METHOD FOR PRODUCING WELL DEFINED COMB POLYMERS

Abstract

A method for producing improved comb polymers having a block or gradient structure. The comb polymers are highly suitable for dispersing fine powder.

Claims

1. A process for preparing comb polymers having block or gradient structure, wherein at least one section A of the comb polymer is formed by polymerizing a monomer mixture M comprising a polyalkylene glycol (meth)acrylate, wherein the monomer mixture M includes less than 2% by weight of (meth)acrylic acid, based on the weight of the polyalkylene glycol (meth)acrylate present in the monomer mixture M.

2. The process as claimed in claim 1, wherein the monomer mixture M includes less than 1.8% by weight of (meth)acrylic acid, based on the weight of the polyalkylene glycol (meth)acrylate present in the monomer mixture M.

3. The process as claimed in claim 1, wherein the polyalkylene glycol (meth)acrylate has been prepared by a process in which neither (meth)acrylic acid nor the anhydride of (meth)acrylic acid is used.

4. The process as claimed in claim 1, wherein the polyalkylene glycol (meth)acrylate is obtained by transesterifying an alkyl (meth)acrylate with a polyalkylene glycol capped at one end or by alkoxylating a hydroxyalkyl(meth)acrylate.

5. The process as claimed in claim 4, wherein at the start of the transesterification reaction, the molar ratio of alkyl (meth)acrylate to polyalkylene glycol capped at one end is 1:1 to 50:1.

6. The process as claimed claim 4, wherein, during and/or after the transesterification, excess alkyl (meth)acrylate is partly or fully removed from the reaction mixture.

7. The process as claimed in claim 1, wherein the monomer mixture M comprises the reaction mixture which is obtained by transesterifying an alkyl (meth)acrylate with a polyalkylene glycol capped at one end and includes, besides the polyalkylene glycol (meth)acrylate, at least one compound selected from the group comprising alkyl (meth)acrylate, polyalkylene glycol capped at one end, transesterification catalyst and polymerization inhibitor.

8. The process as claimed in claim 1, wherein the monomer mixture M comprises polyalkylene glycol (meth)acrylate and alkyl (meth)acrylate in a molar ratio of 1:0 to 1:10.

9. The process as claimed in claim 1, wherein the polymerization of the monomer mixture M to form the at least one section A and the further steps for preparation of the comb polymers are effected by means of living free-radical polymerization.

10. The process as claimed in claim 1, wherein the comb polymer having block or gradient structure has the following structural units: 4-68 mol %, of structural units S1 of the formula (IV), 10-95 mol %, of structural units S2 of the formula (V), 0-85 mol %, of structural units S3 of the formula (VI) and 0-50 mol % of structural units S4, ##STR00004## where R.sup.1, in each case independently, is H or CH.sub.3, R.sup.2, in each case independently, is H, a C.sub.1- to C.sub.20-alkyl group, -cyclohexyl group or -alkylaryl group, R.sup.3, in each case independently, is an alkyl group having 1 to 5 carbon atoms, R.sup.4, in each case independently, is COOM, SO.sub.2OM, OPO(OM).sub.2 and/or PO(OM).sub.2, R.sup.5, in each case independently, is H, CH.sub.2COOM or an alkyl group having 1 to 5 carbon atoms, R.sup.6, in each case independently, is 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, or where R.sup.4 forms a ring with R.sup.7 to give COOCO (anhydride), M, independently, is H.sup.+, alkali metal ion, alkaline earth metal ion, di- or trivalent metal ion, ammonium ion or an organic ammonium group; A=C.sub.2-C.sub.4 alkylene and n=2 to 250, and structural unit S4 is derived from an unsaturated monomer polymerizable into the comb polymer.

11. The process as claimed in claim 1, wherein the at least one section A of the comb polymer having block or gradient structure is formed on average to an extent of at least 90 mol %, based on all structural units in section A, from structural units S1, S3 and/or S4, where structural unit S1 is present in section A to an extent of at least 10 mol %.

12. A process for preparing comb polymers having block or gradient structure, comprising the steps of: transesterifying an alkyl (meth)acrylate with a polyalkylene glycol capped at one end up to a conversion of at least 60 mol %, based on polyalkylene glycol capped at one end, with continuous removal of the alkyl alcohol formed from the reaction mixture, optionally distilling off excess alkyl (meth)acrylate, diluting the reaction mixture obtained to 10% to 90% by weight, optionally adding one or more monomers, adding a RAFT agent and a polymerization initiator to the reaction mixture, polymerizing the reaction mixture up to a conversion of 50 to 95 mol %, based on polyalkylene glycol (meth)acrylate, adding or metering in at least one monomer comprising acid groups and optionally further monomers to the reaction mixture, and further polymerizing the mixture thus obtained up to a conversion of at least 90 mol %, based on a monomer comprising acid groups.

