represent the integrated areas of the spectral peaks in the integration intervals A, B, C, D, E, G, H, I, J, K, L, M and N respectively.

[0078] The present invention provides a method for rapid analysis of the structure of high-density polyethylene. The method for rapid analysis of the structure of high-density polyethylene provided by the present invention is a carbon nuclear magnetic quantitative method, which is consistent with the recognized high accuracy quantitative method. 13 Compared with C NMR spectra, the present invention has the following three advantages: (1) Using the method of the present invention and the corrected branching rate calculation formula, the branching rate content test accuracy of high-density polyethylene is comparable to that of quantitative carbon spectrum; (2) Under the same sample concentration conditions, while ensuring quantitative accuracy, the experimental time is greatly saved, which has certain guiding significance for production process quality monitoring and new product development; (3) The invention can greatly reduce the damage to the instrument caused by high temperature and the demand for nitrogen consumption, and has high economic value; (4) The requirements for sample solubility and nuclear magnetic hardware sensitivity are greatly reduced, and it can be more widely applied to samples with poor solubility, and the scope of detection and characterization objects is greatly expanded. BRIEF DESCRIPTION OF THE DRAWINGS

[0079] Figure 1 This is a graph showing the INEPT spectrum of high-density polyethylene of Example 1 of the present invention;

[0080] Figure 2 Figure 2 is a second INEPT spectrum of high-density polyethylene of Example 1 of the present invention;

[0081] Figure 3 Three figures are the INEPT spectra of the high-density polyethylene of Example 1 of the present invention;

[0082] Figure 4 The conventional quantitative high-density polyethylene for comparison in Example 1 of the present invention 13 C NMR spectrum;

[0083] Figure 5 This is the INEPT spectrum of the high-density polyethylene of Example 2 of the present invention. DETAILED DESCRIPTION

[0084] The present application discloses a rapid analysis method of high density polyethylene structure. The skilled in the art can improve the process parameters according to the content of the present application. It is particularly pointed out that all similar substitutions and changes are obvious to the skilled in the art, and they are considered to be included in the present application. The method and application of the present application have been described by the preferred embodiments, and the related personnel can obviously modify or appropriately change and combine the method and application of the present application without departing from the content, spirit and scope of the present application, to realize and apply the present application technology.

[0085] The process of the present application includes: (1) sample preparation; (2) INEPT spectrum sampling and optimization of data processing parameters; (3) obtaining the branching formula of the sample and calculating the branching rate; (4) limit of quantification, limit of detection, precision, repeatability, stability experiment. The calculation formula of the branching rate will change with the type of the branched chain in the sample, which will be given in the examples.

[0086] The present application is further described below in combination with examples:

[0087] Example 1

[0088] The branching degree of high density polyethylene represented by ethylene / butene copolymer is measured:

[0089] (1) Weigh 40 milligrams of high density polyethylene HDPE represented by ethylene / butene copolymer into a 5 millimeter NMR tube, then add 10 milligrams of chromium acetylacetone, inject 0.6 mL of deuterated o-dichlorobenzene, and heat to fully dissolve into a homogeneous polymer solution.

[0090] (2) Spectrum sampling and optimization of data processing parameters

[0091] (2.1) INEPT spectrum of a certain HDPE (S1) is collected on a 400 MHz instrument equipped with a common 5 millimeter BBFO probe. The sampling parameters are as follows: td=32k, ns=2000, ds=16, sw=130ppm, d1=2s, cnst2=125Hz, d3=0.001 second, O1P=30ppm, cnst8=125Hz, temperature 110 degrees, and experimental time is 2.0 hours. After sampling, the INEPT spectrum is obtained by using NMR spectrum analysis software for baseline correction and phase correction, as shown in Figure 1 , which is one of the INEPT spectra of high density polyethylene of Example 1 of the present application. Figure 1

