Polyalkyl silicate

Abstract

The present invention discloses a polymeric alkyl silicate of formula (I), wherein Z represents a group of formula -Si(OR b ) 3 or a group of formula -CR c 3 , R a represents a divalent unsubstituted or substituted carbon-bonded group or a divalent silicon-bonded group, R b represents a monovalent unsubstituted or substituted hydrocarbon group which contains from 4 to 40 C atoms and is branched at the α-carbon atom or is double-branched at the β-carbon atom, R c represents a monovalent unsubstituted or substituted hydrocarbon group containing from 1 to 50 C atoms, X represents a halogen atom, an oxygen-bonded unsubstituted or substituted C 1 to C 40 hydrocarbon group in which a single carbon atom may be replaced by an oxygen atom, a group of formula -O-Si(OR b ) 3 or a group of formula -OSiR x 3 , R x represents a monovalent unsubstituted or substituted C 1 to C 40 hydrocarbon group, and m is an integer between 2 and 1000.

Description

Technical Field

[0001] The present invention relates to novel polymeric alkyl silicates. Background Art

[0002] Silicones are a very important class of substances in industry, which are used in a variety of technical fields. An industrially important property of silicones is, for example, their low tendency to crystallize, which distinguishes silicones from carbon-based polymers. Silicones remain liquid over a wide temperature range and have a very low glass transition temperature.

[0003] However, due to the presence of Si-bonded alkyl moieties, silicones are not readily degradable in the environment at all. This property gradually limits the possible applications of silicones. Therefore, there is a growing need for alternative materials that can, in principle, undergo hydrolytic cleavage but still have sufficient hydrolytic stability for practical use and can replace conventional silicones.

[0004] US 3992429 and US 4132664 disclose silicon-containing compounds of the formula [(R a O) 3 SiO] 3 Si-O-KW-O-Si[OSi(OR a ) 3 3 where KW represents a hydrocarbon group. However, these systems have low molecular weights.

[0005] However, in many technical applications, low molecular weight compounds are undesirable because of their volatility and their migration behavior.

[0006] Therefore, the object of the present invention is to overcome the above disadvantages and provide polymeric alkyl silicates that have properties similar to those of silicones and can thus replace silicones. Summary of the Invention

[0007] This object is achieved by the present invention.

[0008] The present invention provides a polymeric alkyl silicate of formula (I)

[0009]

[0010] wherein,

[0011] Z represents a group of the formula -Si(OR b ) 3 or a group of the formula -CR c 3 ,

[0012] R a ​Independently represents, at each occurrence, a divalent unsubstituted or substituted carbon-bonded group or a divalent silicon-bonded group.

[0013] R b Independently represents, at each occurrence, a monovalent unsubstituted or substituted hydrocarbon group having 4 to 40 carbon atoms, which is branched at the α-carbon atom or doubly branched at the β-carbon atom.

[0014] R c Independently represents, at each occurrence, a monovalent unsubstituted or substituted hydrocarbon group having 1 to 50 carbon atoms, preferably 1 to 10 carbon atoms, more preferably 1 to 5 carbon atoms.

[0015] X represents a halogen atom, an oxygen-bonded unsubstituted or substituted C 1 - to C 40 -hydrocarbon group, where individual carbon atoms can be replaced by an oxygen atom, a group of the formula -O-Si(OR b ) 3 group or a group of the formula -OSiR x 3 group.

[0016] R x Independently represents, at each occurrence, a monovalent unsubstituted or substituted C 1 - to C 40 -hydrocarbon group, and

[0017] m represents an integer of at least 2, preferably at least 5 and at most 1000, preferably at most 500, preferably at most 100.

[0018] The term "branched" means the presence of two carbon groups on one carbon atom.

[0019] The term "doubly branched" means the presence of three carbon groups on one carbon atom.

[0020] The groups R a 、R b 、R c and R x as well as the group X, when X is not a halogen atom, can be acyclic, cyclic, saturated, or mono- or poly-unsaturated, or aromatic and can also have the following substitutions:

[0021] -OR 1 、-NR 1 2 、-SH、-SR 1 、epoxy group, -COOR 1 、-CHO、-CN、-OCOOR 2 、-NR 1 -COOR1 , -NR 1 -CO-NR 1 , -SiR 1 3 and -OSiR 3 1 , wherein

[0022] R 1 represents a hydrogen atom or a monovalent C 1 - to C 18 -hydrocarbyl group, and

[0023] R 2 represents a monovalent C 1 to C 18 -hydrocarbyl group.

