Production of dispersants by nitroxide-mediated solution polymerization

Abstract

The present invention relates to processes for preparing a copolymer, especially a dispersant for solid particles, in particular a dispersant for mineral binder compositions, wherein ionizable monomers m1 and side chain-bearing monomers m2 are polymerized by nitroxide-mediated solution polymerization to give a copolymer, wherein the polymerization is conducted in the presence of an agent comprising a carboxyl group-bearing and phosphated alkoxy amine.

Claims

1. A process for preparing a copolymer, comprising polymerizing ionizable monomers m1 and side chain-bearing monomers m2 by nitroxide-mediated solution polymerization to give the copolymer, wherein the polymerization is conducted in the presence of an agent comprising a carboxyl-bearing phosphated alkoxy amine; wherein the nitroxide-mediated solution polymerization is conducted at a pH in the range of 7.5-13, and the monomers are converted to a copolymer having block structure, wherein the side chain-bearing monomers m2 are present in at least one first block A and ionizable monomers m1 are present in at least one second block B any proportion of monomers m1 present in the first block A is less than 15 mol % based on all the monomers m2 in the first block A, and any proportion of monomers m2 present in the second block B is less than 15 mol % based on all the monomers m1 in the second block B.

2. The process as claimed in claim 1, wherein the proportion of monomers m1 present in the first block A is less than 5 mol % based on all the monomers m2 in the first block A, and the proportion of monomers m2 present in the second block B is less than 5 mol % based on all the monomers m1 in the second block B.

3. The process as claimed in claim 1, wherein the proportion of monomers m1 present in the first block A is less than 1 mol % based on all the monomers m2 in the first block A, and the proportion of monomers m2 present in the second block B is less than 1 mol % based on all the monomers m1 in the second block B.

4. 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.

5. The process as claimed in claim 1, wherein the solution polymerization is effected in a polar solvent.

6. The process as claimed in at claim 1, wherein the nitroxide-mediated solution polymerization is conducted at a temperature of 40-120° C.

7. The process as claimed in claim 1, wherein the nitroxide-mediated solution polymerization is effected in the presence of a base.

8. The process as claimed in claim 1, wherein the nitroxide-mediated solution polymerization is conducted at a pH in the range of 7.5-10.

9. The process as claimed in claim 1, wherein the nitroxide-mediated solution polymerization is conducted at a pH in the range of 7.5-8.5.

10. The process as claimed in claim 1, wherein the agent has exactly one carboxyl group and exactly one nitroxide group.

11. The process as claimed in claim 1, wherein the agent is a compound of the formula X: ##STR00005## where R.sup.11 is a linear or branched alkyl radical having 1-6 carbon atoms; R.sup.12 and R.sup.13 are each independently hydrogen or a linear or branched alkyl radical having 1-6 carbon atoms; R.sup.14 and R.sup.15 are each independently a linear or branched alkyl radical having 1-6 carbon atoms; R.sup.16 and R.sup.17 are each independently a linear or branched alkyl radical having 1-6 carbon atoms; T independently 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.

12. The process as claimed in claim 1, wherein the ionizable monomers m1 have a structure of the formula I: ##STR00006## and the side chain-bearing monomers m2 have a structure of the formula II: ##STR00007## where R.sup.1, in each case independently, is —COOM, —SO.sub.2—OM, —O—PO(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 —CO—O—CO—, 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 of the formula -[AO].sub.n—R.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.

13. The process as claimed in claim 12, 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—.

14. The process as claimed in claim 1, wherein at least one further monomer ms is present and is polymerized during the polymerization, wherein ms is optionally a monomer of the formula III: ##STR00008## 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, 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—; and 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.

Description

WORKING EXAMPLES

1. Preparation Examples for Polymers

(1) 1.1 Statistical Polymer R1

(2) 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 1′000 g/mol; ˜20 ethylene oxide units/molecule), so as to result in a molar ratio of methacrylic acid units to ester groups of 2 (m1/m2=2). The solids content of the polymer R1 is around 40% by weight.

(3) 1.2 Diblock Copolymer P1

(4) For preparation of a diblock copolymer P1 by means of nitroxide-mediated solution polymerization, a round-bottom flask equipped with a reflux condenser, stirrer system, thermometer and an inert gas inlet tube was initially charged with 11.6 g of 50% methoxy polyethylene glycol.sub.1000 methacrylate (average molecular weight: 1′000 g/mol; ˜20 ethylene oxide units/molecule), 53.2 mg of styrene and 5 g of deionized water. The reaction mixture was heated to 90° 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.

