Preparation method of high-boron filling type dynamic crosslinking organic silicon elastomer

Abstract

The invention discloses a preparation method of a high-boron filling type dynamic crosslinking organic silicon elastomer. The high-boron filling type dynamic crosslinking organic silicon elastomer is prepared from the following raw materials: 100 parts of vinyl silicone rubber, 0.1-10 parts of a thermal initiator, 1-20 parts of sulfydryl-terminated boric acid ester and 1-50 parts of polyborosiloxane gel PBS. The preparation method comprises the following steps: firstly, preparing polyborosiloxane (PBS) gel by utilizing esterification reaction; secondly, synthesizing sulfydryl-terminated boric acid ester, and preparing a high-boron filling type dynamic crosslinking organic silicon elastomer by utilizing a mixing reactor; and finally, an organic silicon sample piece is processed by compression molding. The invention develops a method which is simple to operate and can be used for preparing the high-boron filling type dynamic crosslinking organic silicon elastomer in batches, and the obtained organic silicon elastomer has the advantages of sensitive strain rate response, good metal adhesion, good heat resistance and repeated thermoplastic processing.

Description

Technical Field

[0001] The invention belongs to the field of organic silicon elastomers, and in particular relates to a method for preparing a high-boron filled dynamically cross-linked organic silicon elastomer. Background Art

[0002] Silicone elastomer is composed of [-Si(CH 3 ) 2 -O-] as the main chain of the molecular chain, with a very low glass transition temperature (Tg = -120 ° C) and excellent thermal stability. It is an excellent elastomeric material with a wide temperature range. It also has comprehensive properties such as UV resistance, dielectric, and biocompatibility. It is widely used in aerospace, microelectronics and other fields. Traditionally, silicone elastomers usually need to be chemically cross-linked before use, mainly including platinum-catalyzed hydrosilylation reaction, peroxide cross-linking vinyl side chains, polysilazane-cured terminal hydroxyl siloxane, etc. This type of chemically cross-linked silicone elastomer is usually an irreversible chemical network, facing the problems of non-repeatable processing and non-recyclable reuse. Therefore, the development and application of thermoplastic silicone elastomers have received extensive attention from researchers.

[0003] A variety of effective strategies have been reported for the repeated processing of silicone elastomers at home and abroad. 2+) and other metal ions to form coordination bonds. Silicone elastomers based on this type of Coulomb force cross-linking show good strength (>5MPa), toughness (>1300%) and excellent thermoplasticity [Jinfeng Shi, Na Zhao, Dongying Yan et al., J. Mater. Chem. A, 2020, 8, 5943-5951]. By click chemistry, coumarin groups are grafted on the side chains of silicone, and the curing and thermoplasticity of silicone elastomers can be achieved by utilizing the two-way association between coumarins. The amount of coumarin grafting can adjust the head-to-tail π stacking and cross-linking density to regulate the mechanical properties [Amanda S. Fawcett, Michael A. Brook, Macromolecules, 2014, 47, 1656-1663]. The hot-pressing reshaping of silicone elastomers can be achieved by conjugating Meldrum acid derivatives to eliminate thiols to form reversible dynamic cross-linking bonds, and the mechanical properties will not deteriorate significantly after repeated processing [Jacob SAI Shibashi, Julia A. Kalow, ACS macro Lett., 2018, 7, 482-486]. In recent years, the research on dynamic cross-linking silicone elastomers based on dynamic chemical bonds has been very active. For example, patent CN110358032B discloses a self-repairable and recyclable silicone elastomer based on dynamic imine bonds, in which the matrix used is amino-terminated polydimethylsiloxane, and patent CN109575291B discloses a self-repairing silicone elastomer with coexistence of urea and imine bonds, and the hydrogen bonds and imine bonds formed inside it ensure the mechanical strength of the material and achieve reproducibility. However, although most of the existing research work has designed a sophisticated molecular structure, the chemical synthesis is complex, some raw materials are expensive, and it is not easy to prepare in batches. In previous studies, our research group has achieved dynamic crosslinking of commercial methyl vinyl silicone rubber, achieving thermoplasticity and strain rate response properties. However, the low vinyl content (<5%) in commercial silicones limits the number of dynamic bonds that can be introduced.

