Method for determining the boron content in a polyborosiloxane

Abstract

The present application relates to the technical field of silicone rubber self-adhesive tape, and particularly relates to a method for determining the boron content in a polyborosiloxane tackifier in a silicone rubber self-adhesive tape. The method comprises the following steps: (1) in the presence of an organic solvent, polyborosiloxane is hydrolyzed with sodium hydroxide as a catalyst, and the liquid is separated; (2) the water layer is adjusted to be neutral or weakly alkaline; (3) mannitol is added, and sodium hydroxide is titrated to an end point, and the volume consumed is recorded; (4) the same steps are adopted, and hydroxyl silicone oil is used as a blank experiment, and the volume of sodium hydroxide consumed is recorded; (5) according to the concentration and volume of sodium hydroxide consumed, the mass percentage of boron in the polyborosiloxane is calculated. The present application does not require expensive professional analysis equipment, and the sample does not need to be subjected to high-temperature cracking treatment in a large amount of strong acid or strong base, the process is simple, the detection method is convenient, and the result is accurate and reliable.

Description

Technical Field

[0001] This invention relates to the field of silicone rubber self-adhesive tape technology, and more particularly to a method for determining the boron content in polyborosiloxane. Background Technology

[0002] Silicone rubber self-adhesive tape, when stretched, overlapped, and wrapped around the object being protected, melts into a single piece within a certain time. It is an elastomer material with excellent water resistance, weather resistance, and heat resistance, and is commonly used for moisture protection of high-voltage motor coils and external insulation protection of high-voltage power transmission and distribution equipment. Silicone rubber has a non-polar molecular structure and does not inherently possess self-adhesive properties; however, self-adhesive properties can be achieved by adding polyborosiloxane tackifiers.

[0003] Currently, both domestically and internationally, the reaction of boric acid with hydroxyl silicone oil is commonly used to prepare polyborosiloxane tackifiers, which are then added to silicone rubber compounds and vulcanized to obtain silicone rubber self-adhesive tapes. The amount of polyborosiloxane added to the silicone rubber compound and the boron content in the polyborosiloxane have a significant impact on the self-adhesive properties of silicone rubber. Establishing a convenient method for determining the boron content in polyborosiloxanes and rapidly measuring the boron content is of great significance for the preparation of silicone rubber self-adhesive tapes.

[0004] There are many methods for determining boron content, including spectrophotometry, chemical titration, inductively coupled plasma mass spectrometry (ICP-MS), and inductively coupled plasma atomic emission spectrometry (ICP-AES). Existing methods for boron content detection suffer from drawbacks such as expensive analytical instruments (e.g., spectrophotometers, ICP-MS), cumbersome sample processing (e.g., using highly corrosive acids like hydrofluoric acid, nitric acid, or concentrated sulfuric acid for pyrolysis, or high-temperature alkali fusion with potassium hydroxide (sodium hydroxide), which are complex, prone to interference, and slow in measurement.

[0005] Therefore, we urgently need to find a method for determining boron content that is easy to obtain analytical equipment, has a simple sample processing procedure, and is fast in detection. Summary of the Invention

[0006] The present invention aims to overcome the shortcomings of existing methods for determining boron content, such as expensive equipment, cumbersome sample processing, and slow measurement speed. Therefore, it provides a method for determining boron content in polyborosiloxanes.

[0007] To achieve the above-mentioned objectives, the present invention is implemented through the following technical solution:

[0008] This invention provides a method for determining the boron content in polyborosiloxanes, comprising the following steps:

[0009] S1: Accurately weigh the polyborosiloxane sample, dissolve it in an organic solvent, mix it with sodium hydroxide solution, stir to react, let it stand and separate the liquids. The upper layer is the organic layer and the lower layer is the hydrolysate.

[0010] S2: Add methyl red indicator to the hydrolysate obtained in step S1, adjust to a slightly red color with hydrochloric acid, and adjust to a bright yellow color with dilute sodium hydroxide solution; add phenolphthalein indicator and mannitol, shake well, and titrate with standard sodium hydroxide solution. The titration endpoint is when the solution changes from colorless to pink. Record the volume of standard sodium hydroxide solution consumed, V1.

