A method for testing the mq ratio in mq silicone resin

Abstract

The application discloses a method for testing the MQ ratio of MQ silicone resin, and the method comprises the following steps: integrating the absorption peaks of Si-O-Si at 1080cm ‑1 and Si-CH3 at 1250cm ‑1 of specific groups by infrared spectroscopy through a series of standard samples with known MQ ratio, establishing the quantitative relationship between the peak area ratio and the MQ ratio, and fitting to obtain the corresponding calibration curve. According to the calibration curve, the MQ ratio of the MQ silicone resin can be accurately calculated in combination with the infrared spectrum of the MQ silicone resin, the result obtained by the method is comparable to the nuclear magnetic resonance spectrum, and the method has the advantages of simplicity and strong operability.

Description

Technical Field

[0001] This invention relates to a method for testing the MQ ratio in MQ silicone resin, specifically a method for characterizing the MQ ratio in MQ silicone resin using FTIR, belonging to the field of polymer material testing technology. Background Technology

[0002] MQ silicone resins are a class of silicone resins composed of monofunctional M-units (R3SiO2). 1 / 2 ) and the four-functional Q-linker (SiO) 4 / 2 The constructed organosilicon resin has a near-three-dimensional spherical shape, and its typical (planar) chemical structure is as follows: Figure 1 As shown. Compared to organic polymers, MQ silicone resin exhibits better high and low temperature resistance, hydrophobicity, chemical resistance, electrical insulation, weather resistance, flexibility, film-forming properties, adhesion, and excellent mechanical properties. It has been widely used in pressure-sensitive adhesives, liquid silicone rubber reinforcement, cosmetics, high-temperature coatings, mold release agents, defoamers, and silicone leather. Currently, there are two main methods for synthesizing MQ silicone resin: the water glass method and the silicate ester method. Specifically, the former uses organochlorosilanes or various disiloxanes as M-chain monomers and water glass as Q-chain monomers, formed through a hydrolysis-condensation reaction; while the latter uses ethyl orthosilicate as the Q-chain precursor, formed by hydrolysis-condensation followed by (partial) end-capping of the M-chain monomers. Regardless of whether the MQ silicone resin is synthesized by the water glass method or the silicate ester method, its physicochemical properties are highly dependent on the resin's chemical composition and structure, such as the type of R groups, the MQ ratio, molecular weight and distribution, three-dimensional topology, and silanol content. Among them, the MQ ratio (the molar ratio of M to Q units) is the most important structural parameter of MQ silicone resin, which profoundly affects its physicochemical properties and may lead to differences in topology. For example, the MQ ratio determines the density, transparency, viscosity, softening point, thermal stability, reactivity, and film-forming properties of MQ silicone resin. The smaller the MQ ratio, the more tetrafunctional Q units there are, the denser the MQ network, and the more spherical the structure. The larger the MQ ratio, the more monofunctional M units there are, and the more branched the structure. Therefore, accurately measuring the MQ ratio of MQ silicone resin is crucial for understanding the relationship between the structure and properties of MQ silicone resin and its applications.

[0003] Currently, the methods for testing the MQ ratio include: based on the initial feed ratio, thermogravimetric analysis (organosilicon materials, 2007, 120(02): 76-80+115.), solid-state nuclear magnetic resonance silicon spectroscopy (Applied Magnetic Resonance, 2013, 44:1015–1025), and internal standard method of nuclear magnetic resonance hydrogen spectroscopy (Journal of applied polymer science, 2013, 128(6): 4189-4200.). Among these methods, the initial feed ratio method deviates significantly from the actual MQ ratio because of the presence of unreacted monomers, leading to substantial errors. Thermogravimetric analysis (TGA) relies on the fact that the M-units in MQ silicone resin undergo weight loss through decomposition at high temperatures, while the Si-O-Si network (Q-units) remains. The MQ ratio can then be calculated using the mass residue rate from the thermogravimetric curve. However, this method also suffers from significant errors because Si-O-Si bonds may break / rearrange or undergo other mechanisms (such as pyrolysis or cyclization), producing organosilicon compounds of various molecular weights. These compounds sublimate at higher temperatures, reducing the mass residue rate of Si and O, resulting in large deviations from the final result. Nuclear magnetic resonance (NMR) spectroscopy is currently the most commonly used method for characterizing the MQ ratio, but NMR spectrometers are expensive and difficult to apply in actual production. Therefore, there is an urgent need to develop a simple, effective, and accurate method for characterizing the MQ ratio of MQ silicone resin.

