Evaluation method for consistency of vinyl polymer and application of evaluation method

Abstract

The invention relates to the field of polymer structure analysis, and discloses a vinyl polymer consistency evaluation method and application thereof. The evaluation method comprises the following steps: grading a vinyl polymer solution to be evaluated to obtain n fractions Si; performing a first test on the fraction Si to obtain a structural parameter Ji of a molecular chain, and calculating according to a formula (1) to obtain a first abnormal index Pi; # imgabs0 # formula (1); wherein JB is the standard value of the structure parameter Ji of the molecular chain of the ith fraction Si; when the first anomaly index Pi exceeds a threshold value, it is indicated that the ith fraction is an abnormal fraction. According to the evaluation method, the vinyl polymer is divided into a plurality of fractions by performing grading treatment on the vinyl polymer, and fine recognition of structural differences is realized by comparing structural parameters of molecular chains of the fractions respectively.

Description

Technical Field

[0001] The present invention relates to the field of polymer structure analysis, and in particular to a method for evaluating the consistency of vinyl polymers and an application thereof. Background Art

[0002] As a key insulating base material for high-voltage cables, the molecular structure consistency of vinyl polymers, both within and between batches, directly impacts cable processing and electrical performance stability. Currently, the molecular chain structure of vinyl polymers is primarily evaluated using methods such as high-temperature gel permeation chromatography (GPC), infrared spectroscopy (FTIR), and nuclear magnetic resonance (NMR).

[0003] However, because polymer materials are mixtures with a certain molecular weight distribution, directly using the above methods to measure them can only obtain a statistical average result of the mixture, which cannot reflect the microstructural differences between different molecular weight fractions. These subtle differences in molecular structure can lead to significant fluctuations in macroscopic properties. For example, although the total branching degree of LDPE can be measured by FTIT or NMR, the distribution of branching degree, branching sites, and branch chain length in different molecular weight fractions can vary significantly. This fine structural consistency cannot be characterized by existing evaluation methods. Summary of the Invention

[0004] The purpose of the present invention is to overcome the problems existing in the prior art and provide a method for evaluating the consistency of vinyl polymers and its application. The evaluation method performs a graded treatment on the vinyl polymer to split it into multiple fractions, and achieves refined identification of structural differences by comparing the structural parameters of the molecular chains of each fraction.

[0005] In order to achieve the above object, the first aspect of the present invention provides a method for evaluating the consistency of vinyl polymers, the evaluation method comprising: The vinyl polymer solution to be evaluated is fractionated to obtain n fractions Si; The first test is performed on the fraction Si to obtain the structural parameter Ji of the molecular chain, and the first abnormal index Pi is calculated according to the formula (1); Formula (1); Among them, J B is the standard value of the structural parameter Ji of the molecular chain of the i-th fraction Si; When the first abnormality index Pi exceeds a threshold, it indicates that the i-th grade is an abnormal grade.

[0006] The second aspect of the present invention provides the use of the aforementioned evaluation method in the production of vinyl polymers.

[0007] Through the above technical solution, the present invention can achieve at least the following beneficial effects: The evaluation method provided by the present invention can accurately identify abnormal fractions that cause differences by fractionating vinyl polymers into multiple fractions and comparing the differences between the structural parameters of the molecular chains of each fraction and the standard values. Furthermore, the evaluation method provided by the present invention is used in the production of vinyl polymers to provide guidance information for the production of vinyl polymers. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] Figure 1 It is a schematic flow chart of the evaluation method of the present invention. DETAILED DESCRIPTION

[0009] The endpoints of the ranges and any values ​​disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoints of each range, the endpoints of each range and individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered to be specifically disclosed herein.

[0010] In the present invention, the vinyl polymer refers to ethylene or vinyl-containing ( ) is a type of polymer obtained by polymerization of monomers, including polymers obtained by self-polymerization of one monomer and copolymers obtained by copolymerization of more than one monomer.