[0011] S3: Replace polyborosiloxane with hydroxyl-terminated polydimethylsiloxane, repeat steps S1 and S2, perform a blank experiment, and record the volume of sodium hydroxide standard solution consumed, V2.

[0012] S4: The mass percentage of boron in polyborosiloxane [ω(B)], calculated as shown in Equation I:

[0013]

[0014] Formula I

[0015] In the formula: ω(B) - boron mass percentage;

[0016] V1 - Volume of sodium hydroxide standard solution consumed in the titration of polyborosiloxane sample, milliliters (mL);

[0017] The volume of sodium hydroxide standard solution consumed in the V2-titration of hydroxyl-terminated polydimethylsiloxane, in milliliters (mL);

[0018] c-Molar concentration of sodium hydroxide standard solution, mol / L;

[0019] Mass of m-polyborosiloxane sample, in grams (g).

[0020] Polyborosiloxanes are polymers containing Si-OB bonds, with structural units as shown in Formula III:

[0021]

[0022] Formula III

[0023] In the formula, n is the degree of polymerization, and R1 and R2 are organic substituents.

[0024] The Si-OB and BOB bonds in polyborosiloxanes are sensitive to water and readily undergo hydrolysis to generate boric acid. In this application, under organic solvent and alkaline catalysis, all Si-OB and BOB bonds in polyborosiloxanes are hydrolyzed to convert to boric acid. The hydrolysis reaction of polyborosiloxanes in sodium hydroxide solution is shown in Formula IV:

[0025]

[0026] Formula IV

[0027] Meanwhile, the addition of mannitol effectively increases the acidity of boric acid, making it easier to titrate with sodium hydroxide standard solution, and the boron content can be easily calculated based on the volume of sodium hydroxide standard solution consumed.

[0028] The addition of organic solvents not only protects the Si-O-Si bonds from hydrolysis and breakage, but also extracts the polysiloxanes produced during hydrolysis, reducing interference with boric acid titration and improving detection accuracy. Sodium hydroxide catalyzes the hydrolysis of Si-OB and BOB bonds, converting them entirely into boric acid.

[0029] There are many methods for preparing polyborosiloxanes. They can be obtained by condensation of boric acid with chlorosilanes or alkoxysilanes, or by co-hydrolysis and polycondensation of borate esters and alkoxysilanes. Preferably, the polyborosiloxane of this invention is obtained by reacting boric acid with hydroxyl-terminated polydimethylsiloxane at 180–250°C for 8–24 h. More preferably, the reaction is carried out at 190–210°C for 10–16 h. Preferably, the mass ratio of boric acid to hydroxyl-terminated polydimethylsiloxane is 1–10:100.

[0030] Preferably, the structure of the hydroxyl-terminated polydimethylsiloxane of the present invention is shown in Formula II:

[0031]

[0032] Formula II

[0033] Where n is a positive integer, and the viscosity at 25℃ is 3000~20000mPa·S.

[0034] Under heating conditions, the hydroxyl groups in hydroxyl-terminated polydimethylsiloxane undergo a dehydration reaction with boric acid to form Si-OB bonds; boric acid can also break the Si-O-Si bonds in polysiloxane at high temperatures to form Si-OB bonds, thus forming polyborosiloxane.

[0035] Preferably, the mass of the polyborosiloxane sample is 2–5 g, accurate to 0.0001 g. Weighing too little sample results in a low total boron content, leading to an indistinct color change at the titration endpoint and a large error in the detection result; weighing too much sample results in a high total boron content and a high concentration of the sodium hydroxide standard solution, also leading to a large error in the detection result.

[0036] Preferably, the polyborosiloxane is dissolved in an organic solvent that is insoluble in water, such as one or more mixed solvents selected from diethyl ether, petroleum ether, n-hexane, n-octane, toluene, and benzene, with the mass ratio of the organic solvent to the polyborosiloxane sample being 5 to 10:1.

[0037] Preferably, the organic solvent containing polyborosiloxane is mixed with a sodium hydroxide solution and the mixture is stirred to react. More preferably, the reaction temperature is 10–60°C, even more preferably 30–40°C; more preferably, the reaction time is 2–10 h, even more preferably 4–8 h.