[0004] Infrared spectroscopy has been widely used for qualitative and quantitative analysis of the composition and structure of various organic and inorganic substances. When organic molecules are irradiated with infrared light, the chemical bonds or functional groups in the molecules can undergo vibrational absorption, and different chemical bonds or functional groups have different absorption frequencies. For example, when Peng Di et al. performed infrared spectroscopy analysis on MQ silicone resin in "Preparation of MQ Silicone Resin by Water Capture Method" (Organosilicon Materials, 2009, 33(3): 171-175), it can be seen from its FTIR chromatogram that the synthesized compound has different absorption frequencies at 2960 cm⁻¹. -1 1250cm -1 845cm -1 754cm -1 1080cm -1 The stretching vibration peaks appearing nearby indicate that it possesses methyl, Si-CH3, and Si-O-Si- groups, classifying it as a methyl MQ silicone resin. Furthermore, based on curves a, b, and c in its FTIR spectrum, the intensity of the Si-OH absorption peak and the 2960 cm⁻¹ peak are... -1 The change in the intensity of the CH absorption peak is related to the feed ratio of M and Q repeating units in the compound. Therefore, the intensity of the Si-OH absorption peak and the 2960 cm⁻¹ value can be used as a basis for analysis. -1The intensity change of the CH absorption peak is used to determine the MQ ratio in MQ silicone resin. However, for most MQ silicone resins with low hydroxyl content (<1%), the MQ ratio is not significantly related to the hydroxyl content. It can be seen that this method can only qualitatively determine the relative size of the M / Q value under the premise of known feed ratio. Based on this, when it is necessary to measure the MQ ratio of MQ silicone resin, even if the intensity of its Si-OH and CH absorption peaks can be obtained by infrared spectroscopy, it is not possible to quantitatively characterize the MQ ratio in MQ silicone resin. Summary of the Invention

[0005] The purpose of this invention is to provide a method for testing the MQ ratio in MQ silicone resin. This method uses a series of standard samples with known MQ ratios to integrate the absorption peaks of specific groups in the infrared spectrum, establishes a quantitative relationship between the peak area ratio and the MQ ratio, fits the corresponding calibration curve, and then, based on the extrapolated portion of the calibration curve and the infrared spectrum of the MQ silicone resin, reverse calibration of its MQ ratio can be performed. This method has the advantages of simple operation, being unaffected by other impurities, high accuracy, and low cost.

[0006] This invention is achieved through the following technical solution: a method for testing the MQ ratio in MQ silicone resin, comprising the following steps:

[0007] S1. Prepare standard samples with known MQ ratios;

[0008] S2. Infrared spectroscopy detection was performed using standard samples. The absorption peaks of Si-O-Si groups and Si-CH3 groups in the standard samples were selected for integration to obtain the quantitative relationship between the area ratio of the absorption peaks of Si-O-Si groups and Si-CH3 groups and the MQ ratio. Then, the calibration curve was constructed.

[0009] S3. The MQ silicone resin sample to be tested is detected by infrared spectroscopy to obtain the area ratio of the absorption peaks of Si-O-Si groups and Si-CH3 groups in the MQ silicone resin sample. According to the standard curve, the MQ ratio is obtained.