(5) Thereafter, a solution of 10 g of 0.1 N sodium hydrogencarbonate and 85 mg of “BlocBuilder MA” (agent; CAS No.: 654636-62-1; available from Arkema, France) was added. Then the conversion of the methoxy polyethylene glycol.sub.1000 methacrylate was monitored by means of HPLC. As soon as this exceeded 85%, 1.0 g of methacrylic acid was added. As soon as the conversion of methacrylic acid exceeded 80%, the reaction was stopped.

(6) The molar ratio of methacrylic acid units to methoxy polyethylene glycol methacrylate was 2 (m1/m2=2) and the solids content of polymer P1 was about 40% by weight.

(7) 1.3 Statistical Polymer P2

(8) 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 was again around 40% by weight.

(9) 1.4 Statistical Polymer P3

(10) A third polymer P3 having statistical or random monomer distribution was prepared. The procedure was analogous to the preparation of polymer P2 (chapter 1.3), using a mixture of methacrylic acid, methoxy polyethylene glycol.sub.1000 methacrylate and 2-hydroxyethyl acrylate (HEA, as further monomer ms) at a temperature of 80° C. as the initial charge. The solution polymerization was then effected at a pH of 8. This was established via the amount of base added in the solution containing BlocBuilder MA. The conversion of the monomers increased in an essentially linear manner over a period of about 50 minutes. Correspondingly, the reaction can be efficiently controlled.

(11) The molar ratio of methacrylic acid units:methoxy polyethylene glycol methacrylate:2-hydroxyethyl acrylate was 4:2:1 and the solids content of polymer P3 was about 40% by weight. The polymers P3 were additionally found to be stable. More particularly, during and after the preparation of the polymers, no significant hydrolysis of the acrylate or methacrylate monomers was detectable in the HPLC measurements.

(12) 1.5 Statistical Polymer P4

(13) A fourth polymer P4 having statistical or random monomer distribution was prepared. The procedure was analogous to the preparation of polymer P3 (chapter 1.4) (temperature likewise 80° C.), except that a pH of 4 was set rather than the pH of 8 by dispensing with the addition of a base. In this case, by contrast with the preparation of polymer P3 what was obtained at first was not a solution but a heterogeneous reaction mixture. As checked on the basis of HPLC measurements, the conversion of the monomers rose very rapidly in the preparation of polymer P4. After about 10 minutes all monomers had already been converted.

(14) Although it is possible in this way to prepare polymers, controlled preparation of polymers is difficult in practice. The polymers P4 were therefore not given further consideration.

(15) 1.6 Statistical Polymer P5

(16) A fifth polymer P5 having statistical or random monomer distribution was again prepared in the manner of polymer P3 (chapter 1.4) (temperature likewise 80° C.). However, rather than the pH of 8, a pH of 11 was established (via the amount of base added). HPLC measurements showed that, under these conditions, a portion of the acrylate/methacrylate monomers is already hydrolyzed during the polymerization and thereafter. This means that methoxy polyethylene glycol groups or hydroxyethyl groups are eliminated, and these can no longer be/are no longer bound to the polymer. However, the conversion of the monomers, as in the case of polymer P3, increased in an essentially linear manner over a period of about 50 minutes. Correspondingly, good control of the reaction is possible under these conditions as well.

(17) The molar ratio of methacrylic acid units:methoxy polyethylene glycol methacrylate:2-hydroxyethyl acrylate was 4:2:1 and the solids content of polymer P5 was about 40% by weight.

2. Polydispersity

(18) 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

(19) To determine the dispersancy of the polymers, the slump of a series of cement pastes mixed with water was measured at different times according to EN 1015-3. The mortars were produced using cement (CEM I type), and water (w/c=0.31).

(20) It was found here that the copolymers of the invention have a good and long-lasting plasticizing effect.

(21) A comparison of polymers P3 and P5 shows the following: with polymer P3 in cement pastes, a slump immediately after mixing of 160 mm is measured, while polymer P5 gives a slump of 80 mm. This shows that particularly preferred polymers are obtained especially by a solution polymerization at a pH of about 8.

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