A method for determining the 1,4 structure content in liquid isoprene rubber.

Abstract

This invention relates to a method for determining the 1,4 structure content in liquid isoprene rubber. The method involves obtaining the absorbance of the 1,4 and 3,4 structures in the liquid isoprene rubber using infrared spectroscopy, and then substituting the absorbance values ​​into the following formula to calculate the percentage content of the 1,4 structure. 1,4 =100 × 8.03A 836 / (7.83A 836 +A 888 )%; of which, W 1,4 Represents the percentage content of the 1,4 structure, A 836 and A 888 These represent the corrected absorbance values ​​for structures 1,4 and 3,4 in the infrared spectrum, respectively. Compared with existing technologies, the detection method of this invention is simple to operate, environmentally friendly, and produces highly accurate results, providing a new method for the analysis of 1,4 structures in LIR.

Description

Technical Field

[0001] This invention relates to the field of detection technology, and in particular to a method for determining the 1,4 structure content in liquid isoprene rubber. Background Technology

[0002] Liquid polyisoprene rubber (LIR) is a low molecular weight liquid polymer with isoprene as the repeating unit. It is viscous and fluid at room temperature. During rubber processing, LIR replaces aromatic oils and participates in crosslinking reactions during vulcanization, co-crosslinking with non-polar rubbers such as natural rubber. It is a highly promising "reactive plasticizer." LIR possesses characteristics such as low relative molecular mass, low glass transition temperature, colorless and odorless, transparent, and free of residual halogens. It can be used as a plasticizer for solid rubber, in adhesives, electrical insulation materials, resin modification, and sealing materials.

[0003] The microstructure of rubber oxidants (LIRs) mainly includes 1,4-structures (including cis and trans), 3,4-structures, and 1,2-structures. Differences in structure and content lead to variations in performance and applications. Currently, the majority of LIRs produced and used are of the 1,4-structure, primarily because a higher 1,4-structure content results in a product structure closer to that of natural rubber, leading to better performance as a rubber processing plasticizer. Therefore, rapid and accurate determination of the 1,4-structure content will help understand the impact of LIRs on rubber processing properties, facilitate quality control of LIR products, and better guide their application.

[0004] Currently, the determination of the 1,4 structure and its content in LIR is mainly done by nuclear magnetic resonance (NMR) and infrared spectroscopy. NMR can identify and quantify the 1,4 structure (including cis and trans), 3,4 structure and 1,2 structure in LIR. The analytical results are accurate and have been used as a standard for determining the content of microstructures in LIR (see SH / T 1832-2020 Determination of Microstructure of Isoprene Rubber by NMR 1H Spectroscopy). However, the NMR method is complex to operate, requires the use of deuterated reagents, and has a high detection cost, which is not conducive to the detection and analysis of large batches of samples. Su Zhongkui et al. (see Su Zhongkui, Chen Xiaoli, Hou Hongxia, et al. Synthesis and structural characterization of novel liquid polyisoprene rubber [J]. Shandong Chemical Industry, 2018, 47(12):35-37.) discovered an infrared spectroscopy method to determine the content of the 1,4 structure in LIR. This method requires the use of CS2 as a solvent for dissolution and coating testing. The pretreatment is complex and uses toxic, harmful and volatile reagents, which does not meet the requirements of green environmental protection. The method for determining the content of 1,4 structure in LIR provided by He Xiaojin et al. (see He Xiaojin, Kang Xinhe, Liu Hui, et al. Synthesis and structural characterization of liquid isoprene rubber [J]. Elastomers, 2011, 21(02): 32-35.) involves directly coating the LIR solution onto a KBr glass slide and determining it using infrared spectroscopy. The method for calculating the content of 1,4 structure is to directly integrate the characteristic peak area. The calculation method itself is subject to randomness and differs significantly from the results obtained by nuclear magnetic resonance.

