A method for synthesizing branched vinylphenyl silicone oil

Abstract

The application belongs to the technical field of organic silicon polymer synthesis, and discloses a synthesis method of branched vinyl phenyl silicone oil. The method first pre-hydrolyzes and condenses hydrolysable silane containing vinyl to form a branched siloxane core containing vinyl, then performs siloxane equilibrium copolymerization with phenyl ring siloxane monomer and dimethyl siloxane segment source, and adopts a siloxane end group blocking agent to close residual silicon hydroxyl and chain end active sites to obtain branched vinyl phenyl silicone oil. The method can control the construction of branched nodes, phenyl segments and vinyl sites in the same siloxane skeleton, reduce microgel and viscosity after growth, and improve the transparency, storage stability and addition curing uniformity of the silicone oil.

Description

Technical Field

[0001] This invention belongs to the field of organosilicon polymer synthesis technology and discloses a method for synthesizing branched vinylphenyl silicone oil. Background Technology

[0002] Branched vinylphenyl silicone oil belongs to the functionalized silicone oil category in organopolysiloxane synthesis technology. It is commonly used in addition-cure silicone rubber, optical encapsulants, heat-resistant coatings, and modified resin systems. Existing synthetic routes primarily use cyclic dimethylsiloxanes, phenylcyclosiloxanes, and vinyl-terminated siloxanes as main raw materials. These materials undergo equilibrium copolymerization of siloxanes under acidic or alkaline catalytic conditions, followed by neutralization, de-oxidation, and filtration to obtain linear or slightly branched vinylphenyl silicone oil. This method is mature, with stable raw material sources, and can introduce phenyl segments into the siloxane backbone while retaining vinyl reaction sites at the chain ends or some side positions. This route is suitable for ordinary linear silicone oils, but when used for branched vinylphenyl silicone oils, all monomers enter the reaction system at the same stage. Chain growth, chain transfer, ring-opening equilibrium, and end-capping reactions occur simultaneously. The product structure mainly depends on the monomer reactivity and catalytic equilibrium state, making it difficult for branching points, phenyl segments, and vinyl sites in the molecular skeleton to form in a predetermined order.

[0003] To obtain branched structures, existing technologies often employ multifunctional silanes, multifunctional siloxane oligomers, or silicone resin intermediates as branching units, which are then hydrolyzed, condensed, or copolymerized with cyclic siloxane monomers. These routes typically involve directly adding multifunctional units to the polymerization system, relying on their multiple reactive silicon functional groups to form branching nodes. While this method increases the degree of molecular branching, multifunctional units may continue to participate in condensation in both the early and late stages of the reaction, leading to secondary connections between branching nodes and resulting in the formation of localized high-molecular-weight components or microgels. In phenyl-containing systems, phenylsiloxane segments have significant steric hindrance, and their ring-opening and equilibrium rates differ from those of dimethylsiloxane segments. If branching units participate in the reaction simultaneously, phenyl segments tend to accumulate in some branched regions. This accumulation exacerbates localized segment stacking, making the product more prone to increased viscosity, decreased transparency, and batch-to-batch structural fluctuations during descaling, filtration, and storage.

[0004] The most common approach involves adding phenylcyclosiloxane, dimethylcyclosiloxane, vinyl end-capping agent, and a small amount of polyfunctional silane to a reactor, heating under an inert atmosphere for equilibrium copolymerization, and then adding a neutralizing agent to terminate the catalytic activity after the reaction. Low-molecular-weight rings and unreacted small molecules are then removed by depressurization. In this process, vinyl groups are mainly provided by the end-capping agent or a small amount of vinylsiloxane monomer, and their positions are mostly concentrated at the chain ends or random side groups. Phenyl segments randomly enter the main chain after ring opening. When polyfunctional silanes are used as a source of branching, their hydrolysis and condensation rates are inconsistent with the ring-opening equilibrium rate, easily causing structural deviations such as branching-first or chain segment-first formation. To avoid gelation, the amount of polyfunctional units added is often reduced during production. However, when the degree of branching is insufficient, high-phenyl silicone oil still exhibits an approximately linear structure, and the crosslinking point distribution is not uniform during subsequent addition curing. The post-treatment steps are mainly used to remove catalytic residues and low-boiling substances, making it difficult to readjust the already formed molecular framework.

[0005] Therefore, the main technical problem of existing technologies lies in the fact that during the synthesis of branched vinylphenyl silicone oil, the formation of branching nodes, the incorporation of phenyl siloxane segments, and the retention of vinyl active sites are usually in a competitive reaction state, making it difficult to form a controlled spatial distribution within the same siloxane backbone. When the proportion of phenyl segments is increased to meet the requirements of refractive index and heat resistance, the viscosity of the system and the tendency of segment stacking increase; when the degree of branching is increased to improve the curing network, residual silanol groups and multifunctional active sites may trigger further condensation; when the vinyl source is increased to ensure reactivity, vinyl sites may still be concentrated at the chain ends or in random regions. A synthetic method is needed to first form a vinyl-containing branched core as the basis for the growth of subsequent siloxane segments, then incorporate phenyl and dimethylsiloxane segments into this core, and seal the residual silanol groups and chain-end active sites, thereby solving the problem of the difficulty in the controlled formation of high phenyl, high vinyl, and branched structures. Summary of the Invention

[0006] To address the shortcomings of existing methods for synthesizing branched vinylphenyl silicone oils, where the formation of branching nodes, the incorporation of phenyl siloxane segments, and the retention of vinyl active sites are in a competitive reaction state, making it difficult to co-construct high-phenyl segments, high-vinyl active sites, and a controlled branched backbone within the same siloxane molecule, this invention provides a method for synthesizing branched vinylphenyl silicone oils. This method involves first constructing a vinyl-branched siloxane core, then performing a balanced copolymerization of siloxanes derived from phenyl cyclosiloxane monomers and dimethylsiloxane segments, and finally sealing residual silanol groups and terminal active sites. This allows the branched structure, phenyl segments, and vinyl sites to form a continuous and controlled structural association within the same siloxane backbone.