[0024] R a independently preferably represents a divalent hydrocarbyl group having 1 to 200 carbon atoms, preferably 3 to 50 carbon atoms, wherein these carbon atoms may be substituted by an oxygen atom or a siloxanyl group of the formula -(R y 2 SiO) O -SiR y 2 , wherein

[0025] R y independently represents a C 1 - to C 20 -hydrocarbyl group, preferably a C 1 - to C 6 -hydrocarbyl group, and

[0026] o is an integer from 0 to 100, preferably an integer from 0 to 20.

[0027] Examples of the group R a are 1,3-propylene, 1,4-butylene, 1,2-cyclohexylene, 1,3-cyclohexylene, 1,4-cyclohexylene, 1,2-phenylene, 1,3-phenylene and 1,4-phenylene groups.

[0028] Other examples of the group R a are groups of the formula -CHR 3 -CHR 3 -(OCHR 3 -CHR 3 ) p , wherein

[0029] R 3 represents a hydrogen atom or a C 1 - to C 18 -hydrocarbyl group, preferably a hydrogen atom or a methyl group, and ​

[0030] p is an integer from 0 to 100, preferably from 0 to 20,

[0031] and a group of the formula:

[0032] -(Me 2 SiO) o -Me 2 Si-、

[0033] -CH 2 -CH 2 -CH 2 -(Me 2 SiO) o -Me 2 Si-CH 2 -CH 2 -CH 2 -and

[0034] -CH 2 -(Me 2 SiO) o -Me 2 Si-CH 2 -,

[0035] wherein, Me is methyl, and

[0036] o is as defined above.

[0037] Preferred examples of the group R b are 2-butyl, 3-methyl-2-butyl, 3-methyl-2-pentyl, 3-pentyl, 2-hexyl, 3-hexyl, 2-heptyl, 2-octyl, 1-phenylethyl, 1-phenyl-1-propyl, 2,2-dimethyl-1-propyl, 1,1-dimethylethyl and 1,1-dimethylpropyl.

[0038] R c independently preferably represents, each time it appears, a straight-chain or branched acyclic hydrocarbon group having 1 to 50 carbon atoms, preferably a straight-chain or branched acyclic hydrocarbon group having 1 to 10 carbon atoms, and particularly preferably a straight-chain or branched acyclic hydrocarbon group having 1 to 5 carbon atoms.

[0039] Examples of the group R c are methyl, ethyl, n-propyl, n-butyl, n-pentyl, vinyl and allyl groups.

[0040] X preferably represents a chlorine atom, an oxygen-bonded unsubstituted or substituted C 1 - to C 40 -hydrocarbon group, wherein individual carbon atoms may be replaced by oxygen or the chemical formula -O-Si(OR b ) 3 or -OSiRx 3 is replaced by a group, where R x independently and preferably represents C 1 - to C 10 -hydrocarbyl each time it appears.

[0041] Examples of the group X are a chlorine atom, 4-hydroxycyclohexyloxy, and groups having the following formula:

[0042] -O-(CH 2 -CH 2 ) r -OH and -O-(CH 2 -CH 2 ) r -OCH 3 , where r = 1 - 20,

[0043] -O-Si(CH 3 ) 3 , -O-Si(2-BuO) 3 , -O-SiH(CH 3 ) 2 ,

[0044] -O-Si(CH 3 ) 2 -CH 2 -CH 2 -CH 2 -NH 2 ,

[0045] -O-Si(CH 3 ) 2 -CH 2 -CH 2 -CH 2 -NH-CH 2 -CH 2 -NH 2 ,

[0046] -O-Si(CH 3 ) 2 -CH=CH 2 and -O-Si(CH 3 ) 2 -CH 2 -CH 2 -CH 2 -O-CH 2 -epoxy group.