[0005] Therefore, there is an urgent need to develop a simple, rapid and accurate detection method to determine the content of 1,4 structure in LIR. Summary of the Invention

[0006] The purpose of this invention is to provide a method for determining the 1,4 structure content in liquid isoprene rubber, which is simple to operate, environmentally friendly, and produces highly accurate test results.

[0007] The objective of this invention can be achieved through the following technical solution: a method for determining the content of 1,4 structure in liquid isoprene rubber (LIR), wherein the absorbance of 1,4 structure and 3,4 structure in liquid isoprene rubber is obtained by infrared spectroscopy, and the absorbance value is substituted into formula I for calculation to obtain the percentage content of 1,4 structure.

[0008] W 1,4 =100 × 8.03A 836 / (7.83A 836 +A 888 Formula I;

[0009] Among them, W 1,4 Represents the percentage content of the 1,4 structure, A 836 and A888 Representing 836±2cm in the infrared spectrum respectively -1 (corresponding to structures 1 and 4) and 888±1cm -1 Corrected absorbance values ​​at (corresponding to structures 3 and 4). Unless otherwise specified, all 836 cm⁻¹ values ​​below are corrected absorbance values. -1 and 888cm -1 All points are located at 836±2cm -1 and 888±1cm -1 scope.

[0010] Preferably, the method for determining the 1,4 structure content in the liquid isoprene rubber specifically includes the following steps:

[0011] (1) Liquid isoprene rubber was directly coated onto a KBr glass slide, and infrared spectroscopy was used to measure the position at 836 cm⁻¹. -1 and 888cm -1 Corrected absorbance value A at the location 836 and A 888 ;

[0012] (2) Take the A obtained in step (1) 836 and A 888 Substituting into Equation I, we obtain the percentage content of the 1,4 structure.

[0013] More preferably, the infrared spectroscopy test in step (1) is performed using a Fourier transform infrared spectrometer. A clean and dry KBr glass slide is used as the background for scanning. Then, liquid isoprene rubber is directly coated onto the KBr glass slide and scanned under the same test conditions. After scanning, the spectrum after background subtraction is recorded.

[0014] More preferably, in step (1), the spectrum after background subtraction is observed at 836 cm⁻¹. -1 Is the absorbance of the absorption peak at 836 cm⁻¹ between 0.1 and 0.9? -1 The absorbance at the absorption peak is less than 0.1, so liquid isoprene rubber is added to thicken it; if 836 cm⁻¹ -1 If the absorbance of the absorption peak is higher than 0.9, clean the KBr slide and recoat it.

[0015] More preferably, the KBr glass slide in step (1) is 25mm (diameter) × 4mm (thickness) and needs to be dried at 100-110℃ for 10-20min before testing.

[0016] More preferably, the scanning wavenumber for the infrared spectroscopy test in step (1) is 1000–650 cm⁻¹. -1 32 scans, 4cm resolution -1 .

[0017] Preferably, the liquid isoprene rubber does not contain 1,2 structural units, that is, the LIR does not contain 1,2 structural units, which can be determined by the SH / T 1832-2020 determination of the microstructure of isoprene rubber by proton nuclear magnetic resonance spectroscopy.

[0018] More preferably, the percentage content of the 3,4 structure in the liquid isoprene rubber is obtained according to Formula II:

[0019] W 3,4 =100% - W 1,4 Formula II;

[0020] Among them, W 3,4 This represents the percentage content of the 3,4 structure, which is the percentage content of the 3,4 structure calculated when the LIR does not contain the 1,2 structure.

[0021] When the LIR does not contain the 1,2 structure, the percentage content of the 3,4 structure can be calculated according to Equation II.

[0022] Preferably, the infrared spectroscopy test includes attenuated total reflectance infrared spectroscopy test or transmission infrared spectroscopy test.

[0023] More preferably, the infrared spectroscopy test is a transmission infrared spectroscopy test. Since the overall intensity of the reflection spectrum is much smaller than that of the transmission spectrum, and the reflection spectrum is affected by the different absorption of infrared light by the crystal material at different wavelengths, it needs to be corrected before analysis to ensure the accuracy of the conclusions. Therefore, transmission infrared spectroscopy is preferred.