[0007] To address the aforementioned technical problems, this invention provides a method for synthesizing branched vinylphenyl silicone oil, comprising the following technical features: pre-hydrolyzing and condensing a vinyl-containing hydrolyzable silane to obtain a vinyl-containing branched siloxane core; mixing the vinyl-containing branched siloxane core with a phenylcyclosiloxane monomer and a dimethylsiloxane chain segment source and performing siloxane equilibrium copolymerization to form a branched vinylphenyl siloxane intermediate; and using a siloxane end-group blocking agent to block the residual silanol groups and chain-end active sites in the branched vinylphenyl siloxane intermediate to obtain branched vinylphenyl silicone oil.

[0008] During the pre-hydrolysis condensation process of the vinyl-containing hydrolyzable silane, the hydrolyzable groups on the silicon atoms first hydrolyze to generate silanol groups, which then condense to form siloxane bonds, thereby forming a branched siloxane core with a vinyl structure. This core serves as the growth basis for the molecular skeleton in the subsequent siloxane equilibrium copolymerization, allowing phenylcyclosiloxane monomers and dimethylsiloxane chain segments to undergo ring-opening, rearrangement, and incorporation around the vinyl-containing branched siloxane core, forming a branched vinylphenylsiloxane intermediate. Since the vinyl group has entered the branched core during the pre-hydrolysis condensation stage, and the phenyl segment is incorporated into the same skeleton during the siloxane equilibrium copolymerization stage, the two no longer compete entirely for random copolymerization in the same stage. After the siloxane end-group blocking agent blocks the residual silanol groups and chain-end active sites, the reaction source for further condensation in the siloxane skeleton is limited, and the product structure remains relatively stable during de-oxidation, cooling, and storage.

[0009] Furthermore, in the above technical solution, the vinyl-containing hydrolyzable silane includes vinyl-containing trifunctional silanes and vinyl-containing difunctional silanes. The vinyl-containing trifunctional silanes form branching nodes, and the vinyl-containing difunctional silanes connect to the short siloxane segments between the branching nodes. The pre-hydrolysis condensation is carried out in segments in the presence of a hydrolysis medium and a condensation regulator.

[0010] In specific implementation, the vinyl-containing trifunctional silane has numerous reaction sites capable of forming siloxane-silicon bonds, and can form branched nodes after hydrolysis; the vinyl-containing difunctional silane, after hydrolysis and condensation, forms relatively linear siloxane short-chain segments, which are then integrated between the branched nodes. The hydrolysis medium provides the reaction environment required for the hydrolyzable groups to convert into silanol groups, and the condensation regulator is used to regulate the silanol condensation process. Through segmented pre-hydrolysis and condensation, the vinyl-containing trifunctional silane and the vinyl-containing difunctional silane do not condense simultaneously in a completely disordered manner, thereby allowing the vinyl-containing branched siloxane core to retain siloxane short-chain segments while forming branched nodes.

[0011] Furthermore, in the above technical solution, the phenylcyclosiloxane monomer includes a cyclic body containing monophenylsiloxane segments and a cyclic body containing diphenylsiloxane segments, the dimethylsiloxane segment source includes cyclic dimethylsiloxane or hydroxyl-terminated dimethylsiloxane, and the phenylcyclosiloxane monomer is added after the formation of the vinyl-branched siloxane core.

[0012] In specific implementation, the cyclic monomers containing monophenylsiloxane segments and the cyclic monomers containing diphenylsiloxane segments enter the molecular backbone through ring-opening and rearrangement of siloxane bonds during the equilibrium copolymerization of siloxanes, forming phenylsiloxane segments. The cyclic dimethylsiloxane or hydroxyl-terminated dimethylsiloxane provides dimethylsiloxane segments, introducing flexible siloxane segments into the branched backbone. The phenyl cyclosiloxane monomer is added after the formation of the vinyl-containing branched siloxane core, allowing the phenyl segments to integrate into the already formed branched core, rather than competing disorderly with the vinyl-containing hydrolyzable silane during the pre-hydrolysis condensation stage. This distinguishes the formation of the branched core from the integration of the phenyl segments in the reaction sequence.

[0013] Furthermore, in the above technical solution, the siloxane balanced copolymerization includes first pre-balancing the vinyl-branched siloxane core with a portion of the phenylcyclosiloxane monomer, and then adding the remaining phenylcyclosiloxane monomer and the dimethylsiloxane chain segment source to continue copolymerization. Both the pre-balancing and the continued copolymerization are carried out under a siloxane balanced catalytic system.

[0014] In specific implementation, during the pre-equilibrium stage, the vinyl-branched siloxane core first undergoes siloxane bond exchange and chain segment incorporation with some phenylcyclosiloxane monomers, causing phenylsiloxane segments to preferentially form initial connections around the branched core. Subsequently, the remaining phenylcyclosiloxane monomers and the dimethylsiloxane chain segment source are added for further copolymerization, allowing the phenylsiloxane segments and dimethylsiloxane segments to continue expanding within the same framework. The siloxane equilibrium catalytic system endows siloxane bonds with ring-opening, breaking, and rearrangement capabilities, thereby enabling the vinyl-branched siloxane core, phenylcyclosiloxane monomers, and dimethylsiloxane chain segment source to form a branched vinylphenylsiloxane intermediate through siloxane bond rearrangement.