13. A process for preparing comb polymers having block or gradient structure, comprising the steps of: alkoxylating a hydroxyalkyl(meth)acrylate with at least one alkylene oxide using a suitable catalyst, optionally removing the catalyst and/or adding acid or alkali, diluting the reaction mixture obtained to 10% to 90% by weight, optionally adding one or more monomers, adding a RAFT agent and a polymerization initiator to the reaction mixture, polymerizing the reaction mixture up to a conversion of 50 to 95 mol %, based on polyalkylene glycol (meth)acrylate, adding or metering in at least one monomer comprising acid groups and optionally further monomers to the reaction mixture, and further polymerizing the mixture thus obtained up to a conversion of at least 90 mol %, based on a monomer comprising acid groups.

14. A dispersant suitable for use with fine powders, wherein the dispersant comprises the comb polymer prepared by a process as claimed in claim 1.

15. A shaped body obtainable by curing an aqueous inorganic binder composition comprising at least one inorganic binder and a comb polymer prepared by a process as claimed in claim 1.

Description

EXAMPLES

Determination of Molecular Weight and Polydispersity of the Polymers and the Solids Content of the Polymer Solutions

[0144] The weight-average molecular weight M.sub.w and the number-average molecular weight M.sub.n of the polymers were determined by gel permeation chromatography (GPC) with polyethylene glycol (PEG) as standard.

[0145] Column cascade used: three 8300 mm Suprema GPC columns (10 m, 21000 , 130 , with precolumn), from PSS Polymer Standards Service, Germany,

0.1N NaNO.sub.3 solution, the pH of which has been adjusted to 12 with NaOH, Flow rate:
Detector: 2414 RI detector from Waters, USA,
temperature of column oven and detector: 45 C.

[0146] Polydispersity was calculated as the M.sub.w/M.sub.n ratio.

[0147] The solids content of the solutions was determined with an HG 63 halogen drier from Mettler Toledo, Switzerland.

Preparation of the Monomer Mixture M1

[0148] In a three-neck flask equipped with a thermometer, stirrer and a Vigreux column with distillation attachment, 60.1 g (0.6 mol) of methyl methacrylate and 150 g (0.3 mol) of polyethylene glycol monomethyl ether (M.sub.w 500) were mixed, and then 2.94 g of concentrated sulfuric acid and 2.1 g of phenothiazine were added while stirring. The reaction mixture was heated to 120 C. while stirring. The methanol formed during the reaction was distilled off continuously. After 8 hours, the temperature was increased to 135 C., and the methanol and remaining methyl methacrylate were distilled off.

Preparation of Comb Polymer P1 Having Block Structure

[0149] Subsequent to the preparation, monomer mixture M1 was diluted with 600 ml of water in the same reaction vessel and heated to 80 C. A gentle inert gas stream (N.sub.2) was passed through the stirred solution during the heating and throughout the remaining reaction time. 7.7 g of 4-cyano-4-(thiobenzoylthio)pentanoic acid (0.027 mol; RAFT agent) was added. Once the substance had fully dissolved, 1.34 g of azobisisobutyronitrile (0.008 mol) was added. From then on, the conversion was determined regularly by means of HPLC. As soon as the conversion, based on methoxy polyethylene glycol methacrylate, exceeded 85%, 95.3 g of methacrylic acid (1.1 mol) was added to the reaction mixture. After 2.5 hours, all the methacrylic acid had reacted according to HPLC measurement.

[0150] A reddish polymer solution was obtained. The molecular weight M.sub.w of the polymer was 36,200 g/mol and the polydispersity 1.21.

Preparation of the Comb Polymer P2 Having Gradient Structure

[0151] The preparation of the monomer mixture M1 was repeated in the same amount as described above. Subsequent to the preparation, the reaction mixture was diluted with 600 ml of water in the same reaction vessel and heated to 80 C. A gentle inert gas stream (N.sub.2) was passed through the stirred solution during the heating and throughout the remaining reaction time. 7.7 g of 4-cyano-4-(thiobenzoylthio)pentanoic acid (0.027 mol; RAFT agent) was added. Once the substance had fully dissolved, 1.34 g of azobisisobutyronitrile (0.008 mol) was added. From then on, the conversion was determined regularly by means of HPLC. As soon as the conversion, based on methoxy polyethylene glycol methacrylate, exceeded 50%, 95.3 g of methacrylic acid (1.1 mol) was added to the reaction mixture within 20 minutes. The reaction mixture was then stirred at 80 C. for another 2 hours.