[0024] More preferably, the infrared spectroscopy test is a Fourier transform infrared spectroscopy test.

[0025] Preferably, the corrected absorbance value A 836 and A 888 To select 908-780cm -1 The absorbance value is obtained by subtracting the values ​​from the straight line between them, which serves as the baseline.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] 1. The detection method of the present invention is simple to operate, environmentally friendly, and has excellent accuracy, providing a new method for the analysis of 1,4 structure in LIR.

[0028] 2. The detection results obtained by the detection method provided by the present invention are compared with the absolute quantitative results measured by nuclear magnetic resonance method. The error is only within 0.6%. Moreover, the method of the present invention has high sensitivity for detecting changes in LIR microstructure and can meet the requirements of analytical accuracy and large-scale detection.

[0029] 3. The method of the present invention can be directly tested without the need for pretreatment such as dissolving the sample, which significantly improves the testing efficiency. In addition, the accuracy of the data results obtained by using the formula of the present invention is also greatly improved. Attached Figure Description

[0030] Figure 1 This is the transmission infrared spectrum obtained from the test in Example 1 of the present invention.

[0031] Figure 2 This is the transmission infrared spectrum obtained from the test in Example 2 of the present invention.

[0032] Figure 3 This is the transmission infrared spectrum obtained from the test in Example 3 of the present invention.

[0033] Figure 4 This is the attenuated total reflectance infrared spectrum obtained from the test in Example 4 of the present invention. Detailed Implementation

[0034] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. These embodiments are based on the technical solution of the present invention and provide detailed implementation methods and specific operating procedures. However, the scope of protection of the present invention is not limited to the following embodiments.

[0035] Unless otherwise specified, the reagents, methods, instruments, and equipment used in this invention are conventional in the art. Unless otherwise specified, the reagents and materials used in the following examples are all commercially available.

[0036] The LIR spectrometers described in the following examples were synthesized using isoprene as the monomer, n-butyllithium as the initiator, and cyclohexane as the solvent via a living anionic polymerization process. In Example 1, a small amount of tetrahydrofuran was added as a structure modifier. This invention is applicable to various types of infrared spectrometers. The instruments and main test parameters used in the following examples were: an ALPHA II Fourier transform infrared spectrometer (Bruker, Germany), with a scanning wavenumber range of 1000–650 cm⁻¹. -1 32 scans, 4cm resolution -1 Data collection was performed using the following steps:

[0037] (1) Liquid isoprene rubber was directly coated onto a KBr glass slide, and infrared spectroscopy was used to measure the position at 836±2 cm⁻¹. -1 and 888±1cm -1 Corrected absorbance value A at the location 836 and A 888 ;

[0038] (2) Take the A obtained in step (1) 836 and A888 Substituting into Equation I, we obtain the percentage content of the 1,4 structure.

[0039] In this process, a clean and dry KBr glass slide was used as the background for scanning. Then, liquid isoprene rubber was directly coated onto the KBr glass slide and scanned under the same test conditions in an infrared spectrometer. After scanning, the spectrum after background subtraction was recorded, and the vertical axis of the spectrum was expressed as absorbance.

[0040] To verify the accuracy of the detection method provided by this invention, the quantitative detection results obtained using this method can be compared with those obtained using nuclear magnetic resonance (NMR) testing. An error within 0.6% indicates high accuracy of the detection method. The specific NMR testing procedure can be found in SH / T 1832-2020, "Determination of Microstructure of Isoprene Rubber: 1H NMR Spectroscopy".