[0015] Furthermore, in the above technical solution, the siloxane end-blocking agent includes vinyl-terminated siloxane and inert-terminated siloxane. The vinyl-terminated siloxane is attached to the reactive chain end of the branched vinylphenyl siloxane intermediate, and the inert-terminated siloxane blocks the residual silanol groups in the branched vinylphenyl siloxane intermediate.

[0016] In specific implementation, the vinyl-terminated siloxane undergoes end-group attachment with the reactive chain end of the branched vinylphenyl siloxane intermediate, retaining the vinyl structure at the chain end; the inert-terminated siloxane reacts with the residual silanol, converting the residual silanol into a blocked siloxane end group. The vinyl-terminated siloxane and the inert-terminated siloxane correspond to the reactive chain end and the residual silanol, respectively, ensuring that the chain end reactivity and hydroxyl residue are controlled within the same end-capping step. This method prevents the residual silanol from continuing to condense during subsequent storage, while simultaneously ensuring that the product retains vinyl end groups suitable for addition curing.

[0017] Furthermore, in the above technical solution, the pre-hydrolysis condensation includes first contacting the vinyl-containing trifunctional silane with a hydrolysis medium to form a silanolization intermediate, then adding the vinyl-containing difunctional silane and a condensation regulator for condensation, and obtaining the vinyl-containing branched siloxane core by removing free water and low-boiling alcohol byproducts after condensation.

[0018] In specific implementation, the vinyl-containing trifunctional silane first contacts a hydrolysis medium, whereby the hydrolyzable groups are converted into silanol groups, forming a silanolization intermediate. This silanolization intermediate retains multiple condensation sites. After adding the vinyl-containing difunctional silane and a condensation regulator, the silanol groups formed by the hydrolysis of the difunctional silane condense with the silanolization intermediate, forming a branched structure with short siloxane segments. Removing free water and low-boiling alcohol byproducts after condensation reduces reverse hydrolysis, chain transfer, or side reactions caused by water and low-boiling byproducts in subsequent siloxane equilibrium copolymerization, allowing the vinyl-containing branched siloxane core to enter the next reaction stage as a relatively stable precursor structure.

[0019] Furthermore, in the above technical solution, the cyclic body containing monophenylsiloxane segments first contacts the core containing vinyl branched siloxane, and the cyclic body containing diphenylsiloxane segments is then added synchronously with the dimethylsiloxane segment source. The phenylcyclosiloxane monomer participates in the equilibrium copolymerization of the siloxane after dehydration pretreatment.

[0020] In specific implementation, the cyclic monomer containing monophenylsiloxane segments first contacts the vinyl-branched siloxane core, participating in ring-opening under siloxane equilibrium conditions to form initial phenyl-containing segments around the branched core. The cyclic monomer containing diphenylsiloxane segments is then added synchronously with the dimethylsiloxane segment source, allowing the more rigid diphenylsiloxane segments and the flexible dimethylsiloxane segments to enter the equilibrium copolymerization process together. The phenylcyclosiloxane monomer participates in the reaction after dehydration pretreatment, reducing the entry of exogenous moisture into the equilibrium copolymerization system and decreasing the possibility of siloxane bond hydrolysis or an increase in residual silanol groups, thus ensuring consistency between the phenyl segment incorporation process and the siloxane backbone expansion process.

[0021] Furthermore, in the above technical solution, the siloxane equilibrium catalytic system includes an alkaline silanolate catalyst and a neutralization terminator. The alkaline silanolate catalyst is used for the pre-equilibrium and the continued copolymerization. The neutralization terminator is added after the branched vinylphenyl siloxane intermediate is formed, and solid-liquid separation and de-lowering treatment are performed after termination.

[0022] In specific implementation, the alkaline silanolate catalyst promotes the ring-opening, breaking, and recombination of siloxane bonds, allowing the pre-equilibrium and continued copolymerization to proceed under the same siloxane equilibrium mechanism. After the branched vinylphenyl siloxane intermediate is formed, a neutralization terminator is added to terminate the alkaline activity of the catalytic system, reducing the driving force for further siloxane bond rearrangement. After termination, solid-liquid separation removes solid neutralization products or insoluble impurities from the reaction system; subsequently, a de-lowering treatment removes low-molecular-weight rings and low-boiling components that did not participate in copolymerization from the system, reducing interference from low-molecular-weight residues during the conversion of the resulting intermediate to the target branched vinylphenyl silicone oil.

[0023] Furthermore, in the above technical solution, the vinyl-branched siloxane core is closed and regulated before the addition of the phenylcyclosiloxane monomer. The closed and regulated process uses a monofunctional siloxane regulator to selectively treat the free silanol groups in the vinyl-branched siloxane core. The treated vinyl-branched siloxane core then enters the siloxane equilibrium copolymerization process.

[0024] In practice, the vinyl-containing branched siloxane core may retain free silanol groups after pre-hydrolysis and condensation. If these free silanol groups directly participate in condensation during subsequent equilibrium copolymerization, further connections may occur between the branched cores. The monofunctional siloxane regulator provides only limited end-group reactivity; by selectively treating the free silanol groups, it can convert some of the free silanol groups into a monofunctional siloxane closed structure. When the vinyl-containing branched siloxane core, after being closed and regulated, re-enters siloxane equilibrium copolymerization, the branched core mainly undergoes skeletal expansion through siloxane equilibrium rearrangement with phenylcyclosiloxane monomers and dimethylsiloxane chain segment sources, rather than through disordered condensation via excess free silanol groups.

