PRODUCTION OF DISPERSANTS BY LIVING RADICAL POLYMERIZATION

Abstract

A method for producing a dispersant for solid particles, in particular a dispersant for mineral binder compositions. Ionizable monomers m1 and sidechain-carrying monomers m2 are polymerized to a copolymer, polymerization taking place as a living free radical polymerization.

Claims

1. A process for preparing a dispersant for solid particles, wherein ionizable monomers m1 and side chain-bearing monomers m2 are polymerized to give a copolymer, wherein the polymerization is effected by a living free-radical polymerization.

2. The process as claimed in claim 1, wherein the polymerization is effected by reversible addition-fragmentation chain-transfer polymerization (RAFT).

3. The process as claimed in claim 1, wherein the monomers are converted to a copolymer having block structure, wherein the side chain-bearing monomers m2 are present essentially in at least one first block A and ionizable monomers m1 essentially in at least one second block B.

4. The process as claimed in claim 3, wherein any proportion of monomers m1 present in the first block A is less than 25 mol % based on all the monomers m2 in the first block A, and wherein any proportion of monomer units m2 present in the second block B is less than 25 mol % based on all the monomer units m1 in the second block B.

5. The process as claimed in claim 1, wherein the ionizable monomers m1 and the side chain-bearing monomers m2 are polymerized together to form a section having a concentration gradient and/or a gradient structure.

6. The process as claimed in claim 1, wherein, in a first step a), at least a portion of the side chain-bearing monomers m2 is reacted or polymerized and, on attainment of a particular conversion, in a second step b), the ionizable monomers m1 are polymerized, optionally together with any as yet unconverted side chain-bearing monomers m2.

7. The process as claimed in claim 6, wherein step a) is effected in the absence of ionizable monomers m1.

8. The process as claimed in claim 6, wherein the polymerization in step a) is conducted until 25-85 mol % of the side chain-bearing monomers m2 have been converted or polymerized.

9. The process as claimed in claim 1, wherein the ionizable monomers m1 have a structure of the formula I: ##STR00004## and the side chain-bearing monomers m2 have a structure of the formula II: ##STR00005## where R.sup.1, in each case independently, is COOM, SO.sub.2OM, OPO(OM).sub.2 and/or PO(OM).sub.2, R.sup.2, R.sup.3, R.sup.5 and R.sup.6, in each case independently, are H or an alkyl group having 1 to 5 carbon atoms, R.sup.4 and R.sup.7, in each case independently, are H, COOM or an alkyl group having 1 to 5 carbon atoms, or where R.sup.1 forms a ring together with R.sup.4 to give COOCO, M, independently of one another, represents tit an alkali metal ion, an alkaline earth metal ion, a di- or trivalent metal ion, an ammonium ion or an organic ammonium group; m=0, 1 or 2, p=0 or 1, X, in each case independently, is O or NH, R.sup.8 is a group of the formula -[AO].sub.nR.sup.a where A=C.sub.2.sup. to C.sub.4-alkylene, R.sup.a is H, a C.sub.1- to C.sub.20-alkyl group, -cyclohexyl group or -alkylaryl group, and n=2-250.

10. The process as claimed in claim 1, wherein a molar ratio of the ionizable monomers m1 used to the side chain-bearing monomers m2 used is in the range of 0.5-6.

11. The process as claimed in claim 9, wherein R.sup.1=COOM; R.sup.2 and R.sup.5, independently of one another, are H, CH.sub.3 or mixtures thereof; R.sup.3 and R.sup.6, independently of one another, are H or CH.sub.3, R.sup.4 and R.sup.7, independently of one another, are H or COOM, and where X in at least 75 mol % of all monomers m2 is O.

12. The process as claimed in claim 1, wherein at least one further monomer ms is present and is polymerized during the polymerization, which is a monomer of the formula III: ##STR00006## where R.sup.5, R.sup.6, R.sup.7, m and p are as defined for R.sup.5, R.sup.6, R.sup.7, m and p in claim 5; Y, in each case independently, is a chemical bond or O; Z, in each case independently, is a chemical bond, O or NH; R.sup.9, in each case independently, is an alkyl group, cycloalkyl group, alkylaryl group, aryl group, hydroxyalkyl group or acetoxyalkyl group, each having 1-20 carbon atoms.

13. The process as claimed in claim 1, wherein the polymerization is effected at least partly in an aqueous solution.

14. A copolymer obtainable by a process as claimed in claim 1.

15. A method comprising preparing a copolymer as claimed in claim 14 as a dispersant for solid particles for water reduction and/or for extending the workability of a mineral binder composition.

Description

BRIEF DESCRIPTION OF THE DRAWING

[0204] The figures used to elucidate the working examples show:

[0205] FIG. 1: The plot of the monomer conversions against time in the preparation of a copolymer of the invention (P4);

[0206] FIG. 2: A schematic diagram of a possible structure of a copolymer which can be derived from the conversions according to FIG. 1.