[0092] ​(2.2) INEPT spectra of HDPE were collected on a 400 MHz instrument equipped with a conventional 5 mm BBFO probehead. The sampling parameters were dl = 5 s, experimental time 3.5 hours, otherwise unchanged. The spectra were baseline and phase calibrated using the NMR spectral analysis software as shown in Figure 2 Figure 2B, which is a second plot of the INEPT spectra of the high density polyethylene of Example 1 of the present invention. Figure 2

[0093] (2.3) INEPT spectra of HDPE were collected on a 500 MHz instrument equipped with a 5 mm prodigy cryoprobe. The sampling parameters were as follows: td = 32k, ns = 512, ds = 16, sw = 130 ppm, dl = 2 s, cnst2 = 125 Hz, d3 = 0.001 s, OIP = 30 ppm, cnst8 = 125 Hz, experimental temperature 110 °C, experimental time 0.5 hours. The spectra were baseline and phase calibrated using the NMR spectral analysis software as shown in Figure 3 Figure 3B, which is a third plot of the INEPT spectra of the high density polyethylene of Example 1 of the present invention. Figure 3

[0094] (2.4) Conventional quantitative 13 C NMR spectra of HDPE were collected on an instrument equipped with a 5 mm BBOF probehead. The acquisition parameters were as follows: dl = 14 s, cnst2 = 100 Hz, td = 32k, ns = 5000, ds = 10, sw = 130 ppm, OIP = 30 ppm, experimental time 24 hours. The spectra were baseline and phase calibrated using the NMR spectral analysis software as shown in Figure 4 Figure 4B, which is a conventional quantitative 13 C NMR spectrum of the high density polyethylene of Example 1 of the present invention for comparison. Figure 4

[0095] (2.5) Conventional quantitative 13 C NMR spectra of HDPE were collected as in (2.4) except that the experimental time was changed to 4 hours.

[0096] (3) The branching index formula and branching index of the sample were obtained as follows. First, the carbon spectrum signals were assigned and the spectrum peaks were integrated. Then, the sequence formula was corrected, the branching index formula was proposed, and the branching index was obtained. More specifically:

[0097] (3.1) The integral interval was defined according to the atomic arrangement structure in the polymer chain.

[0098] The integral interval was defined based on the following four assumptions:

[0099] Assumption one: the polymer molecular weight is moderate, not ultra-high polyethylene, and the weight average molecular weight is less than 1 million;​​​

[0100] Assumption two: the end groups exist when the molecular weight of polymer is small, and the end groups do not participate in the calculation;

[0101] Assumption three: the signal-to-noise of the spectrum is high enough;

[0102] Assumption four: the content of the branched chain of high-density polyethylene is less than 1%, and there is no sequence of continuous branched chain.

[0103] The integral interval is defined as follows:

[0104] A: δ 38.5-41.5 ppm;

[0105] B: δ 33.8-34.8 ppm;

[0106] C: δ 29.5-31.0 ppm;

[0107] D: δ 26.2-27.3 ppm;

[0108] E: δ 24.2-24.6 ppm;

[0109] F: δ 10.5-11.7 ppm;

[0110] Based on the above assumptions, according to the defined integral interval, the formula is as follows:

[0111] Molar fraction of butene:

[0112] B mol%={(I B -I A ) / (I B -I A +0.5I C +0.25I D -0.75I F )}×100% Formula (I);

[0113] Molar fraction of ethylene:

[0114] E mol%=100%-B mol% Formula (II);

[0115] Branching rate of high-density polyethylene:

[0116] C bb ={(5I B -5I A ) / (I B -I A +0.5I C +0.25I D -0.75I F )}×1000‰ Formula

[0117] (III);

[0118] For HDPE containing only one type of branch chain, the mole fraction of ethylene is as shown in formula (II). Based on the structural attribution of the spectral peaks and the peak characteristics of the INEPT spectrum in the present invention, the formula for calculating the molar content and branching rate of the branch chain using the INEPT spectrum is as follows:

[0119] Mole fraction of butene:

[0120] B mol%={(I B -1.30I A ) / (I B –1.30I A +0.5I C +0.25I E -0.75I F )}×100%

[0121] Formula (IV);

[0122] Branching rate of high-density polyethylene:

[0123] C bb ={(5I B –6.5I A ) / (I B –1.30I A +0.5I C +0.25I D -0.75I E )}×1000‰

[0124] Formula (V);

[0125] (3.2) According to the above corrected formulas (IV) to (V), calculate Figures 1 to 3 The molar content of butene and the branching rate of the sample in the spectrum shown are compared with the traditional quantitative carbon spectrum of the sample ( Figure 4 ), and the specific values ​​are listed in Table 1.

