Grafted polymers

Field of the invention

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The present invention is related to the area of polymers and refers to new comb polymers, a process for their production and their use as super-plasticizers or defoamers for concrete or plaster retarders.

Background of the invention

Polyolefinic acids, particularly polyacrylic acids, grafted with polyglycolethers and mono- methylpolyglycolethers (MPEG) and their use as additives for the manufacture of concrete are well known from literature. Examples for the state of the art can be found inter alia in FR 2776285 Bl (Chryso), EP 1260536 Al (BASF) or WO 97/039037 Al (Mbt). In this context, reference is also made to international patent application WO 06/050850 Al (Cognis) disclosing anionic polymers useful as super-plasticizers for concrete, which are obtained by polymerisation of (meth)acrylic acid or their esters with dipropylendiglycolacrylate (DPGDA), tripropylenglycoldiacrylate (TPGDA), acrylamidomethyl propanesulfonic acid (AMPS) and/or acryl acetate (AA) and subsequent treatment of the intermediates with mixtures of short- and long-chain alkylpolyalkyleneglycols. Another group of concrete plasticizers obtained from the polymerisation of maleic acid (anhydride) and (meth)acrylic acid is known from EP 1319676 Al (Cognis). Polyacrylic acids grafted by polyethyleneglycols and their use as superplasticiz- ers for concrete is also known from EP 1396506 Al (Cognis). Finally, WO 97/39037 Al (Sandoz) describes the use of a styrene/maleic acid anhydride co-polymer, post esterified with a monomethoxy polyglycol ether for the same purpose; the maleate moiety, however, has a symmetric structure.

The products which can be found in the market either provide high fluidity to high-strength cement and concrete compositions or allow an extremely low water-to-cement or concrete ratio. Others reduce the decrease in fluidity, which takes place after a certain time, or control the generation of foam during the making of the final preparations. Unfortunately, none of

these products provide a combination of all these properties on a satisfying level. Especially products allowing efficient foam control and to remove air bubbles in the early stage of the manufacture of the concrete show a strong tendency to separate from the mixture and form an organic layer.

Therefore the problem which underlies the present invention was to develop new polymers with improved super-plasticizing and retarding properties in order to overcome the disadvantages known from the state of the art. In particular, the new polymers should allow simultaneously the establishment of an extremely low water-to-cement or concrete ratio, providing high slump retention while maintaining good flowability, and developing low foam during the preparation of the cement or concrete.

Detailed description of the invention

The present invention refers to grafted polymers, obtainable in that

(a) (Meth)acrylic acid,

(b) Monomethoxypolyethyleneglycol (meth)acrylates, and

(c) Ci ₂ -C ₂₂ fatty alcohol+EO+PO (meth)acrylates

are subjected to copolymerisation and the reaction product thus obtained is subsequently neutralised with an alkaline base and solubilised in water.

Surprisingly it has been observed that the new polymers fulfil the complex requirements as outlined above. They provide high fluidity to high-strength cement and concrete while allowing low water-to-cement ratios. Good slump retentions is obtained, while flowability during this time is maintained. Especially, the products allow an effective control of foam generation and reduce the formation of air bubbles while the problem of surface layering is avoided.

Process

Another object of the present invention concerns a process for the manufacture of grafted polymers comprising the steps of

(i) subjecting mixtures of

(a) (meth)acrylic acid,

(b) monomethoxypolyethyleneglycol (meth)acrylates, and

(c) C ₁₂ -C ₂₂ fatty alcohol+EO+PO (meth)acrylates to a free-radical polymerisation,

(ii) neutralising the acid groups of the polymers thus obtained by means of an alkaline base, and (iii) solubilising the neutralised polymers in water.

Monomethoxypolyethylene glycol (meth)acrylates

Suitable monomethoxypolyethyleneglycol (meth)acrylates, forming component (b) usually follow general formula (I),

CH ₃ O(CH2CH2θ) _n OC-CR ¹ =CH ₂ (I)

in which R ¹ stands for hydrogen or a methyl group and n denotes an integer of from 1 to 200, preferably 25 to 150 and more preferably 50 to 100. Suitable products therefore show average molecular weights of 100 to 10000, preferably 200 to 6000 and most preferably 350 to 5000 Dalton.