[0038] Preferably, the concentration of the sodium hydroxide solution is 1-5%; the mass ratio of sodium hydroxide solution to polyborosiloxane is 5-10:1. High sodium hydroxide concentration, high reaction temperature, and long reaction time can cause Si-O-Si bond cleavage, generating sodium silicate, which is detrimental to the detection of boron content.

[0039] Preferably, methyl red indicator is added to the hydrolysate, resulting in a yellow color. Upon addition of hydrochloric acid, the system changes from strongly alkaline to acidic, and the solution color changes from yellow to red. The preferred hydrochloric acid concentration is 1–6 mol / L.

[0040] Preferably, after adjusting with hydrochloric acid, the solution is then adjusted to neutral or weakly alkaline using a dilute sodium hydroxide solution, changing the color from red to yellow. The concentration of the dilute sodium hydroxide solution is preferably 0.01–0.05 mol / L.

[0041] Preferably, mannitol and phenolphthalein indicator are added. Mannitol complexes with boric acid, forming a strongly acidic solution. Preferably, the amount of mannitol used is 5-10g, which ensures complete complexation with boric acid.

[0042] Preferably, titration is performed using a sodium hydroxide standard solution, with the titration endpoint defined as the color changing from colorless to pink. The volume of sodium hydroxide standard solution consumed, V1, is recorded. Preferably, the concentration of the sodium hydroxide standard solution is 0.0300–0.1000 mol / L.

[0043] As a preferred option, hydroxyl-terminated polydimethylsiloxane is used instead of polyborosiloxane. The same steps are followed to perform a blank experiment, and the volume of sodium hydroxide standard solution consumed, V2, is recorded.

[0044] Compared with the prior art, the advantages of this invention are: the analytical equipment is conventional glassware, which is simple and readily available, and does not require expensive spectrophotometers, inductively coupled plasma, pH meters and other professional analytical equipment; the sample processing technology for polyborosiloxane is simple, requiring only alkaline catalytic hydrolysis reaction in an organic solvent, without the need for high-temperature pyrolysis in a large amount of strong acid or strong alkali, and the detection method is convenient and fast. Attached Figure Description

[0045] Figure 1 This is the infrared spectrum of polyborosiloxane.

[0046] Figure 2 This is the infrared spectrum of the organic layer product after hydrolysis of polyborosiloxane. Detailed Implementation

[0047] The present invention will be further described below with reference to the accompanying drawings and specific embodiments. Those skilled in the art will be able to implement the present invention based on these descriptions. Furthermore, the embodiments of the present invention described below are generally only some, not all, of the embodiments of the present invention. Therefore, all other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort should fall within the scope of protection of the present invention.

[0048] Example 1

[0049] 1. Preparation of polyborosiloxane

[0050] Weigh out 1.0000g of boric acid and 40.0000g of hydroxyl-terminated polydimethylsiloxane HO(Me2SiO) with a viscosity of 3000mPa·S (25℃). n H, mix thoroughly, heat to 250℃, and react for 8 hours. Cool to room temperature to obtain colorless and transparent polyborosiloxane.

[0051] Infrared spectra of polyborosiloxanes, such as Figure 1 As shown. It can be seen that 1336.57cm -1 The absorption peaks are those of Si-OB and BOB bonds, at 1257.75 cm⁻¹. -1 and 789.12cm -1 The absorption peak is a Si-Me bond absorption peak, at 1016.97 cm⁻¹. -1 The absorption peak is the Si-O bond absorption peak. Figure 1 The absence of a distinct B-OH group absorption peak indicates that the boric acid reaction was complete, producing polyborosiloxane.

[0052] 2. Hydrolysis and titration of polyborosiloxane

[0053] Accurately weigh 4.0000 g of polyborosiloxane, add 25.0 g of n-hexane and 25.0 g of 3% sodium hydroxide solution, stir and react at 45 °C for 8 h, then allow to stand and separate into layers. The upper layer is n-hexane containing polydimethylsiloxane, and the lower layer is a hydrolysate containing borate. Add 2 drops of methyl red indicator to the hydrolysate obtained above; the solution turns yellow. Add 4 mol / L hydrochloric acid solution to change the solution from yellow to slightly red. Adjust the solution to a bright yellow color with 0.03 mol / L sodium hydroxide solution. Add 3 drops of phenolphthalein indicator and 8 g of mannitol, shake well, and titrate with 0.05976 mol / L sodium hydroxide standard solution. The titration endpoint is reached when the solution changes from colorless to pink. The volume of sodium hydroxide standard solution consumed, V1, is 26.85 mL.

