CA1297489C - Process for producing low molecular weight, hydroxy functional (meth)acrylate polymers, their use for producing isocyanate terminal group-containing prepolymers as well as sealants and adhesives produced therefrom - Google Patents

Abstract

ABSTRACT

Low molecular weight (meth)acrylate polymers with substantially .alpha.,.omega. -terminal hydroxyl groups with a hydroxyl group equivalent weight of 500 to 5000 are obtained by the polymerization of (meth)acrylates and optionally copolymerizable monomers in the presence of an initiator able to transfer hydroxyl groups to the polymer molecule and regulators of general formula HO-A-Sx-B-OH, in which A and B in each case stand for a divalent organic radical and x ? 2. By reacting with diisocyanates, the hydroxyfunctional (meth)acrylate polymers yield terminal isocyanate groups containing prepolymers, from which can be produced moisture-har-dening adhesives and sealants, which are preferably transparent.

Description

74~9 The present inventlon relates to a process for pro-ducing hydroxyfunctional methacrylate or acrylate polymers of a low molecular weight, whose hydroxyl groups are mainly in the ~ -position of the polymer chain, to-gether with the further use thereof. These acrylate or methacrylate polymers, by reacting with suitable diisocyana-tes, can be converted into polyurethane pre-polymers with mainly terminal isocyanate groups. Such polyurethane prepolymers are suitable for the production of moisture-hardening, one component sealants and ad-hesives.
The production of hydroxyl group-containing acrylate or methacrylate polymers is in principle known and a conventional process is the radical copolymerization of hydroxyethyl or hydroxypropyl-methacrylate or acrylate with non-functional methacrylate or acrylate esters.
Due to the preferred incorporation of hydroxyfunctional comonomers into the polymer chains, the monomer mixture is rapidly depleted of the hydroxyfunctional comonomers.
Thus, with high conversion rates, at the start of the reaction polymer molecules with a high hydroxyl group content are obtained and at the end of the polymerization polymer molecules with a low and in extreme cases no hydroxyl group content are formed. Particularly in the case of low hydroxyl group contents and low molecular weights, chemically very inhomogeneous polymers are obtained with considerable proportions of hydroxyl group-free polymer molecules. In order to produce polyurethane prepolymers for use in sealants, non-uniform hydroxyl group-containing polymer mixtures of this type are not suitable, because they do not make it possible to obtain the properties required by the sealant, such as uniform through-curing, elastic characteristics and low surface tackiness.

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~ 2 --In order to obtain chemically more homogeneous polymers, a two-stage process is described on a number of occasions in the patent literature. In the first stage, a carboxyl group-containing polymer is obtained through the copolymerization of acrylic acid or methacrylic acid.
In a following reaction, these carboxyl groups are then esterified with alkylene oxides, such as ethylene oxide, propylene oxide or glycide in the presence of basic ca-talysts (c~ U.S. patent 3,116,270, British patent 1,002,343 and DE-OS 3,005,945). Although this process leads to an improvement compared with the aforementioned conven-tional procedure, the hydroxyl groups are only statistically distributed and there is also an incomplete esterification of the carboxyl groups. Particularly in the case of low hydroxyl group contents, such as are required for use in sealants, these facts lead to poor product character-istics.
German patent 2,915,864 describes the preparation of hydroxyl group-containing acrylates using 2-hydroxy-ethyl-acrylate and 2-mercaptoethanol as hydroxyl group-containing regulators. When the reaction parameters are -appropriately chosen, this leads to copolymers statisti-cally containing approximately 2 hydroxyl groups per molecule. The hydroxyl group transferred by the regulator is incorporated at the end of the polymer molecule, whilst the hydroxyl group of the comonomer ~2-hydroxyethyl-acry-late) is introduced at a random point of the macromole-cule. As is admitted by the inventors, the thus produced copolymers constitute mixtures, which can obtain con-siderable proportions of polymer molecules, which contain no or only one functional group.
European patent 68,887 describes a process for producing acrylate or methacrylate polymers of low mole-cular weight with ~I~-terminal hydroxyl groups. This process called "~roup transfer polymerization" makes use of silyl ketene acetals with a hydroxyl group, pro-tected by silylation, as the initiator. When using suitable ~Z9'74~3~