[0047] Preferred examples of the group Z are the formula (2-BuO) 3 SiO- and CH 3 -CH 2 -C(CH3 ) 2 a group of O−,

[0048] wherein, 2-Bu is 2-butyl.

[0049] Other examples of group Z are groups of the following formula:

[0050] [CH 3 -CH(CH 3 )-CH(CH 3 )O] 3 SiO−,

[0051] [CH 3 -C(CH 3 ) 2 -CH 2 O] 3 SiO−, [(CH 3 -CH 2 ) 2 -CHO] 3 SiO−,

[0052] [CH 3 -(CH 2 ) 3 -CH(CH 3 )O] 3 SiO−, [CH 3 -(CH 2 ) 2 -CH(C 2 H 5 )O] 3 SiO−,

[0053] (CH 3 ) 3 CO−, (C 2 H 5 ) 3 CO−, (n-C 3 H 7 ) 3 CO−, (n-C 4 H 9 ) 3 CO−, (n-C 5 H 11 ) 3 CO− and CH 3 -CH 2 -C(CH 3 ) 2 O−.

[0054] The compounds of general formula (I) can be prepared in a simple manner, for example by [(R b O)3 SiO] 2 SiCl 2 or (R c 3 CO) 2 SiCl 2 react with a dihydroxy compound HO-R a -OH, where R a 、R b and R c are as defined above. If there is an excess of [(R a O) 3 SiO] 2 SiCl 2 or (R c 3 CO) 2 SiCl 2 , then the silicate ester of formula I with X = Cl is preferentially formed, and if there is an excess of the dihydroxy compound, then the silicate ester of formula I with X = OR a -OH is preferentially formed.

[0055] A further option is to react the Si-Cl end groups present after the reaction with an alcohol or a silanol.

[0056] Accordingly, the present invention provides a process for preparing a polymeric alkyl silicate according to the present invention, characterized in that a chlorosilane (I) of the formula [(R b O) 3 SiO] 2 SiCl 2 or (R c 3 CO) 2 SiCl 2 is reacted with a dihydroxy compound (2) of the formula HO-R a -OH or a salt thereof,

[0057] wherein the dihydroxy compound (2) is used in an amount of 0.1 to 10 mol, preferably 0.5 to 1.5 mol of the dihydroxy compound (2) per mole of chlorosilane (1),

[0058] and R a 、R b and R c are each as defined above.

[0059] Examples of the chlorosilane (1) are

[0060] [(2-BuO) 3 SiO] 2 SiCl 2 、

[0061] {[CH 3 -CH(CH 3 )-CH(CH 3 )O] 3 SiO} 2 SiCl 2 、

[0062] {[CH 3 -CH 2 -CH(CH 3 )-CH(CH 3 )O} 3 SiO] 2 SiCl 2 、

[0063] {[(CH 3 -CH 2 ) 2 CHO] 3 SiO} 2 SiCl 2 、

[0064] {[CH 3 -(CH 2 ) 3 -CH(CH 3 )O] 3 SiO] 2 SiCl 2 、

[0065] {[CH 3 -(CH 2 ) 2 -CH(C 2 H 5 )O] 3 SiO] 2 SiCl 2 、

[0066] {[PhCH(CH 3 )O] 3 SiO] 2 SiCl 2 、

[0067] {[PhCH(C 3 H 7 )O] 3 SiO] 2 SiCl 2 、

[0068] {[CH 3 -CH(CH 3 ) 2 -CH 2 O]3 SiO 2 SiCl 2 、

[0069] [CH 3 -CH(CH 3 ) 2 O] 3 SiO 2 SiCl 2 、

[0070] [CH 3 -CH 2 -CH(CH 3 ) 2 O] 3 SiO 2 SiCl 2 、

[0071] [(CH 3 ) 3 CO] 2 SiCl 2 、

[0072] [(C 2 H 5 ) 3 CO] 2 SiCl 2 、

[0073] [(n-C 3 H 7 ) 3 CO] 2 SiCl 2 、

[0074] [(n-C 4 H 9 ) 3 CO] 2 SiCl 2 、

[0075] [(n-C 5 H 11 ) 3 CO] 2 SiCl 2 and

[0076] [CH 3 -CH 2 -C(CH 3 ) 2 O] 2 SiCl 2 ,

[0077] wherein, 2-Bu is 2-butyl and Ph is phenyl.

