SK279376B6 - Method of functionalised poly-(met)acrylates preparation by anionic polymerisation - Google Patents

Abstract

Polymerisation of acrylate or metacrylate monomers is processed in the presence of initiators selected from the group containing terc.alkylestetors of saturated carboxy acids metallated in an alpha-position by an alk. metal, terc.alkoxide of an alk. metal, optionally in a mixture with terc.alcohol and, optionally, in the presence of terc.alkoxide of an alk. metal as an polymerisation active-centres stabiliser in a medium of solvent selected from the group being composed of aromatic hydrocarbon, cyclic ether or a mixture thereof, at a temperature ranging from -70 to 20 degrees Celsius. Selective hydrolysis of ether- or ester-binding terc.alkoxygroups on the beginnings and/or ends of the polymer chains follows.

Description

Technical field

The invention relates to a process for the preparation of functionalized poly (meth) acrylates by anionic polymerization.

BACKGROUND OF THE INVENTION

Polymers carrying reactive functional groups at the end of their chains have found wide application in the preparation of block and graft copolymers, which have recently become increasingly important, particularly in the context of the study of the miscibility of commercial polymers. For the preparation of these functionalized and telechelic products, it appears to be the most suitable method of utilizing the living nature of the anionic polymerization growth centers by a suitable subsequent reaction which, after consumption of monomer, can incorporate the desired functional group at the end of the polymer chain. This problem has been and still is intensively studied, especially for those monomers whose active growth centers during anionic polymerization are extremely stable and do not undergo spontaneous side reactions.

An example is the hydroxylation of living polystyrrylithium in a hydrocarbon medium by reaction with oxirane and subsequent protonation of the terminal oxyanion (Schulz DN, Sanda JC, Wiloughby BG: in Anionic Polymerization: Kinetics, Mechanisms and Synthesis, McGrath JE, Ed., ACS Symposium Seires). , ACS, Washington, DC 1981). Since the oxirane ring is only very difficult to homopolymerize with lithium initiators due to the low reactivity of strongly associated alkoxides, the product of this process is the hydroxylated polystyrene practically in quantitative yield. Similarly, telechelic alpha, omega-dihydroxy polybutadiene can be prepared using a bifunctional initiator (e.g., a dilute dimer of alpha, omega-methylstyrene) and terminated by the oxirane units of the alpha, omega-dilithium polybutadiene. These processes have already been described and are practically without major complications and are even commercially exploited. Another possibility of hydroxylation is, for example, initiation of polymerization with a lithium acetal, acetaldehyde or tetrahydropyran derivative (SchulzD.N., Halasa AF, Oberster AE: J. Polymer Sci., Pol. Chem. Ed. 12, 153 (1974)) containing masked hydroxyl groups. , releasable upon completion of the reaction by slight hydrolysis. A less reactive, tertiary bonded hydroxy group can also be incorporated at the end of the chain by reacting the living polymer with a suitable carbonyl compound (benzothenone) and then protonating the resulting alkoxide (Quirk R. P. et al .: Rubber Chem. And Technol., 64, 648 (1991)). Functionalization of the carbohydrate polymers (polystyrene) has also been extensively studied, but the results are not as unambiguous as in hydroxylation. Conventionally, it is possible to actively terminate the polymer chains with carbon dioxide in solid or gaseous form. It is preferable to work in an environment with increased solvation ability that reduces the degree of aggregation of the living chains, thereby limiting their dimerization and trimerization. Attempts have been described to give a 60-90% yield of polystyrene or carboxy functionalized polyisoprene under conditions. The formation of byproducts can also be reduced by converting styryl carbanione to steric, more protected and less reactive carbanione by reacting live after lystyrene with 1,1-dithenylethylene and its subsequent carboxylation (Fetters LJ, Young R. N: in Anionic Polymerization: Kinetics, Mechanisms and Synthesis McGrath JE, Ed. ACS Symp. No. 166, AACS, Washington DC, (1981), Quirk RP, Yin J., Fetters LJ: Macromolecules 22, 85, (1989).