[0010] In S1, the MQ ratios of the standard samples are set in an equal gradient, including trimethylsilyl cage polysilsesquioxane (M8Q8), tetra(trimethylsiloxy)silane (M4Q) and their compound products.

[0011] In step S2, a standard sample at 1080 cm⁻¹ is selected. -1 The absorption peaks at Si-O-Si symmetric stretching vibrations and at 1250 cm⁻¹ -1 The absorption peak of the Si-CH3 bending vibration at that location was integrated.

[0012] In the S2, the molecular formula is [(CH3)3SiO 1 / 2 ] m[SiO 4 / 2 ] q The integral area formula for the absorption peak of the Si-O-Si group in methyl MQ silicone resin is shown in the following formula (1):

[0013] (1)

[0014] In equation (1), A1 is the integral area of ​​the absorption peak of the Si-O-Si group;

[0015] The integral area formula for the absorption peak of the Si-CH3 group is shown in equation (2) below:

[0016] (2)

[0017] In equation (2), A2 is the integral area of ​​the absorption peak of the Si-CH3 group.

[0018] Furthermore, the quantitative relationship between the area ratio of the absorption peaks of Si-O-Si groups and Si-CH3 groups and the MQ ratio is shown in the following equation (3):

[0019] (3)

[0020] Based on the above formula (3), the area ratio of the absorption peaks of Si-O-Si groups and Si-CH3 groups is used as the ordinate, and (M / Q) / [M / Q+4] is used as the abscissa to plot a scatter plot of 7 standard samples. Linear fitting yields the calibration curve. Based on this calibration curve and the infrared spectrum of MQ silicone resin, its MQ ratio can be accurately calculated.

[0021] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0022] (1) The method of the present invention is based on infrared spectroscopy for characterization, which is convenient and quick, requires no pretreatment, and is applicable to MQ silicone resins with different molecular weights, synthesis methods and organic groups.

[0023] (2) Compared with the existing characterization methods for the MQ ratio of MQ silicone resin, the method of the present invention is not affected by acid and alkali residues and other impurities in the sample, and its characterization results are highly comparable to the internal standard method of nuclear magnetic resonance hydrogen spectroscopy. Attached Figure Description

[0024] Figure 1 The diagram shows the structure of MQ silicone resin (R, R', R" are organic groups, including hydrogen-containing, methyl, vinyl, phenyl, chloropropyl, (meth)acrylate groups, etc., where R, R', R" can be the same or different).

[0025] Figure 2The structural diagrams are of trimethylsilyl cage polysilsesquioxane (M8Q8) and tetra(trimethylsiloxy)silane (M4Q).

[0026] Figure 3 The infrared spectrum and fitting curve of M8Q8 are shown.

[0027] Figure 4 The infrared spectral calibration curves are obtained for standard samples based on known MQ ratios.

[0028] Figure 5 The image shows the infrared spectrum of the methyl MQ silicone resin in Example 1.

[0029] Figure 6 The infrared spectrum of the methyl MQ silicone resin in Example 2 is shown.

[0030] Figure 7 The image shows the infrared spectrum of methyl MQ silicone resin (i.e., Wacker 803) in Example 3.

[0031] Figure 8 The infrared spectrum of vinyl MQ silicone resin in Example 4 is shown.

[0032] Figure 9 The infrared spectrum of the phenyl MQ silicone resin in Example 5 is shown.

[0033] Figure 10 The infrared spectrum of the (meth)acrylate-based MQ silicone resin in Example 6 is shown. Detailed Implementation

[0034] The invention's objective, technical solution, and beneficial effects will be further explained in detail below.

[0035] It should be noted that the following detailed descriptions are exemplary and intended to provide further illustration of the claimed invention. Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0036] This invention enables the determination of the MQ ratio of MQ silicone resins with different molecular weights, synthesis methods, and organic groups. The MQ ratio of commercial MQ silicone resins can be calibrated using only infrared spectroscopy, which is convenient, fast, and highly accurate.