WORKING EXAMPLES

1. Preparation Examples for Polymers

[0207] 1.1 Statistical Polymer R1

[0208] For comparative purposes, a polymer R1 having statistical or random monomer distribution was prepared. Polymer R1 was prepared by polymer-analogous esterification (PAE). The procedure was essentially as described in EP 1 138 697 B1 at page 7 line 20 to page 8 line 50, and in the examples cited therein. Specifically, a polymethacrylic acid was esterified with methoxy polyethylene glycol.sub.1000 (singly methoxy-terminated polyethylene glycol having an average molecular weight of 1000 g/mol; 20 ethylene oxide units/molecule), so as to result in a molar ratio of methacrylic acid units to ester groups of 1 (M1/M2=1). The solids content of the polymer R1 is around 40% by weight.

[0209] 1.2 Diblock Copolymer P1

[0210] For preparation of a diblock copolymer P1 by means of RAFT polymerization, a round-bottom flask equipped with a reflux condenser, stirrer system, thermometer and an inert gas inlet tube was initially charged with 57.4 g of 50% methoxy polyethylene glycol.sub.1000 methacrylate (0.03 mol; average molecular weight: 1000 g/mol; 20 ethylene oxide units/molecule) and 18.4 g of deionized water. The reaction mixture was heated to 80 C. with vigorous stirring. A gentle inert gas stream (N.sub.2) was passed through the solution during the heating and over all the remaining reaction time.

[0211] 273 mg of 4-cyano-4-(thiobenzoyl)pentanoic acid (0.85 mmol; RAFT agent) were then added to the mixture. Once the substance had fully dissolved, 42 mg of AIBN (0.26 mmol; initiator) were added. From then on, the conversion was determined regularly by means of HPLC.

[0212] As soon as the conversion, based on methoxy polyethylene glycol methacrylate, exceeded 80%, 2.33 g of methacrylic acid (0.03 mol) were added to the reaction mixture. The mixture was left to react for a further 4 h and then to cool. What remained was a clear, pale reddish, aqueous solution having a solids content of around 40% by weight. The molar ratio of methacrylic acid to methoxy polyethylene glycol methacrylate is 1.

[0213] 1.3 Statistical Polymer P2

[0214] A second polymer R1 having statistical or random monomer distribution was prepared. The procedure was analogous to the preparation of polymer P1 (previous chapter), except that the methacrylic acid was included in the initial charge at the start together with the methoxy polyethylene glycol-1000 methacrylate. The solids content of the polymer P1 is again around 40% by weight.

[0215] 1.4 Diblock Copolymer P3

[0216] Diblock copolymer P3 was prepared analogously to diblock copolymer P1, except that, rather than methoxy polyethylene glycol.sub.1000 methacrylate, the corresponding amount of methoxy polyethylene glycol.sub.400 methacrylate (average molecular weight: 400 g/mol; 9 ethylene oxide units/molecule) was used. The solids content of the polymer P3 is again around 40% by weight.

[0217] 1.5 Copolymer with Gradient Structure P4

[0218] For preparation of the gradient polymer by means of RAFT polymerization, a round-bottom flask equipped with a reflux condenser, stirrer system, thermometer and a gas inlet tube is initially charged with 57.4 g 50% methoxy polyethylene glycol 1000 methacrylate (0.03 mol) and 22 g of deionized water. The reaction mixture is heated to 80 C. with vigorous stirring. A gentle N2 inert gas stream is passed through the solution during the heating and over all the remaining reaction time. 378 mg of 4-cyano-4-(thiobenzoyl)pentanoic acid (1.35 mmol) are then added to the mixture. Once the substance has fully dissolved, 67 mg of AIBN (0.41 mmol) are added. From then on, the conversion is determined regularly by means of HPLC.

[0219] As soon as the conversion, based on methoxy polyethylene glycol methacrylate, is 65 mol %, 4.66 g of methacrylic acid (0.05 mol) dissolved in 20 g of H.sub.2O are added dropwise within 20 min. After this has ended, the mixture is left to react for a further 4 h and then to cool. What remains is a clear, pale reddish, aqueous solution having a solids content of around 35%.

[0220] The copolymer with gradient structure thus obtained is referred to as copolymer P4.

[0221] FIG. 1 shows the plot of the monomer conversions against time in the preparation of the copolymer P4. The monomer conversions were determined in a manner known per se at the times given in FIG. 1 during the preparation of the copolymer by high-performance liquid chromatography (HPLC). The upper dotted curve which begins at the origin at time t=0 minutes represents the percentage conversion of the methoxy polyethylene glycol methacrylate monomers (=side chain-bearing monomers m2) (scale to the right). The lower dotted curve which begins at time t=25 minutes represents the percentage conversion of the methacrylic acid monomers (=ionizable monomers m1) (scale to the right). The solid line with the diamond-shaped points indicates the number of side-chain-bearing monomers m2 which have been polymerized since the preceding measurement point (=n(M2); left-hand scale). Correspondingly, the solid line with the triangular points indicates the number of ionizable monomers m1 which have been polymerized since the preceding measurement point (=n(M1); left-hand scale).