catalysts "living" pol,ymers are obtained, which after coupling with a dihalogen compound and hydrolysis supply the ~ -dihydroxyfunctional acrylate or methacrylate polymer. This process is not only complicated (it is necessary to work with an absolute exclusion of moisture) but a further disadvantage results from the use of very expensive starting materials, namely silyl ketene acetals.
This is particularly a decisive economic disadvantage in the case of low molecular weight polymers, because the silyl ketene acetal is required in stoichiometric quantities.
The object of the present invention is to find a simpler process for producing low molecular weight hydroxyl group-containing acry].ate or methacrylate polymers. The hydroxyl groups are mainly to be in the ~ -position of the polymer chain, so that there is a mainly linear growth during the subsequent condensation reactions.
This problem is solved with the aid of a radical polymerization process, in which both the initiator and the regulator used can transfer a hydroxyl group to the polymer molecule.
The present invention therefore specifically relates to a process for the production of low molecular weight ~meth)acrylate polymers with substantially ~ -ter-minal hydroxyl groups with a hydroxyl equivalent weigh-t of 500 to 5000, in which process, in each case based on the monomer mixture, 10 to 100% by weight of an alkyl methacrylate with 1 to 14 carbon atoms in the alkyl radical and/or 0 to 100% by weight of an alkyl acrylate with 2 to 14 carbon atoms in the alkyl radical and 0 to 40%
by weight of a monomer copolymerizable with the methacrylates or acrylates, undergo radical polymerization in the presence of an initiator from the group of peroxides, hydroper-oxides or azocompounds and able to transfer hydroxyl groups to the polymer molecule, or under UV radiation, ~Z~'7~9 in the presence of hydroxyl group-containing regulators or general formula HO - A - Sx~ B - OH (I) in which A and B in each case represent a divalent organic radical and x ~ 2.
A and s can be the same or different. Preferably, A and B stand for an optionally substituted o-, m- or p-arylene radical, a -(CH2) -group with y ~ 2, or a S