[0054] After removing the hexane from the upper layer by evaporation, the hydrolysis product of polyborosiloxane is obtained, and its infrared spectrum is as follows: Figure 2As shown. It can be seen that 1258.09cm -1 and 787.43cm -1 The absorption peak is a Si-Me bond absorption peak, at 1013.55 cm⁻¹. -1 The absorption peak is the Si-O bond absorption peak, 3400 cm⁻¹. -1 The absorption peak is a Si-OH group absorption peak. (Comparison) Figure 1 and Figure 2 , Figure 2 The absence of Si-OB and BOB bond absorption peaks indicates that boron atoms were completely transferred to the hydrolysate after the hydrolysis of polyborosiloxane.

[0055] 3. Blank titration

[0056] 4.0000g of hydroxyl-terminated polydimethylsiloxane HO(Me2SiO) with a viscosity of 3000mPa·S (25℃) was applied. n Add 25.0 g of n-hexane and 25.0 g of 3% sodium hydroxide solution to H, stir and react at 45 °C for 8 h, then allow to stand and separate into layers. The upper layer is a hexane layer containing polydimethylsiloxane, and the lower layer is the hydrolysate. Add 2 drops of methyl red indicator to the hydrolysate obtained above; the solution turns yellow. Add 4 mol / L hydrochloric acid solution to change the solution from yellow to slightly red. Adjust the solution to a bright yellow color with 0.03 mol / L sodium hydroxide dilute solution. Add 3 drops of phenolphthalein indicator and 8 g of mannitol, and titrate with 0.05976 mol / L sodium hydroxide standard solution. The titration endpoint is reached when the solution changes from colorless to pink. The volume of sodium hydroxide standard solution consumed, V2, is 0.20 mL.

[0057] 4. Calculation of boron content

[0058] The mass percentage of boron [ω(B)] in polyborosiloxane is calculated using the following formula:

[0059]

[0060] The theoretical value of boron mass percentage is 0.4265, the measured value is 0.43, and the absolute error is 0.4265-0.43=0.0035.

[0061] Example 2

[0062] 1. Preparation of polyborosiloxane

[0063] Accurately weigh 5.0000g of boric acid and 100.0000g of hydroxyl-terminated polydimethylsiloxane HO(Me2SiO) with a viscosity of 5000mPa·S (25℃). n H, mix thoroughly, heat to 180℃, and react for 24 h. Cool to room temperature to obtain colorless and transparent polyborosiloxane.

[0064] Infrared spectrum of polyborosiloxane: IR: 789.95, 1015.10, 1257.25, 1337.07 cm⁻¹ -1 .

[0065] 2. Hydrolysis and titration of polyborosiloxane

[0066] Accurately weigh 3.5000 g of polyborosiloxane, add 10.5 g of petroleum ether and 7.0 g of n-hexane, add 21.0 g of 3% sodium hydroxide solution, stir and react at 40 °C for 10 h, then allow to stand and separate into layers. The upper layer is an organic solvent layer containing dissolved polysiloxane, and the lower layer is a hydrolysate containing borate.

[0067] Add 2 drops of methyl red indicator to the hydrolysate obtained above; the solution turns yellow. Add 2 mol / L hydrochloric acid to change the solution from yellow to slightly pink. Adjust the solution to a bright yellow color with 0.01 mol / L sodium hydroxide solution. Add 3 drops of phenolphthalein indicator and 5 g of mannitol, shake well, and titrate with 0.08482 mol / L sodium hydroxide standard solution. The titration endpoint is reached when the solution changes from colorless to pink. The volume of sodium hydroxide standard solution consumed, V1, is 32.37 mL.