[0025] Furthermore, in the above technical solution, the de-lowering treatment is followed by a refining step, which includes contacting the de-lowered silicone oil with an adsorbent containing siloxane-compatible segments, separating the adsorbent, and then subjecting it to inert gas replacement and filtration to obtain the branched vinylphenyl silicone oil.

[0026] In practice, the degraded silicone oil may still contain small amounts of catalytic residues, adsorbent impurities, or insoluble fine particles. The adsorbent containing siloxane-compatible segments can maintain compatible contact with the siloxane system, allowing the adsorption and purification process to take place in the silicone oil phase. After the degraded silicone oil comes into contact with the adsorbent, the adsorbable residues in the system are enriched on the surface or inside of the adsorbent; after separating the adsorbent, the residual impurities are removed from the silicone oil along with the adsorbent. Further inert gas replacement and filtration can reduce the impact of oxygen and fine insoluble particles on the appearance and storage process of the finished product, ultimately yielding the branched vinylphenyl silicone oil.

[0027] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. This invention involves pre-hydrolyzing and condensing a vinyl-containing hydrolyzable silane to obtain a vinyl-containing branched siloxane core. This core is then subjected to siloxane equilibrium copolymerization with a phenylcyclosiloxane monomer and a dimethylsiloxane chain segment source. Subsequently, a siloxane end-blocking agent seals the residual silanol groups and chain-end active sites. This sequence ensures that branching nodes form before the phenyl segments are incorporated, allowing subsequent phenylsiloxane and dimethylsiloxane segments to expand around the vinyl-containing branched core, reducing the chance of random linkage of multifunctional units in the later stages of copolymerization. Vinyl groups are incorporated into the branched core or reactive chain ends, and phenyl segments are incorporated into the same siloxane backbone through equilibrium copolymerization. The end-capping step restricts further condensation of residual silanol groups, resulting in a silicone oil with a continuous structural relationship between its branched structure, phenyl segments, and vinyl sites. Compared to the direct co-addition of multifunctional silanes, phenyl cyclic compounds, and end-capping agents, this method reduces the formation of microgels and localized high-molecular-weight components, minimizes viscosity climb during storage caused by residual active sites, and allows the introduction of high-phenyl segments and retention of addition-reactive activity to coexist in the same product. Because the residual chain ends are blocked, the source of continued condensation during subsequent de-lowering and cooling processes is reduced, resulting in silicone oils that are more suitable for forming transparent, homogeneous, and flowable branched vinylphenyl siloxane systems.

[0028] 2. The segmented pre-hydrolysis and condensation of the vinyl-containing trifunctional and difunctional silanes allows the branching nodes to first form a transition structure with the short siloxane segments. The vinyl-containing branched siloxane core is treated with a monofunctional siloxane regulator before copolymerization to limit the number of free silanol groups. The monophenyl siloxane cyclic body first contacts the branched core, followed by the diphenyl siloxane cyclic body and the dimethyl siloxane chain segment source, ensuring that the phenyl chain segment incorporation process and the system flowability adjustment process are coordinated. The phenyl cyclosiloxane monomer participates in copolymerization after dehydration pretreatment, reducing the amount of water introduced and the source of condensation side reactions. The continuous setting of pre-equilibrium, continued copolymerization, neutralization termination, and de-lowering treatment ensures that catalytic equilibrium stops after the formation of the branched vinylphenyl siloxane intermediate, and low-molecular-weight cyclic bodies and volatile small molecules are removed from the system. Vinyl-terminated siloxanes and inert-terminated siloxanes treat the reactive chain ends and residual silanol groups respectively, reducing structural rearrangement during post-processing and storage. After the silicone oil is degraded, it is treated with an adsorption purifier containing siloxane-compatible segments, replaced with an inert gas and filtered. The residual catalytic components, adsorbent impurities and insoluble fine particles are separated out. The resulting silicone oil has more stable physical properties in terms of transparency, filterability, low volatile component control and uniformity of subsequent addition curing. Detailed Implementation

[0029] The present invention will be further described in detail below with reference to embodiments. Those skilled in the art can reproduce the technical solution of the present invention and achieve its claimed technical effects based on the content disclosed in this specification. It should be noted that the following embodiments are only used to explain the present invention and are not intended to limit the scope of protection of the present invention. Any non-substantial improvements and adjustments made based on the core concept of the present invention should fall within the scope of protection of the present invention.

[0030] Example 1: This example is the best embodiment. The branched vinylphenyl silicone oil is prepared from the following raw materials: 60g of vinyltrimethoxysilane, a vinyl-containing trifunctional silane; 40g of methylvinyldimethoxysilane, a vinyl-containing difunctional silane; 32g of deionized water, a condensation regulator of 20g of hydroxyl-terminated dimethylsiloxane; 6g of hexamethyldisiloxane, a monofunctional siloxane regulator; and 26g of methylphenylcyclosiloxane, a cyclic compound containing monophenylsiloxane segments. 0g, containing 110g of diphenylcyclosiloxane containing diphenylsiloxane segments, 500g of octamethylcyclotetrasiloxane as the dimethylsiloxane segment source, 1.8g of potassium siloxane as the basic silanolate catalyst, 18g of tetramethyldivinyldisiloxane as the vinyl-terminated siloxane, 8g of hexamethyldisiloxane as the inert-terminated siloxane, 2.5g of sodium dihydrogen phosphate as the neutralization terminator, and 10g of polydimethylsiloxane segment-modified silica gel as the adsorbent containing siloxane-compatible segments.