[0011] In the present invention, the molecular chain structure of the vinyl polymer has the conventional interpretation in the field, including both the macroscopic structural properties of the polymer and the composition and connection mode of the polymer molecular chain, etc., which are usually reflected by structural parameters such as mass, density, weight-average molecular weight, number-average molecular weight, molecular weight distribution, degree of branching, double bond content, comonomer content and crystallinity.

[0012] A first aspect of the present invention provides a method for evaluating the consistency of a vinyl polymer, the method comprising: The vinyl polymer solution to be evaluated is fractionated to obtain n fractions Si; The first test is performed on the fraction Si to obtain the structural parameter Ji of the molecular chain, and the first abnormal index Pi is calculated according to the formula (1); Formula (1), where J B is the standard value of the structural parameter Ji of the molecular chain of the i-th fraction Si; When the first abnormality index Pi exceeds a threshold, it indicates that the i-th grade is an abnormal grade.

[0013] The present invention fractionates vinyl polymers into multiple fractions and compares the structural parameters of the molecular chains in each fraction. Compared to traditional evaluation methods, the present method can achieve refined identification of structural differences and accurately locate abnormal structural points.

[0014] In the present invention, the number n of graded fractions can be selected according to the accuracy requirement of the evaluation.

[0015] According to the present invention, preferably, 4≤n≤12.

[0016] In the present invention, the number of fractions n is within the above range, which can collect as much of the vinyl polymer in the solution as possible while meeting the accuracy of the consistency evaluation, thereby reducing the analysis error.

[0017] More preferably, 4≤n≤9.

[0018] According to the present invention, the standard value J B is the structural parameter Ji of the i-th fraction Si in the qualified batch of vinyl polymer.

[0019] In the present invention, qualified batches of vinyl polymers in the production process are used as standard samples, and the structural parameters of the sample to be evaluated are compared with them, which can accurately determine the difference sites between the sample to be evaluated and the qualified batches of vinyl polymers. Furthermore, this method can be applied to correcting production processes.

[0020] According to the present invention, the standard value J B is the structural parameter Ji of the i-th fraction Si in the vinyl polymer obtained by an unknown process.

[0021] In the present invention, the vinyl polymer obtained by the unknown process is used as a standard sample, and the structural parameters of the sample to be evaluated are compared with it. The difference sites based on the molecular chain structure can be located to the difference sites of the production process, which can guide the adjustment and optimization of the production process.

[0022] In the present invention, the purpose of the classification is to classify the vinyl polymer based on different molecular chain structures to obtain a fraction with a specific molecular chain structure within a specific range. Preferably, in the present invention, the vinyl polymer is classified based on different crystallinity or weight-average molecular weight.

[0023] According to the present invention, preferably, the fractionation method is a temperature-increasing fractionation elution method and / or a gel permeation chromatography column separation method.

[0024] Further preferably, the classification method is a temperature-increasing classification elution method.

[0025] In the present invention, the flow rate, cooling rate, elution heating rate and type of eluent of the vinyl polymer solution in the temperature-increasing fractional elution method are not particularly limited, as long as the fractionation purpose of the present invention can be achieved.

[0026] In some specific embodiments of the present invention, the conditions of the temperature-rising fractional elution method include: the eluent is xylene, the cooling rate is 0.5-2°C / min, the elution heating rate is 1-3°C / min, the elution flow rate is 1-5mL / min, the insulation time of each fraction at the collection temperature is 5-15h, and the elution time is 0.5-6h.

[0027] In some specific embodiments of the present invention, the initial collection temperature is 30±5°C, and the final collection temperature is 85±5°C.

[0028] In the present invention, when the temperature-increasing fractional elution method is used for fractionation, the slice temperature difference can be selected according to the number of desired components, for example, it can be 5-10°C; wherein the slice temperature difference is the difference between the collection temperatures of two adjacent fractions.

[0029] According to the present invention, preferably, the structural parameter is selected from at least one of mass, density, weight average molecular weight, number average molecular weight, molecular weight distribution, degree of branching, double bond content, comonomer content and crystallinity.