[0004] Polyborosiloxane molecules contain boron oxygen bonds (bond energy 537.6 kJ / mol) and silicon oxygen bonds (bond energy 422.5 kJ / mol). The two chemical bonds have high bond energies, and the molecular structure contains d-π and p-π structures. They have good high temperature resistance, oxidation resistance and high stability, and are widely used in flame retardant materials, high temperature resistant coatings, ceramic precursors, protection and shock absorption. Polyborosiloxane contains Si-OB structure. The boron atoms in this structure can form reversible BO electron bridge pairs with oxygen atoms in adjacent molecular chains. The electron bridge pairs can continuously dissociate and recombine. This physical crosslinking is dynamically reversible. In addition, the presence of BO electron bridge pairs also has a certain effect on the viscoelasticity of polyborosiloxane. When the material is subjected to high-speed impact, the electron bridge pairs cannot keep up with the changes in external stimuli and will be blocked, hindering the movement of the molecular chain. The material will show rigid mechanical behavior, which makes polyborosiloxane have a certain impact resistance and the effect of absorbing energy during the impact process. Patent CN111187516B discloses a method for preparing polyborosiloxane modified with polyvinyl alcohol, and the introduction of carbon chains improves the compatibility of polyborosiloxane in compounding with other polymer materials. Patent CN115093709A discloses that the hydrolysis resistance is improved by blending purified polyborosiloxane with amine compounds. In general, polyborosiloxane has unique viscoelasticity, and its apparent liquid-like tendency under static conditions limits its use alone. It also has defects such as water resistance and fear of deliquescence.

[0005] Compared with existing reports, this article uses polyborosiloxane gel to fill silicone elastomers, introduces dynamic boron-oxygen bonds through reactive processing to achieve dynamic crosslinking of vinyl side chains, and achieves complete compatibility between polyborosiloxane and silicone elastomer based on efficient boron-oxygen bond exchange, thereby realizing the preparation of high-boron-filled dynamically crosslinked silicone elastomers. The high-boron content filling achieved by this invention improves the shortcomings of low strength and easy deliquescent deterioration faced by polyborosiloxane when used alone. The most important thing is that the prepared high-boron-filled silicone elastomer has better strain rate response characteristics and thermoplastic reprocessing characteristics, showing great potential in impact resistance, vibration control and other aspects. The preparation process is simple, the reaction conditions are mild, and batch preparation is easy to achieve. The high-boron-filled dynamically crosslinked silicone elastomer prepared by the present invention realizes the effective regulation of the heavy boron content of the modified silicone elastomer, has a sensitive strain rate response, and exhibits excellent energy dissipation performance and thermoplastic reprocessing capability. Summary of the invention

[0006] The purpose of the present invention is to prepare a high-boron filled dynamically cross-linked silicone elastomer, which not only improves the problem of poor mechanical properties of traditional polyborosiloxane gel, but also solves the problem of limited boron content in the dynamically cross-linked silicone elastomer, and develops a high-performance thermoplastic silicone elastomer with high rate correlation, impact resistance and metal bonding.

[0007] In order to achieve the above purpose, the technical solution is as follows:

[0008] Step 1: preparing polyborosiloxane gel PBS, dissolving terminal hydroxyl polysiloxane and boric acid small molecules in a low boiling point solvent at a molar ratio of 1:1 for esterification reaction, reacting at 60°C for 6 hours using a magnetic stirrer, transferring the reactant to a vacuum oven for heat treatment at 120°C for 12 hours to solidify and remove the solvent, thereby obtaining polyborosiloxane gel PBS;

[0009] Step 2: Prepare terminal mercapto borate, mix 1,4-phenyldiboronic acid and α-thioglycerol in a molar ratio of 1:2, dissolve in 10 times the mass of tetrahydrofuran, and continuously stir on a magnetic stirrer to obtain a colorless transparent solution; add 5 times the mass of anhydrous magnesium sulfate or molecular sieve, and continuously stir at room temperature for 24 hours; filter through a solvent filter to obtain a colorless transparent solution, remove the tetrahydrofuran solvent with a rotary evaporator, and then dry in an oven to obtain the terminal mercapto borate, which is a white solid powder;

[0010] Step 3: Weigh 100 parts of vinyl silicone rubber, add it into a mixing reactor, heat and stir, set the heating temperature to 80-250°C, add 0.1-10 parts of thermal initiator, add 1-20 parts of terminal mercapto borate, reactively process for 10-60 minutes, add 1-50 parts of polyborosiloxane gel PBS, continue stirring for 10-30 minutes, take out the silicone prepolymer and put it into a vacuum oven for heat treatment for 12-24 hours to obtain a high boron-filled dynamically cross-linked silicone elastomer;

[0011] Step 4: Take an appropriate amount of high-boron filled dynamically cross-linked silicone elastomer, and use compression molding processing at a hot pressing temperature of 100-250°C to obtain silicone elastomer samples of specific shape and size for testing.