[0031] In the preparation process, nitrogen gas was introduced into a reactor equipped with stirring, condensation, and vacuum desorption devices for purging. Vinyltrimethoxysilane and deionized water were added, and the mixture was stirred at 35°C for 50 min to form a silanolized intermediate from the vinyl-containing trifunctional silane. Then, methylvinyldimethoxysilane and hydroxyl-terminated dimethylsiloxane were added, and the mixture was condensed at 60°C for 2 h. After condensation, the mixture was treated at 75°C and -0.090 MPa for 1 h to remove free water and low-boiling alcohol byproducts, yielding a vinyl-branched siloxane core. 6 g of hexamethyldisiloxane was added to the vinyl-branched siloxane core, and the mixture was sealed and conditioned at 80°C for 45 min.

[0032] Methylphenylcyclosiloxane and diphenylcyclosiloxane were pre-treated for dehydration at 100℃ and -0.095MPa for 1.5 h. Methylphenylcyclosiloxane and potassium silanolate were added to the sealed and conditioned vinyl-branched siloxane core, and pre-equilibrated at 120℃ for 90 min; subsequently, diphenylcyclosiloxane and octamethylcyclotetrasiloxane were added, and copolymerization continued at 135℃ for 4 h to form a branched vinylphenylsiloxane intermediate. The system was cooled to 105℃, and tetramethyldivinyldisiloxane and 8 g of hexamethyldisiloxane were added, and the mixture was kept at this temperature for 1 h to block residual silanol groups and chain-terminal active sites. Sodium dihydrogen phosphate was added, and the mixture was stopped at 90℃ for 40 min for solid-liquid separation; the filtrate was dehydrated at 150℃ and -0.098MPa for 2 h. The degraded silicone oil was added to polydimethylsiloxane segment-modified silica gel and contacted at 80°C for 1 hour. After separating the adsorbent and purifying agent, nitrogen was purged for 30 minutes, and then filtered through a 0.45 μm filter to obtain branched vinylphenyl silicone oil.

[0033] Example 2: The difference between this example and Example 1 is that the amount of vinyltrimethoxysilane used is 50g, and the amount of methylvinyldimethoxysilane used is 50g. This change is used to investigate the effect of the ratio of vinyl-containing trifunctional silanes to vinyl-containing difunctional silanes on the formation of vinyl-containing branched siloxane cores. All other raw material types, amounts, and preparation conditions are the same as in Example 1.

[0034] Example 3: The difference between this example and Example 1 is that the amount of vinyltrimethoxysilane used is 70g, and the amount of methylvinyldimethoxysilane used is 30g. This change is used to investigate the adaptability of pre-hydrolysis condensation and siloxane equilibrium copolymerization under conditions with higher branching nodes. The other raw material types, raw material amounts, and preparation conditions are the same as in Example 1.

[0035] Example 4: The difference between this example and Example 1 is that the amount of methylphenylcyclosiloxane is 310g and the amount of diphenylcyclosiloxane is 60g. This change is used to examine the incorporation of phenylcyclosiloxane monomers onto vinyl-branched siloxane cores when the ratio of cyclic compounds containing monophenylsiloxane segments to cyclic compounds containing diphenylsiloxane segments changes. All other raw material types, amounts, and preparation conditions are the same as in Example 1.

[0036] Example 5: The difference between this example and Example 1 is that the amount of methylphenylcyclosiloxane is 210g and the amount of diphenylcyclosiloxane is 160g. This change is used to investigate the effect of the dimethylsiloxane repeating source on the flowability of the siloxane equilibrium copolymerization system under the condition of higher diphenylsiloxane repeating introduction. All other raw material types, amounts, and preparation conditions are the same as in Example 1.

[0037] Example 6: The difference between this example and Example 1 is that 500g of octamethylcyclotetrasiloxane was replaced with an equal amount of 500g of hydroxyl-terminated dimethylsiloxane as the dimethylsiloxane chain segment source. This change was used to examine the applicability of cyclic dimethylsiloxane and hydroxyl-terminated dimethylsiloxane as dimethylsiloxane chain segment sources. All other raw material types, amounts, and preparation conditions remained the same as in Example 1.

[0038] Example 7: The difference between this example and Example 1 is that the amount of tetramethyldivinyldisiloxane used is 22g, and the amount of hexamethyldisiloxane used as the inert end-capping siloxane is 4g. This change is used to examine the effect of varying the ratio of vinyl-terminated siloxane to inert end-capped siloxane on the chain-end closed structure. All other raw material types, amounts, and preparation conditions are the same as in Example 1.

[0039] Example 8: The difference between this example and Example 1 is that the amount of hexamethyldisiloxane, the monofunctional siloxane regulator used in the closed-loop regulation, is 3g. This change is used to investigate the effect of the degree of selective treatment of free silanol groups in the vinyl-branched siloxane core on the subsequent siloxane equilibrium copolymerization. All other raw material types, amounts, and preparation conditions are the same as in Example 1.

[0040] Example 9: The difference between this example and Example 1 is that the adsorbent containing siloxane-compatible segments is replaced by methylphenylsiloxane-modified silica gel instead of polydimethylsiloxane-modified silica gel, with a dosage of 10g. This change is used to investigate the adaptability of adsorbents with different siloxane-compatible segments to the silicone oil refining process after desaturation. All other raw material types, dosages, and preparation conditions are the same as in Example 1.

[0041] Example 10: This example maintains the same formulation as Example 1, except that the temperature at which vinyltrimethoxysilane is contacted with deionized water to form the silanol intermediate is adjusted from 35°C to 45°C. The remaining steps of pre-hydrolysis condensation, blocking adjustment, dehydration pretreatment, pre-equilibrium, continued copolymerization, end-group blocking, neutralization termination, solid-liquid separation, de-lowering treatment, and purification are the same as in Example 1.