"
-C-M-(CH2 )y-group with y - 2, in which M is an oxygen atom or a radical R-N- with R = alkyl.
The regulators used are preferably those having a symmetrical molecular structure and being of the di-sulphide type. In the presence of radical Eorming agents, e.g. the growing polymer radical, such disulphides de-compose into two thiyl radical fragments. The thus Eormed thiyl radicals can on the one hand react with a growing polymer radical and so stop its growth. They can also start a new polymerization chain with existing monomers.
As with each thiyl radical a hydroxyl group is also trans-ferred to the polymer chain, no polymer chain ends can form, which can transfer no hydroxyl function, as is the case when using mercaptanes (including 2-mercapto-ethanol) as the chain tansfer reagent. The regulator quantity used, based on the monomers, is approximately 2 to 20, preferably 2 to 8 mol%.
It has surprisingly been found that it is also possible to use simple and readily accessible hydroxy functional disulphides, such as e.g. bis-(hydroxyethyl)-bisulphide as the functionalizing regulator, although they are described in the literature as only slightly active chain transfer agents (cf e.g. R. M. Pierson, A.J. Con-stanza and A.H. ~einstein, Journal of Polymer Science, Vol. 17, p.221, 1955). Further preferred disulphides are bis-(2-hydroxypropyl)-disulphide, bis-(2-hydroxymethyl-phenyl)-disulphide, bis-(2-hydroxyethyl xanthogen)-di-.~ , ~L2974~9 sulphide and bis-(N-methyl-N-hydroxyethylthiocarbamoyl)-di-sulphide. The preparation of the compounds is described in Houben-Weyl, Methoden der organischen Chemie, 4th edition, Vol.9, p. 55ff.
The initiators used are hydroxyl group-containing organic peroxides or hydroperoxides or hydroxyl group-containing azo-compounds, but preferably an aqueous hydrogen peroxide solution is used as the initiator.
Based on the monomers, approximately 2 to 50 and preferably 2 to 20% by weight of a 60% H202 solution are used. In order to speed up the polymerization, it is possible to use the redox reagents conventionally employed in radlcal polymerizat:ion, such as e.g. socliurn bisulphite, sodium formaldehyde sulphoxylate, ascorblc acid, .i.soascorblc acid, iron(II) salts, cobalt(II) salts, copper(II) salts, manganese(II) salts or cerium(III) salts.
On the other hand it is also possible to initiate the reaction with UV radiation.
The polymerization can be performed in bulk, in a suitable organic solvent or in an aqueous emulsion.
A preferred embodiment is polymerization in a water-miscible solvent, so that during the complete synthesis a homo-geneous solution is present, which leads to a product with a uniform molecular weight distribution.
The average molecular weight, as well as the hy-hydroxyl equivalent weight (calculated from the hydroxyl number) can be varied within wide limits by a suitable ratio of initiator and regulator to the monomer used.
If more than two hydroxyl groups per molecule are required then a small quantity of a hydroxyl group-containing acrylate or methacrylate can be copolymerized. Examples for this are 2-hydroxyethyl-methacrylate or 2-hydroxy-ethyl-acrylate. The hydroxyl groups obtained from the conomoners are naturally statistically distributed along the polymer chain.

12~'74~

A particularly uniform distribution is obtained through polymerizing by the feed process. The comonomer mixture and the regulator are then dosed over a long period into the reaction vessel at the same speed as they are consumed by the polymerization reaction. This process permits polymerization to substantially quanti-tative conversion rates, without disadvantageous properties being encountered in the product.
The average molecular weights of the copolymers (determined by gel permeation chromatography) are between 1000 and 10,000, but preferably between 2000 and 5000.
The hydroxyl equivalent weight (determined by acetylatlon) of the copolymers is between 500 and 5000, preEerably between 1000 and 2500. This leads to an average number of hydroxyl groups per molecule between 1.5 and 3.5 and preferably between 2.0 and 3Ø
Esters of acrylic or methacrylic acid of general formula R
CH 2 = C - COOR (II) are mainly used as monomers, whereby in said formula R is a hydrogen atom or a methyl group and R is an alkyl group with 1 to 14 carbon atoms. The alkyl group can be linear or branched. Typical examples are n-butyl acrylate or methacrylate, 2-ethylhexyl acrylate or meth-acrylate, methyl methacrylate, dodecyl acrylate or meth-acrylate. Based on the monomer mixture, 10 to 100, pre-ferably 30 to 100% by weight of methacrylate and/or 0 to 100, preferably 0 to 50% by weight of acrylate are used.
Part of the acrylate or methacrylate monomers can be replaced by other monomers, which are copolymerizable with the acrylate or methacrylate monomers. Examples ~Z9'74~ `

of these are styrene, butadiene, isoprene, acrylic acid methacrylic acid, esters and semi-esters of maleic acid and itaconic acid, acrylonitrile, acrylamide and gly-cidyl acrylate or methacrylate. The nature and quantity of the particular monomers are selected on the basis of the intended use of the polymer and, based on the monomer mixture, up to 40, preferably up to 20 and in certain cases only up to 10% by weight of said comono-mers are used.
The reaction temperature is dependent on the reactivity of the monomers used and the initiator used, as well as the nature of the solvent or dispersant. It is con-ventionally between 30 and 140C, preferably between 50 and 90C. The reaction temperatures are preferably kept constant at the predetermined level, i.e. the re-sulting polymerization heat is iE necessary removed from the reaction mixture by cooling.
The reaction time is determined by the reactivity of the monomers. In the feed process which is preferred, after the end of dosing in the monomer mixture-and re-gulator, the reaction is continued until virtually all the monomers have been consumed.
It is a further object of the invention to convert the aforementioned hydroxyl group-containing (meth)acry-late (co)polymer into an isocyanate group-containing prepolymer by reacting it with organic diisocyanates according to methods known per se.
Prior to the reaction of the hydroxyl group-containing polymer with diisocyanates, water and solvents ,; , ~Z9~