For polar vinyl monomers, the preparation of functionalized polymers is clearly more difficult because their living chains undergo spontaneous side reactions much more rapidly and the reactions with the appropriate reagents are not unambiguous. Thus, more complicated procedures are used, such as initiating polymerization of methyl methacrylate with allylithium in tetrahydrofuran (THF) at -78 ° C to give polymethyl methacrylate (polyMMA) with an allyl double bond at the starting unit. This is then converted to the hydroxy group by hydroboration and reaction with peroxide. If the polymerization is terminated with an allyodide before spontaneously stopping, polymethyl methacrylate with double bonds at both chain ends is prepared, followed by telechelic polymethyl methacrylate with two hydroxy groups (Al-Takrity ETB, Jenkins AD, Walton DRM: Makromol. Chem. 191,3077). (1990)).

Further possibilities have been developed in recent years by the polymer grpptransfer (GTP) (Webstcr O.W., Hertler W.R., Sogah D.Y., Farnham W. B., Rajan Babu T.W .: J. Am. Chem. Soc., 105, 5706 (1983)). Instead of conventional 1-methoxy-1-trimethylsiloxy-2-methylpropene, for example, 1-methoxy-1-trimethylsiloxy-2- (2-trimethylsiloxyethoxy) propene can be used, and the trimethylsiloxy group at the beginning of the polymer chains can then be hydrolysed to the hydroxylic acid to mild conditions. By combining the two living polymer chains with a suitable bifunctional terminating agent, such as dibromo-p-xylylene or terephthalic bifluoride followed by hydrolysis of trimethylsiloxy groups, as before, a telechelic polymer with hydroxyl groups can be prepared at both ends of the chain, J. Polymer Sci., Pol Lett. Ed., 21,927 (1983), Cohen G.M .: Pol Prepr., Am. Chem. Soc., Div. Pol. Chem. 29 (2), 46 (1988)) The authors also envisage the possibility of functionalizing the polymer with a carboxy group, however, further details are not yet available.

However, carboxylic polymers can also be prepared by free-radical polymerization using a functionalized trans-reagent such as thioglycolic acid (2-thiopropionic acid), by which the appropriate group can be introduced directly at the beginning of the polymer chains. Although the process is even commercially used, it cannot be reliably managed and gives not quite clear results.

All these methods are particularly complicated for polar vinyl monomers and require prior synthesis of special initiators (GTP), more complex multi-stage synthesis (anionic polymerization followed by hydroboration) or are not readily operable (radical polymerization).

SUMMARY OF THE INVENTION

The above-mentioned disadvantages are overcome by the process of the present invention which utilizes the studied initiation systems and relatively simple hydrolysis of the intermediates.

SK 279376 Β6 with masked functional groups. SUMMARY OF THE INVENTION The present invention provides a process for the preparation of functionalized poly (meth) acrylates wherein the polymerization of acrylate or methacrylate monomers is carried out in the presence of initiators selected from the group consisting of tertiary alkyl esters of saturated carboxylic acids. alkali metal alkoxides, optionally in admixture with a tert, alcohol, and optionally in the presence of a tert, alkali metal alkoxide as a stabilizer of active polymerization centers, in a solvent selected from the group consisting of an aromatic hydrocarbon, cyclic ether or mixtures thereof at temperatures ranging from - 70 ° C to 20 ° C, then selectively hydrolyzing the ether or ester-linked tert-alkoxy groups at the beginning and / or at the ends of the polymer chains.