[0042] Example 11: This example maintains the same formulation as Example 1, except that the pre-equilibration temperature of the vinyl branched siloxane core and methylphenylcyclosiloxane is adjusted from 120°C to 115°C. The remaining steps of pre-hydrolysis condensation, blocking adjustment, dehydration pretreatment, continued copolymerization, end-group blocking, neutralization termination, solid-liquid separation, dehydration treatment, and purification are the same as in Example 1.

[0043] Example 12: This example maintains the same formulation as Example 1, except that the dehydration treatment temperature is adjusted from 150°C to 140°C. The remaining steps of pre-hydrolysis condensation, sealing adjustment, dehydration pretreatment, pre-equilibrium, continued copolymerization, end-group sealing, neutralization termination, solid-liquid separation, and purification are the same as in Example 1.

[0044] Comparative Example 1: This comparative example is a comparison example lacking the core component. The difference from Example 1 is that vinyltrimethoxysilane is not added, and it is replaced by an equal amount of 60g methylvinyldimethoxysilane, thus eliminating the branching nodes formed by vinyl-containing trifunctional silanes. All other raw material types, amounts, and preparation conditions are the same as in Example 1.

[0045] Comparative Example 2: This comparative example uses a conventional preparation process. Following the same raw material types and total amounts as in Example 1, vinyltrimethoxysilane, methylvinyldimethoxysilane, deionized water, hydroxyl-terminated dimethylsiloxane, methylphenylcyclosiloxane, diphenylcyclosiloxane, octamethylcyclotetrasiloxane, tetramethyldivinyldisiloxane, hexamethyldisiloxane, and potassium silanolate were added to a reactor and subjected to equilibrium copolymerization at 135°C for 4 hours. No pre-construction of vinyl-branched siloxane cores was performed, and no segmented incorporation of phenylcyclosiloxane monomers was carried out. After the reaction, neutralization termination, solid-liquid separation, de-lowering treatment, purification, nitrogen purging, and filtration were performed as in Example 1.

[0046] Comparative Example 3: This comparative example shows a deviation of the preparation method parameters from the comparative example. The difference from Example 1 is that the condensation temperature after adding methylvinyldimethoxysilane and hydroxyl-terminated dimethylsiloxane was adjusted from 60°C to 95°C. The other raw material types, amounts, and preparation conditions are the same as in Example 1.

[0047] Comparative Example 4: This comparative example is a missing preparation method. The difference from Example 1 is that, after forming the branched vinylphenylsiloxane intermediate, tetramethyldisiloxane and hexamethyldisiloxane as an inert end-capping siloxane are not added, and the residual silanol groups and chain-end active sites are not blocked. The other raw material types, amounts, and preparation conditions are the same as in Example 1.

[0048] Test method: The viscosity of the silicone oils obtained in each example and comparative example was measured at 25°C using a rotational viscometer. The sample was placed in a sealed, light-protected environment at 25°C for 30 days, and the viscosity growth rate was calculated. The transmittance at 450 nm was measured using a 10 mm cuvette; the volatile matter was determined at 150 °C for 2 h. The residual silanol content was determined by infrared external standard method; The filtration residue was determined by weighing using a 0.45µm filter membrane. The vinyl retention rate was verified by iodometric titration combined with proton nuclear magnetic resonance spectroscopy. The refractive index at 25℃ was determined using an Abbe refractometer.

[0049] The hardness difference of the cured cross section was measured using the same evaluation system, that is, each sample was mixed with the same hydrogen-containing silicone oil and platinum catalyst, cured and shaped under the same conditions, and the Shore A hardness was measured on the upper, middle and lower surfaces of the cured material, and the difference between the maximum and minimum values ​​was recorded.

[0050] The test results are shown in Table 1 and Table 2.

[0051] Table 1 Performance test results of each embodiment and comparative example

[0052] Table 2 Performance test results of each embodiment and comparative example

[0053] Results analysis: Example 1 uses a vinyl-containing trifunctional silane to first form a silanolization intermediate, which is then pre-hydrolyzed and condensed with a vinyl-containing difunctional silane to obtain a vinyl-containing branched siloxane core. This core is treated with a monofunctional siloxane regulator, then pre-equilibrated with a cyclic compound containing monophenyl siloxane segments, followed by copolymerization with a cyclic compound containing diphenyl siloxane segments and a dimethyl siloxane segment source, and finally closed with vinyl-terminated and inert-terminated siloxanes. As shown in the table, Example 1 has a transmittance of 98.4%, a 30-day viscosity increase of 1.8%, a residual silanol content of 12 mmol / kg, a filter residue of 18 mg / kg, a vinyl retention rate of 96.8%, and a hardness difference of 2.1 Shore A across the cured product cross-section. The above data indicate that the branching nodes, phenylsiloxane segments, and vinyl sites form a relatively uniform structural association in the stepwise reaction. After the residual silanol groups and chain-end active sites are blocked, the sources of condensation continue to decrease during storage, resulting in a smaller difference in hardness between different cross sections in the subsequent addition curing evaluation.

[0054] Examples 2 and 3 only varied the ratio of vinyl-containing trifunctional silanes to vinyl-containing difunctional silanes. In Example 2, the source of branching nodes decreased, the viscosity at 25°C dropped to 4100 mPa·s, and the hardness difference of the cured product cross-section was 2.5 Shore A. In Example 3, the source of branching nodes increased, the viscosity at 25°C rose to 5100 mPa·s, and the filter residue increased to 34 mg / kg. Compared with Example 1, both examples maintained a transmittance greater than 97.0%, a vinyl retention rate greater than 95.0%, and a 30-day viscosity increase rate less than 3.5%, indicating that the pre-construction of vinyl-containing branched siloxane cores can adapt to different branching node ratios and maintain the operability of siloxane balanced copolymerization.