reacting with ~socyanates such as alcohols are removed by distlllationt optionally in vacuo. For the case where part;cular purity requirements are made w~th respect to the polymer, lnitiator residues~ activator residues and unreacted regulator portions can be removed from the polymer by washing. For this purpose, the polymer solution i~ preferably mixed with a solvent which is immiscible with water, in order to accelerate a sepration o the phases.
'~ 10 The hydroxyl group ocontaining polymer, freed from the water and solvent ls then rea~ted in per se known manner with diisocyanate~, ~o that a low molecular weight polymer with reactive isocyanate groups at the ends of the molecule is obtained. Examples of suitable dliso-cyanates are diphenyl methane diisocyanate (MVI~, toluylene dilsocyanate (TDI), naphthalene diisocyanate p-phenylene diisocyanate, tran~-1,4-cyclohexane diiso-cyanate (CHDI), 1,3-bis-(isocyanatomethyl)-benzene, 4,4'-dicyclohexylmethane diisocynate (H12MDI), 1,3-big-(isocyanatomethyl)-cyclohexane (H6XDI)~ hexamethylene diisocyanate (HDI) J 3-isocyanatomethyl-3,5,5l-trimethyl cyclohexylisocyanate (IPDI), meta-tetramethylxyléne diisocyanate or para~tetramethylxylene diisocyanate (m-TMXDI, p-TMXDI). For applications where importance 2S is attached to the light resistance o~ the cured polymer, use is preferably made of aliphatic or cycloaliphatic di~socyanate9, such as e.g. CHDI, Hl~MDI, H6XDI, HDI, IPDI, m-~XDI or p-TMXDI.
The reaction of the hydroxyl group-containing polymer with the diisocyanate can either be p~formed at ,, , , . I

~Z~7~

ambient temperature or at an elevated temperature between 50 and 100C in a manner known per se, it being posslble to add the known polyurethane catalysts for speeding up the reaction. Examples for this are given inter alia in J.H. Saunders and K.C. Frisch, Polyurethanes - Chemistry and Technology, Part I, pp. 129-217, John Wiley ~ Sons Inc., New York, 1962. The reaction can either be performed in bulk, or it is possible to add diluents which do not react with the isocyanates. Such diluents are e.g.
plasticizers, such as esters of phthalic, adipic or sebacic acid.
According to another embodiment of the invention one may use reactive diluents, i.e. oligomers carrying two or more hydroxyl groups, which are compatible with hydroxyl group containing acrylate or methacrylate poly-mers, i.e. are miscible without phase separation. Examples of such reactive diluents are low molecular weight hy-droxyl group-containing polyesters or polyethers, such as e.g. polypropylene oxides, polyethylene oxides and their copolymers, as well as polytetramethylene oxides.
Examples of hydroxyl group-containing polyesters are condensation products of dicarboxylic acids, such as adipic, sebacic, azelaic, hexahydrophthalic or ph-thalic acids with dihydric alcohols such as ethylene glycol, 1,4-butane diol, 1,6-hexane diol, or 1,10-decane diol.
As a rule, two isocyanate equivalents of the diiso-cyanate are used for each hydroxyl equivalent and the reaction is continued until all the hydroxyl groups have reacted (measured by the consumption of the iso-cyanate groups).