[0068] 3. Blank drop orientation: 3.5000g hydroxyl-terminated polydimethylsiloxane HO(Me2SiO) with a viscosity of 5000mPa·S (25℃). n Add 10.5 g of petroleum ether and 7.0 g of n-hexane to solution H, then add 21.0 g of 3% sodium hydroxide solution. Stir the mixture at 40°C for 10 h, then allow it to stand and separate into layers. The upper layer is a petroleum ether layer containing dissolved polysiloxane, and the lower layer is a hydrolysate layer containing a small amount of silanol. Add 2 drops of methyl red indicator to the hydrolysate obtained above; the solution turns yellow. Add 2 mol / L hydrochloric acid to change the solution from yellow to slightly red, then adjust to a bright yellow with 0.01 mol / L sodium hydroxide solution. Add 3 drops of phenolphthalein indicator and 5 g of mannitol, and titrate with 0.08482 mol / L sodium hydroxide standard solution. The titration endpoint is reached when the solution changes from colorless to slightly red, and the volume of sodium hydroxide standard solution consumed, V2, is 0.31 mL.

[0069] 4. Calculation of boron content

[0070] The mass percentage of boron [ω(B)] in polyborosiloxane is calculated using the following formula:

[0071]

[0072] The theoretical value of boron mass percentage is 0.8325, the measured value is 0.84, and the absolute error is 0.0075.

[0073] Example 3

[0074] 1. Preparation of polyborosiloxane

[0075] Accurately weigh 1.0000g of boric acid and 100.0000g of hydroxyl-terminated polydimethylsiloxane HO(Me2SiO) with a viscosity of 10000mPa·S (25℃). n H, mix thoroughly, heat to 220℃, and react for 13 h. Cool to room temperature to obtain colorless and transparent polyborosiloxane.

[0076] Infrared spectrum of polyborosiloxane: IR: 790.05, 1016.35, 1259.15, 1336.47 cm⁻¹ -1 .

[0077] 2. Hydrolysis and titration of polyborosiloxanes

[0078] Accurately weigh 4.9550 g of polyborosiloxane, add 35.0 g of toluene, and add 34.8 g of 1% sodium hydroxide solution. Stir the mixture at 40 °C for 6 h, then allow it to stand and separate into layers. The upper layer is a toluene layer containing dissolved polysiloxane, and the lower layer is a hydrolysate containing borate.

[0079] Add 2 drops of methyl red indicator to the hydrolysate obtained above; the solution turns yellow. Add 5 mol / L hydrochloric acid to change the solution from yellow to slightly pink. Adjust the solution to a bright yellow color with 0.02 mol / L sodium hydroxide solution. Add 3 drops of phenolphthalein indicator and 7 g of mannitol, shake well, and titrate with 0.03015 mol / L sodium hydroxide standard solution. The titration endpoint is reached when the solution changes from colorless to pink. The volume of sodium hydroxide standard solution consumed, V1, is 26.32 mL.

[0080] 3. Blank drop orientation: 4.9550g hydroxyl-terminated polydimethylsiloxane HO(Me2SiO) with a viscosity of 10000mPa·S (25℃). n Add 35.0 g of toluene and 34.8 g of 1.0% sodium hydroxide solution to solution H. Stir the mixture at 40°C for 6 hours, then allow it to stand and separate into layers. The upper layer is a toluene layer containing dissolved polysiloxane, and the lower layer is a hydrolysate layer containing a small amount of silanol. Add 2 drops of methyl red indicator to the hydrolysate obtained above; the solution turns yellow. Add 5 mol / L hydrochloric acid to change the solution from yellow to slightly red. Adjust the solution to a bright yellow color with 0.02 mol / L sodium hydroxide solution. Add 3 drops of phenolphthalein indicator and 7 g of mannitol, and titrate with 0.03015 mol / L sodium hydroxide standard solution. The titration endpoint is reached when the solution changes from colorless to pink. The volume of sodium hydroxide standard solution consumed, V2, is 0.70 mL.

[0081] 4. Calculation of boron content

[0082] The mass percentage of boron [ω(B)] in polyborosiloxane is calculated using the following formula:

[0083]

[0084] The theoretical value for the boron mass percentage is 0.1685, the measured value is 0.17, and the absolute error is 0.0015.

[0085] Example 4

[0086] 1. Preparation of polyborosiloxane

[0087] Accurately weigh 8.0000g of boric acid and 100.0000g of hydroxyl-terminated polydimethylsiloxane HO(Me2SiO) with a viscosity of 15000mPa·S (25℃). n H, mix thoroughly, heat to 210℃, and react for 18 h. Cool to room temperature to obtain colorless and transparent polyborosiloxane.