[0078] Preferred examples of the chlorosilane (1) are those of the formula [(2-BuO) 3 SiO] 2 SiCl 2 and [CH 3 -CH 2 -C(CH 3 ) 2 O] 2 SiCl 2 , where 2-Bu is 2-butyl.

[0079] Examples of the dihydroxy compound (2) are ethylene glycol, propylene glycol, 1,3-propylene glycol, 1,4-butylene glycol, 2,4-pentylene glycol, 1,2-cyclohexanediol, 1,3-cyclohexanediol, 1,4-cyclohexanediol, 1,2-dihydroxybenzene, 1,3-dihydroxybenzene, 1,4-dihydroxybenzene, polyethylene glycol, polypropylene glycol, HO-SiMe

[0080] -(O-SiMe 2 -(O-SiMe 2 ) x -OH, and HO-CH 2 -CH 2 -CH 2 -SiMe 2 -(O-SiMe 2 ) x -CH 2 -CH 2 -CH 2 -OH, where x is an integer from 1 to 50 and Me is methyl.

[0081] Preferred examples of the dihydroxy compound (2) are 1,4-cyclohexanediol, ethylene glycol, propylene glycol, triethylene glycol, and polyethylene glycol.

[0082] Hydrogen chloride formed during the reaction can be removed directly from the reaction mixture by distillation or extraction, or a dihydroxy compound in the form of a base or its salt that accepts hydrogen chloride can be used. Preferably nitrogen bases.

[0083] Examples of the base are pyridine, ammonia, urea, diethylurea, ethylenediamine, methylamine, ethylamine, triethylamine, diethylamine, tributylamine, piperidine, pyrimidine, pyridazine, imidazole, and diethylenetriamine.

[0084] Preferred examples of the base (3) are pyridine, ammonia, urea, ethylenediamine, triethylamine, and tributylamine.

[0085] The process according to the invention can be carried out in the presence of one or more solvents. Examples of solvents are hydrocarbons such as toluene or isohexane, ethers such as methyl tert-butyl ether or siloxanes such as hexamethyldisiloxane, octamethyltrisiloxane or (Me 3 SiO) 4 Si where Me = methyl). The solvent is preferably used in a weight fraction of at least 1% to at most 100 times, particularly preferably from at least 10% to at most 10 times by weight, in each case based on the total weight of components (1) and (2).

[0086] The process can be carried out batchwise, semi-batchwise or continuously. In the semi-batch process, preferably component (2) is first added, optionally together with a base, and then component (1) is added.

[0087] In other embodiments, a polymeric alkyl silicate of the general formula (I) in which Z is a group of the formula -CR c 3 is prepared by reacting silicon tetrachloride with a monohydroxy compound (4) of the formula HO-CR c 3 and with a dihydroxy compound (2) of the formula HO-R a -OH or a salt thereof, either simultaneously in one step or continuously in two steps, where the monohydroxy compound (4) is used in an amount of 1.5 to 3.0 mol, preferably 1.8 to 2.2 mol per mole of silicon tetrachloride, the dihydroxy compound (2) is used in an amount of 1.5 to 3.0 mol, preferably 1.8 to 2.2 mol per mole of silicon tetrachloride, and R a and R c are as defined above. For this purpose, for example, 1 mol of silicon tetrachloride can be reacted with 2 mol of HO-CR c 3 and with 2 mol of the dihydroxy compound (2). It is preferred when HO-CR c 3 is initially added and then the dihydroxy compound (2) is added.

[0088] The process according to the invention is carried out at a temperature of preferably -20 °C to +250 °C, preferably +20 °C to +150 °C. It can be carried out at ambient atmospheric pressure (about 1020 hPa) or at a higher or lower pressure. Preferably, it can be carried out at ambient atmospheric pressure.

[0089] The polymeric alkyl silicate according to the invention preferably has a molar weight M n (number average) of 5000 to 50000 and an M w (weight average) of 10000 to 100000.