~Z974E39 The invention also relates to one-component, pre-ferably transparent, moisture-hardening adhesives and sealants based on the terminal isocyanate groups contain-ing prepolymer prepared according to the invention, optionally other isocyanate group-containing prepolymers with polyether or polyester groups in the backbone, conventional plasticizers, as well as optionally suitable fillers, pigments, thixotropic agents and hardening agents, e.g. latent amine hardeners.
The latter can be blocked diamines or polyamines.
Such blocked amines are e.g. the enamines referred to in DE-AS 2,115,882, DE-AS 2,125,247, DE-AS 2,521,841 and DE-AS 2,166,502, as well as oxazolidines as referred to in DE-AS 2,446,438, or aldimines or ketimines, as described e.g. in Bxitish patent 1,064,8~1 or DE-OS

3,306,373.
These prepolymers are used in a preferred manner in transparent sealant formulations, which contain no pigments and as fillers only those which are very finely divided and/or which have a similar refractive index as the prepolymer. Examples of such fillers are highly dispersed silicas, very finely divided glass powders or fibres, very finely divided polymethyl methacrylate powders, very finely divided polystyrene powders or powders of copolymers of methyl methacrylate and other methacry-lates, acrylonitrile or styrene. The selection criteria are the grain fineness of the polymer powder and the similarity of the refractive index to that of the pre-polymer or prepolymer mixture. In the case of a substantial-ly identical refractive index, the filler can have an ~1~9';'415 9 average particle size of up to 200 and in exceptional cases up to 400 /um. Otherwise, the average particle size must not exceed 4O to 50 /um. Particular reference must be made in connection with these transparent sealing formulations to the good light resistance, which can solely be attributed to the good stability of the acrylate or particularly the methacrylate backbone.
The parts and percentages given in the following typical examples are parts and percentages by weight.
The given hydroxyl equivalent weights (E(OH)) are de-termined by acetylation with acetic anhydride and ti-tration with potassium hydroxlde, whilst the isocyanate equivalent weights (E(NCO)) were determined by the dibutyl amine method. The indicated average molecular weights (M(GPC)) were determined by gel permeation chromatography and constitute uncorrected peak values (calibrated against the polystyrene standard).

Example 1 150 parts of isopropanol, 20 parts of water, 0.004 parts of iron (II)-sulphate, 0.04 parts of ethylene diamine tetraacetic acid and 0.6 parts of 70% perchloric acid are placed in a four-necked flask with reflux condenser, stirrer, internal thermometer and two feed vessels, dissolved oxygen is removed therefrom and heat-ing takes place in a nitrogen stream to 80C. Of 300 parts of n-butyl methacrylate, 5% are now added all at once to the reaction vessel, followed by the dropwise addition into the latter of 55 parts of 60% aqueous , .. , ~. . . .

~Z~317~~9 hydrogen peroxide within 10 minutes. When the exothermic reaction dies away~ the remaining monomer and a solution o 15 parts o bis (hydroxyethyl)-disulphide ln 50 parts of isopropanol are dosed in within 5 hours. Stirring 5 then takes place for 2 hours at 75C~ After cooling, the polymer solution is mixed with 500ml o toluene and the separating aqueous phase i~ removed. The organic phase is washed 4 times with saturated aqueous sodium bisulphite solutior~ and then with water. The ~lightly ! 10 turbid polymer solution is filtered clear and the solvent distilled off in VaC~lO- The yield of highly viscous, clear, colourless polymer is almost quantitative.
E(OH): 3.450, M(GPC): 3. 650 .

Examp~, .

The process of example 1 is repeated, but 26 parts of bis-(hydroxyethyl)-disulphide are used.
E(OE~):2. sal; M(GPC):4.270.

ExamPle 3 - The procedure of example 1 is repeated, but 39 parts of bis-(hydroxyethyl)-disulphide are used.
E(OH):1.844; M(GPC):3.760, ~!
The procedure of example 1 is repeated, but in addition 22 parts of hydroxyethyl methacrylate are dissolved in the monomer. E(OH):1.219, M(GPC):3.350.

