SILYLBENZPINACOL RADICAL INITIATOR

Description

[0001] The invention relates to a process for the preparation of silylbenzpinacol radical initiators from benzophenone, reducing agent and chloroalkylsilane.

[0002] Silylbenzpinacols are thermal radical initiators used for the controlled crosslinking of unsaturated resins. Their preparation, described, for example, in DE2632294A, occurs by reacting benzophenone with magnesium and subsequently adding a dichloro-, trichloroalkylsilane with a C1 or C2 alkyl radical, or a mixture. Typically, trichloromethylsilane or dichlorodimethylsilane are used, which, after hydrolysis and workup, leads to a complex, active product mixture.

[0003] The products obtainable by the processes known from the literature (see Comparative Example 1) are cloudy, inhomogeneous suspensions. They exhibit the desired reactivity as free-radical initiators for unsaturated, free-radically polymerizable substances. However, due to their inhomogeneity, precise adjustment of the curing rate of unsaturated, free-radically polymerizable substances is difficult, especially on an industrial scale, and the dosage of the free-radical initiator often has to be readjusted to obtain thermally polymerizable mixtures with a constant curing rate.

[0004] Additionally, sediment forms during storage due to the settling of the finely dispersed solids in the suspension. These separated suspensions require a laborious additional step for homogenization, which understandably often presents problems for the expert on an industrial scale.

[0005] DE2615039A1 describes monomeric benzpinacol silyl ethers for use as free radical initiators, which can be prepared by the reductive reaction of benzophenone with trialkylmonochlorosilanes. Depending on the substituents, the products can be solids or liquids; in the case of long-chain alkyl substituents, liquid, homogeneous products can be obtained. However, these exhibit much lower activities compared to their oligomeric counterparts, which can be obtained from dialkyldichlorosilanes or alkyltrichlorosilanes. They are therefore less suitable for industrial use. A process for the preparation of 5,8-dioxa-4,9-disiladodecane is described in the Journal of Polymer Science Part A: Polymer Chemistry, Vol. 24, No. 6, June 1, 1986 (1986-06-01), pages 1197-1215.

[0006] There is therefore a need for radical initiators that exist as homogeneous solutions and simultaneously exhibit high reactivity. The higher the reactivity of the radical initiator, the less radical initiator can be used, which is preferable for cost reasons.

[0007] The invention relates to a process for the preparation of silylbenzpinacol radical initiators, in which benzophenone is reacted with a reducing agent selected from alkali and alkaline earth metal and silane of the general formula (I) R 1< R 2< SiCl 2 (I), in which R 1< a C3-C32 alkyl radical and R 2< a C1-C32 alkyl radical or Cl.

[0008] The invention also relates to the silylbenzpinacol radical initiators obtainable by the process.

[0009] The silylbenzpinacol radical initiators of the invention are clear and homogeneous product mixtures, which significantly facilitate their use in applications. Due to long-chain alkyl substituents on the silicon atom, the initiator mixtures are liquid and opaque. They are therefore easier to process because they do not cause sedimentation, which in turn causes fluctuations in activity. They exhibit high reactivity as radical initiators.

[0010] Preferably, the reducing agent is selected from lithium, sodium, potassium, magnesium and calcium, in particular it is magnesium.

[0011] A silane of the general formula (I) or a mixture of different silanes of the general formula (I) can be used.

[0012] The alkyl radicals R 1< can be linear, branched, or cyclic. Examples of alkyl radicals R 1< are n-propyl, iso-propyl, n-butyl, sec-butyl, iso-butyl, tert-butyl, n-pentyl, sec-pentyl, isopentyl, neo-pentyl, tert-pentyl radicals; hexyl radicals, such as the n-hexyl radical; heptyl radicals, such as the n-heptyl radical; octyl radicals, such as the n-octyl radical and iso-octyl radicals, such as the 2,4,4-trimethylpentyl radical; nonyl radicals, such as the n-nonyl radical; decyl radicals, such as the n-decyl radical; dodecyl radicals, such as the n-dodecyl radical; hexadecyl radicals, such as the n-hexadecyl radical; octadecyl radicals, such as the n-octadecyl radical; Cycloalkyl radicals, such as cyclopentyl, cyclohexyl, cycloheptyl and methylcyclohexyl.