[0037] The specific testing methods can be summarized as follows:

[0038] A series of MQ standard samples with known MQ ratios are selected. Infrared spectroscopy is used to integrate the absorption peaks of specific functional groups to establish a quantitative relationship between the peak area ratio and the MQ ratio. A corresponding calibration curve is obtained through fitting. Based on this calibration curve and the infrared spectrum of the MQ silicone resin, its MQ ratio can be calculated. The specific steps are as follows:

[0039] Step 1: Preparation and Infrared Spectroscopy Testing of MQ Standard Samples

[0040] Experimental samples: M8Q8 and M4Q (see...) Figure 2 ) and a series of MQ standard samples with equal gradient MQ ratios (see table below);

[0041] Experimental instrument: Infrared spectrometer;

[0042] Experimental parameters: spectral range 4000–400 cm⁻¹ -1 Spectral resolution 4 cm -1 Transmission mode.

[0043]

[0044] Step 2, Infrared Spectroscopy Analysis

[0045] First, the absorption peaks in the infrared spectrum are assigned. The bending vibration absorption peak of Si-CH3 is generally around 1250 cm⁻¹. -1 The absorption peak of the Si-O-Si symmetric stretching vibration is generally around 1080 cm⁻¹. -1 The two absorption peaks above can be fitted separately, taking M8Q8 as an example, see... Figure 3 The fitted curve equation is y=0.28143x+0.07475, where y=A(Si-CH3) / A(Si-O-Si) and x=(M / Q) / [M / Q+4].

[0046] Step 3: Establishing quantitative relationships

[0047] The product of the absorption peak intensity (I) and the full width at half maximum (FWHM) is used as the basis for quantification (see the table below). Its integral area (A = I × FWHM) is proportional to its chain segment content (see the following three calculation formulas).

[0048] The molecular formula of methyl MQ silicone resin is [(CH3)3SiO2]. 1 / 2 ] m [SiO 4 / 2 ] q

[0049]

[0050] The quantitative relationship between peak area ratio and MQ ratio is as follows:

[0051] (1)

[0052] (2)

[0053] (3)

[0054] In equation (1), A1 is 1080 cm. -1 The fitted peak area of ​​the Si-O-Si bond at the point is A2, which is 1250 cm⁻¹. -1 The fitted peak area of ​​the Si-CH3 bond at the position, where the M-unit contains 1 Si-O bond and 3 Si-CH3 bonds; the Q-unit contains 4 Si-O bonds.

[0055] Equations (1) and (2) show the direct proportional relationship between the integral area and the composition of the chain links.

[0056] Equation (3) is obtained by dividing equation (1) and equation (2), thus establishing a quantitative relationship between the peak area ratio and the MQ ratio.

[0057] Step 4: Establishing the calibration curve

[0058] Infrared spectroscopy was used to characterize a series of MQ standard samples with known MQ ratios in S1. The infrared spectra were analyzed using the method in S2, and the peak area ratio (A2 / A1) of the two absorption peaks was fitted. Using this ratio as the ordinate and (M / Q) / [M / Q+4] as the abscissa, a scatter plot of the seven standard samples was drawn. Linear fitting yielded the calibration curve (see...). Figure 4 ).

[0059] Step 5: Characterization of the MQ ratio of commercial MQ silicone resins

[0060] Commercial MQ silicone resin is characterized using infrared spectroscopy. The infrared spectrum is analyzed using the method in S2, and the peak area ratio (A2 / A1) of the two absorption peaks is obtained by fitting. The MQ ratio can be calculated by referring to the calibration curve.

[0061] It should be noted that the “MQ ratio” mentioned in this invention can also be recorded as “M / Q value”. In addition, “m” and “M” are the same in this invention, and “q” and “Q” are the same.

[0062] The following examples illustrate specific implementations of the present invention. Of course, the scope of protection of the present invention is not limited to the following examples. For detailed processes and parameters, please refer to the above-described test methods of the present invention.