In carrying out the process of the invention, the polymerization can be carried out by tert-alkyl-saturated carboxylic acid, metallized in the alpha position with an alkali metal initiator, in the presence of tert-alkali metal alkoxide as stabilizer of active polymerization centers. an alkali metal alpha-position to the tert, the alkali metal alkoxide is in the range of 1: 1 to 1:20, preferably 1: 3 to 1: 10, in a mixed solvent composed of an aromatic hydrocarbon and 0 to 10% by volume of cyclic ether at at temperatures between -70 ° C and 0 ° C, the acid-catalyzed hydrolysis then selectively saponifies the ester-linked t-alkoxy group at the beginning of each polymer chain.

Further, according to the invention, after the monomer has been consumed, before the end of the polymerization, tert-butyl acrylate or methacrylate is added to the reaction mixture in a concentration equal to or higher than the active growth center concentration, then the polymerization is terminated, followed by ester-linked product. tert, the alkoxy groups at the beginning and one or more groups at the end of each polymer chain undergo selective acid hydrolysis.

The initiators used in the process according to the invention are tert-alkyl esters of saturated carboxylic acids having 2 to 10 carbon atoms in the chain, preferably tert-alkyl esters of isobutyric acid and propionic acid, metallized in the alpha position with an alkali metal selected from the group consisting of lithium, sodium, potassium and cesium.

The initiators or stabilizers of the active polymerization centers are tert, alkali metal alkoxides having 4 to 10 carbon atoms in the chain and an alkali metal selected from the group consisting of lithium, sodium, potassium and cesium.

A further feature of the process of the invention is that the polymerization of the monomer is carried out in the presence of 1 to 10 mol%, based on monomer concentration, of tert, alkali metal alkoxide initiator, in cyclic ether or aromatic hydrocarbon, at temperatures in the range of -60 ° C to 20 ° C, for which the product with an ether-linked tert-alkyl group at the beginning of each chain is subjected to acidic cleavage.

The process according to the invention can be further carried out by polymerizing the monomer in the presence of a mixture of tert-alkali metal alkoxide and tert-alcohol, wherein the molar ratio of monomer to tert-alcohol is selected according to the desired polymerization degree in the range of 2 to 100. of a polar cyclic ether in an amount of 5 to 20% by volume based on the monomer volume and at a temperature ranging from 0 ° C to 50 ° C, for which the ether-linked tert-alkyl product is acid-cleaved at the beginning of each chain.

Thus, in the preparation of the carboxy-functionalized poly (meth) acrylates by the process of the invention, a tert-alkyl, preferably isobutyric, propionic, alkyl ester, metallized in the alpha-position with an alkali metal, together with the tert, alkali metal alkoxide as stabilizing additive is used to initiate polymerization. The initiator carbonyne is incorporated as an initiating particle at the beginning of each polymer chain and, upon completion of polymerization, its tertiary alkoxy group can be liberated by selective hydrolysis, while the other ester groups on the polymer chain are not subject to acid hydrolysis and thus the chemical structure of the prepared polymer remains. The telechelic polymer can be prepared by adding a small amount of tert-butyl acrylate or methacrylate at a concentration approximately equal to that of the active centers to form a polymer, such as polymethyl methacrylate (p), immediately after consuming the initial dose of monomer such as methyl methacrylate (MMA). -MMA), terminated by an average of one tert. butyl (meth) acrylate. Acidic hydrolysis of both tert-butoxy groups then yields a polymer such as polymethyl methacrylate (p-MMA), functionalized on average by two carboxy groups, at both ends of the chain. When this monomer is used at a concentration several times higher than the concentration of the active chains, a polymer is obtained at the end stage, carrying a correspondingly higher number of carboxy groups at the end of each chain.

For the preparation of hydroxyl-functionalized polymers, a tert-alkoxide, preferably butoxide, pentoxide, an alkali metal of lithium, sodium, potassium and cesium is used as initiator, the initiating particle of which is e.g. tert, the alkoxy group incorporated at the beginning of each polymer chain is converted to the hydroxy group by acidic cleavage upon completion of the polymerization. In this process, it is possible to utilize the transfer of growth centers with tertiary alcohol and specifically to prepare oligomeric products with a selected polymerization stage.