[0041] Example 1

[0042] A method for determining the 1,4 structure content in an LIR spectra. The transmission infrared spectrum of an LIR spectra obtained using the preferred transmission method in step (1) of this invention is shown below. Figure 1 As shown. The LIR was confirmed by nuclear magnetic resonance to contain both cis and trans 1,4, 3,4, and 1,2 structures. Figure 1 At 836cm -1 The peak at 888 cm⁻¹ is a characteristic peak of the 1,4 structure. -1 The peaks at 909 cm⁻¹ are characteristic of the 3,4 structure, while the 1,2 structure is less abundant. -1 No obvious characteristic peaks of the 1,2 structure were observed. The baseline was taken at 908-780 cm⁻¹. -1 Between, from Figure 1 A obtained from the infrared spectrum 836 and A 888 The corrected absorbance values ​​at the locations are 0.589 and 0.249, respectively. Substituting these absorbance values ​​into Equation I, we can calculate W. 1,4 It is 97.3%.

[0043] The LIR sample provided in this embodiment was tested using nuclear magnetic resonance (NMR), and the test results W were obtained. 1,4 The accuracy rate was 97.5%, and the error was 0.2%, indicating that the 1,4 structure content detection results provided by this invention are very accurate.

[0044] Example 2

[0045] A method for determining the 1,4 structure content in LIR spectra, differing from Example 1 only in that the LIR spectra are confirmed by NMR to contain no 1,2 structure. The baseline is 908-780 cm⁻¹. -1 Between, from Figure 2 A obtained from the transmission infrared spectrum 836 and A 888 The corrected absorbance values ​​at the locations are 0.297 and 0.105, respectively. Substituting these absorbance values ​​into Equations I and II, we can calculate W. 1,4 It was 98.1%, W 3,4 It is 1.9%.

[0046] The LIR sample provided in this embodiment was tested using nuclear magnetic resonance (NMR), and the test results W were obtained. 1,4 and W 3,4 The values ​​were 98.1% and 1.9% respectively, which are basically consistent with the results calculated by this invention, indicating that the detection results of the 1,4 structure and 3,4 structure content provided by this invention are very accurate.

[0047] Example 3

[0048] A method for determining the content of 1,4-structure in LIR spectrophotometry, differing from Example 1 only in that the LIR spectrophotometry is confirmed by NMR to be free of trans-1,4-structure and 1,2-structure. The baseline is set at 908-780 cm⁻¹. -1 Between, from Figure 3 A obtained from the transmission infrared spectrum 836 and A 888 The corrected absorbance values ​​at the locations are 0.151 and 0.070, respectively. Substituting these absorbance values ​​into Equations I and II, we can calculate W. 1,4 It was 96.8%, W 3,4 It is 3.2%.

[0049] The LIR sample provided in this embodiment was tested using nuclear magnetic resonance (NMR), and the test results W were obtained. 1,4 and W 3,4 The results were 96.7% and 3.3% respectively. The error was 0.1%, indicating that the detection results of the 1,4 structure and 3,4 structure provided by the present invention are very accurate.

[0050] Example 4

[0051] A method for determining the 1,4 structure content in LIR is different from Example 1 only in that step (1) is an attenuated total reflectance infrared spectroscopy test, with diamond as the reflective material. Other parameters and steps are the same as in Example 1.

[0052] from Figure 4 A obtained from the attenuated total reflectance infrared spectrum 836 and A 888 The corrected absorbance values ​​at the locations are 0.249 and 0.089, respectively. Substituting these absorbance values ​​into Equation I, we can calculate W. 1,4 It is 98.1%.

[0053] The test results W obtained by nuclear magnetic resonance method 1,4 The accuracy was 97.5%. After comparison, it can be seen that the error was 0.6%, indicating that the accuracy of the test results using attenuated total internal reflection infrared method is not as high as that of transmission method.

[0054] LIR (Lithography) with a high proportion of 1,4-structure has been widely used. Rapid and accurate determination of the 1,4-structure content will help understand the impact of LIR on rubber processing properties, facilitate quality control of LIR products, and better guide LIR applications. The detection results obtained using the method provided in this invention show smaller errors compared to the absolute quantitative results obtained using nuclear magnetic resonance (NMR). Furthermore, the method of this invention is rapid and non-destructive, with advantages such as simple operation, low cost, environmentally friendly process, and suitability for large-scale rapid testing.