[0090] The molecular weight was determined by gel permeation chromatography (size exclusion chromatography) at 35 °C using Agilent Mesopore and OligoPore columns with a length of 300 mm, an inner diameter of 7.5 mm, and a particle size of 3 / 6 mm, with toluene as the eluent, a flow rate of 0.3 ml / min, an RI-detector, and calibration with polydimethylsiloxane.

[0091] The alkyl silicate of formula (I) according to the invention has the following advantages over the prior art: They are polymeric and thus non-volatile and therefore do not migrate in the material. Furthermore, despite their high molecular weight, they are liquid and have a very low glass transition temperature and are thus suitable for replacing silicones. Another advantage of the alkyl silicate of formula (I) according to the invention is that they have a modular structure and thus their molecular weight is variable as desired. In addition, the chain ends of the alkyl silicate according to the invention carry reactive groups (such as chlorine or hydroxyl) to which a plurality of other optionally functionalized moieties can be attached. This makes it possible to broaden the application spectrum of the alkyl silicate according to the invention.

[0092] The polymeric alkyl silicate according to the invention can be subjected to further processing, for example by crosslinking to provide elastomers, and can be used, for example, in the fields of hydrophobization, defoamers, textiles, cosmetics, building preservation, and household care, in cases where silicones are used. Detailed Description

[0093] Embodiment

[0094] The compound [(2-BuO) 3 SiO] 2 SiCl 2 used in the examples was prepared from (2-BuO) 3 SiOH and SiCl 4 for example, as described in Abe, Bull. Soc. Chim. Jpn. 1969, 42, 111 - 1123.

[0095] The compound [CH 3 -CH 2 -C(CH 3 ) 2 O] 2 SiCl 2 used in the examples was prepared from CH 3 -CH 2 -C(CH 3 ) 2 OH and SiCl 4Preparation, for example, as described in Docherty et al., Helv. Chim. Acta 2018, 101, e1700298.

[0096] Example 1:

[0097] A polymer of formula (I), where R a = 1,4 - cyclohexylene, Z = Si(OR b ) 3 , where R b = 2 - butyl, X = Cl, O - C 6 H 10 -OH, and m = 14. 1.54 g of [(2 - BuO) 3 SiO] 2 SiCl 2 (2.44 mmol) in 0.5 ml of toluene was added dropwise to a mixture of 284 mg (2.44 mmol) of 1,4 - cyclohexanediol and 430 mg (5.43 mmol) of pyridine in 1 ml of toluene. A white precipitate of pyridine hydrochloride was formed. The mixture was then heated to 100 °C for 4 hours. The solution contained a polymeric product with M n = 10000 Da / M w = 21000. This gave m = 14. The formed pyridine hydrochloride precipitate was filtered off, and toluene was removed by rotary evaporation under vacuum. This provided a colorless oil with a dynamic viscosity η = 1.13 Pa·s at 25 °C. The glass transition temperature T g = -107.6 °C.

[0098] 29 Si - NMR (CD 2 Cl 2 ): δ = -92.5 and -98.6 ppm, ratio 2:1.

[0099] Example 2:

[0100] A polymer of formula (I), where R a = -CH 2 -CH 2 -(O - CH 2 -CH 2 ) 2 -, Z = Si(OR b ) 3 , where R b = 2 - butyl, X = -CH 2 -CH 2 -(O - CH 2 -CH 2 ) 2-OH, and m = 13. 3.07 g of [(2-BuO) 3 SiO] 2 SiCl 2 (93%, 4.56 mmol) was mixed with 1 ml of toluene. A mixture of 737 mg (4.91 mmol) of triethylene glycol, 856 mg (10.8 mmol) of pyridine, and 0.5 ml of toluene was slowly added to the solution. A white precipitate of pyridine hydrochloride immediately formed. The mixture was then heated to 100 °C for 4 hours. The solution contained a polymeric product with M n = 9700 Da / M w = 22000. This gave m = 13.

[0101] 29 Si-NMR(CD 2 Cl 2 ): δ = -92.3 and -96.8 ppm, in a ratio of 2:1.

[0102] Example 3:

[0103] A polymer of formula (I), wherein R a = -CH 2 -CH 2 -(O-CH 2 -CH 2 ) 2 -, Z = Si(OR b ) 3 , where R b = 2-butyl, X = -CH 2 -CH 2 -(O-CH 2 -CH 2 ) 2 -OH, and m = 13.

