Dispersant for calcium sulphate-based compositions

Abstract

The present invention relates to the use of a copolymer as a dispersant for binder compositions based on calcium sulfate, the copolymer having a polymer backbone and sidechains bound thereto, and at least one ionizable monomeric unit M1 and at least one sidechain-carrying monomeric unit M2, characterized in that the copolymer has, in a direction along the polymer backbone, a non-random distribution of the monomeric units M1 and/or of the monomeric units M2.

Claims

1. A method comprising introducing a copolymer as a dispersant into a binder composition that includes at least one mineral binder, the binder composition being based on calcium sulfate, wherein the copolymer comprises a polymer backbone and side chains bonded thereto and there are at least one ionizable monomer unit M1 and at least one side chain-bearing monomer unit M2, the copolymer has a nonrandom distribution of the monomer units Ml and/or the monomer units M2 in a direction along the polymer backbone in that the copolymer has a gradient structure in at least one section AA in a direction along the polymer backbone with respect to the ionizable monomer unit M1 and/or with respect to the side chain-bearing monomer unit M2, and the copolymer, in addition to the at least one section AA having a gradient structure, has a further section AB, wherein there is essentially a constant local concentration of the monomers and/or a statistical or random distribution of the monomers over the entire section AB, a proportion of the calcium sulfate, based on all the mineral binder in the binder composition, is at least 30% by weight, a molar ratio of the monomer units Ml to the monomer units M2 in the copolymer is in the range of 0.5-6, the ionizable monomer unit M1 in the copolymer has a structure of the formula I ##STR00007## the side chain-bearing monomer unit M2 includes a structure of the formula II ##STR00008## where R.sup.1 forms a ring together with R.sup.4 to give —CO—O—CO—, or R.sup.1, in each case independently, is —COOM and/or —SO.sub.2-0M, and R.sup.4, in each case independently, is H, —COOM or an alkyl group having 1 to 5 carbon atoms; M, independently of one another, represents H.sup.+, an alkali metal ion, an alkaline earth metal ion, a di- or trivalent metal ion, an ammonium ion or an organic ammonium group; 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.7, in each case independently, is H, —COOM or an alkyl group having 1 to 5 carbon atoms; 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.n—R.sup.a, where A=C.sub.2.sup.− to C.sub.4-alkylene, R.sup.a is H, a C.sub.l- to C.sub.20-alkyl group, -cycloalkyl group or -alkylaryl group; and n=2-250.

2. The method as claimed in claim 1, wherein the copolymer comprises the gradient structure and a block structure comprising an essentially constant local concentration of monomers.

3. The method as claimed in claim 1, wherein the copolymer comprises at least one further monomer unit MS of the formula III: ##STR00009## where 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.7′ is H, —COOM or an alkyl group having 1 to 5 carbon atoms, m′=0, 1 or 2, and p′=0 or 1; 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.

4. The method as claimed in claim 1, wherein the copolymer further comprises at least one first block A consisting of the ionizable monomer unit M1 and at least one second block B consisting of the side chain-bearing monomer unit M2.

5. The method as claimed in claim 1, wherein the polydispersity of the copolymer is <1.5.

6. The method as claimed in claim 1, wherein the molar ratio of the monomer units M1 to the monomer units M2 in the copolymer is in the range of 2-3.5.

7. The method as claimed in claim 1, 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, and where X in at least 75 mol % of all monomer units M2 is —O—.

8. The method as claimed in claim 1, wherein the copolymer is prepared by a controlled free-radical polymerization and/or a living free-radical polymerization.

9. The method as claimed in claim 1, wherein the copolymer is used for control of the setting characteristics of the binder composition.

10. The method as claimed in claim 1, wherein all the copolymer present in the binder composition as a dispersant contains only monomer units that are selected from the group consisting of the ionizable monomer unit M1 and the side chain-bearing monomer unit M2.

Description

BRIEF DESCRIPTION OF THE DRAWING

(1) The figures used to elucidate the working examples show:

(2) FIG. 1: The plot of the monomer conversions against time in the preparation of a copolymer of the invention (CP4);

(3) 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

(4) 1. Copolymers

(5) 1.1 Copolymer CP1 (Block Copolymer)

(6) For preparation of the copolymer, a round-bottom flask equipped with a reflux condenser, stirrer system, thermometer and an inert gas inlet tube is initially charged with 57.4 g of 50% methoxy polyethylene glycol 1000 methacrylate (0.03 mol) and 21 g of deionized water. The reaction mixture is heated to 80° C. with vigorous stirring. A gentle 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 (1.4 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.

(7) As soon as the conversion, based on methoxy polyethylene glycol methacrylate, exceeds 90%, 3.9 g of acrylic acid (0.05 mol) are added to the reaction mixture. The mixture is left to react for a further 4 h and then to cool.

(8) What remains is a clear, pale reddish, aqueous solution having a solids content of around 40%.

(9) Owing to the virtually complete conversion (90%) of the methoxy polyethylene glycol 1000 methacrylate prior to the addition of the acrylic acid, the copolymer CP1 has a block structure.

(10) 1.2 Copolymer CP2 (Block Copolymer)

(11) For preparation of the copolymer, a round-bottom flask equipped with a reflux condenser, stirrer system, thermometer and an inert gas inlet tube is initially charged with 57.4 g of 50% methoxy polyethylene glycol 1000 methacrylate (0.03 mol) and 21 g of deionized water. The reaction mixture is heated to 80° C. with vigorous stirring. A gentle inert gas stream is passed through the solution during the heating and over all the remaining reaction time. 504 mg of 4-cyano-4-(thiobenzoyl)pentanoic acid (1.8 mmol) are then added to the mixture. Once the substance has fully dissolved, 90 mg of AIBN (0.55 mmol) are added. From then on, the conversion is determined regularly by means of HPLC.