[0013] In a preferred embodiment, R 1< an alkyl radical having 3 to 20 carbon atoms, in particular 3 to 10 carbon atoms.

[0014] The alkyl radicals R 1< can be linear, branched, or cyclic. Examples of alkyl radicals R 2< are methyl and ethyl residues, as well as the R 1< alkyl radicals listed. In a preferred embodiment, R 2< an alkyl radical having 1 to 6 carbon atoms, in particular methyl, ethyl, n-propyl or iso-propyl radical, in particular methyl radical.

[0015] In a preferred embodiment, R 1< an alkyl radical having 3 to 18 carbon atoms and R 2< is Cl.

[0016] Surprisingly, silylbenzpinacols derived from dialkyldichlorosilanes exhibit increased reactivity.

[0017] This increased reactivity has already been observed with dichlorodimethylsilane, but the corresponding silylbenzpinacol is a solid and therefore difficult or impossible to process.

[0018] Increased reactivity can also be observed in a mixture with trichloromethylsilane, but the product is also cloudy or solid.

[0019] In particular, products from dialkyldichlorosilanes surprisingly show a significantly increased reactivity compared to their trichloroalkylsilane analogues.

[0020] In a preferred embodiment, therefore, R 1< an alkyl radical having 3 to 32 carbon atoms, and R 2< is an alkyl radical having 1 to 32 carbon atoms, preferably R 1< an alkyl radical having 3 to 20 carbon atoms, and R 2< is an alkyl radical having 1 to 20 carbon atoms, particularly preferred is R 1< an alkyl radical having 6 to 12 carbon atoms, and R 2< is an alkyl radical having 1 to 3 carbon atoms, in particular R 1< an alkyl radical having 6 to 14 carbon atoms, and R 2< is a methyl residue.

[0021] The process can be carried out in the presence or absence of aprotic solvents. Aprotic and polar solvents are preferred. If aprotic solvents are used, solvents or solvent mixtures with a boiling point or boiling range of up to 250°C at 0.1 MPa are preferred.Examples of such solvents are ethers such as dioxane, tetrahydrofuran, diethyl ether, methyl tert-butyl ether, diisopropyl ether, diethylene glycol dimethyl ether; chlorinated hydrocarbons such as dichloromethane, trichloromethane, tetrachloromethane, 1,2-dichloroethane, trichloroethylene; hydrocarbons such as pentane, n-hexane, hexane isomer mixtures, heptane, octane, white spirit, petroleum ether, benzene, toluene, xylenes; siloxanes, in particular linear dimethylpolysiloxanes with trimethylsilyl end groups having preferably 0 to 6 dimethylsiloxane units, or cyclic dimethylpolysiloxanes with preferably 4 to 7 dimethylsiloxane units, for example hexamethyldisiloxane, octamethyltrisiloxane, octamethylcyclotetrasiloxane and decamethylcyclopentasiloxane; N-NN-disubstituted amides such as dimethylformamide, N-NN-dimethylacetamide, and phosphoric acid tris-(dimethylamide); alkyl phosphates such as trialkyl phosphates, especially triethyl phosphate, or mixtures of these solvents.

[0022] Ethers, hydrocarbons, trialkyphosphates and mixtures thereof are preferred.

[0023] The term "solvent" does not mean that all reaction components must be soluble in it. The reaction can also be carried out in a suspension or emulsion of one or more reactants. The reaction can also be carried out in a solvent mixture with a miscibility gap, where at least one reactant is soluble in each of the mixed phases.

[0024] In a preferred embodiment, the reaction is activated with iodine. Preferably, 0.001 to 0.1 mole of iodine is added per mole of reducing agent.