C ₁₁ -C ₂ Z fattv alcohol+EO+PO (meth)acrylates

Suitable C ₁₂ -C ₂₂ fatty alcohol+EO+PO (meth)acrylates, forming component (c), usually follow general formula (II),

R ² O(CH ₂ CH2θ)pi(CHCH ₃ CH ₂ θ) _q (CH ₂ CH ₂ θ)p ₂ θC-CR ¹ =CH2 (II)

in which R ¹ stands for hydrogen or a methyl group, R ² represents an alkyl or alkenyl radical having 12 to 22, preferably 16 to 18 carbon atoms, pi and p2 independently stand for 0 or integers of 1 to 50, preferably 2 to 20, and q for an integer of from 1 to 50, preferably 2 to 20. The distribution of ethylene glycol (EO) and propylene glycol (PO) units in the monomer may be block wise or random. For example, it is possible to add a small quantity of EO to the fatty alcohol, followed by PO and optionally another quantity of EO in order to prepare a block

polymer, or to mix the quantities of EO and PO, so that a randomised chain of alkylene oxide units is added to the alcohol.

Therefore, fatty alcohol+EO+PO (meth)acrylates (component c) according to general formula 5 (II) can be used, in which

o R ² stands for an alkyl group having 16 to 18 carbon atoms, pi represents an integer between 1 and 5, p2 stands for 0 and q means an integer between 10 and 15 (block polymers), or

) o R ² stands for an alkyl group having 16 to 18 carbon atoms, pi and p2 represents an average integer between 1 and 5 and q means an average integer between 10 and 15 (random polymers).

A preferred example for component (b) is an adduct of 3 moles EO and 13 moles PO to cetyl 5 stearyl alcohol, which is available in the market under the trademark Agnique ^® DMF 250 (Cognis).

Polymerisation

Polymerisation is conducted according to the state of the art. Components a, b and c are transferred into a flask where the polymerisation takes place. The monomers can be used in a molar ratio (a):(b):(c) of from l :(0.1-10):(0.1 :10), preferably l :(O.5:8):(O.5:8) and most preferably l :(l-7):(l-7). Usually, the polymerisation takes place in aqueous solution at elevated temperatures of about 60 °C to about 100 °C, and preferably about 80 °C and is initiated by the addition of a conventional starter, such as, for example, ammonium persulfate. Once the polymerisation is completed, the reaction mixture is cooled down and treated with an alkaline base, preferably an aqueous sodium or potassium hydroxide solution in a quantity sufficient to neutralise the acidic functions in the polymer and to prepare salts. Finally, the products are diluted by addition of water in order to adjust the desired active matter content of typically 20 to 50 % b.w., and preferably about 35 % b.w.

Industrial application

The grafted polymers obtained according to the present invention provide high fluidity and better workability to cement, concrete and plaster compositions. Another object of the present invention is therefore the use of said new polymers as so-called super-plasticizers and/or de- foamers for concrete or plaster retarders.

Examples

Example 1 Preparation of the grafted polymer

1 MoI acrylic acid, 0.3 MoI monomethoxyethyleneglycol methacrylate and 0.2 MoI Agnique ^® DFM 250 were placed in a 250-ml-polymerisation flask at room temperature. The mixture was diluted with 58.6 ml water and set under nitrogen bubbling in order to remove all traces of oxygen. Then the mixture was heated to about 80 °C and 1.4 g starter (ammonium persul- fate) was added. Since the polymerisation represents an exothermic reaction, the flask was cooled in order to maintain a reaction temperature of 80 to 90 ⁰ C. Once the polymerisation had finished, the product was cooled to room temperature and treated with aqueous sodium hydroxide solution to neutralise the acidic groups in the polymer and diluted with water to adjust a polymer content of 30 % b.w.

Example 2 Preparation of the grafted polymer

1 MoI methacrylic acid, 0.35 MoI monomethoxyethyleneglycol methacrylate, and 0.15 MoI Agnique ^® DFM 250 were placed in a 250-ml-polymerisation flask at room temperature. The mixture was diluted with 58.6 ml water and set under nitrogen bubbling in order to remove all traces of oxygen. Then the mixture was heated to about 80 °C and 1.4 g starter (ammonium persulfate) was added. Since the polymerisation represents an exothermic reaction, the flask was cooled in order to maintain a reaction temperature of 80 to 90 °C. Once the polymerisation had finished, the product was cooled to room temperature and treated with aqueous sodium hydroxide solution to neutralise the acidic groups in the polymer and diluted with water to adjust a polymer content of 30 % b.w.