[0088] Infrared spectra of polyborosiloxane: IR: 791.65, 1016.95, 1260.05, 1336.89 cm⁻¹ -1 .

[0089] 2. Hydrolysis and titration of polyborosiloxanes

[0090] Accurately weigh 2.5483 g of polyborosiloxane, add 20.4 g of benzene, and add 15.3 g of 4.0% sodium hydroxide solution. Stir the mixture at 20°C for 8 hours, then allow it to stand and separate into layers. The upper layer is a benzene layer containing dissolved polysiloxane, and the lower layer is a hydrolysate containing borate.

[0091] Add 2 drops of methyl red indicator to the hydrolysate obtained above; the solution turns yellow. Add 4 mol / L hydrochloric acid to change the solution from yellow to slightly pink. Adjust the solution to a bright yellow color with 0.04 mol / L sodium hydroxide solution. Add 3 drops of phenolphthalein indicator and 5 g of mannitol, shake well, and titrate with 0.08320 mol / L sodium hydroxide standard solution. The titration endpoint is reached when the solution changes from colorless to pink. The volume of sodium hydroxide standard solution consumed, V1, is 36.87 mL.

[0092] 3. Blank titration

[0093] 2.5483g of hydroxyl-terminated polydimethylsiloxane HO(Me2SiO) with a viscosity of 15000mPa·S (25℃) was applied. n20.4 g of benzene and 15.3 g of a 4.0% sodium hydroxide aqueous solution were added to solution H. The mixture was stirred at 20°C for 8 hours and then allowed to stand to separate into layers. The upper layer was a benzene layer containing dissolved polysiloxane, and the lower layer was a hydrolysate layer containing a small amount of silanol. Two drops of methyl red indicator were added to the hydrolysate, turning the solution yellow. 4 mol / L hydrochloric acid was added to change the solution from yellow to slightly red, and then the solution was adjusted to a bright yellow color with a 0.04 mol / L sodium hydroxide solution. Three drops of phenolphthalein indicator and 5 g of mannitol were added, and the solution was titrated with a 0.08320 mol / L sodium hydroxide standard solution. The titration endpoint was reached when the solution changed from colorless to pink, and the volume of sodium hydroxide standard solution consumed, V2, was 0.16 mL.

[0094] 4. Calculation of boron content

[0095] The mass percentage of boron [ω(B)] in polyborosiloxane is calculated using the following formula:

[0096]

[0097] The theoretical value for the boron mass percentage is 1.2950, ​​the measured value is 1.29, and the absolute error is 0.0050.

[0098] Example 5

[0099] 1. Preparation of polyborosiloxane

[0100] Accurately weigh 3.0000g of boric acid and 100.0000g of hydroxyl-terminated polydimethylsiloxane HO(Me2SiO) with a viscosity of 20000mPa·S (25℃). n H, mix thoroughly, heat to 230℃, and react for 10 h. Cool to room temperature to obtain colorless and transparent polyborosiloxane.

[0101] Infrared spectrum of polyborosiloxane (IR): 789.97, 1015.00, 1259.05, 1334.68 cm⁻¹ -1 .

[0102] 2. Hydrolysis and titration of polyborosiloxanes

[0103] Accurately weigh 4.1587 g of polyborosiloxane, add 37.5 g of diethyl ether and 35.0 g of 3.5% sodium hydroxide solution, stir and react at 10 °C for 7 h, then allow to stand and separate into layers. The upper layer is an ether layer containing dissolved polysiloxane, and the lower layer is a hydrolysate containing borate.

[0104] Add 2 drops of methyl red indicator to the combined solution obtained above. The solution turns yellow. Add 5 mol / L hydrochloric acid to change the solution from yellow to slightly red. Adjust the solution to bright yellow with 0.03 mol / L sodium hydroxide solution. Add 3 drops of phenolphthalein indicator and 10 g of mannitol, shake well, and titrate with 0.04746 mol / L sodium hydroxide standard solution. The titration endpoint is reached when the solution changes from colorless to pink. The volume of sodium hydroxide standard solution consumed, V1, is 41.37 mL.