[0030] The method provided by the present invention can specifically evaluate the consistency of different vinyl polymer structural parameters. Since the influence of each structural parameter on the molecular chain structure or its macroscopic properties varies, the threshold for judging abnormal fractions is also different.

[0031] According to the present invention, when the molecular chain structure parameter is molecular weight distribution: The threshold of Pi is ±10%.

[0032] According to the present invention, when the molecular chain structure parameter is the weight average molecular weight; The threshold of Pi is ±10%.

[0033] According to the present invention, when the molecular chain structure parameter is mass; The threshold of Pi is ±10%.

[0034] According to the present invention, when the molecular chain structure parameter is the degree of branching: The threshold of Pi is ±10%.

[0035] According to the present invention, when the molecular chain structure parameter is the double bond content; The threshold of Pi is ±5%.

[0036] According to the present invention, the method further comprises: testing the fraction Si to obtain the structural parameter Ji of the molecular chain, and calculating the homogeneity index according to the formula (2): w ; Formula (2); Wherein, J0 is calculated according to formula (3); Formula (3) Wherein, a and b are integers, and 1≤a<b≤n; When the uniformity coefficient does not exceed the threshold, it indicates that the structural parameters Ji in different fractions Si are uniformly distributed; The structural parameter Ji is selected from at least one of the degree of branching, double bond content, and comonomer content.

[0037] In the present invention, the method of the present invention can also determine the uniformity of a specific molecular chain structure parameter between different fractions of the vinyl polymer, and further determine whether the vinyl polymer has molecular structure defects and whether the production process is stable and controllable.

[0038] In the present invention, since the influence of various structural parameters on the molecular chain structure or its macroscopic properties varies, the criteria for determining the uniformity coefficient also vary. A smaller uniformity coefficient indicates a more uniform distribution of the structural parameter among certain fractions, while a larger uniformity coefficient indicates a more dispersed distribution of the structural parameter among certain fractions.

[0039] In some specific embodiments of the present invention, when the molecular chain structure parameter is the double bond content: Homogeneity index w The threshold value is 10%. That is, when the homogeneity index of double bond content is between 0-10%, it is considered that the double bond content is evenly distributed among the various fractions.

[0040] According to the present invention, the method further comprises: performing a second classification on the fractions whose first abnormality index does not exceed the threshold value to obtain m fractions Sj; Perform a second test on the fraction Sj to obtain the molecular chain structure parameter Jj and calculate the second anomaly index Pj; The calculation method of the abnormality index Pj is: ; Among them, J B ' is the standard value of the structural parameter Jj of the molecular chain of the jth fraction Sj; When the second abnormality index Pj exceeds the threshold, it indicates that the mth grade is an abnormal grade.

[0041] In the present invention, J B' is the structural parameter Jj of the jth fraction Sj in a qualified batch of vinyl polymer or the structural parameter Jj of the jth fraction Sj in a vinyl polymer obtained by an unknown process.

[0042] In the present invention, the second fractionation method differs from the first fractionation method in order to further separate fractions whose first abnormality index does not exceed the threshold value based on different molecular chain structural characteristics. For example, when the first fractionation utilizes a temperature-increasing fractionation elution method, the second fractionation method may utilize temperature-increasing fractionation elution conditions different from those used for the first fractionation, or may utilize gel permeation chromatography column separation for separation.

[0043] In the present invention, for the fractions whose first abnormality index does not exceed the threshold, the fractions are subjected to second classification and second abnormality index calculation, which can further separate the fractions and locate the structural differences more precisely.

[0044] In the present invention, since the influence of each structural parameter on the molecular chain structure or its macroscopic properties is different, the threshold value of the second abnormal index is also different. For example, the threshold value of Pj and the threshold value of Pi can be the same or different.