[0025] Preferably, benzophenone and the reducing agent and optionally iodine are first combined and then the silane of the general formula (I) is added.

[0026] 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 the reducing agent lithium, sodium and potassium, or 0.3 to 0.75, in particular 0.4 to 0.6 for the reducing agent magnesium and calcium.

[0027] Preferably, the molar ratio of benzophenone to silane of the general formula (I), based on the Cl, is between 0.6 and 1.8, in particular between 0.8 and 1.2.

[0028] The process is preferably carried out at a temperature between 0°C and 80°C, particularly preferably between 10 and 60°C, in particular between 20 and 50°C.

[0029] The reaction time after addition of the silane of the general formula (I) is preferably 30 min to 1 d, particularly preferably between 1 to 8 h, in particular 2 to 6 h.

[0030] The reaction is preferably worked up by adding water, neutralizing with a weak base such as sodium bicarbonate and separating the aqueous phase.

[0031] If the process is carried out in the presence of aprotic solvents, these are preferably separated by distillation.

[0032] The silylbenzpinacol radical initiators according to the invention are used as thermal radical initiators for unsaturated vinylic compounds, such as unsaturated polyester resins and styrenes. Analytics for the entire invention: Gel time measurement to determine reactivity

[0033] The measurement is performed on a commercially available unsaturated polyester resin (PALATAL P04-1) from BÜFA using a gelation meter from Rosentreter. For the measurement, the resin is mixed with 1% of the product mixture, filled into a test tube (160 x 16 mm), and attached to the gelation meter. The sample is heated to 90 °C, and the piston stroke cycle and the gelation timer are started. The gelation time is stopped as soon as the device's pressure sensor is triggered.

[0034] In the following examples, unless otherwise stated, all quantities and percentages are based on weight, all pressures are 0.10 MPa (abs.) and all temperatures are 20°C. Examples Example 1 (not according to the invention):

[0035] 50 g of benzophenone are dissolved in xylene at 30 °C, and then 3.4 g of magnesium, 15 ml of THF, 34 ml of triethyl phosphate, and 0.06 g of iodine are added. 11 ml of trichloromethylsilane are added over a period of 180 minutes, and the reaction is stirred for a further 60 minutes at 40 °C. After the reaction, 40 ml of water is added over a period of 10 minutes, and the phases are then separated. The organic phase is neutralized with sodium bicarbonate solution, and after further phase separation, volatile components are removed by distillation in a short-path evaporator. A viscous, yellow liquid is formed, which becomes cloudy upon storage. The gel time is 9.7 minutes. Example 2 (not according to the invention):

[0036] 50 g of benzophenone are dissolved in xylene at 30 °C, followed by 3.4 g of magnesium, 15 ml of THF, 34 ml of triethyl phosphate, and 0.06 g of iodine. 20 ml of dichlorodimethylsilane are added, and the reaction is stirred for 4 h at 40 °C. After the reaction, 40 ml of water is added over 10 minutes, and the phases are separated. The organic phase is neutralized with sodium bicarbonate solution, and after another phase separation, volatile components are removed by distillation. A white, sparingly soluble solid is formed. The gel time is 6.5 minutes. The polymerized resin is inhomogeneous. Example 3 (not according to the invention):

[0037] 50 g of benzophenone are dissolved in xylene at 30 °C, and then 3.4 g of magnesium, 15 ml of THF, 34 ml of triethyl phosphate, and 0.06 g of iodine are added. 35 ml of chlorotrimethylsilane are added, and the reaction is stirred for 4 h at 40 °C. Solid formation can be observed during the reaction. After the reaction is complete, 40 ml of water are added over a period of 10 minutes, and the aqueous phase is then separated. The organic phase and the resulting solid are neutralized with sodium bicarbonate solution, and after the aqueous phase is again separated, volatile components are removed by distillation. A white, sparingly soluble solid is formed. The gel time is 25 minutes. The fully polymerized resin is inhomogeneous. Example 4 (not according to the invention):

