Copolymers having a gradient structure as dispersant for alkalinically activated binding agents

Abstract

A copolymer as dispersant in a binder composition comprising an alkaline activating agent, wherein the activating agent is especially suitable for activation of a latently hydraulic and/or pozzolanic binder, wherein the copolymer has a polymer backbone and side chains bonded thereto and comprises at least one ionizable monomer unit M1 and at least one side chain-bearing monomer unit M2, and wherein the copolymer has a gradient structure in at least one section A in a direction along the polymer backbone with regard to the ionizable monomer unit M1 and/or with regard to the side chain-bearing monomer unit M2.

Claims

1. A binder composition comprising: an organic binder and/or a mineral binder, an alkaline activating agent, and a copolymer, as dispersant, having a polymer backbone and side chains bonded thereto and comprising: at least one ionizable monomer unit M1, and at least one side chain-bearing monomer unit M2, wherein: the copolymer has a gradient structure in at least one section A in a direction along the polymer backbone with regard to the ionizable monomer unit M1 and/or with regard to the side chain-bearing monomer unit M2, the copolymer has a further section B, where there is essentially a constant local concentration of monomers and/or a statistical or random distribution of monomers over the entire section B, the ionizable monomer unit M1 has a structure represented by formula I: ##STR00007## and the side chain-bearing monomer unit M2 includes a structure represented by formula II: ##STR00008## where: R.sup.1, in each case independently, is COOM, SO.sub.2OM, OPO(OM).sub.2, 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 R.sup.1 forms a ring together with R.sup.4 to give COOCO, 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, m=0, 1, or 2, p=0 or 1, X, in each case independently, is O or NH, R.sup.8 is a group represented by formula -[AO].sub.nR.sup.a, where A is a C.sub.2- to C.sub.4-alkylene, R.sup.a is H, a C.sub.1- to C.sub.20-alkyl group, a cycloalkyl group, or an alkylaryl group, and n=2-250.

2. The binder composition as claimed in claim 1, wherein the binder comprises a latently hydraulic binder and/or a pozzolanic binder.

3. The binder composition as claimed in claim 1, wherein the binder composition includes 5-95% by weight of a latently hydraulic binder and/or a pozzolanic binder, and 5-95% by weight of a hydraulic binder.

4. The binder composition as claimed in claim 1, wherein, in the at least one section A of the copolymer, a local concentration of the at least one ionizable monomer unit M1 increases continuously along the polymer backbone, while a local concentration of the at least one side chain-bearing monomer unit M2 decreases continuously along the polymer backbone, or vice versa.

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

6. The binder composition as claimed in claim 1, wherein the at least one section A having the gradient structure has a proportion of at least 30% of monomer units, based on a total number of monomer units in the polymer backbone.

7. The binder composition as claimed in claim 1, wherein: the further section B comprises ionizable monomer units M1 and/or side chain-bearing monomer units M2.

8. The binder composition as claimed in claim 7, wherein the further section B having the essentially constant local concentration, based on all the monomer units present therein, comprises at least 30 mol % of side chain-bearing monomer units M2, and any proportion of ionizable monomer units M1 present in the further section B is less than 25 mol % based on all the monomer units M2 in the further section B.

9. The binder composition as claimed in claim 1, wherein a molar ratio of the monomer units M1 to the monomer units M2 is in the range of 0.5-6.

10. The binder composition as claimed in claim 1, wherein R.sup.1COOM; 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 X in at least 75 mol % of all monomer units M2 is O.

11. The binder composition as claimed in claim 1, wherein the copolymer is obtainable by a process that includes polymerizing together ionizable monomers m1 and side chain-bearing monomers m2 to form a concentration gradient structure and/or a gradient structure, and the polymerization is effected by a controlled free-radical polymerization and/or a living free-radical polymerization.

12. The binder composition as claimed in claim 1, wherein the mineral binder is present.

13. A process for producing a binder composition as claimed in claim 12, the process comprising mixing the mineral binder, the copolymer, and the alkaline activating agent.

14. A shaped article produced by curing the binder composition as claimed in claim 12 after addition of water.

15. The binder composition according to claim 1, wherein R.sup.1, in each case independently, is COOM or SO.sub.2OM.

16. The binder composition according to claim 1, wherein R.sup.1 is COOM.

17. The binder composition according to claim 1, wherein the copolymer includes at least 50 mol % of the ionizable monomer units M1 and the side chain-bearing monomer units M2.

18. The binder composition according to claim 1, wherein the copolymer includes at least 75 mol % of the ionizable monomer units M1 and the side chain-bearing monomer units M2.

19. The binder composition according to claim 1, wherein the binder composition includes cement.

20. The binder composition according to claim 1, wherein a proportion of cement in the binder composition is at least 60% by weight.

21. The binder composition according to claim 1, wherein a concentration of the activating agent is 0.1-1.5% by weight based on a weight of the binder.

