Silylbenzopinacol radical initiator

Abstract

The present invention relates to a method for preparing a silylbenzopinacol radical initiator, comprising reacting benzophenone with a reducing agent selected from alkali metals and alkaline earth metals and a compound of general formula (I) R 1 R 2 SiCl2 (wherein, R 1 is C3 to C32 alkyl, R 2 is C1-C32 alkyl or Cl) with a silane, and a silylbenzopinacol radical initiator obtained by said method.

Description

[Technical Field]

[0001] The present invention relates to a method for preparing a silylbenzopinacol free radical initiator from benzophenone, a reducing agent, and a chloroalkylsilane. [Background technology]

[0002] Silylbenzopinacols are thermal free radical initiators used for the controlled crosslinking of unsaturated resins. They are prepared by the reaction of benzophenone with magnesium followed by the addition of alkyldichlorosilanes or alkyltrichlorosilanes or mixtures having C1 or C2 alkyl groups, as described, for example, in DE 2632294A. Typically, methyltrichlorosilane or dimethyldichlorosilane is used, which leads to a complex mixture of reactive products after hydrolysis and workup.

[0003] The products obtainable by known literature methods (see Comparative Example 1) are cloudy, heterogeneous suspensions. They exhibit the desired reactivity as free radical initiators for unsaturated free radical polymerizable materials. However, their heterogeneity makes it difficult to accurately set the curing rate of the unsaturated free radical polymerizable material, especially on an industrial scale, and the dosage of the free radical initiator often needs to be further adjusted to obtain a thermally polymerizable mixture with a consistent curing rate.

[0004] Furthermore, settling of finely dispersed solids in suspensions leads to the formation of sediments during storage, and these separated suspensions have to be laboriously rehomogenized through further processing steps, which, as will be appreciated by those skilled in the art, often poses problems on an industrial scale.

[0005] DE 2615039 A1 describes monomeric benzopinacol silyl ethers for use as free radical initiators, which can be prepared by the reduction reaction of benzophenone with trialkylmonochlorosilanes. Depending on the substituents, the products can exist as solids or liquids; in the case of long-chain alkyl substituents, it is possible to obtain liquid, homogeneous products. However, they exhibit much lower activity than their oligomeric counterparts obtainable from dialkyldichlorosilanes or alkyltrichlorosilanes. This makes them less suitable for industrial use. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] DE 2632294 A1 [Patent Document 2] DE 2615039 Summary of the Invention [Problem to be solved by the invention]

[0007] Therefore, there is a need for a free radical initiator that exists as a homogeneous solution and at the same time exhibits high reactivity. With the increase in reactivity of the free radical initiator, the amount of the free radical initiator can be reduced, which is preferable for cost reasons. [Means for solving the problem]

[0008] The present invention provides a method for preparing a silylbenzopinacol free radical initiator, in which benzophenone is reacted with a reducing agent selected from alkali metals and alkaline earth metals and a silane of general formula (I). R 1 R 2 SiCl2(I), [In the formula, R 1 is a C3 to C32 alkyl group, R 2 is a C1 to C32 alkyl group or Cl.]

[0009] The present invention also provides a silylbenzopinacol free radical initiator obtainable by this method. DETAILED DESCRIPTION OF THE INVENTION

[0010] The silylbenzopinacol free radical initiators of the present invention are transparent and homogeneous product mixtures, which greatly facilitate their use in applications.The initiator mixtures are liquid and do not show turbidity due to the long-chain alkyl substituents on the silicon atoms.As a result, they are more easily processable because they do not cause sedimentation, which would otherwise cause fluctuations in activity.They exhibit high reactivity as free radical initiators.

[0011] The reducing agent is preferably selected from lithium, sodium, potassium, magnesium and calcium, especially magnesium.

[0012] Silanes of general formula (I) or mixtures of different silanes of general formula (I) can be used.

[0013] Alkyl group R 1 The alkyl group R can be linear, branched or cyclic. 1 Examples are n-propyl, isopropyl, n-butyl, sec-butyl, isobutyl, tert-butyl, n-pentyl, sec-pentyl, isopentyl, neopentyl and tert-pentyl groups, hexyl groups such as n-hexyl, heptyl groups such as n-heptyl, octyl groups such as n-octyl and isooctyl groups such as 2,4,4-trimethylpentyl, nonyl groups such as n-nonyl, decyl groups such as n-decyl, dodecyl groups such as n-dodecyl, hexadecyl groups such as n-hexadecyl, octadecyl groups such as n-octadecyl, cycloalkyl groups such as cyclopentyl, cyclohexyl, cycloheptyl and methylcyclohexyl groups.