[0038] 50 g of benzophenone are dissolved in xylene at 30 °C, followed by 3.4 g of magnesium, 15 ml of THF, 34 ml of triethyl phosphate, and 0.06 g of iodine. 64 ml of chlorodimethyloctylsilane are added, and the reaction is stirred for 4 h at 40 °C. After the reaction, 40 ml of water is added over 10 minutes, and the phases are separated. The organic phase is neutralized with sodium bicarbonate solution, and after further phase separation, the volatile components are removed by distillation. A yellow liquid is formed. The gel time is 20 minutes. Example 5:

[0039] 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 trichloropropylsilane are added, and the reaction is stirred for 4 h at 40 °C. After the reaction, 80 ml of water is added over 10 minutes, and the phases are separated. The organic phase is neutralized with sodium bicarbonate solution, and after further phase separation, volatile components are removed by distillation in a short-path evaporator. A viscous, yellow liquid is formed. The product remains clear even after storage. The gel time is 11 minutes. Example 6:

[0040] 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. 20 ml of trichlorohexadecylsilane are added, and the reaction is stirred for 4 h at 40 °C. After the reaction, 80 ml of water is added over 10 minutes, and the phases are separated. The organic phase is neutralized with sodium bicarbonate solution, and after further phase separation, volatile components are removed by distillation in a short-path evaporator. A viscous, yellow liquid is formed. The product remains clear even after storage. The gel time is 8.9 minutes. Example 7:

[0041] 50 g of benzophenone are dissolved in xylene at 30 °C, followed by 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 added, and the reaction is stirred for 4 h at 40 °C. After the reaction, 40 ml of water is added over 10 minutes, and the phases are separated. The organic phase is neutralized with sodium bicarbonate solution, and after further phase separation, volatile components are removed by distillation in a short-path evaporator. A viscous, yellow liquid is formed. The product remains clear even after storage. The gel time is 6.2 minutes. Example 8:

[0042] 40 g of benzophenone are 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-octadecyldichlorosilane are added, and the reaction is stirred for 4 h at 40 °C. After the reaction, 40 ml of water is added over a period of 10 minutes, and the phases are separated. The organic phase is neutralized with sodium bicarbonate solution, and after further phase separation, volatile components are removed by distillation in a short-path evaporator. A viscous, yellow liquid is formed. The product remains clear even after storage. The gel time is 5.9 minutes. Example 9:

[0043] 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 dichlorodioctylsilane are added, and the reaction is stirred for 4 h at 40 °C. After the reaction, 20 ml of water is added over 10 minutes, and the phases are separated. The organic phase is neutralized with sodium bicarbonate solution, and after further phase separation, volatile components are removed by distillation in a short-path evaporator. A viscous, yellow liquid is formed. The product remains clear even after storage. The gel time is 8.0 minutes.

Claims

1. Method for preparing silyl benzopinacol free-radical initiators, in which benzophenone is reacted with a reductant selected from alkali metal and alkaline earth metal and silane of the general formula (I)         R1R2SiCl2     (I), in which R1 is a C3-C32 alkyl radical and R2 is a C1-C32 alkyl radical or Cl.

2. Method according to Claim 1, in which R1 is an alkyl radical having 3 to 18 carbon atoms and R2 is Cl.

3. Method according to either of the preceding claims, in which R1 is an alkyl radical having 3 to 20 carbon atoms and R2 is an alkyl radical having 1 to 20 carbon atoms.

4. Method according to any of the preceding claims, in which the reductant is magnesium.

5. Method according to any of the preceding claims, which is carried out in the presence of aprotic solvents.

6. Method according to any of the preceding claims, in which the reaction is activated with iodine.

7. Method according to any of the preceding claims, in which first benzophenone and the reductant and optionally iodine are combined and then the silane of the general formula (I) is added.

8. Method according to any of the preceding claims, in which the reaction is worked up by adding water, neutralizing with a weak base, and removing the aqueous phase.