[0104] The procedure of Example 2 was repeated at room temperature. After 3 hours, a polymer with M n = 12000 Da / M w = 24000 Da was formed. This gave m = 13.

[0105] Example 4:

[0106] A polymer of formula (I), wherein R a = -CH 2 -CH 2 -(O-CH 2 -CH 2 ) 2 -, Z = -C(CH 3 ) 2 -CH 2 -CH3 and X = CH 2 -CH 2 -(O-CH 2 -CH 2 ) 2 -OH, Cl.

[0107] The procedure of Example 2 was repeated, except that a compound of the formula [CH 3 -CH 2 -C(CH 3 ) 2 O] 2 SiCl 2 was used instead of [(2-BuO) 3 SiO] 2 SiCl 2 , the molar ratio of [CH 3 -CH 2 -C(CH 3 ) 2 O] 2 SiCl 2 : triethylene glycol = 1.0, and the reaction was carried out at 80 °C. After 4 hours at 80 °C, a polymer with M n = 15500 Da / M w = 38300 Da was formed, and after an additional 5 hours at 80 °C, the mixture was worked up as described in Example 1. 6.2 g of the polymeric product in the form of a colorless oil was obtained. M n = 16900 Da / M w = 42400 Da. This gave m = 48. 29 Si-NMR(CD 2 Cl 2 ): δ = -89.72 ppm.

Claims

1. A polymeric alkyl silicate of formula (I) wherein The group of the formula -Si(OR b ) 3 or the group of the formula -CR c 3 , R a independently represents, each time it appears, a divalent hydrocarbon group having 3 to 200 carbon atoms, wherein the carbon atoms may be replaced by oxygen atoms or by a siloxanyl group of the formula -(R y 2 SiO) O -SiR y 2 -, where R y independently represents C at each occurrence 1 - to C 20 -hydrocarbyl, and o is an integer from 0 to 100, R b independently represents, each time it appears, a monovalent unsubstituted or substituted hydrocarbon group having 4 to 40 carbon atoms, said hydrocarbon group being branched at the α-carbon atom or doubly branched at the β-carbon atom R c independently represents, each time it appears, a monovalent unsubstituted or substituted hydrocarbon radical having 1 to 50 carbon atoms X represents a halogen atom, an unsubstituted or substituted C 1 - to C 40 -hydrocarbyl group, wherein individual carbon atoms may be replaced by an oxygen atom, a group of the formula -O-Si(OR b ) 3 group or a group of the formula -OSiR x 3 group, R x independently represents, each time it appears, a monovalent unsubstituted or substituted C 1 - to C 40 -hydrocarbyl, and m represents an integer of at least 2 and at most 1000.

2. The polymeric alkyl silicate according to claim 1, characterized in that R a independently represents, each time it appears, a divalent hydrocarbon group having 3 to 50 carbon atoms, wherein the carbon atoms may be replaced by oxygen atoms or by siloxanyl groups of the formula -(R y 2 SiO) O -SiR y 2 -.

3. The polymeric alkyl silicate according to claim 1, characterized in that R y independently represents C 1 - to C 6 -hydrocarbyl each time it appears.

4. The polymeric alkyl silicate according to claim 1, characterized in that o is an integer from 0 to 20.

5. The polymeric alkyl silicate according to claim 1, characterized in that m is an integer of at least 5 and at most 100.

6. The polymeric alkyl silicate according to claim 1, characterized in that Group R a a group selected from the group consisting of: 1,3 - propylene, 1,4 - butylene, 1,2 - cyclohexylene, 1,3 - cyclohexylene, 1,4 - cyclohexylene, 1,2 - phenylene, 1,3 - phenylene, 1,4 - phenylene and a group of the following formula: -CHR 3 -CHR 3 -(OCHR 3 -CHR 3 ) p -、 -CH 2 -CH 2 -CH 2 -(Me 2 SiO) o -Me 2 Si-CH 2 -CH 2 -CH 2 - and -CH 2 -(Me 2 SiO) o -Me 2 Si-CH 2 -, wherein Me is methyl, R 3 represents a hydrogen atom or a C 1 - to C 18 -hydrocarbyl group, o is as defined in claim 1, and p is an integer from 0 to 100.