[0222] Using the data in FIG. 1 for the period from 0 to 55 minutes at the particular time to calculate the ratio n(M2)/[n(M1)+n(M2)] and n(M1)/[n(M1)+n(M2)], the following values are found:

TABLE-US-00001 TABLE 1 Monomer ratios during the preparation of the copolymer P4. Time n(M2)/[n(M1) + n(M2)] n(M1)/[n(M1) + n(M2)] 15 100% 0% 25 100% 0% 30 33% 67% 35 29% 71% 40 25% 75% 45 17% 83% 55 10% 90%

[0223] It is apparent from table 1 that, in the preparation of the copolymer P4, during the first 25 minutes, a section consist of 100% side chain-bearing monomers m2 is formed, followed by a section in which the proportion of side chain-bearing monomers m2 decreases continuously while the proportion of ionizable monomers m1 increases continuously.

[0224] FIG. 2 additionally shows a schematic of a possible structure of the copolymer P4. This can be inferred directly from the conversions shown in FIG. 1. The side chain-bearing monomers m2 (=polymerized methoxy polyethylene glycol methacrylate monomers) are represented as a circle with a twisted appendage. The ionizable monomers m1 are represented as dumbbell-shaped symbols.

[0225] It is apparent from FIG. 2 that copolymer P4 comprises a first section with gradient structure and a further section AB consisting essentially of side chain-bearing monomers.

[0226] 1.5 Copolymer with Gradient Structure P5

[0227] For preparation of the gradient polymer by means of RAFT polymerization, a round-bottom flask equipped with a reflux condenser, stirrer system, thermometer and a gas inlet tube is initially charged with 57.4 g 50% methoxy polyethylene glycol 1000 methacrylate (0.03 mol) and 22 g of deionized water. The reaction mixture is heated to 80 C. with vigorous stirring. A gentle N2 inert gas stream is passed through the solution during the heating and over all the remaining reaction time. 378 mg of 4-cyano-4-(thiobenzoyl)pentanoic acid (1.35 mmol) are then added to the mixture. Once the substance has fully dissolved, 67 mg of AIBN (0.41 mmol) are added. From then on, the conversion is determined regularly by means of HPLC.

[0228] As soon as the conversion, based on methoxy polyethylene glycol methacrylate, is 45 mol %, 4.66 g of methacrylic acid (0.05 mol) dissolved in 20 g of H.sub.2O are added dropwise within 20 min. After this has ended, the mixture is left to react for a further 4 h and then to cool. What remains is a clear, pale reddish, aqueous solution having a solids content of around 35%.

[0229] The copolymer with gradient structure thus obtained is referred to as copolymer P2.

[0230] 1.5 Copolymer with Gradient Structure P6

[0231] For preparation of the gradient polymer by means of RAFT polymerization, a round-bottom flask equipped with a reflux condenser, stirrer system, thermometer and a gas inlet tube is initially charged with 57.4 g 50% methoxy polyethylene glycol 1000 methacrylate (0.03 mol) and 22 g of deionized water. The reaction mixture is heated to 80 C. with vigorous stirring. A gentle N2 inert gas stream is passed through the solution during the heating and over all the remaining reaction time. 378 mg of 4-cyano-4-(thiobenzoyl)pentanoic acid (1.35 mmol) are then added to the mixture. Once the substance has fully dissolved, 67 mg of AIBN (0.41 mmol) are added. From then on, the conversion is determined regularly by means of HPLC.

[0232] As soon as the conversion, based on methoxy polyethylene glycol methacrylate, is 30 mol %, 4.66 g of methacrylic acid (0.05 mol) dissolved in 20 g of H.sub.2O are added dropwise within 20 min. After this has ended, the mixture is left to react for a further 4 h and then to cool. What remains is a clear, pale reddish, aqueous solution having a solids content of around 35%. The copolymer with gradient structure thus obtained is referred to as copolymer P6.

2. Polydispersity

[0233] The polydispersity of the polymers of the invention is about 1.2 across the board. By contrast, the comparative polymer R1 prepared by polymer-analogous esterification has a polydispersity of about 1.5.

3. Mortar Tests

[0234] To determine the dispersants the of the polymers, the slump of a series of made-up mortar mixtures was measured at different times according to EN 1015-3. The mortars were produced using cement (CEM I type), sands (maximum grain size 8 mm), limestone filler and water (w/c=0.49).

[0235] It was found here that all the copolymers have a good and long-lasting plasticizing effect.

[0236] However, the above-described embodiments should be regarded merely as illustrative examples which can be modified as desired within the scope of the invention.