[0012] The boronic acid small molecule described in step 1 is any one or a combination of boric acid, 1,4-phenyldiboronic acid, and 3-aminophenylboronic acid.

[0013] The low boiling point solvent described in step 1 is any one or a combination of methanol, ethanol, and isopropanol.

[0014] The vinyl silicone rubber described in step three is any one or a combination of methyl vinyl silicone rubber, methyl phenyl vinyl silicone rubber or phenyl vinyl silicone rubber.

[0015] The mixing reactor described in step 3 is any one of a Hake mixer, a twin-roll mill or a twin-screw extruder.

[0016] The thermal initiator described in step three is any one of diisopropylbenzene peroxide or 2,5-dimethyl-2,5-bis-(tert-butylperoxy)hexane.

[0017] The vacuum oven heat treatment temperature in step 3 is 60-200°C.

[0018] The present invention aims at the problems of low mechanical strength and insufficient heat resistance of organic silicon elastomer and poor water resistance of polyborosiloxane, combines the reinforcement and performance improvement functions of dynamic covalent bonds, mixes polyborosiloxane gel with organic silicon elastomer, introduces boron-oxygen dynamic covalent bonds into the organic silicon elastomer, and increases its boron content, thereby developing a high-performance thermoplastic organic silicon elastomer with high rate correlation, impact resistance, metal bonding and repeatable processing.

[0019] Compared with the prior art, the present invention has the following beneficial effects:

[0020] 1. The preparation process is simple and suitable for industrial mass production.

[0021] 2. The heat resistance of silicone elastomer is improved by introducing high boron filling.

[0022] 3. By introducing boron-oxygen dynamic covalent bonds, the strain rate response and impact resistance of organic elastomers are greatly improved, and they also have excellent repeatable processing performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 .Stress-strain curves of different samples at room temperature

[0024] Figure 2 .Stress relaxation curves of typical examples at different temperatures

[0025] Figure 3 Thermogravimetric curve of typical example samples

[0026] Figure 4 . Photographs of thermoplastic reprocessing of typical example samples DETAILED DESCRIPTION

[0027] In order to further explain the technical solution of the present invention, the following is a specific description in conjunction with the embodiments, but the protection scope of the present invention is not limited to these embodiments, and non-essential improvements and adjustments made to the present invention by those skilled in the art all fall within the protection scope of the present invention.

[0028] Example 1

[0029] 100 parts of methyl vinyl silicone rubber MVQ, 10 parts of terminal mercapto borate BDB and 1 part of thermal initiator dipentadienyl DBPH were weighed by weight. 100 parts of MVQ were first added into an internal mixer, and the temperature was set to 190°C. After the torque was stable, 10 parts of BDB and 1 part of DBPH were added, and the torque change was observed. After the torque reached a platform, the internal mixing was stopped to obtain a silicone prepolymer. The mixture obtained by internal mixing was placed in a vacuum oven at 80°C for heat treatment for 24 hours to obtain a high-boron-filled dynamically cross-linked silicone elastomer 1.

[0030] Example 2

[0031] Dissolve terminal hydroxyl polysiloxane and boric acid in methanol at a molar ratio of 2:3, react at 60°C for 6 hours using a magnetic stirrer, transfer the reactant to a vacuum oven for heat treatment at 120°C for 12 hours to solidify and remove the solvent, and obtain polyborosiloxane gel PBS;

[0032] Weigh 99 parts of methyl vinyl silicone rubber MVQ, 1 part of polyborosiloxane gel PBS, 4.95 parts of terminal mercapto borate BDB and 0.495 parts of thermal initiator dipentadienyl DBPH by weight, first add 99 parts of MVQ into the internal mixer, set the temperature to 190°C, add BDB after the torque is stable, add DBPH, reactively process for 30 minutes, add 1 part of polyborosiloxane gel PBS, continue stirring for 30 minutes, take out the silicone prepolymer and put it in, and heat treat it in a vacuum oven at 80°C for 24 hours to obtain a high boron filled dynamically cross-linked silicone elastomer 2.