[0055] The above description of the embodiments is provided to enable those skilled in the art to understand and use the invention. It will be apparent to those skilled in the art that various modifications can be made to these embodiments, and the general principles described herein can be applied to other embodiments without inventive effort. Therefore, the present invention is not limited to the above embodiments, and any improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the invention should be within the protection scope of the present invention.

Claims

1. A method for determining the 1,4 structure content in liquid isoprene rubber, characterized in that, The absorbance of the 1,4 and 3,4 structures in liquid isoprene rubber was obtained by infrared spectroscopy. The absorbance values ​​were then substituted into the following formula to calculate the percentage content of the 1,4 structure. W 1,4 =100×8.03A 836 / (7.83A 836 +A 888 )%; Among them, W 1,4 Represents the percentage content of the 1,4 structure, A 836 and A 888 These represent the corrected absorbance values ​​for structures 1, 4 and 3, 4 in the infrared spectrum, respectively.

2. The method for determining the 1,4 structure content in liquid isoprene rubber according to claim 1, characterized in that, Specifically, the following steps are included: (1) Liquid isoprene rubber was directly coated onto a KBr glass slide, and infrared spectroscopy was used to measure the position at 836±2 cm⁻¹. -1 and 888±1cm -1 Corrected absorbance value A at the location 836 and A 888 ; (2) Take the A obtained in step (1) 836 and A 888 Substituting into Equation I, we obtain the percentage content of the 1,4 structure.

3. The method for determining the 1,4 structure content in liquid isoprene rubber according to claim 2, characterized in that, The infrared spectroscopy test in step (1) is performed using a Fourier transform infrared spectrometer. A clean and dry KBr glass slide is used as the background for scanning. Then, liquid isoprene rubber is directly coated onto the KBr glass slide and scanned under the same test conditions. After scanning, the spectrum after background subtraction is recorded.

4. The method for determining the 1,4 structure content in liquid isoprene rubber according to claim 3, characterized in that, Step (1) Observe the spectrum after background subtraction at 836±2cm. -1 Check if the absorbance of the absorption peak is between 0.1 and 0.

9. If so, check if the absorbance is between 836 ± 2 cm⁻¹. -1 The absorbance at the absorption peak is less than 0.1; liquid isoprene rubber is added to thicken it; if 836±2cm -1 If the absorbance of the absorption peak is higher than 0.9, clean the KBr slide and recoat it.

5. The method for determining the 1,4 structure content in liquid isoprene rubber according to claim 2, characterized in that, The KBr slide in step (1) is 25mm in diameter and 4mm in thickness. It needs to be dried at 100-110℃ for 10-20 minutes before testing.

6. The method for determining the 1,4 structure content in liquid isoprene rubber according to claim 2, characterized in that, The infrared spectroscopy test in step (1) uses a scanning wavenumber of 1000–650 cm⁻¹. -1 32 scans, 4cm resolution -1 .

7. The method for determining the 1,4 structure content in liquid isoprene rubber according to claim 1, characterized in that, The liquid isoprene rubber does not contain 1,2 structural units.

8. The method for determining the 1,4 structure content in liquid isoprene rubber according to claim 7, characterized in that, The percentage content of the 3,4 structure in the liquid isoprene rubber is obtained according to the following formula: IN 3,4 =100%-W 1,4 ; Among them, W 3,4 Represents the percentage content of the 3,4 structure.

9. The method for determining the 1,4 structure content in liquid isoprene rubber according to claim 1, characterized in that, The infrared spectroscopy test includes attenuated total reflectance infrared spectroscopy test or transmission infrared spectroscopy test.

10. The method for determining the 1,4 structure content in liquid isoprene rubber according to claim 1, characterized in that, The corrected absorbance value A 836 and A 888 To select 908-780cm -1 The absorbance value is obtained by subtracting the values ​​from the straight line between them, which serves as the baseline.

Images