[0045] According to the present invention, preferably, the vinyl polymer is at least one selected from low-density polyethylene, ethylene-ethyl acrylate copolymer, ethylene-butyl acrylate copolymer and ethylene-vinyl acetate copolymer.

[0046] In the present invention, the solvent in the vinyl polymer solution is a conventional choice in the art, as long as it can dissolve the vinyl polymer.

[0047] In one embodiment of the present invention, the solvent in the vinyl polymer solution is xylene.

[0048] In one embodiment of the present invention, the evaluation method comprises: fractionating the low-density polyethylene solution to be evaluated by a temperature-increasing fractional elution method to obtain 8-10 fractions Si; The first test is performed on the fraction Si to obtain the structural parameter Ji of the molecular chain, and the first abnormal index Pi is calculated according to the formula (1); Ji is the weight average molecular weight, molecular weight distribution and mass; Formula (1), where J B is the structural parameter Ji of the i-th fraction Si in the qualified batch of vinyl polymer; The threshold of Pi is ±10%; When the first abnormality index Pi of at least one structural parameter Ji exceeds a threshold, it indicates that the i-th grade is an abnormal grade.

[0049] In one embodiment of the present invention, the evaluation method comprises: fractionating the low-density polyethylene solution to be evaluated by a temperature-increasing fractional elution method to obtain 8-10 fractions Si; The first test is performed on the fraction Si to obtain the structural parameter Ji of the molecular chain, and the first abnormal index Pi is calculated according to the formula (1); Ji is the weight average molecular weight and the degree of long chain branching; Formula (1), where J B is the structural parameter Ji of the i-th fraction Si in the vinyl polymer obtained by an unknown process; The threshold of Pi is ±10%; When the first abnormality index Pi of at least one structural parameter Ji exceeds a threshold, it indicates that the i-th grade is an abnormal grade.

[0050] In one embodiment of the present invention, the evaluation method comprises: fractionating the low-density polyethylene solution to be evaluated by a temperature-increasing fractional elution method to obtain 4-6 fractions Si; The first test is performed on the fraction Si to obtain the structural parameter Ji of the molecular chain, and the first abnormal index Pi is calculated according to the formula (1); Ji is the weight average molecular weight and double bond content; Formula (1), where J B is the structural parameter Ji of the i-th fraction Si in the vinyl polymer obtained by an unknown process; When Ji is the weight-average molecular weight, the threshold of Pi is ±10%, and when Ji is the double bond content, the threshold of Pi is ±5%; When the first abnormality index Pi of at least one structural parameter Ji exceeds a threshold, it indicates that the i-th grade is an abnormal grade.

[0051] In the present invention, the long-chain branching degree refers to the branching degree of the branches with more than 6 carbon atoms in the vinyl polymer. In the present invention, the long-chain branching degree is obtained by testing the number of branches with more than 6 carbon atoms per 1000 carbon atoms on the vinyl polymer molecular chain, and the testing method is nuclear magnetic resonance spectroscopy.

[0052] The second aspect of the present invention provides the use of the aforementioned evaluation method in the production of vinyl polymers.

[0053] In the present invention, the evaluation method of the present invention is applied to the production of vinyl polymers, and the process can be as follows: Figure 1 As shown, the vinyl polymer that does not meet the performance evaluation standards is prepared into a vinyl polymer solution and fractionated to obtain n fractions Si; The first test is performed on the fraction Si to obtain the structural parameter Ji of the molecular chain, and the first abnormal index Pi is calculated according to the formula (1); Formula (1); Among them, J B is the standard value of the structural parameter Ji of the molecular chain of the i-th fraction Si; When the first abnormality index Pi exceeds a threshold, it indicates that the i-th grade is an abnormal grade.

[0054] Abnormal fractions are judged as abnormal sites that cause vinyl polymers to fail to meet standards. By locating and analyzing the abnormal fractions and tracing them back to the production process, the production process of vinyl polymers can be corrected and optimized, and further, qualified products that meet standards can be obtained.