(12) As soon as the conversion, based on methoxy polyethylene glycol methacrylate, exceeds 90%, 3.9 g of acrylic acid (0.05 mol) are added to the reaction mixture. 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 40%.

(13) 1.3 Copolymer CP3 (Block Copolymer)

(14) For preparation of the copolymer, a round-bottom flask equipped with a reflux condenser, stirrer system, thermometer and an inert gas inlet tube is initially charged with 57.4 g of 50% methoxy polyethylene glycol 1000 methacrylate (0.03 mol) and 23 g of deionized water. The reaction mixture is heated to 80° C. with vigorous stirring. A gentle inert gas stream is passed through the solution during the heating and over all the remaining reaction time. 504 mg of 4-cyano-4-(thiobenzoyl)pentanoic acid (1.8 mmol) are then added to the mixture. Once the substance has fully dissolved, 90 mg of AIBN (0.55 mmol) are added. From then on, the conversion is determined regularly by means of HPLC.

(15) As soon as the conversion, based on methoxy polyethylene glycol methacrylate, exceeds 90%, 5.2 g of acrylic acid (0.07 mol) are added to the reaction mixture. 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 40%.

(16) 1.4 Copolymer CP4 (Gradient Polymer)

(17) 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 of 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.

(18) 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%. The copolymer with gradient structure thus obtained is referred to as copolymer CP4.

(19) FIG. 1 shows the plot of the monomer conversions against time in the preparation of the copolymer CP4. 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).

(20) 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:

(21) TABLE-US-00001 TABLE 1 Monomer ratios during the preparation of the copolymer CP4. 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%

(22) It is apparent from table 1 that, in the preparation of the copolymer CP4, during the first 25 minutes, a section consisting of 100% side chain-bearing monomer units M2 is formed, followed by a section in which the proportion of side chain-bearing monomer units M2 decreases continuously while the proportion of ionizable monomer units M1 increases continuously.

(23) FIG. 2 additionally shows a schematic of a possible structure of the copolymer CP4. This can be inferred directly from the conversions shown in FIG. 1. The side chain-bearing monomer units M2 (=polymerized methoxy polyethylene glycol methacrylate monomers) are represented as a circle with a twisted appendage. The ionizable monomer units M1 are represented as dumbbell-shaped symbols.

(24) It is apparent from FIG. 2 that copolymer CP4 comprises a first section AA with gradient structure and a further section AB consisting essentially of side chain-bearing monomer units.

(25) 1.5 Comparative Polymer PR1 (Statistical Copolymer)

(26) For comparative purposes, a commercially available dispersant of the “Sika® ViscoCrete® G-2” type (obtainable from Sika Deutschland GmbH) was used. This is a comb polymer having a polycarboxylate backbone and polyether side chains which is prepared by a polymer-analogous reaction of a polycarboxylic acid with singly hydroxy- and amine-terminated polyether side chains. The sequence of the monomer units in the comparative polymer is purely random, i.e. purely statistical. Otherwise, the comparative polymer, however, is comparable to the copolymers described above.

(27) 2. Tests in Calcium Sulfate-Based Binder Compositions

(28) 2.1 Production of the Binder Compositions

(29) For production of a gypsum slurry, 140 g of water were initially charged together with 1 g in each case of a 40% copolymer solution (corresponding to 0.2% by weight of plasticizer based on the total weight of the calcium sulfate β-hemihydrate). Then 200 g of calcium sulfate β-hemihydrate, 0.2 g (0.1% by weight based on the total weight of the calcium sulfate β-hemihydrate) of an accelerator in the form of calcium sulfate dihydrate (obtainable, for example, from Fluka Schweiz) were scattered into the water within 15 seconds and the gypsum slurry was left to settle for 15 seconds. Subsequently, the mixture was manually stirred vigorously for 30 seconds.

(30) 2.2 Test Methods

(31) To test the flow and setting characteristics, a mini-cone having a diameter of 50 mm and a height of 51 mm was filled with the gypsum slurry made up in each case and the slump (ABM) in mm was determined after 75 seconds (in accordance with EN 1015-3). The diameter of the gypsum cake that forms was measured as soon as no flow was observed any longer. The diameter in mm is referred to as the slump.

(32) The initial setting time and the final setting time were determined by the knife cut method according to DIN EN 13279-2 and the thumbprint method. The initial setting time (VB) has been reached when, after a knifecut through the gypsum cake, the cut edges no longer flow together. The final setting time (VE) has been attained when no water separates any longer from the gypsum cake when a fingerprint expends pressure of about 5 kg.

(33) 2.3 Test Results

(34) Table 2 gives an overview of the experiments conducted and the results achieved. Experiment V1 is a blank experiment conducted for comparative purposes without addition of a polymer.

(35) TABLE-US-00002 TABLE 2 Results ABM VB VE Δ.sub.VE−VB No. Polymer [mm] [h:min] [h:min] [h:min] V1 — 120 2:25 6:12 3:47 V2 PR1 206 4:07 12:34  8:27 V3 CP1 203 2:53 7:41 4:48 V4 CP2 212 3:40 8:49 5:09 V5 CP3 211 4:08 10:29  6:21

(36) The experiments show that the copolymers of the invention (experiments V3 to V5) compared to the conventional dispersant (experiment V2), given the same dosage, result in comparable or even better slump, but at the same time clearly have lower retardation and enable quicker setting.

(37) However, the above-described embodiments should be regarded merely as illustrative examples which can be modified as desired within the scope of the invention.