[0063] Example 1:

[0064] In this embodiment, infrared spectroscopy was used to characterize a high molecular weight methyl MQ silicone resin (synthesized by the water glass method), and the infrared spectrum was obtained. See [link to infrared spectrum]. Figure 5 .

[0065] First, the two characteristic absorption peaks on the infrared spectrum were assigned, including the one at 1250 cm⁻¹. -1The left and right sides are the bending vibration absorption peaks of Si-CH3, at 1080 cm⁻¹. -1 The left and right sides are absorption peaks of the Si-O-Si symmetric stretching vibration. After fitting each peak, the peak area ratio is obtained, and then the MQ ratio is calculated according to the calibration curve equation.

[0066]

[0067] Therefore, the MQ ratio of the high molecular weight methyl MQ silicone resin in this embodiment is 0.57.

[0068] Example 2:

[0069] In this embodiment, infrared spectroscopy was used to characterize a low molecular weight methyl MQ silicone resin (synthesized by the water glass method), and the infrared spectrum was obtained. See [link to infrared spectrum]. Figure 6 .

[0070] First, the two characteristic absorption peaks on the infrared spectrum were assigned, including the one at 1250 cm⁻¹. -1 The left and right sides are the bending vibration absorption peaks of Si-CH3, at 1080 cm⁻¹. -1 The left and right sides are absorption peaks of the Si-O-Si symmetric stretching vibration. After fitting each peak, the peak area ratio is obtained, and then the MQ ratio is calculated according to the calibration curve equation.

[0071]

[0072] Therefore, the MQ ratio of the low molecular weight methyl MQ silicone resin in this embodiment is calculated to be 0.90.

[0073] Example 3:

[0074] In this embodiment, infrared spectroscopy was used to characterize an MQ silicone resin synthesized by the tetraethyl orthosilicate (TEOS) method, and the infrared spectrum was obtained. See [link to infrared spectrum]. Figure 7 .

[0075] First, the two characteristic absorption peaks on the infrared spectrum were assigned, including the one at 1250 cm⁻¹. -1 The left and right sides are the bending vibration absorption peaks of Si-CH3, at 1080 cm⁻¹. -1 The left and right sides are absorption peaks of the Si-O-Si symmetric stretching vibration. After fitting each peak, the peak area ratio is obtained, and then the MQ ratio is calculated according to the calibration curve equation.

[0076]

[0077] Therefore, the MQ ratio of the MQ silicone resin synthesized by the tetraethyl orthosilicate method (TEOS method) in this embodiment is calculated to be 0.58.

[0078] Example 4:

[0079] This embodiment uses infrared spectroscopy to characterize a vinyl MQ silicone resin (synthesized by the water glass method), and the infrared spectrum is shown below. Figure 8 .

[0080] First, the three characteristic absorption peaks on the infrared spectrum were assigned, including the one at 1640 cm⁻¹. -1 The left and right sides are the absorption peaks of the Si-CH=CH2 (C=C) stretching vibration, at 1250 cm⁻¹. -1 The left and right sides are the bending vibration absorption peaks of Si-CH3, at 1080 cm⁻¹. -1 The peaks on the left and right are absorption peaks of the Si-O-Si symmetric stretching vibration. Since the vinyl molar fraction of MQ silicone resin is only 3.54%, the vinyl peak is very weak and can be ignored for now. We will first fit the two absorption peaks of Si-CH3 and Si-O-Si to obtain the peak area ratio, and then calculate the MQ ratio according to the calibration curve equation.

[0081]

[0082] Therefore, the MQ ratio of the vinyl MQ silicone resin in this embodiment is calculated to be 0.86.

[0083] Example 5:

[0084] In this embodiment, infrared spectroscopy was used to characterize a phenyl MQ silicone resin (synthesized by the water glass method), and the infrared spectrum was obtained. See [link to infrared spectrum]. Figure 9 .