[0033] Example 3

[0034] Dissolve terminal hydroxyl polysiloxane and boric acid in methanol at a molar ratio of 2:3, react at 60°C for 6 hours using a magnetic stirrer, transfer the reactant to a vacuum oven for heat treatment at 120°C for 12 hours to solidify and remove the solvent, and obtain polyborosiloxane gel PBS;

[0035] Weigh 95 parts of methyl vinyl silicone rubber MVQ, 5 parts of polyborosiloxane gel PBS, 4.75 parts of terminal mercapto borate BDB and 0.475 parts of thermal initiator dipentadienyl DBPH by weight, first add 95 parts of MVQ into the internal mixer, set the temperature to 190°C, add BDB after the torque is stable, add DBPH, reactively process for 30 minutes, add 5 parts of polyborosiloxane gel PBS, continue stirring for 30 minutes, take out the silicone prepolymer and put it in, and heat treat it in a vacuum oven at 80°C for 24 hours to obtain a high boron filled dynamically cross-linked silicone elastomer 3.

[0036] Example 4

[0037] Dissolve terminal hydroxyl polysiloxane and boric acid in methanol at a molar ratio of 2:3, react at 60°C for 6 hours using a magnetic stirrer, transfer the reactant to a vacuum oven for heat treatment at 120°C for 12 hours to solidify and remove the solvent, and obtain polyborosiloxane gel PBS;

[0038] Weigh 90 parts of methyl vinyl silicone rubber MVQ, 10 parts of polyborosiloxane gel PBS, 4.50 parts of terminal mercapto borate BDB and 0.45 parts of thermal initiator dipentadienyl DBPH by weight, first add 90 parts of MVQ into the internal mixer, set the temperature to 190°C, add BDB after the torque is stable, add DBPH, reactively process for 30 minutes, add 10 parts of polyborosiloxane gel PBS, continue stirring for 40 minutes, take out the silicone prepolymer and put it in, and heat treat it in a vacuum oven at 80°C for 24 hours to obtain a high boron filled dynamically cross-linked silicone elastomer 4.

[0039] Example 5

[0040] Dissolve terminal hydroxyl polysiloxane and boric acid in methanol at a molar ratio of 2:3, react at 60°C for 6 hours using a magnetic stirrer, transfer the reactant to a vacuum oven for heat treatment at 120°C for 12 hours to solidify and remove the solvent, and obtain polyborosiloxane gel PBS;

[0041] Weigh 80 parts of methyl vinyl silicone rubber MVQ, 20 parts of polyborosiloxane gel PBS, 4.00 parts of terminal mercapto borate BDB and 0.40 parts of thermal initiator dipentadienyl DBPH by weight, first add 80 parts of MVQ into the internal mixer, set the temperature to 190°C, add BDB after the torque is stable, add DBPH, reactively process for 30 minutes, add 20 parts of polyborosiloxane gel PBS, continue stirring for 50 minutes, take out the silicone prepolymer and put it in, and heat treat it in a vacuum oven at 80°C for 24 hours to obtain a high boron filled dynamically cross-linked silicone elastomer 5.

[0042] Example 6

[0043] Dissolve terminal hydroxyl polysiloxane and 1,4-phenylenediboric acid in methanol at a molar ratio of 2:1, react at 60°C for 6 hours using a magnetic stirrer, transfer the reactant to a vacuum oven for heat treatment at 120°C for 12 hours to solidify and remove the solvent, and obtain polyborosiloxane gel PBS;

[0044] Weigh 60 parts of methyl vinyl silicone rubber MVQ, 40 parts of polyborosiloxane gel PBS, 3.00 parts of terminal mercapto borate BDB and 0.30 parts of thermal initiator dipentadienyl DBPH by weight, first add 60 parts of MVQ into the internal mixer, set the temperature to 190°C, add BDB after the torque is stable, add DBPH, reactively process for 30 minutes, add 40 parts of polyborosiloxane gel PBS, continue stirring for 60 minutes, take out the silicone prepolymer and put it in, and heat treat it in a vacuum oven at 80°C for 24 hours to obtain a high boron filled dynamically cross-linked silicone elastomer 6.

[0045] Comparative Example 1

[0046] 90 parts of MVQ, 10 parts of polyborosiloxane gel PBS and 0.45 parts of initiator DBPH were weighed by weight. 90 parts of MVQ were first added into an internal mixer, the temperature was set to 80°C, 10 parts of PBS were added after the torque was stable, and the mixture was stirred for 10 minutes. 0.45 parts of thermal initiator DBPH were added and the mixture was continuously mixed for 15 minutes. The mixture after internal mixing was taken out and processed into a silicone rubber sheet by compression molding. The silicone rubber sheet was taken out and placed in a vacuum oven at 190°C for heat treatment for 24 hours to obtain a boron-modified silicone rubber 1.