[0055] Examples 4 and 5 only varied the ratio of rings containing monophenylsiloxane segments to rings containing diphenylsiloxane segments. Example 4 had a refractive index of 1.514 and a viscosity of 3900 mPa·s; Example 5 had a refractive index of 1.536 and a viscosity of 6100 mPa·s. This result corresponds to the changes in phenyl segment content and structural rigidity. Example 5 maintained 96.0% transmittance and a 3.7% 30-day viscosity increase rate even with a higher diphenylsiloxane segment content, indicating that the dimethylsiloxane segment source and stepwise equilibrium copolymerization can buffer the segment stacking caused by the diphenylsiloxane segments, and the product did not exhibit the high residue and significant turbidity commonly seen in the comparative examples.

[0056] In Example 6, the cyclic dimethylsiloxane was replaced with a hydroxyl-terminated dimethylsiloxane. The resulting silicone oil had a residual silanol content of 24 mmol / kg and a 30-day viscosity increase of 3.6%, which was higher than that of Example 1, but still lower than the comparative examples. This result indicates that the morphological change of the dimethylsiloxane chain segment source affects the residual terminal hydroxyl content and the stability after de-saturation. However, with the combined effects of end-group blocking and purification steps, the product still maintained 97.0% transmittance and 94.8% vinyl retention.

[0057] In Example 7, after increasing the proportion of vinyl-terminated siloxanes, the vinyl retention rate was 97.2%, and the hardness difference of the cured product cross-section was 2.0 Shore A, indicating that the participation of vinyl-terminated siloxanes in chain end-closure can make the crosslinking reaction sites in the curing evaluation more fully distributed. In Example 8, after reducing the amount of monofunctional siloxane regulator, the residual silanol groups increased to 26 mmol / kg, the filter residue increased to 60 mg / kg, and the 30-day viscosity growth rate increased to 4.8%, indicating that blocking and regulating the free silanol groups before the vinyl-branched siloxane core enters the copolymerization of phenylcyclosiloxane monomers is beneficial to reducing subsequent secondary condensation and microgel formation. In Example 9, after replacing the adsorbent with one containing siloxane-compatible segments, the filter residue was 14 mg / kg, and the transmittance was 98.7%, indicating that the siloxane-compatible segments of the adsorbent are beneficial to completing the enrichment and separation of residues in the silicone oil phase.

[0058] Examples 10, 11, and 12 maintained the same formulation, only changing the silanization intermediate formation temperature, pre-equilibrium temperature, or de-lowering treatment temperature. The light transmittance of all three examples was not less than 97.6%, the vinyl retention rate was not less than 95.7%, and the hardness difference of the cured product cross-section was not higher than 2.7 Shore A. In Example 12, due to the lower de-lowering treatment temperature, the volatile matter content increased to 0.70%, but remained at a low level. These results indicate that, with the formulation unchanged, the combined process of pre-hydrolysis condensation, segmented siloxane equilibrium copolymerization, end-group blocking, and refining has process tolerance; slight changes in process parameters will not damage the main structural characteristics of the branched vinylphenyl silicone oil.

[0059] Comparative Example 1 lacks branched nodes formed by vinyl-containing trifunctional silanes. Although its light transmittance is 98.8% and the filtration residue is 20 mg / kg, its viscosity at 25°C is only 2200 mPa·s, and the hardness difference of the cured product cross-section reaches 7.8 Shore A. This result indicates that siloxane segments formed solely by vinyl-containing difunctional silanes cannot replace branched nodes, and the resulting silicone oil exhibits insufficient uniformity in cross-linking structure distribution during subsequent curing evaluation. Compared to Example 1, the main difference in Comparative Example 1 stems from the absence of branched nodes, thus demonstrating that the vinyl-containing branched siloxane core is the fundamental structure for forming branched vinylphenyl silicone oil.

[0060] Comparative Example 2 employed a conventional co-feed equilibrium process without pre-construction of the vinyl-branched siloxane core or segmental incorporation of the phenylcyclosiloxane monomer. This sample exhibited a reduced transmittance of 88.5%, a viscosity at 25°C reaching 9800 mPa·s, a filtration residue of 320 mg / kg, and a 30-day viscosity increase of 16.5%. These results indicate that when multifunctional silanes, phenylcyclosiloxane monomers, dimethylsiloxane chain segment sources, and end-capped siloxanes coexist in the same stage, hydrolysis-condensation, ring-opening equilibrium, and end-group blocking reactions compete with each other, easily forming localized high-molecular-weight components and microgels, and reducing vinyl retention to 82.4%. Compared to Example 1, the stepwise construction of the branched core and segmental incorporation of the phenyl chain segment alters the formation sequence of the branching nodes and phenyl segments, making the product structure more controllable.

[0061] Comparative Example 3, with the pre-hydrolysis condensation temperature increased to 95°C, yielded a sample with a transmittance of only 76.2%, a viscosity of 16800 mPa·s at 25°C, a filter residue of 1250 mg / kg, and a 30-day viscosity increase of 28.0%. These results indicate that vinyl-containing trifunctional and difunctional silanes are prone to over-condensation at excessively high condensation temperatures, forming highly branched aggregates that are difficult to disperse uniformly in subsequent siloxane equilibrium copolymerization. When these aggregates enter the copolymerization stage of phenylcyclosiloxane monomers and dimethylsiloxane chain segments, they cause system turbidity, increased filter residue, and a widening of the hardness difference across the cured product cross-section. Compared to Example 1, moderate control of the pre-hydrolysis condensation stage is a key condition for maintaining the copolymerizability of vinyl-containing branched siloxane cores.