Functionalized (reactive) poly (meth) acrylates may find widespread use, for example, in the preparation of block copolymers with polyurethane or polyamide sequences containing a terminal isocyanate group, optionally polyester, hydroxy- or carboxy-terminated, in the cleavage of polymers with side carboxy-, hydroxy- or epoxy groups, reactive injection, etc.

The invention is illustrated by the examples without being limited thereto.

DETAILED DESCRIPTION OF THE INVENTION

Example 1

0.45 g (0.00467 mol) of sodium tert-butoxide was added to a baked and dried flask equipped with a three-way inert gas inlet flask and a magnetic stirrer and dissolved in 2 ml of dried tetrahydrofuran.

SK 279376-6

0.44 ml (0.00463 mol) of distilled and dried tert-butanol are then added with stirring, and the mixture is stirred for an additional 5 minutes, still at normal temperature. 10 ml (0.0936 mol) of distilled and dried methyl methacrylate are then added, the flask is placed in a 25 ° C bath and the mixture is stirred at this temperature for 20 minutes. All reagent dosing operations are performed in countercurrent with inert gas (argon, nitrogen).

The temperature is then raised to 40 ° C and the mixture is allowed to polymerize at this temperature for 5 hours. The reaction is then quenched by the addition of 1 ml of methanol in 10 ml of chloroform, in which the resulting polymer is dissolved. The product was isolated by precipitation to twenty times the volume of heptane and dried to constant weight under vacuum at 40 ° C. The following molecular weights of the product M _w '4580, M _n = 2840 were determined by the SEC method, the theoretical value M _n , calculated from the ratio of methyl methacrylate to tert-butanol, was equal to 2100.

From the polymer thus prepared, 5 g was weighed into a 100 ml flask with a magnetic stirrer, and dissolved in 60 ml of distilled 1,4-dioxane. Concentrated hydrochloric acid (20 ml) was added and the mixture was heated under reflux for 6 hours with stirring. The solution is cooled, rotary evaporated to dryness, the polymer is dissolved in about 40 ml of benzene and precipitated to a 20-fold volume of hexane or heptane and dried to constant weight under vacuum. The product obtained does not contain the initial tert-butoxy groups from the alkoxide initiator, and by cleaving them a functionalized hydroxymethylmethacrylate (poly-MMA) with a hydroxy group is prepared at the starting unit of each polymer chain. In the @ 1 C NMR spectra of the final product, the band disappeared completely at 26.11 ppm and in the IR spectrum a broad band appeared by vibration of the OH groups of about 3500 cm ^- E. The extent of cleavage of methoxy groups on the polymethylmethacrylate (PMMA) chain is negligible.

Example 2

As in Example 1, a mixture of potassium t-hexanolate (0.640 g, i.e. 0.00467 mol) and t-butanol (0.22 ml, i.e. 0.00234 mol) in 2 ml of distilled and dried tetrahydrofuran (THF) was prepared. and polymerize with 10 ml of methyl methacrylate (MMA). After the end of the polymer was isolated by SEC Mn _of 5400. The product was then subjected to acid cleavage of the tert-alkoxy as in Example 1 was prepared, and polymethylmethacrylate (PMMA) with one hydroxy group at the start of each chain.

Example 3

As in Example 1, a solution of sodium tert-butanolate and tert-butanol in tetrahydrofuran was prepared, followed by the addition of 14.8 ml (0.0936 mol) of butyl methacrylate. After the polymerization, the formed polymer with _Mn = 3800 isolated by precipitation into methanol / water = 9: 1 and hydrolysed as described in Example 1 except that the precipitation is carried out in a mixture of methanol / water in a ratio of 9 to 1. The final product is quantitatively functionalized with hydroxy and does not contain residual t-butoxy groups according to spectral analysis.