[0055] When the first abnormality index Pi does not exceed the threshold, the fractions whose first abnormality index does not exceed the threshold can be subjected to a second classification to obtain m fractions Sj; Perform a second test on the fraction Sj to obtain the molecular chain structure parameter Jj and calculate the second anomaly index Pj; The calculation method of the abnormality index Pj is: ; Among them, J B ' is the standard value of the structural parameter Jj of the molecular chain of the jth fraction Sj.

[0056] The abnormal structural sites can be further located and analyzed through the second classification and the second abnormal index calculation.

[0057] The present invention will be described in detail below through examples. It should be understood that the following examples are only used to further explain and illustrate the present invention, and are not intended to limit the present invention.

[0058] Unless otherwise specified, the reagents and materials used in the following examples were purchased from regular chemical reagent suppliers and were of analytical grade.

[0059] Example 1 A qualified batch of low-density polyethylene is used as a standard product and is recorded as LDPE-B1; A batch of low-density polyethylene in the production process is recorded as LDPE-A1.

[0060] 10g each of LDPE-B1 and LDPE-A1 were dissolved in 500mL of xylene and fractionated using a temperature-increasing fractionation elution method. Using xylene as the eluent, the cooling rate was set at 1°C / min, the elution heating rate was set at 2°C / min, and the elution flow rate was set at 4mL / min. After cooling to room temperature, the temperature was increased. Each collection temperature was maintained for 12h, followed by elution for 4h. Fractions collected at 30°C, 35°C, 45°C, 55°C, 65°C, 70°C, 75°C, 80°C, and 85°C were evaporated to remove the solvent, yielding a total of nine fractions, S1-S9. Each fraction was weighed, and its weight-average molecular weight (Mw) and molecular weight distribution (PDI) were determined using high-temperature GPC.

[0061] The structural parameters of each fraction are shown in Table 1.

[0062] Table 1

[0063] According to the abnormal index P, it can be seen that the abnormal fraction is mainly reflected in the ultra-high molecular weight range of S7-S9.

[0064] Example 2 The low-density polyethylene obtained by an unknown process was used as a standard product and was recorded as LDPE-B2; A batch of low-density polyethylene in the production process is recorded as LDPE-A2.

[0065] 10 g of each LDPE-B2 and LDPE-A2 were dissolved in 500 mL of xylene and fractionated using the temperature-increasing fractionation elution method. The fractionation method was the same as in Example 1. Fractions obtained at 30°C, 35°C, 45°C, 55°C, 65°C, 70°C, 75°C, and 80°C were collected and evaporated to remove the solvent, yielding a total of 8 fractions S1-S8. The weight-average molecular weight (Mw) of each fraction was determined by high-temperature GPC. The weight-average molecular weight (Mw) of each fraction was determined by carbon nuclear magnetic resonance spectroscopy (C NMR). 13 C-NMR) was used to test the long chain branching degree of each fraction.

[0066] The structural parameters of each fraction are shown in Table 2.

[0067] Table 2

[0068] According to the abnormal index P, it can be seen that the abnormal fraction is mainly reflected in the low molecular weight range of S1-S3.

[0069] Example 3 The low-density polyethylene obtained by an unknown process was used as a standard product and was recorded as LDPE-B3; A batch of low-density polyethylene in the production process is recorded as LDPE-A3.

[0070] 10 g of each LDPE-B3 and LDPE-A3 were dissolved in 500 mL of xylene and fractionated using the temperature-increasing fractionation elution method, using the same method as in Example 1. Xylene was used as the eluent. Fractions obtained at 55°C, 65°C, 70°C, and 75°C were collected and evaporated to remove the solvent, yielding four fractions, S1-S4. The weight-average molecular weight (Mw) of each fraction was determined by high-temperature GPC. The molecular weight (Mw) of each fraction was determined by H NMR spectroscopy ( 1 H-NMR) was used to determine the double bond content of each fraction.

[0071] The structural parameters of each fraction are shown in Table 3.