[0105] 3. Blank titration

[0106] 4.1587g of hydroxyl-terminated polydimethylsiloxane HO(Me2SiO) with a viscosity of 20000mPa·S (25℃) was applied. n Add 37.5 g of diethyl ether and 35.0 g of 3.5% sodium hydroxide solution to H, stir and react at 10 °C for 7 h, then allow to stand and separate into layers. The upper layer is an ether layer containing dissolved polysiloxane, and the lower layer is a hydrolysate containing a small amount of silanol. Add 2 drops of methyl red indicator to the hydrolysate obtained above; the solution turns yellow. Add 5 mol / L hydrochloric acid to change the solution from yellow to slightly red, and adjust to bright yellow with 0.03 mol / L sodium hydroxide dilute solution. Add 3 drops of phenolphthalein indicator and 10 g of mannitol, and titrate with 0.04746 mol / L sodium hydroxide standard solution. The titration endpoint is when the solution changes from colorless to pink. The volume of sodium hydroxide standard solution consumed, V2, is 0.10 mL.

[0107] 4. Calculation of boron content

[0108] The mass percentage of boron [ω(B)] in polyborosiloxane is calculated using the following formula:

[0109]

[0110] The theoretical value of boron mass percentage is 0.5092, the measured value is 0.51, and the absolute error is 0.0008.

Claims

1. A method for determining the boron content of a polyborosiloxane, characterized by, Includes the following steps: S1: Accurately weigh the polyborosiloxane sample, dissolve it in an organic solvent, and mix it with a 1-5% sodium hydroxide solution. The mass ratio of sodium hydroxide solution to polyborosiloxane sample is 5-10:

1. Stir the reaction at 10-60℃ for 2-10 hours, let it stand and separate the liquids. The upper layer is the organic layer and the lower layer is the hydrolysate. S2: Add methyl red indicator to the hydrolysate obtained in step S1, adjust to a slightly red color with hydrochloric acid, and adjust to a bright yellow color with dilute sodium hydroxide solution; add phenolphthalein indicator and mannitol, shake well, and titrate with standard sodium hydroxide solution. The titration endpoint is when the solution changes from colorless to pink. Record the volume of standard sodium hydroxide solution consumed, V1. S3: Replace polyborosiloxane with hydroxyl-terminated polydimethylsiloxane, repeat steps S1 and S2, perform a blank experiment, and record the volume of sodium hydroxide standard solution consumed, V2. S4: The mass percentage of boron in polyborosiloxane [ω(B)], calculated as shown in Equation I: Formula I; In the formula: ω(B) - percentage of boron by mass; V1 - Volume of sodium hydroxide standard solution consumed in titration of polyborosiloxane sample, milliliters (mL). The volume of sodium hydroxide standard solution consumed in the V2-titration of hydroxyl-terminated polydimethylsiloxane, in milliliters (mL). c-Molar concentration of sodium hydroxide standard solution, mol / L; Mass of m-polyborosiloxane sample, in grams (g).

2. The method for determining the boron content in a polyborosiloxane according to claim 1, characterized in that, The polyborosiloxane is obtained by reacting boric acid and hydroxyl-terminated polydimethylsiloxane at 180–250 °C for 8–24 h, with the mass ratio of boric acid to hydroxyl-terminated polydimethylsiloxane being 1–10:

100.

3. A method for determining the boron content in polyborosiloxane according to claim 1 or 2, characterized in that, The structure of the hydroxyl-terminated polydimethylsiloxane is shown in Formula II: Formula II; Where n is a positive integer, and the viscosity at 25℃ is 3000~20000mPa•S.

4. The method for determining the boron content in polyborosiloxane according to claim 1, characterized in that, The mass of the polyborosiloxane sample is 2–5 g, accurate to 0.0001 g.

5. The method for determining the boron content in polyborosiloxane according to claim 1, characterized in that, In step S1, the organic solvent includes any one or more mixed solvents selected from diethyl ether, petroleum ether, n-hexane, n-octane, toluene, and benzene.

6. The method of determining the boron content of a polyborosiloxane according to claim 1 or 5, characterized in that, The mass ratio of the organic solvent to the polyborosiloxane sample is 5 to 10:

1.

7. The method for determining the boron content in polyborosiloxane according to claim 1, characterized in that, In step S2, the amount of mannitol used is 5-10g.

8. The method for determining the boron content in polyborosiloxane according to claim 1, characterized in that, In step S2, the concentration of the sodium hydroxide standard solution is 0.0300–0.1000 mol / L.

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