[0014] In a preferred embodiment, R 1 is an alkyl group having 3 to 20 carbon atoms, particularly 3 to 10 carbon atoms.

[0015] Alkyl group R 1 The alkyl group R can be linear, branched or cyclic. 2 Examples of R are methyl and ethyl groups. 1 In a preferred embodiment, R 2 is an alkyl group having 1 to 6 carbon atoms, in particular a methyl group, an ethyl group, an n-propyl group or an isopropyl group, in particular a methyl group.

[0016] In a preferred embodiment, R 1 is an alkyl group having 3 to 18 carbon atoms, and R 2 is Cl.

[0017] Surprisingly, silylbenzopinacols from dialkyldichlorosilanes have improved reactivity.

[0018] This enhanced reactivity has already been observed with dimethyldichlorosilane, but the corresponding silylbenzopinacol is a solid and therefore has poor or no processability.

[0019] Enhanced reactivity can also be observed in mixtures with methyltrichlorosilane, but the products are cloudy or even solid.

[0020] In particular, products from dialkyldichlorosilanes surprisingly exhibit significantly improved reactivity compared to their alkyltrichlorosilane analogs.

[0021] Therefore, in a preferred embodiment, R 1 is an alkyl group having 3 to 32 carbon atoms, and R 2 is an alkyl group having 1 to 32 carbon atoms, preferably R 1is an alkyl group having 3 to 20 carbon atoms, and R 2 is an alkyl group having 1 to 20 carbon atoms, and more preferably R 1 is an alkyl group having 6 to 12 carbon atoms, and R 2 is an alkyl group having 1 to 3 carbon atoms, in particular, R 1 is an alkyl group having 6 to 14 carbon atoms, and R 2 is a methyl group.

[0022] This process can be carried out in the presence or absence of an aprotic solvent. Aprotic and polar solvents are preferred. When an aprotic solvent is used, a solvent or solvent mixture having a boiling point or boiling range of up to 250°C at 0.1 MPa is preferred. Examples of such solvents are ethers such as dioxane, tetrahydrofuran, diethyl ether, methyl tert-butyl ether, diisopropyl ether, and diethylene glycol dimethyl ether; chlorinated hydrocarbons such as dichloromethane, trichloromethane, tetrachloromethane, 1,2-dichloroethane, and trichloroethylene; hydrocarbons such as pentane, n-hexane, hexane isomer mixtures, heptane, octane, petroleum spirit, petroleum ether, benzene, toluene, and xylene; siloxanes, especially those having trimethylsilyl end groups, preferably 0 to 6 linear dimethylpolysiloxanes having dimethylsiloxane units or cyclic dimethylpolysiloxanes having preferably 4 to 7 dimethylsiloxane units, such as hexamethyldisiloxane, octamethyltrisiloxane, octamethylcyclotetrasiloxane and decamethylcyclopentasiloxane, N,N-disubstituted amides, such as dimethylformamide, N,N-dimethylacetamide and tris(dimethylamide)phosphate, alkyl phosphates, such as trialkylphosphates and especially triethylphosphate, or mixtures of these solvents.

[0023] Ethers, hydrocarbons, trialkyl phosphates, and mixtures thereof are preferred.

[0024] The term "solvent" does not imply that all reaction components necessarily dissolve therein. Reactions may also be carried out in a suspension or emulsion of one or more reactants. Reactions may also be carried out in solvent mixtures with a miscibility gap, where at least one of the reactants is soluble in each phase of the mixture.

[0025] In a preferred embodiment, the reactants are activated with iodine, preferably at 0.001 to 0.1 moles of iodine per mole of reducing agent.

[0026] Preferably, first the benzophenone and the reducing agent and optionally the iodine are combined, and then the silane of general formula (I) is added.

[0027] Preferably, the molar ratio of benzophenone to reducing agent is between 0.8 and 1.5, in particular between 0.9 and 1.1 for lithium, sodium or potassium as reducing agent, or between 0.3 and 0.75, in particular between 0.4 and 0.6 for magnesium or calcium as reducing agent.

[0028] Preferably, the molar ratio of benzophenone to silane of general formula (I) is between 0.6 and 1.8, in particular between 0.8 and 1.2, based on Cl.