Example 4

To a flask as in Example 1 was charged 0.0224 g (0.00028 mol) of lithium tert-butoxide in 0.67 mL of dry heptane and diluted with 2.33 mL of dry toluene. 3 ml of distilled and dried methyl methacrylate were then added with stirring, the flask was placed in a 20 ° C bath and the mixture was allowed to polymerize for 3 hours. The reaction was quenched by addition of 1 mL of methanol in 30 ml of chloroform, and after dissolution is isolated by precipitation into methanol, a twenty-fold amount of polymethyl methacrylate with molecular weight measurement of the SEC M _w = 268,000 and M _n = 174,000th polymer hydrolyzed as in Example 1, and upon completion of the reaction, it precipitates again into hexane or heptane. The product obtained is functionalized with hydroxy and does not contain tert-butoxy groups at the beginning of the chains.

Example 5

A 200 ml glass reactor equipped with a stirrer, a three-way stopcock for inert gas inlet and a side tempering and dosing flask of about 40 ml is used to prepare the polymer, connected to the main reactor space with a metering tube and also equipped with a three-way cock. 50 ml of distilled and dried tetrahydrofuran and 0.462 g (0.00577 mol) of lithium tert-butoxide dissolved in 20 ml of dry tetrahydrofuran are charged to the main flask. A mixture of 20 ml (0.0961 mol) of distilled and dried 2-ethylhexyl acrylate and 10 ml of dry tetrahydrofuran is charged to a side flask and the reactor is placed in a -20 ° C bath. After tempering (about 15 min), the acrylate solution is transferred from the side to the reactor main flask with inert gas overpressure as soon as possible (less than 1 s) with vigorous stirring. The reaction mixture is allowed to polymerize with stirring for 8 hours, then the polymerization is stopped by addition of 1 ml of methanol, the polymer is precipitated by pouring the mixture into a twenty-fold volume of 9: 1 methanol-water and dried under vacuum at 40 ° C. According to SEC measurements, it has an M _w = 37,300 and an M _n = 16,500. In the same manner as in Example 1, the tert-butoxy groups from the starting units of the chain are cleaved to give a hydroxy functionalized product which precipitates into a 9: 1 methanol-water mixture.

Example 6

66.5 ml of distilled and dried toluene are added to the reactor main bank, as in Example 5, followed by a solution of 0.256 g (0.00171 mol) of tert-butyl-alpha-lithium isobutyrate (2-tert-butylcarbonyl-2-). propyllithium) and 0.412 g (0.00515 mol) of lithium tert-butoxide in 9.5 ml of dry tetrahydrofuran. A solution of 5 ml (0.0240 mol) of distilled and dried 2-ethylhexyl acrylate in 20 ml of dry toluene is charged to a side flask. The reactor is cooled to -60 ° C in a thermostate, and then the acrylate solution is transferred to the main reactor flask as in Example 5 with vigorous stirring, and the mixture is allowed to polymerize with stirring for 5 minutes, and then quenched with 1 ml of methanol. . The reaction mixture is then concentrated in a vacuum evaporator to a volume of about 30 ml and the polymer is precipitated to a twenty-fold volume of 8: 2 methanol-water and dried under vacuum. According to SEC, M _w = 4190 and M _n = 3700.

SK 279376-6

As in Example 1, the polymer (ca. 4 g) is dissolved in 60 ml of distilled 1,4-dioxane, 20 ml of concentrated hydrochloric acid is added, and the mixture is heated under reflux for 8 hours with stirring with a magnetic stirrer. , butoxy groups of the starting chain units (tert, butyl isobutyrate) to give a carboxy-functionalized polymer. The volume of the mixture was then adjusted to about 40 mL by evaporation of dioxane and the product precipitated to a twenty-fold excess of methanol: water 8: 2. In the 1M CNMR spectrum of the hydrolyzed product the initially present tert-butoxy carbon band completely disappeared at 26.21 ppm; a carbonyl band at 174.14 ppm, attributable to the isobutyrate unit initially present at the beginning of each polymer chain, wherein the loss of 2-hexoxy groups is virtually non-measurable.