[0126] Table 1

[0127]

[0128] From the data in Table 1, it can be seen that, using INEPT as the experimental method, the test results obtained by using the modified and corrected branching ratio formula have little difference compared with the results of traditional quantitative carbon spectrum, the experimental errors are all within the acceptable range, and it is proved that the present application can realize accurate determination of the structure of ethylene-butene copolymer type high density polyethylene. From the comparison of experimental time, it is obvious that the experimental time can be greatly saved, and the characterization efficiency is improved. Since the characterization of polyolefins is carried out under high temperature experimental conditions, high purity nitrogen protection is required, and the probe has a large loss. Therefore, the saving of experimental time essentially saves the experimental cost.

[0129] (4) Quantitative limit, detection limit, precision, repeatability, stability experiment.

[0130] (4.1) According to the nuclear magnetic carbon spectrum, the detection concentration when the signal-to-noise ratio S / N is 3 is the corresponding detection limit (LOD), and the detection concentration when the signal-to-noise ratio S / N is 10 is the corresponding quantitative limit (LOQ). The standard solution of HDPE was used for experiment, and the results showed that the LOD of the method was 2.50 mg / mL, and the LOQ was 8.50 mg / mL.

[0131] (4.2) Take the same sample solution, perform INEPT spectrum test according to step (2.1), measure 6 times, and calculate the precision RSD according to formula (V) is 0.95%, which shows that the precision of the method is good.

[0132] (4.3) Six sample solutions were prepared in parallel, and INEPT spectrum test was performed according to step (2.1), and the repeatability RSD calculated according to formula (V) was 2.38%, which showed that the repeatability of the method was good.

[0133] (4.4) Take one HDPE sample solution, perform INEPT spectrum test according to step (2.1) at 0, 2, 4, 8, 24, 48 and 72 hours respectively, and calculate the RSD of the determination results at each time point according to formula (V) is 0.98%, which shows that the stability of the method is good.

[0134] Example 2

[0135] Measurement of branching degree of high density polyethylene represented by ethylene / butene / 1-hexene copolymer:

[0136] (1) Weigh 40 milligrams of high density polyethylene HDPE (S2) represented by ethylene / butene / 1-hexene copolymer, add it to a 5 millimeter nuclear magnetic tube, add appropriate amount of paramagnetic reagent, inject 0.6 mL of deuterated o-dichlorobenzene, and heat to dissolve into a homogeneous polymer solution.

[0137] (2) Optimization of spectrum sampling and data processing parameters

[0138] (2.1) The NMR test was performed according to Example 1, step (2.1), except that the experimental time was changed to 3.5 hours, and each sample was measured 3 times. A typical spectrum is shown in Figure 2. Figure 5 , Figure 5 Figure 2 is an INEPT spectrum of the high density polyethylene of Example 2.

[0139] (2.2) The NMR test was performed according to Example 1, step (2.1), except that the probe was changed to 500 MHz, and the experimental time was changed to 1.0 hour, and each sample was measured 3 times.

[0140] (2.3) The conventional quantitative C NMR spectrum of the HDPE was collected according to Example 1, step (2.4). 13 The spectrum was baseline and phase corrected using NMR spectral analysis software.