[0085] First, the two characteristic absorption peaks on the infrared spectrum were assigned, including the one at 1250 cm⁻¹. -1 The left and right sides are the bending vibration absorption peaks of Si-CH3, at 1080 cm⁻¹. -1 The left and right sides are absorption peaks of the Si-O-Si symmetric stretching vibration. After fitting each peak, the peak area ratio is obtained, and then the MQ ratio is calculated according to the calibration curve equation.

[0086]

[0087] Therefore, the MQ ratio of the phenyl MQ silicone resin in this embodiment is calculated to be 0.55.

[0088] Example 6:

[0089] In this embodiment, infrared spectroscopy was used to characterize a (meth)acrylate-based MQ silicone resin (synthesized by the water glass method), and the infrared spectrum was obtained. See [link to infrared spectrum]. Figure 10 .

[0090] First, the two characteristic absorption peaks on the infrared spectrum were assigned, including the one at 1250 cm⁻¹. -1The left and right sides are the bending vibration absorption peaks of Si-CH3, at 1080 cm⁻¹. -1 The left and right sides are absorption peaks of the Si-O-Si symmetric stretching vibration. After fitting each peak, the peak area ratio is obtained, and then the MQ ratio is calculated according to the calibration curve equation.

[0091]

[0092] Therefore, the MQ ratio of the (meth)acrylate-based MQ silicone resin in this embodiment is calculated to be 0.54.

[0093] For the MQ silicone resins of Examples 1 to 6, the internal standard method of nuclear magnetic resonance hydrogen spectroscopy was used simultaneously ( 1 The MQ ratio was determined by ¹H NMR and thermal analysis (TGA). The silanol content of Examples 1 to 6 above and the silanol content after titration were summarized in the table below.

[0094]

[0095] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Any simple modifications or equivalent changes made to the above embodiments based on the technical essence of the present invention shall fall within the protection scope of the present invention.

Claims

1. A method for testing the MQ ratio in MQ silicone resin, characterized in that: Includes the following steps: S1. Prepare standard samples with known MQ ratios, wherein the MQ ratios of the standard samples are set in an equal gradient, including trimethylsilyl cage polysilsesquioxane (M8Q8), tetra(trimethylsiloxy)silane (M4Q) and their compound products; S2. Infrared spectroscopy detection was performed using standard samples, selecting the 1080 cm⁻¹ standard sample. -1 The absorption peaks at Si-O-Si symmetric stretching vibrations and at 1250 cm⁻¹ -1 The absorption peak of the Si-CH3 bending vibration at that location was integrated. According to the molecular formula [(CH3)3SiO 1 / 2 ] m [SiO 4 / 2 ] q The integral area formula for the absorption peak of the Si-O-Si group in methyl MQ silicone resin is shown in the following formula (1): （1） In equation (1), A1 is the integral area of ​​the absorption peak of the Si-O-Si group. The integral area formula for the absorption peak of the Si-CH3 group is shown in equation (2) below: （2） In equation (2), A2 is the integral area of ​​the absorption peak of the Si-CH3 group. The quantitative relationship between the area ratio of the absorption peaks of Si-O-Si groups and Si-CH3 groups and the MQ ratio is shown in the following formula (3): （3） The standard curve is then obtained by reconstruction; S3. The MQ silicone resin sample to be tested is detected by infrared spectroscopy to obtain the area ratio of the absorption peaks of Si-O-Si groups and Si-CH3 groups in the MQ silicone resin sample. According to the standard curve, the MQ ratio of the sample to be tested is obtained.

2. The method according to claim 1, characterized in that: Using the ratio of the absorption peak areas of Si-O-Si groups and Si-CH3 groups as the ordinate and (M / Q) / [M / Q+4] as the abscissa, a scatter plot of 7 standard samples was drawn, and a standard curve was obtained by linear fitting.

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