[0047] Comparative Example 2

[0048] 100 parts of MVQ and 0.45 parts of initiator DBPH were weighed by weight. 100 parts of MVQ were first added into an internal mixer, the temperature was set to 80°C, 0.45 parts of thermal initiator DBPH were added, and mixing was continued for 15 minutes. The mixed mixture was taken out and processed into a silicone rubber sheet by compression molding. The silicone rubber sheet was taken out and placed in a vacuum oven at 190°C for heat treatment for 24 hours to obtain silicone rubber 1.

[0049] In order to investigate the comprehensive performance of the organosilicon elastomer obtained by the present invention, its mechanical and elastic properties were studied by uniaxial stretching and cyclic stretching, its viscoelasticity and stress relaxation behavior were analyzed by rheometer, and its heat resistance was evaluated by thermogravimetric analysis. The experimental results show that the high boron filled dynamic cross-linked organosilicon elastomer of the present invention has the advantages of strain rate response, metal adhesion, good heat resistance and thermoplastic repeated processing.

Claims

1. A method for preparing a high-boron-filled dynamically cross-linked silicone elastomer, characterized in that The steps include: Step 1: preparing polyborosiloxane gel PBS, dissolving terminal hydroxyl polysiloxane and boric acid small molecules in a low boiling point solvent at a molar ratio of 1:1 for esterification reaction, reacting at 60°C for 6 hours using a magnetic stirrer, transferring the reactant to a vacuum oven for heat treatment at 120°C for 12 hours to solidify and remove the solvent, thereby obtaining polyborosiloxane gel PBS; Step 2: Prepare terminal mercapto borate, mix 1,4-phenyldiboronic acid and α-thioglycerol in a molar ratio of 1:2, dissolve in 10 times the mass of tetrahydrofuran, and stir continuously on a magnetic stirrer to obtain a colorless transparent solution; add 5 times the mass of anhydrous magnesium sulfate or molecular sieve, and stir continuously at room temperature for 24 hours; filter through a solvent filter to obtain a colorless transparent solution, remove the tetrahydrofuran solvent with a rotary evaporator, and then dry in an oven to obtain the terminal mercapto borate, and the obtained terminal mercapto borate is a white solid powder; Step 3: Weigh 100 parts of vinyl silicone rubber, add it into a mixing reactor, heat and stir, set the heating temperature to 80-250°C, add 0.1-10 parts of thermal initiator, add 1-20 parts of terminal mercapto borate, reactively process for 10-60 minutes, add 1-50 parts of polyborosiloxane gel PBS, continue stirring for 10-30 minutes, take out the silicone prepolymer and put it into a vacuum oven for heat treatment for 12-24 hours to obtain a high boron-filled dynamically cross-linked silicone elastomer; Step 4: Take an appropriate amount of high-boron filled dynamically cross-linked silicone elastomer, and use compression molding processing at a hot pressing temperature of 100-250°C to obtain silicone elastomer samples of specific shape and size for testing.

2. The method for preparing the high-boron-filled dynamically cross-linked silicone elastomer according to claim 1, characterized in that The boric acid small molecule is any one or a combination of boric acid, 1,4-phenyldiboronic acid, and 3-aminophenylboronic acid.

3. The method for preparing the high-boron-filled dynamically cross-linked silicone elastomer according to claim 1, characterized in that The low boiling point solvent is any one or a combination of methanol, ethanol and isopropanol.

4. The method for preparing the high-boron-filled dynamically cross-linked silicone elastomer according to claim 1, characterized in that The vinyl silicone rubber is any one or a combination of methyl vinyl silicone rubber, methyl phenyl vinyl silicone rubber or phenyl vinyl silicone rubber.

5. The method for preparing the high-boron-filled dynamically cross-linked silicone elastomer according to claim 1, characterized in that The mixing reactor is any one of a Hake internal mixer, a twin-roll mill or a twin-screw extruder.

6. The method for preparing the high-boron-filled dynamically cross-linked silicone elastomer according to claim 1, characterized in that The thermal initiator is any one of dicumyl peroxide or 2,5-dimethyl-2,5-bis-(tert-butylperoxy)hexane.

7. The method for preparing the high-boron-filled dynamically cross-linked silicone elastomer according to claim 1, characterized in that The heat treatment temperature of the vacuum oven is 60-200°C.

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