Example 7

As in Example 6, 62 ml of dry toluene and a solution of 0.090 g (0.00060 mol) of tert-butyl alpha-lithium isobutyrate and 0.144 g (0.00180 mol) of lithium tert -butoxide in 8 ml of dry tetrahydrofuran are metered into the main reactor flask. and to a side flask a solution of 20 ml (0.0961 mol) of 2-ethylhexyl acrylate, which, after bringing the reactor to -60 ° C, was transferred to the main flask. The mixture was allowed to polymerize with stirring for 30 min. and the polymer is isolated in the same manner. Its M _w = 63 200 M _n = 55 000. The acid hydrolysis of the tert-butoxy groups at the initial polymer units is carried out in dioxane solution as in Example 6 and the carboxy functionalized polymer is precipitated into methanol- water 9: 1a dried.

Example 8

As in Example 6, 70 ml of toluene and 0.105 g (0.0007 mol) of tert-butyl-alpha-lithium isobutyrate and 0.337 g (0.00421 mol) of lithium tert-butoxide in 5 ml of tetrahydrofuran are added to the main flask and a side flask is charged. 5 ml (0.0351 mol) of n-butyl acrylate in 20 ml of toluene. After cooling to -60 ° C and mixing of the two components, the mixture was allowed to polymerize with stirring for 5 minutes, and then the reaction was stopped by adding 1 ml of methanol. The polymer is precipitated into a 9: 1 methanol-water mixture after concentration and dried, its M _n = 12,500. Hydrolysis of the tert-butoxy groups is again carried out in dioxane solution as in Example 6, and then functionalized polybutylacrylate precipitates from the mixture. carboxy.

Example 9

As in Example 6, but in a side flask, a solution of 5 mL of methyl methacrylate (0.0468 mol) in 20 mL of toluene was charged. After cooling to -20 ° C, polymerization takes place for 30 min. and the polymer is precipitated in the concentrated methanol (M _n = 13 000). Hydrolysis of tert-butoxy groups is carried out in the same manner as in Example 6, the polymer is precipitated into heptane or hexane to prepare carboxy-functionalized polymethylmethacrylate.

Example 10

As in Example 6, a tetrahydrofuran (THF) solution of 0.260 g (0.00171 mol) of tert-butyl alpha-sodium propionate and 0.639 g (0.00515 mol) of sodium tert-hexoxide was initiated into the main reactor flask. After warming to -20 ° C, a solution of methyl methacrylate (NiMA) in toluene as in Example 9 was added from a secondary flask. After 15 minutes the polymerization was terminated and the product precipitated into hexane (M _n = 12,700). This was subjected to acid hydrolysis as in the previous examples to give polymethyl methacrylate (PMMA) with initial carboxy groups.

Example 11

0.210 g (0.0014 mol) of tert-butyl .alpha.-isobutyrate and 0.674 g (0.0084 mol) of lithium tert-butoxide in 70 ml of dry tetrahydrofuran (THF) are charged to the main reactor flask as in the previous examples. . 10 ml (0.0936 mol) of distilled and dried methyl methacrylate (MMA) in 20 ml dry tetrahydrofuran (THF) are charged to a side flask, which is charged to the main flask after the reactor has warmed up as in the previous examples and allowed to polymerize. min. Meanwhile, 0.15 ml (0.0010 mol) of distilled and dried tert-butyl acrylate in 20 ml of dry THF is metered into the emptied side flask, and this solution is transferred to the main reactor flask with vigorous stirring after 15 minutes of polymerization. After a further 5 minutes, the polymerization is quenched, the polymer is precipitated into heptane and subjected to acid hydrolysis as in the previous examples. After isolation, a polymethyl methacrylate with an average of two carboxy groups per polymer chain is obtained.