[0029] The process is preferably carried out at a temperature between 0°C and 80°C, more preferably between 10°C and 60°C, especially between 20°C and 50°C.

[0030] Preferably, the reaction time after addition of the silane of general formula (I) is between 30 minutes and 1 day, more preferably between 1 and 8 hours, especially between 2 and 6 hours.

[0031] The reaction is preferably worked up by adding water, neutralizing with a weak base such as sodium bicarbonate, and removing the aqueous phase.

[0032] If the process is carried out in the presence of an aprotic solvent, the solvent is preferably removed by distillation.

[0033] The silyl benzopinacol free radical initiators of the present invention find use as thermal free radical initiators for unsaturated polyester resins and unsaturated vinyl compounds such as styrene.

[0034] <Analysis of the entire invention>

[0035] <Gel time measurement to determine reactivity> The measurements are carried out using a Rosentreter gelation measuring device with a commercial unsaturated polyester resin (Palatal P04-1) from BUEFA. For the measurement, the resin is mixed with 1% of the product mixture, transferred to a test tube (160 x 16 mm) and attached to the gelation device. The sample is heated to 90°C and the stroke cycle of the plunger and gelation timer is initiated. The gelation time is stopped as soon as the pressure sensor of the device is activated.

[0036] In the following examples, all amounts and percentages are by weight, all pressures are 0.10 MPa (absolute) and all temperatures are 20° C. unless otherwise stated in any case. [Example]

[0037] [Example 1 (Non-invention)] 50 g of benzophenone is dissolved in xylene at 30°C, followed by the addition of 3.4 g of magnesium, 15 ml of THF, 34 ml of triethyl phosphate, and 0.06 g of iodine. 11 ml of methyltrichlorosilane is metered in over 180 minutes, and the reaction is stirred for another 60 minutes at 40°C. At the end of the reaction, 40 ml of water is added over 10 minutes, after which the phases are separated. The organic phase is neutralized with sodium bicarbonate solution, and after repeated phase separation, the volatiles are removed by distillation in a short-path evaporator. This results in a viscous yellow liquid that becomes cloudy upon storage. The gelation time is 9.7 minutes.

[0038] [Example 2 (Non-invention)] 50 g of benzophenone is dissolved in xylene at 30°C, followed by the addition of 3.4 g of magnesium, 15 ml of THF, 34 ml of triethyl phosphate, and 0.06 g of iodine. 20 ml of dimethyldichlorosilane is metered in, and the reaction mixture is stirred at 40°C for 4 hours. At the end of the reaction, 40 ml of water is added over 10 minutes, after which the phases are separated. The organic phase is neutralized with sodium bicarbonate solution, and after repeated phase separation, the volatile substances are removed by distillation. This results in a white, sparingly soluble solid. The gelation time is 6.5 minutes. The polymerized resin is heterogeneous.

[0039] [Example 3 (Non-invention)] 50 g of benzophenone is dissolved in xylene at 30°C, followed by the addition of 3.4 g of magnesium, 15 ml of THF, 34 ml of triethyl phosphate, and 0.06 g of iodine. 35 ml of trimethylchlorosilane is metered in, and the reaction mixture is stirred at 40°C for 4 hours. Solid formation can already be observed during the reaction. At the end of the reaction, 40 ml of water is added over 10 minutes, after which the aqueous phase is removed. The organic phase and the formed solid are neutralized with sodium bicarbonate solution, the aqueous phase is removed again, and the volatile substances are removed by distillation. This results in a white, sparingly soluble solid. The gelation time is 25 minutes. The polymerized resin is heterogeneous.

[0040] [Example 4 (Non-invention)] 50 g of benzophenone are dissolved in xylene at 30°C, followed by the addition of 3.4 g of magnesium, 15 ml of THF, 34 ml of triethyl phosphate, and 0.06 g of iodine. 64 ml of dimethyloctylchlorosilane are metered in, and the reaction mixture is stirred at 40°C for 4 hours. At the end of the reaction, 40 ml of water are added over 10 minutes, after which the phases are separated. The organic phase is neutralized with sodium bicarbonate solution, and after repeated phase separation, the volatile substances are removed by distillation. This gives a yellow liquid. The gelation time is 20 minutes.