.. ~ ., ~.. . ~ .

~29'7~9 Se~_ Poly~erization takes place as in example 1~ but no regulator solution is used. E(OH):7.633; M(GPC~:3.800, s~e~
Polymerizatlon is carried out ~s in example 19 but the bls-(hydroxyethyl)-disulphide where replac~d by 6.5 parts of 2 mercaptoethanol (same ~olar quantity as in example l)~
E(OH):5.610, M(GPC):3.850.

As is apparent from the above cornparison examples, when the regulator accordLng to the lnvellt~on i~ not u~ed, only a much smaller hydroxyl group functlonality is obtained.

Exam~e~ 5 300 parts o a polymer containing hydroxyl groups and prepared according to example 4 are mixed with 22 parts of dioctyl phthalate and are heated under dry nitrogen to 50C in a reaction ~lask pro~ided wlth an internal thermometer, reflux condenser and ~eed vessel. 103.8 parts of IPDI are added, accompanied by heating to 80C with stirring. After 5 hours, the isocyanate equlvalent weight (titrimetric) is 627, Then, a ~urther 319.8 parts of hydroxyl group-containing polymer o~ example 4 dissolved in 159.2 parks of dioctyl phthalate are a~ded to the reaction mixtureO After a further 7 hours reaction time, the E~NC0) is 2.286 and does not change again. Whilst excluding moisture9 the isocyanate group-containing pre-polymer is filled into a tightly sealed barrel.
' ~97~1~9 C0~ 50~1 t~
1283.9 parts of a difunctional hydroxyl group-containing propylene glycol with a E(oH3 of 1.413 are reacted with 202 1 parts of IPDI and 1 part of tin II)-octoate as S in example S. Ho~ever, no dioctyl phthalate is ~dded in view of the low viscosity. At the end of the reaction, the E~NCO) is 1~908.

Comparison example Sb 499 parts of a difunctional hydroxyl group-~ontaining polyester of adipic acid and neopentyl glycol with a E(OH) of 519 and 216~2 parts of IPDI are reacted as in example 5. At the end o the reaction, the E(NC0) is 785.

Example 6 and comparison examples 6a and 6b The isocyanate group-contalning prepolymers of examples 5, Sa ans 5b are in each case mixed in vacuo with the stoichiometric quantity of an oxazolidine according to DE-AS 2,446~438 as the latent hardener, highly dispersed silica and optionally further dioctyl phthalate.
The mixtures are then applied in the form of a roughly 5mm wide rope to a glass plate and curing takes place at 23C and 55% relative atmospheric humidity. Skin formation times between 1 and several hours are observed (cf table). After complete through-hardening of the test-pieces ~approximately 3 weeks) they undergo W-thermal ageing. For this purpose, the samples are irradiated ~or 430 hours with a W-radiator containing in uniformly distributed manner 16 of the individual radiators per m2, as described in sheet 3 of DIN 52455. The samples are :12974~

directly exposed to this radiation aS a distance of 25cm~ As can be gather~d from the following table, only the sealant based on the polymer according to the invention is unchanged ~ollowing thi~ irradiation 5 ~test 6 ) .

.

~, . .

~Z5~48~9 `

Table __ Test 6 6a 6b Polymer of example 5 (parts) 28.8 -5 Polymer o example Sa (parts) - 28.4 Polymer of example 5b (parts) - - 21.4 DOP (parts) 13.4 14.0 18.0 Oxazolidine (parts) 3.8 3.6 6.6 Silica (AEROSIL) (partQ) 4,0 4.0 4.0 Skin formation ~h) 1 2 Non-tacky after (h) 5 2 Appearance ater Colourless, Colourle~s, Colourlessp harden~ng clear cle~r slight turbidity 15 Appearance after Slight yello- Slightly Colourless, sur-430 hours W- wish tinge, yellowish, ~ace tacky,aprox radiation clear, non- med.viscosity 3mm thick coating tacky, liquid, com- consisting of mechanical pletely de- tacky, highly characteri- polymerized viscous mass stics un-changed *Trade;,~Mark ,.