7. The polymeric alkyl silicate according to claim 6, characterized in that R 3 represents a hydrogen atom or a methyl group.

8. The polymeric alkyl silicate according to claim 6, characterized in that p is an integer from 0 to 20.

9. The polymeric alkyl silicate according to claim 1, characterized in that Group R b selected from the group consisting of: 2-butyl, 3-methyl-2-butyl, 3-methyl-2-pentyl, 3-pentyl, 2-hexyl, 3-hexyl, 2-heptyl, 2-octyl, 1-phenylethyl, 1-phenyl-1-propyl, 2,2-dimethyl-1-propyl, 1,1-dimethylethyl and 1,1-dimethylpropyl.

10. The polymeric alkyl silicate according to claim 1, characterized in that R c independently represents, each time it appears, an acyclic hydrocarbon group having 1 to 10 carbon atoms, which is linear or branched.

11. The polymeric alkyl silicate according to claim 1, characterized in that Z is the group of formula (2-BuO) 3 SiO- or CH 3 -CH 2 -C(CH 3 ) 2 O-.

12. A method for preparing the polymeric alkyl silicate according to any one of claims 1 to 11, characterized in that React the chlorosilane (1) of formula [(R b O) 3 SiO] 2 SiCl 2 or (R c 3 CO) 2 SiCl 2 with a dihydroxy compound (2) of formula HO-R a -OH or a salt thereof, wherein the dihydroxy compound (2) is used in an amount of 0.1 to 10 mol per mole of chlorosilane (1), And R a , R b and R c are defined according to claim 1.

13. The method according to claim 12, characterized in that the dihydroxy compound (2) is used in an amount of 0.5 to 1.5 mol per mole of chlorosilane (1).

14. The method according to claim 12, characterized in that The chlorosilane (1) used is of the formula [(2-BuO) 3 SiO] 2 SiCl 2 or [CH 3 -CH 2 -C(CH 3 ) 2 O] 2 SiCl 2 a compound of wherein 2-Bu is 2-butyl.

15. The method according to claim 12, characterized in that the dihydroxy compound (2) used is 1,4-cyclohexanediol, propylene glycol, triethylene glycol or polyethylene glycol.

16. The method according to claim 12, characterized in that the reaction is carried out in the presence of a base (3).

17. The method according to claim 16, characterized in that the base (3) is a nitrogen-containing base.

18. The method according to claim 16, characterized in that the base (3) used is pyridine, ammonia, urea, ethylenediamine, triethylamine or tributylamine.

19. A process for preparing a polymeric alkyl silicate of formula (I) according to any one of claims 1 to 6, provided that Z is a group of formula -CR c 3 as defined above characterized in that React tetrachlorosilane with a monohydroxy compound (4) of the formula HO-CR c 3 and a dihydroxy compound (2) of the formula HO-R a -OH or a salt thereof simultaneously in one step or consecutively in two steps, wherein the monohydroxy compound (4) is used in an amount of 1.5 to 3.0 mol per mole of tetrachlorosilane, and the dihydroxy compound (2) is used in an amount of 1.5 to 3.0 mol per mole of tetrachlorosilane, And R a and R c are defined in claim 1.

20. The method according to claim 19, characterized in that the monohydroxy compound (4) is used in an amount of 1.8 to 2.2 mol per mole of tetrachlorosilane.

21. The method according to claim 19, characterized in that the dihydroxy compound (2) is used in an amount of 1.8 to 2.2 mol per mole of tetrachlorosilane.

22. The method according to claim 19, characterized in that R c Each occurrence independently represents a straight-chain or branched acyclic hydrocarbon group having 1 to 10 carbon atoms.

23. The method according to claim 19, characterized in that The reaction is carried out in the presence of a base (3).

24. The method according to claim 23, characterized in that the base (3) is a nitrogen-containing base.

25. The method according to claim 23, characterized in that the base (3) is a base selected from the group consisting of pyridine, ammonia, urea, ethylenediamine, triethylamine or tributylamine.

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