[0152] A reddish polymer solution was obtained. The molecular weight M.sub.w of the polymer was 35,900 g/mol and the polydispersity 1.20.

Monomer Mixtures M2 to M9

[0153] The monomer mixtures M2 to M9 used for the preparation of comb polymers had the composition shown in table 1.

[0154] Table 1 shows the composition of the monomer mixtures M2 to M9 in mol %, the water content of the mixtures in % by weight, and the % by weight of methacrylic acid based on methoxy polyethylene glycol-1000 methacrylate.

TABLE-US-00001 TABLE 1 Methyl Meth- % by Monomer MPEG- meth- acrylic Water weight of mixture 1000MA.sup.1) acrylate acid content MAA.sup.2) M2 100 0 0 60 M3 90 10 0 60 M4 50 50 0 56 M5 25 75 0 48 M6 90 0 10 59 0.9 M7 80 0 20 59 2.0 M8 70 0 30 59 3.5 M9 50 0 50 57 8.1 [0155] .sup.1) Methoxy polyethylene glycol methacrylate having an average molecular weight of the polyethylene glycol chain of about 1,000 g/mol (corresponding to about 23 ethylene glycol units). [0156] .sup.2) % by weight of methacrylic acid based on the weight of methoxy polyethylene glycol-1000 methacrylate.

Preparation of Comb Polymer P3 Having Block Structure

[0157] For preparation of comb polymer P3, a round-bottom flask equipped with a reflux condenser, stirrer system, thermometer and an inert gas inlet tube was initially charged with 800 g of monomer mixture M2 (0.3 mol). The reaction mixture was heated to 80 C. while stirring. A gentle inert gas stream (N.sub.2) was passed through the solution during the heating and throughout the remaining reaction time. 7.7 g of 4-cyano-4-(thiobenzoylthio)pentanoic acid (0.027 mol; RAFT agent) was added. Once the substance had fully dissolved, 1.34 g of azobisisobutyronitrile (0.008 mol) was added. From then on, the conversion was determined regularly by means of HPLC. As soon as the conversion, based on methoxy polyethylene glycol methacrylate, exceeded 85%, 95.3 g of methacrylic acid (1.1 mol) was added to the reaction mixture. The mixture was left to react for a further 2 hours. After cooling, a reddish polymer solution was obtained, which was adjusted to a solids content of about 40% by weight by addition of water.

Preparation of Comb Polymers P4 to P10 Having Block Structure

[0158] Comb polymers P4 to P10 were prepared analogously to comb polymer P3, except that, rather than monomer mixture M2, monomer mixtures M3 to M9 as shown in table 1 were used for comb polymers P4 to P10. Such an amount of monomer mixture that contained 0.3 mol of total monomer was used in each case.

Tests in Mortar

Preparation of the Mortar Mixtures

[0159] The mortar mixture used for test purposes has the dry composition described in table 2.

TABLE-US-00002 TABLE 2 Dry composition of the mortar mixture Component Amount Cement (CEM I 42.5) 750 g Limestone filler 141 g Sand 0-1 mm 738 g Sand 1-4 mm 1.107 g Sand 4-8 mm 1.154 g

[0160] 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, 352.5 g of mixing water into which the respective polymer according to table 3 had been mixed beforehand was added, and the mixture was stirred for a further 2.5 minutes. The total wet mixing time was 3 minutes in each case.

Determination of Dispersing Action

[0161] To determine the dispersancy of the polymers, the slump of made-up mortar mixtures was respectively measured at different times. The slump of the mortar was determined in accordance with EN 1015-3.

Results of the Mortar Tests

[0162] Table 3 gives an overview of the mortar tests conducted (T1 to T8). The dosage of the respective comb polymer was 0.5% by weight of a 40% by weight polymer solution, based on the weight of the cement. The W/C (weight ratio of water to cement) was 0.47.

TABLE-US-00003 TABLE 3 Results of the mortar tests Comb Monomer Slump [mm] after x minutes polymer mixture 0 30 60 90 120 T1 P3 M2 220 165 141 138 128 T2 P4 M3 240 191 170 141 130 T3 P5 M4 205 159 145 137 128 T4 P6 M5 235 196 171 143 135 T5 P7 M6 219 166 147 133 126 T6 P8 M7 143 127 .sup.1) T7 P9 M8 143 126 T8 P10 M9 138 124 .sup.1) poor processibility, too stiff