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 (P1);

(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. Preparation Examples for Polymers

(5) 1.1 Reference Polymer R1 (Comparative Example, Statistical Copolymer)

(6) For preparation of a comparative polymer, a reaction vessel is initially charged with 1.4 g of sodium hypophosphite and 36 g of deionized water. The reaction solution is heated to 80 C. To this solution is added dropwise, within 120 min, a solution of 108.3 g of 50% methoxy polyethylene glycol-1000 methacrylate, 8.6 g of methacrylic acid and 20 g of water. At the same time, within 130 min, a solution of 0.89 g of sodium persulfate and 20 g of water is added dropwise.

(7) After this has ended, the solution is cooled down. What remains is a pale yellowish, slightly viscous polymer.

(8) The copolymer thus obtained is referred to as reference polymer R1 and has a purely statistical or random distribution of the monomer units (methacrylic acid units and polyethylene glycol methacrylate units).

(9) 1.2 Copolymer P1

(10) 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.

(11) 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 P1.

(12) FIG. 1 shows the plot of the monomer conversions against time in the preparation of the copolymer P1. 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).

(13) 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:

(14) TABLE-US-00001 TABLE 1 Monomer ratios during the preparation of the copolymer P1. 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%

(15) It is apparent from table 1 that, in the preparation of the copolymer P1, during the first 25 minutes, a section consist 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.

(16) FIG. 2 additionally shows a schematic of a possible structure of the copolymer P1. 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.

(17) The ionizable monomer units M1 are represented as dumbbell-shaped symbols.

(18) It is apparent from FIG. 2 that copolymer P1 comprises a first section A with gradient structure and a further section B consisting essentially of side chain-bearing monomer units.

(19) 1.3 Copolymer P2

(20) 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.

(21) 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 10 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 P2.

(22) 1.3 Copolymer P3

(23) 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.

(24) 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%. The copolymer with gradient structure thus obtained is referred to as copolymer P3.

(25) 1.4 Copolymer P4

(26) 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.

(27) 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 P4.

(28) 2. Mortar Mixtures

(29) 2.1 Production

(30) The mortar mixture used for test purposes has the dry composition described in table 2:

(31) TABLE-US-00002 TABLE 2 Dry composition of mortar mixture Component Amount [g] Cement (CEM I 42.5 N; Normo 4; available 750 g from Holcim Schweiz) Limestone filler 141 g Sand 0-1 mm 738 g Sand 1-4 mm 1107 g Sand 4-8 mm 1154 g

(32) To make up a mortar mixture, the sands, the limestone filler and the cement were dry-mixed in a Hobart mixer for 1 minute. Within 30 seconds, the makeup water (ratio of water to cement w/c=0.49) admixed was added and the mixture was mixed for a further 2.5 minutes. The total wet mixing time was 3 minutes in each case.

(33) Prior to the addition to the mortar mixture, the respective polymer (proportion: 0.24% by weight; based on solids content of the polymer and based on cement content) and optionally a basic activating agent (NaOH; 0.17% by weight based on cement content) were mixed into the makeup water. If both a copolymer and a basic activating agent have been mixed in, the basic activating agent is mixed into the makeup water prior to the addition of the copolymer.

(34) 2.2 Mortar Tests

(35) To determine the dispersancy of the polymers, the slump (ABM) of a series of made-up mortar mixtures was measured at different times. The slump (ABM) of the mortar was determined in accordance with EN 1015-3.

(36) 2.3 Results of the Mortar Tests

(37) Table 3 gives an overview of the mortar tests conducted and the results achieved. Experiment V1 is a blank experiment conducted for comparative purposes without addition of a polymer.

(38) TABLE-US-00003 TABLE 3 Results of mortar tests Activating ABM.sup.# [mm] after No. Polymer.sup.+ agent* 0 min 30 min 60 min V1 <120 n.m. n.m. V2 R1 202 185 176 V3 R1 NaOH 157 (22%) 150 (19%) 156 (11%) V4 P1 250 242 239 V5 P1 NaOH 254 (+2%) 236 (3%) 219 (8%) V6 P2 258 249 229 V7 P2 NaOH 239 (7%) 227 (9%) 214 (7%) V8 P3 252 242 220 V9 P3 NaOH 236 (6%) 225 (7%) 225 (+2%) n.m. = not measurable .sup.+polymer content = 0.24% by weight based on solids content of the polymer and cement content. *content of activating agent = 0.17% by weight based on cement content. .sup.#= slump according to EN 1015-3. The time 0 min corresponds to the first measurement immediately after the making-up of the mortar sample. The percentage in brackets in the experiments with NaOH corresponds to the percentage change in the slump based on the slump of the corresponding experiment without NaOH in the line above.

(39) The experiments show clearly that, in the case of use of copolymers P1-P3 having gradient structure (see experiments V4-V9), the percentage change in the slump owing to the addition of NaOH is clearly smaller than in the case of use of the reference polymer R1 (see experiments V2 and V3).

(40) It can thus be concluded from the results presented that the copolymers of the invention are advantageous over known polymers in various respects. More particularly, with the polymers of the invention, high dispersancies and plasticizations can be achieved, and these can also be maintained at a level of practical interest over a comparatively long period. Moreover, the polymers of the invention are distinctly less susceptible to alkaline activating agents than conventional polymers.

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