[0141] (3) The integral regions were defined according to the four assumptions of Example 1;

[0142] The integral regions were:

[0143] G: δ 23.3-23.5 ppm;

[0144] H: δ 26.6-26.8 ppm;

[0145] I: δ 29.4-29.6 ppm;

[0146] J: δ 29.9-30.1 ppm;

[0147] K: δ 30.4-30.6 ppm;

[0148] L: δ 34.0-34.1 ppm;

[0149] M: δ 34.2-34.3 ppm;

[0150] N: δ 39.6-39.8 ppm;

[0151] For HDPE containing two or more branches, the corresponding monomer content and branching rate calculation formula can be obtained according to the corresponding assignment and spectrum correction, as shown in formula (VI), (VII), (VIII) and (IX):

[0152] Mole fraction of butene:

[0153] B mol% = {(0.333I H + 0.167I L + 0.443I N ) / (0.333I H + 0.167I L + 0.443I N+

[0154] 0.5I G +0.5I M +0.5I J +0.5I K -0.5I I )}×100%Formula (VI);

[0155] Mole fraction of 1-hexene:

[0156] H mol%={(0.5I G +0.5I M )} / (0.333I H +0.167I L +0.443I N +0.5I G +0.5

[0157] I M +0.5I J +0.5I K -0.5I I}×100%Formula (VII);

[0158] Mole fraction of ethylene:

[0159] E mol%=100%-B mol%-H mol% formula (VIII);

[0160] Branching rate of high-density polyethylene:

[0161] C bb ={(3.33I H +1.67I L +4.43I N +5I G +5I M ) / (0.666I H +0.333I L +0.886I N

[0162] +I G +I M +I J +I K -I I )}×1000%Formula (IX);

[0163] The integrated areas of the peaks of the spectra obtained in (2.1) and (2.2) of Example 2 of the present invention were similarly substituted into formulas (VI) to (IX) to calculate the component content and branching rate of the high-density polyethylene HDPE (S2), and compared with the calculated results of the traditional quantitative carbon spectrum of the sample, as shown in Table 2.

[0164] Table 2

[0165]

[0166] The above description is merely that of the preferred embodiments of the present application, but the present application is not limited thereto. Any modifications and changes made in the scope of the technical range disclosed in the present application based on the technical idea of the present application and the inventive concept thereof should be construed as falling within the scope of the present application.

Claims

1. A rapid analysis method for high-density polyethylene structure, characterized in that: The following steps are involved: S1) obtaining an INEPT spectrum of the pretreated high-density polyethylene and defining an integration interval, then assigning and integrating peaks of the INEPT spectrum according to the integration interval, and obtaining a monomer content formula and a branching ratio formula for the high-density polyethylene according to the integration interval; When the high-density polyethylene contains only one type of branched chain, the integral interval is: A: δ38.5~41.5ppm; B: δ33.8~34.8ppm; C: δ29.5~31.0ppm; D: δ26.2~27.3ppm; E: δ24.2~24.6ppm; F: δ10.5~11.7ppm; When the high-density polyethylene contains two or more branched chains, the integral interval is: G: δ23.3~23.5ppm; H: δ26.6~26.8ppm; I: δ29.4~29.6ppm; J: δ29.9~30.1ppm; K: δ30.4~30.6ppm; L: δ34.0~34.1ppm; M: δ34.2~34.3ppm; N: δ39.6~39.8ppm; S2) correcting the monomer content formula according to the result of the attribution in step S1) to obtain a monomer content correction formula, and obtaining the monomer content of the high-density polyethylene according to the monomer content correction formula and the result of the integration in step S1); The branching rate formula is corrected according to the result of the attribution in step S1) to obtain a branching rate correction formula, and the branching rate of the high-density polyethylene is obtained according to the branching rate correction formula and the result of the integration in step S1).

2. The method according to claim 1, characterized in that In step S1), the pretreated high-density polyethylene is obtained from the high-density polyethylene, a paramagnetic agent and deuterated tetrachloroethane.

3. The method according to claim 1, characterized in that In step S1), the sampling parameters of the INEPT spectrogram include: d1=1~10s, cnst2=100~200Hz, cnst8=100~150Hz.