[0041] [Example 5] 45 g of benzophenone are dissolved in xylene at 30°C, followed by the addition of 3.1 g of magnesium, 15 ml of THF, 30 ml of triethyl phosphate, and 0.06 g of iodine. 13 ml of propyltrichlorosilane are metered in, and the reaction is stirred at 40°C for 4 hours. At the end of the reaction, 80 ml of water are added over 10 minutes, after which the phases are separated. The organic phase is neutralized with sodium bicarbonate solution, and after repeated phase separation, the volatiles are removed by distillation in a short-path evaporator. This results in a viscous yellow liquid. The product remains clear even after storage. The gelation time is 11 minutes.

[0042] [Example 6] 45 g of benzophenone is dissolved in xylene at 30°C, followed by the addition of 3.1 g of magnesium, 15 ml of THF, 30 ml of triethyl phosphate, and 0.06 g of iodine. 20 ml of hexadecyltrichlorosilane is metered in, and the reaction is stirred at 40°C for 4 hours. At the end of the reaction, 80 ml of water is added over 10 minutes, after which the phases are separated. The organic phase is neutralized with sodium bicarbonate solution, and after repeated phase separation, the volatiles are removed by distillation in a short-path evaporator. This results in a viscous yellow liquid. The product remains clear even after storage. The gelation time is 8.9 minutes.

[0043] [Example 7] 50 g of benzophenone are dissolved in xylene at 30°C, followed by the addition of 3.4 g of magnesium, 15 ml of THF, 34 ml of triethyl phosphate, and 0.06 g of iodine. 35 ml of methyl-n-octyldichlorosilane are metered in, and the reaction is stirred at 40°C for 4 hours. At the end of the reaction, 40 ml of water are added over 10 minutes, after which the phases are separated. The organic phase is neutralized with sodium bicarbonate solution, and after repeated phase separation, the volatiles are removed by distillation in a short-path evaporator. This results in a viscous yellow liquid. The product remains clear even after storage. The gelation time is 6.2 minutes.

[0044] [Example 8] 40 g of benzophenone is dissolved in xylene at 30°C, followed by the addition of 2.8 g of magnesium, 12 ml of THF, 27 ml of triethyl phosphate, and 0.05 g of iodine. 47 ml of methyl-n-octyldichlorosilane is metered in, and the reaction is stirred at 40°C for 4 hours. At the end of the reaction, 40 ml of water is added over 10 minutes, after which the phases are separated. The organic phase is neutralized with sodium bicarbonate solution, and after repeated phase separation, the volatiles are removed by distillation in a short-path evaporator. This results in a viscous yellow liquid. The product remains clear even after storage. The gelation time is 5.9 minutes.

[0045] [Example 9] 25 g of benzophenone are dissolved in xylene at 30°C, followed by the addition of 1.7 g of magnesium, 7.4 ml of THF, 17 ml of triethyl phosphate, and 0.03 g of iodine. 25 ml of dioctyldichlorosilane are metered in, and the reaction is stirred at 40°C for 4 hours. At the end of the reaction, 20 ml of water are added over 10 minutes, after which the phases are separated. The organic phase is neutralized with sodium bicarbonate solution, and after repeated phase separation, the volatiles are removed by distillation in a short-path evaporator. This results in a viscous yellow liquid. The product remains clear even after storage. The gelation time is 8.0 minutes.

Claims

1. 1. A method for preparing a silylbenzopinacol free radical initiator, comprising: A process comprising reacting benzophenone with a reducing agent selected from alkali metals and alkaline earth metals and a silane of general formula (I). R １ R ２ SiCS ２ (I), [In the formula, R １ is a C3 to C32 alkyl group, R ２ is a C1 to C32 alkyl group or Cl.

2. R １ is an alkyl group having 3 to 18 carbon atoms, and R ２ The method of claim 1 , wherein is Cl.

3. R １ is an alkyl group having 3 to 20 carbon atoms, and R ２ The method of claim 1 or 2, wherein is an alkyl group having 1 to 20 carbon atoms.

4. The method according to any one of claims 1 to 3, wherein the reducing agent is magnesium.

5. The process according to any one of claims 1 to 4, which is carried out in the presence of an aprotic solvent.

6. 6. The method of any one of claims 1 to 5, wherein the reaction is activated with iodine.

7. 7. The method of any one of claims 1 to 6, wherein the benzophenone and the reducing agent and optionally iodine are first combined, and then the silane of general formula (I) is added.

8. A process according to any one of claims 1 to 7, wherein the reaction is worked up by adding water, neutralising with a weak base and removing the aqueous phase.