[0062] Comparative Example 4, omitting the siloxane end-group blocking agent, yielded a sample with residual silanol groups of 165 mmol / kg, a 30-day viscosity increase of 24.5%, a vinyl retention rate reduced to 74.0%, and a cured product cross-sectional hardness difference of 10.8 Shore A. These results indicate that after the formation of the branched vinylphenyl siloxane intermediate, if the residual silanol groups and chain-end active sites are not blocked, the system still has sources of continued condensation and structural rearrangement during desaturation, storage, and curing evaluation. Example 1, by treating the reactive chain ends and residual silanol groups with vinyl-terminated and inert-terminated siloxanes respectively, maintained a low level of residual activity in the siloxane backbone after post-treatment, resulting in a low viscosity increase rate and a low cured product cross-sectional hardness difference.

Claims

1. A method for synthesizing branched vinylphenyl silicone oil, characterized in that, Includes the following steps: Pre-hydrolysis condensation of vinyl-containing hydrolyzable silanes yields vinyl-branched siloxane cores; The vinyl-branched siloxane core is mixed with phenylcyclosiloxane monomer and dimethylsiloxane chain segment source and subjected to siloxane equilibrium copolymerization to form a branched vinylphenylsiloxane intermediate. The residual silanol groups and chain-end active sites in the branched vinylphenyl siloxane intermediate were blocked by a siloxane end-blocking agent to obtain branched vinylphenyl silicone oil.

2. The method for synthesizing branched vinylphenyl silicone oil according to claim 1, characterized in that, The vinyl-containing hydrolyzable silanes include vinyl-containing trifunctional silanes and vinyl-containing difunctional silanes. The vinyl-containing trifunctional silanes form branching nodes, and the vinyl-containing difunctional silanes are connected to the short siloxane segments between the branching nodes. The pre-hydrolysis condensation is carried out in segments in the presence of a hydrolysis medium and a condensation regulator.

3. The method for synthesizing branched vinylphenyl silicone oil according to claim 1, characterized in that, The phenylcyclosiloxane monomer includes a cyclic body containing monophenylsiloxane segments and a cyclic body containing diphenylsiloxane segments. The dimethylsiloxane segment source includes cyclic dimethylsiloxane or hydroxyl-terminated dimethylsiloxane. The phenylcyclosiloxane monomer is added after the formation of the vinyl-branched siloxane core.

4. The method for synthesizing branched vinylphenyl silicone oil according to claim 1, characterized in that, The siloxane equilibrium copolymerization includes first pre-equilibrating the vinyl-branched siloxane core with a portion of the phenylcyclosiloxane monomer, and then adding the remaining phenylcyclosiloxane monomer and the dimethylsiloxane chain segment source to continue copolymerization. Both the pre-equilibration and the continued copolymerization are carried out under a siloxane equilibrium catalytic system.

5. The method for synthesizing a branched vinylphenyl silicone oil according to claim 1, characterized in that, The siloxane end-blocking agent includes vinyl-terminated siloxanes and inert-terminated siloxanes. The vinyl-terminated siloxanes are attached to the reactive chain ends of the branched vinylphenyl siloxane intermediate, and the inert-terminated siloxanes block the residual silanol groups in the branched vinylphenyl siloxane intermediate.

6. The method for synthesizing a branched vinylphenyl silicone oil according to claim 2, characterized in that, The pre-hydrolysis condensation includes first contacting the vinyl-containing trifunctional silane with a hydrolysis medium to form a silanolization intermediate, then adding the vinyl-containing difunctional silane and a condensation regulator for condensation, and finally obtaining the vinyl-containing branched siloxane core by removing free water and low-boiling alcohol byproducts after condensation.

7. The method for synthesizing branched vinylphenyl silicone oil according to claim 3, characterized in that, The cyclic body containing monophenylsiloxane segments first contacts the core containing vinyl branched siloxane, and the cyclic body containing diphenylsiloxane segments is then added synchronously with the dimethylsiloxane segment source. The phenylcyclosiloxane monomer participates in the equilibrium copolymerization of the siloxane after dehydration pretreatment.

8. The method for synthesizing branched vinylphenyl silicone oil according to claim 4, characterized in that, The siloxane equilibrium catalytic system includes an alkaline silanolate catalyst and a neutralization terminator. The alkaline silanolate catalyst is used for the pre-equilibrium and the continued copolymerization. The neutralization terminator is added after the branched vinylphenyl siloxane intermediate is formed, and solid-liquid separation and de-lowering treatment are performed after termination.

9. The method for synthesizing a branched vinylphenyl silicone oil according to claim 6, characterized in that, The vinyl-branched siloxane core is closed and regulated before the addition of the phenylcyclosiloxane monomer. The closed regulation is achieved by selectively treating the free silanol groups in the vinyl-branched siloxane core with a monofunctional siloxane regulator. The treated vinyl-branched siloxane core then enters the siloxane equilibrium copolymerization.

10. The method for synthesizing a branched vinylphenyl silicone oil according to claim 8, characterized in that, The de-lowering treatment is followed by a refining step, which includes contacting the de-lowered silicone oil with an adsorbent containing siloxane-compatible segments, separating the adsorbent, and then subjecting it to inert gas replacement and filtration to obtain the branched vinylphenyl silicone oil.

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