Copolymers having a gradient structure

Abstract

The present invention relates to a copolymer, especially for use as a dispersant for solid particles, in particular for use as dispersant for mineral binder compositions, having a polymer backbone and side chains bonded thereto, 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.

Claims

1. A process for preparing a copolymer, the process comprising: polymerizing together ionizable monomers m1 and side chain-bearing monomers m2 to form a gradient structure in the copolymer, wherein the polymerization includes: converting or polymerizing a portion of the side chain-bearing monomers m2 to form at least one side chain-bearing monomer unit M2 essentially in the absence of the ionizable monomers m1 until a predetermined conversion is attained, the predetermined conversion being in a range of from 1 to 74 mol % of the side chain-bearing monomers m2 being converted or polymerized, and then polymerizing together unconverted side chain-bearing monomers m2 with the ionizable monomers m1, wherein: the copolymer has a polymer backbone and side chains bonded thereto, the copolymer comprises at least one ionizable monomer unit M1 and the at least one side chain-bearing monomer unit M2, and the copolymer has the 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.

2. The process as claimed in claim 1, wherein a polydispersity of the copolymer is <1.5.

3. The process 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 the monomer units in the polymer backbone.

4. The process as claimed in claim 1, wherein the copolymer, in addition to the at least one section A, has a further section B having an essentially constant local concentration of monomers and/or a random distribution of monomers, and the further section B comprises the ionizable monomer units M1 and/or the side chain-bearing monomer units M2.

5. The process as claimed in claim 4, wherein the further section B, based on all monomer units present therein, comprises at least 30 mol % of the side chain-bearing monomer units M2, and a proportion of the 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.

6. The process as claimed in claim 1, wherein 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 where 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=C.sub.2- to C.sub.4-alkylene, R.sup.a is H, a C.sub.1- to C.sub.20-alkyl group, -cycloalkyl group or -alkylaryl group, and n=2-250.

7. The process 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; R.sup.4 and R.sup.7, independently of one another, are H or COOM; and X in at least 75 mol % of all the monomer units M2 is O.

8. The process as claimed in claim 1, wherein the polymerization of the ionizable monomers m1 and the side chain-bearing monomers m2 to form the gradient structure in the copolymer is effected by a controlled free-radical polymerization and/or a living free-radical polymerization.

9. The process as claimed in claim 1, wherein the ionizable monomers m1 have a structure represented by formula IV: ##STR00009## and the side chain-bearing monomers m2 have a structure represented by formula V: ##STR00010## where 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; m=0, 1, or 2; p=0 or 1; and X in at least 75 mol % of all the monomer units M2 is O.

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, Block Copolymer)

(6) For preparation of a block copolymer 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.

(7) As soon as the conversion, based on methoxy polyethylene glycol methacrylate, is 90 mol %, 4.66 g of methacrylic acid (0.05 mol) are added. The mixture left to react for a further 4 h and then to cool. What remains is a clear, reddish, aqueous solution having a solids content of around 40%.

(8) The copolymer thus obtained is referred to as reference polymer R1 and, owing to the virtually complete conversion of the methoxy polyethylene glycol methacrylate (90 mol %), has a block structure in which the side chain-bearing monomer units (methoxy polyethylene glycol methacrylate) are present in a first block and the ionizable monomer units (methacrylic acid) essentially spatially separately in a second block.

(9) 1.2 Reference Polymer R2 (Comparative Example, Statistical Polymer)

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

(11) The copolymer thus obtained is referred to as reference polymer R2 and has a statistical or random distribution of the monomer units (methoxy polyethylene glycol methacrylate units and methacrylic acid units).

(12) 1.3 Copolymer P1

(13) 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.

(14) 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.

(15) 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).

(16) 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:

(17) 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%

(18) It is apparent from table 1 that, in the preparation of the copolymer P1, 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.

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

(20) 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.

(21) 1.4 Copolymer P2

(22) 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.

(23) 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 P2.

(24) 1.5 Copolymer P3

(25) 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.

(26) 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 P3.

(27) 2. Mortar Mixtures

(28) 2.1 Production

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

(30) TABLE-US-00002 TABLE 2 Dry composition of mortar mixture Component Amount [g] Cement (CEM I 42.5 N; Normo 4; 750 g available 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

(31) 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), into which the respective polymer (proportion: 0.24% by weight; based on solids content of the polymer and based on cement content) had been admixed beforehand, was added and the mixture was mixed for a further 2.5 minutes. The total wet mixing time was 3 minutes in each case.

(32) 2.2 Mortar Tests

(33) 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.

(34) 2.3 Results of the Mortar Tests

(35) 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.

(36) TABLE-US-00003 TABLE 3 Results of mortar tests ABM.sup.# [mm] after No. Polymer 0 min 30 min 60 min 90 min 120 min 150 min 180 min V1 <120 n.m. n.m. n.m. n.m. n.m. n.m. V2 R1 240 184 163 140 127 n.m. n.m. V3 R2 208 194 171 160 148 135 n.m. E1 P1 192 165 162 161 150 152 147 E2 P2 244 225 219 209 205 187 180 E3 P3 230 217 229 219 199 166 138 n.m. = not measurable .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.

(37) A comparison of the experiments shows that all copolymers P1-P3 having gradient structure have good and long-lasting plasticizing action. This is especially true of copolymer P2. By comparison, copolymers R1 and R2, which respectively have a pure block structure and a statistical monomer distribution, give distinctly poorer results.

(38) 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.

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