4. The method according to claim 3, characterized in that In step S1), the sampling parameters of the INEPT spectrogram further include: td=16~64k, ns=128~5000, ds=4~16, sw=50~250ppm, d3=0.0005~0.0015s, O1P=10~40ppm.

5. The method according to claim 3, characterized in that In step S1), the sampling parameters of the INEPT spectrogram further include: The experimental temperature is 80-150°C, and the experimental time is 0.3-5h.

6. The rapid analysis method of high-density polyethylene structure according to claim 1, characterized in that: In step S1), after obtaining the INEPT spectrum, the method further includes performing baseline calibration and phase calibration on the INEPT spectrum.

7. The method according to claim 1, characterized in that In step S1), the definition of the integral interval is performed under the assumption that: Assumption 1: The weight average molecular weight of the high-density polyethylene is less than 1 million; Assumption 2: If the HDPE has terminal end groups, the terminal end groups are not included in the calculation; Assumption 3: The signal-to-noise ratio of the INEPT spectrum is greater than 400; Assumption 4: The branch content of the high-density polyethylene is less than 1%, and there is no sequence of continuous branched chains.

8. The method according to claim 1, characterized in that In step S2), the monomer content formula is corrected according to the result of the attribution: The monomer content formula is corrected by multiplying the calibration factor by comparing the results of the high-temperature quantitative carbon spectrum experiment; The branching rate formula corrected according to the attribution result is specifically: The branching rate formula was corrected by multiplying the calibration factor by comparing the experimental results of high-temperature quantitative carbon spectrum.

9. The method according to any one of claims 1 to 8, characterized in that: In step S2), when the high-density polyethylene contains only one type of branched chain, the monomer content calculation formula of the high-density polyethylene is include: B mol% = { ( I B - 1.30I A ) / ( I B – 1.30I A + 0.5I C + 0.25I E - 0.75I F )} × 100% Equation 1; E mol% = 100% - B mol% Formula 2; When the high-density polyethylene contains two or more branched chains, the monomer content calculation formula of the high-density polyethylene includes: B mol%={(0.333I H +0.167I L +0.443I N ) / (0.333I H +0.167I L +0.443I N + 0.5I G +0.5I M +0.5I J +0.5I K -0.5I I )}×100% Formula 3; H mol%={(0.5I G +0.5I M )} / (0.333I H +0.167I L +0.443I N +0.5I G +0.5 I M +0.5I J +0.5I K -0.5I I }×100% formula 4; E mol% = 100% - B mol% - H mol% Formula 5; Wherein, B mol% represents the molar content of the butene monomer of the high-density polyethylene, H mol% represents the molar content of the 1-hexene monomer of the high-density polyethylene, E mol% represents the molar content of the ethylene monomer of the high-density polyethylene, and I A , I B , I C , I E , I F , I G , I H , I I , I J , I K , I L , I M and I N They represent the integrated areas of the spectral peaks in the integration intervals A, B, C, E, F, G, H, I, J, K, L, M and N respectively.

10. The method according to any one of claims 1 to 8, characterized in that: In step S2), when the high-density polyethylene contains only one type of branched chain, the branching rate calculation formula of the high-density polyethylene includes: C bb = { (5I B – 6.5I A ) / (I B – 1.30I A + 0.5 I C + 0.25 I D - 0.75 I E )}×1000 ‰ Equation 6; When the high-density polyethylene contains two or more branched chains, the branching rate calculation formula of the high-density polyethylene includes: C bb = {(3.33I H + 1.67I L + 4.43I N + 5I G + 5I M ) / (0.666I H + 0.333I L + 0.886I N + I G + I M + I J + I K - I I )} × 1000% Formula 7; Among them, C bb Represents the branching rate of the high-density polyethylene, I A , I B , I C , I D , I E , I G , I H , I I , I J , I K , I L , I M and I N They represent the integrated areas of the spectral peaks in the integration intervals A, B, C, D, E, G, H, I, J, K, L, M and N respectively.

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