Claims (16)

1. A process for preparing low molecular weight hydroxyfunctional (meth)acrylate polymers with .alpha., .omega.-terminal hydroxyl group, said polymers having a hydroxyl equivalent weight of 500 to 5000, in which method 10 to 100% by weight of an alkyl methacrylate with 1 to 14 carbon atoms in the alkyl radical or 0 to 100% by weight of an alkyl acrylate with 2 to 14 carbon atoms in the alkyl radical or mixtures thereof and 0 to 40% by weight of a monomer copolymerizable with the methacrylates or acrylates, in each case based on the monomer mixture, are subjected to a radical polymerization in the presence of an initiator selected from the group comprising peroxides, hydroperoxides or hydroxyl group-containing azo compounds which are able to transfer hydroxyl groups to the polymer molecule [or UV radiation], and in the presence of hydroxyl groups containing regulators in an amount of about 2 to 20 mol % and of general formula I
HO - A - Sx - B - OH (I) in which A and B in each case represent a divalent hydrocarbon radical and x ? 2, at a temperature of about 30 to 140°C with no presence of water and solvents which are reactive with isocyanates.

2. Process according to claim 1, characterized in that a regulator of general formula (I) is used, in which A and B are the same or different and are an optionally substituted 0-, m- or p-arylene radical, a -(CH2)y- group with y ? 2 or a -C-?-(CH2)y - group with y ? 2, M being an oxygen atom or a radical ? with R = alkyl.

3. Process according to claim 2, characterized in that a monomer mixture of 30 to 100% by weight of methacrylate, 0 to 50%
by weight of acrylate and 0 to 20% by weight of a monomer copolymerizable with the (meth)acrylate is used.

4. Process according to claim 3, characterized in that symmetrical disulphides of formula (I) are used as the regulator.

5. Process according to claim 4, characterized in that bis-(hydroxyethyl)-disulphide is used as the regulator.

6. Process according to claim 4, characterized in that an aqueous hydroperoxide solution is used as the initiator.

7. Process according to claim 6, characterized in that a redox compound is added as accelerator.

8. Process according to claim 6, characterized in that the comonomers and regulators are dosed into the reaction mixture in the amount in which they are consumed by the polymerization reaction.

9. Process according to claim 6, characterized in that for the preparation of polmers with more than two hydroxyl groups per molecule, a hydroxyl group-containing acrylate or methacrylate is added to the comonomer mixture.

10. Process for producing terminal isocyanate group-containing prepolymers that comprise reacting low molecular weight hydroxy-functional (meth)acrylate polymers obtained by the process of claim 3 with diisocyanates.

11. Process according to claim 10, characterized in that hydroxyl group-carrying oligomers as are added to the hydroxyfunctional (meth)acrylate polymer as reactive diluents.

12. Process according to claim 10, characterized in that two isocyanate equivalents are used for each hydroxy equivalent and the reaction is continued until all the hydroxyl groups have reacted.

13. One component, moisture-hardening adhesive or sealant composition based on a terminal isocyanate groups containing prepolymer according to claim 10, optionally other isoycanate groups containing prepolymers with polyether or polyester groups in their backbone, conventional plasticizers and optionally suitable fillers, pigments, thixotropic agents and catalysts.

14. Sealant and adhesive according to claim 13, characterized in that it contains as hardener an enamine, aldimine, ketimine or oxazolidine.

15. A process according to claim 1, in which said hydroxyl groups containing regulators is present in an amount of about 2 to 8 mol %.

16. A process according to claim 15, in which said radical polymerization is conducted at a temperature of about 50 to 90° C.