Example 12

The procedure is as in Example 11, but during the polymerization of methyl methacrylate (MMA), a solution of 0.50 ml (0.0030 mol) of tert-butyl methacrylate is metered into the secondary flask and transferred to the main reactor flask in the same manner after 15 minutes of polymerization. The mixture is vigorously stirred with the polymerization mixture and the reaction is stopped after 5 minutes. After hydrolysis of the t-butoxy groups of the thus prepared product, polymethyl methacrylate (PMMA) is obtained with one carboxy group at the beginning and an average of three carboxy groups at the end of each polymer chain.

Claims (9)

A process for the preparation of functionalized poly (meth) acrylates by anionic polymerization, characterized in that the polymerization of the acrylate or methacrylate monomers is carried out in the presence of initiators selected from the group consisting of tert-alkyl esters of saturated carboxylic acids metallized at the alpha position with an alkali metal. alkali metal alkoxides, in a solvent selected from the group consisting of an aromatic hydrocarbon, a cyclic ether or a mixture thereof, at temperatures ranging from -70 ° C to 20 ° C, then selectively hydrolyzing the ether or ester bound tertiary, alkoxy groups at the beginning and or at the ends of the polymer chains. Process according to claim 1, characterized in that the polymerization is carried out in a mixture with a tert-alcohol The process according to claim 1, wherein the polymerization is carried out in the presence of an alkali metal tert-alkoxide as a stabilizer of the active polymerization centers. 4. The process of claim 1 wherein the polymerization is carried out by tert, an alkyl ester of a saturated carboxylic acid metallized in the alpha position with an alkali metal initiator in the presence of tert, an alkali metal alkoxide as a stabilizer of the active centers. is in the range of 1: 1 to 1:20, preferably 1: 3 to 1: 10, in a mixed solvent composed of an aromatic hydrocarbon and up to 10% by volume of a cyclic ether, at temperatures in the range of -70 ° C to 0 ° C, then after the polymerization by acid-catalyzed hydrolysis, the ester-linked tert-alkoxy group is selectively saponified at the beginning of each polymer chain. Process according to claims 1 and 2, characterized in that, after the monomer has been consumed, t-butyl acrylate or methacrylate is added to the reaction mixture at a concentration equal to or higher than the concentration of active growth centers before the polymerization is complete, then the polymerization is terminated and subsequently the product with ester-linked tert-alkoxy groups at the beginning and one or more groups at the end of each polymer chain is subjected to selective acid hydrolysis. Method according to claims 1 to 3, characterized in that tert-alkyl esters of saturated carboxylic acids having 2 to 10 carbon atoms in the chain, preferably tert, isobutyric and propionic alkyl esters metallized in the alpha position by an alkali metal are used as initiators , selected from the group consisting of lithium, sodium, potassium and cesium. Process according to Claims 1 to 4, characterized in that alkali metal tert-alkoxides having 4 to 10 carbon atoms in the alkali metal chain selected from the group consisting of lithium, sodium, potassium and alkali metal are used as initiators or stabilizers of active polymerization centers. cesium. 8. A process according to claim 1, wherein the polymerization of the monomer is carried out in the presence of an alkali metal alkoxide initiator in an amount of 1 to 10 mol%, based on the monomer concentration, in a cyclic ether or aromatic hydrocarbon environment at at temperatures ranging from -60 ° C to 20 ° C, then the ether-linked tert-alkyl product at the beginning of each chain is subjected to acidic cleavage. Process according to claims 1 to 6, characterized in that the polymerization of the monomer is carried out with a mixture of tert-alkali metal alkoxide and tert-alcohol, wherein the molar ratio of monomer to tert-alcohol is selected according to the desired polymerization degree in the range of 2 to 100. of a polar cyclic ether in an amount of 5 to 20% by volume based on the monomer volume and at a temperature ranging from 0 ° C to 50 ° C, then the ether-linked tert-alkyl product at the beginning of each chain is subjected to acidic cleavage.