[0072] Table 3

[0073] According to the anomaly index P, compared with LDPE-B3, the abnormal structural parameters of LDPE-A3 are mainly reflected in the double bond content, especially in fractions S2-S4. And according to the uniformity index w, it can be seen that the double bonds between each fraction of LDPE-B3 are evenly distributed, while the uniformity of the double bond content between each fraction of LDPE-A3 is poor.

[0074] The preferred embodiments of the present invention have been described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, various simple variations of the technical solution of the present invention may be made, including combining the various technical features in any other appropriate manner. These simple variations and combinations should also be regarded as disclosed in the present invention and fall within the scope of protection of the present invention.

Claims

1. A method for evaluating the consistency of vinyl polymers, characterized in that: The evaluation method includes: The vinyl polymer solution to be evaluated is fractionated to obtain n fractions Si; The first test is performed on the fraction Si to obtain the structural parameter Ji of the molecular chain, and the first abnormal index Pi is calculated according to the formula (1); Formula (1); Among them, J B is the standard value of the structural parameter Ji of the molecular chain of the i-th fraction Si; When the first abnormality index Pi exceeds a threshold, it indicates that the i-th grade is an abnormal grade.

2. The evaluation method according to claim 1, wherein 4≤n≤12。 3. The evaluation method according to claim 1 or 2, wherein The standard value J B is the structural parameter Ji of the i-th fraction Si in the qualified batch of vinyl polymer; Alternatively, the standard value J B is the structural parameter Ji of the i-th fraction Si in the vinyl polymer obtained by an unknown process.

4. The evaluation method according to claim 1 or 2, wherein The classification method is a temperature-increasing classification elution method and / or a gel permeation chromatography column separation method.

5. The evaluation method according to claim 1 or 2, wherein: The structural parameter is selected from at least one of mass, density, weight average molecular weight, number average molecular weight, molecular weight distribution, degree of branching, double bond content, comonomer content and crystallinity.

6. The evaluation method according to claim 5, wherein: When the molecular chain structure parameter is molecular weight distribution; The threshold of Pi is ±10%; and / or, when the molecular chain structure parameter is weight average molecular weight; The threshold of Pi is ±10%; and / or, when the molecular chain structure parameter is mass; The threshold of Pi is ±10%.

7. The evaluation method according to claim 5, wherein: When the molecular chain structure parameter is the degree of branching; The threshold of Pi is ±10%.

8. The evaluation method according to claim 5, wherein: When the molecular chain structure parameter is the double bond content; The threshold of Pi is ±5%.

9. The evaluation method according to claim 5, wherein: The method further comprises: testing the fraction Si to obtain the structural parameter Ji of the molecular chain, and calculating the homogeneity index according to the formula (2): w ; Formula (2); Wherein, J0 is calculated according to formula (3); Formula (3) Wherein, a and b are integers, and 1≤a<b≤n; When the uniformity coefficient does not exceed the threshold, it indicates that the structural parameters Ji in different fractions Si are uniformly distributed; The structural parameter Ji is selected from at least one of the degree of branching, double bond content and comonomer content.

10. The evaluation method according to claim 1 or 2, wherein: The method further includes: performing a second classification on the fractions whose first abnormality index does not exceed the threshold value to obtain m fractions Sj; The fraction Sj is tested to obtain the molecular chain structure parameter Jj and the second abnormal index Pj is calculated; The calculation method of the abnormality index Pj is: ； Among them, J B ' is the standard value of the structural parameter Jj of the molecular chain of the jth fraction Sj; When the second abnormality index Pj exceeds the threshold, it indicates that the mth grade is an abnormal grade.

11. The evaluation method according to claim 1 or 2, wherein: The vinyl polymer is at least one selected from the group consisting of low-density polyethylene, ethylene-ethyl acrylate copolymer, ethylene-butyl acrylate copolymer, and ethylene-vinyl acetate copolymer.

12. Use of the evaluation method according to any one of claims 1 to 11 in the production of vinyl polymers.

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