CLAY BLOCKING ADDITIVES FOR GYPSUM COMPOSITIONS

Abstract

A comb polymer is used as an inerting agent for swelling clays and/or non-swelling clays in gypsum compositions, the comb polymer includes: a) at least one poly(alkylene oxide) side chain-bearing monomer unit M1 without ionic groups, b) optionally at least one cationic monomer unit MC, wherein the molar ratio of the cationic monomer units MC to the side chain-bearing monomer units M1 is equal to or less than 10, c) optionally at least one anionic monomer unit MA, wherein the molar ratio of the anionic monomer units MA to the side chain-bearing monomer units M1 is less than 1, preferably equal to or less than 0.5, d) optionally, at least one non-ionic monomer unit M3, wherein the molar ratio of the non-ionic monomer units M3 to the side chain-bearing monomer units M1 is less than 5.

Claims

1-15. (canceled)

16. A method for plasticizing a gypsum composition, comprising the steps of adding to a gypsum composition comprising swelling clays and/or non-swelling clays (i) a comb polymer as an inerting agent and (ii) a plasticizer for gypsum compositions, wherein the comb polymer comprises: a) at least one poly(alkylene oxide) side chain-bearing monomer unit Ml without ionic groups, b) optionally at least one cationic monomer unit MC, wherein the molar ratio of the cationic monomer units MC to the side chain-bearing monomer units Ml is equal to or less than 10, c) optionally at least one anionic monomer unit MA, wherein the molar ratio of the anionic monomer units MA to the side chain-bearing monomer units Ml is less than 1, d) optionally, at least one non-ionic monomer unit M3, wherein the molar ratio of the non-ionic monomer units M3 to the side chain-bearing monomer units Ml is less than 5.

17. The method according to claim 16, wherein the side chain-bearing monomer unit Ml includes a structure of the formula I ##STR00014## wherein R.sup.1, and R.sup.2, in each case independently, are H or an alkyl group having 1 to 5 carbon atoms, R.sup.3, in each case independently, is H, an alkyl group having 1 to 5 carbon atoms, or a group with formula ##STR00015## m = 0, 1 or 2, p = 0 or 1, X, in each case independently, is —O— or —NH—, R.sup.4 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, a cycloalkyl group or an alkylaryl group, and n = 2-250.

18. The method according to claim 16, wherein the cationic monomer unit MC is present in the polymer and includes a monomer which has a structure of the formula II, ##STR00016## wherein R.sup.5, in each case independently, is —[D].sub.d—[E].sub.e—F, with D = -(COO)- and/or -(CONH)-, E = an alkylene group having 1 to 5 carbon atoms, F = -N.sup.+R.sup.10R.sup.11R.sup.12, -S.sup.+R.sup.10R.sup.11R.sup.12 and/or -P.sup.+R.sup.10R.sup.11R.sup.12, wherein R.sup.10, R.sup.11 and R.sup.12 are independently of one another H, an aliphatic hydrocarbon moiety having 1 to 20 C atoms, a cycloaliphatic hydrocarbon moiety having 5 to 8 C atoms and/or an aryl moiety having 6 to 14 C atoms; wherein d = 0 or 1, e = 0 or 1, R.sup.6, R.sup.7 and R.sup.8, in each case independently, are H or an alkyl group having 1 to 5 carbon atoms.

19. The method according to claim 16, wherein the anionic monomer unit MA is present in the polymer and includes a monomer which has a structure of the formula III, ##STR00017## wherein R.sup.13, in each case independently, is —COOM, —SO.sub.2—OM, —O—PO(OM).sub.2 and/or —PO(OM).sub.2, R.sup.14 and R.sup.15, in each case independently, are H or an alkyl group having 1 to 5 carbon atoms, R.sup.16, in each case independently, are H, -COOM or an alkyl group having 1 to 5 carbon atoms, or where R.sup.13 forms a ring together with R.sup.16 to give —CO—O—CO—, M independently from each other is 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.

20. The method according to claim 16, wherein the non-ionic monomer M3 is present in the polymer and has a structure of the formula IV, ##STR00018## wherein R.sup.5′, R.sup.6′, R.sup.7′ in each case independently, are H or an alkyl group having 1 to 5 carbon atoms, and 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.20, 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.

21. The method according to claim 16, wherein the comb polymer, with respect to the total number of monomer units present in the comb polymer, comprises: a) 95 - 100 mol-% of the at least one poly(alkylene oxide) side chain-bearing monomer unit Ml, b) 0 - 1 mol-% of the at least one cationic monomer unit MC, c) 0 - 1 mol-% of the at least one anionic monomer unit MA, d) 0 - 1 mol-% of the at least one non-ionic monomer unit M3.

22. The method according to claim 16, wherein the comb polymer, with respect to the total number of monomer units present in the comb polymer, comprises: a) 30 - 70 mol-% of the at least one poly(alkylene oxide) side chain-bearing monomer unit Ml, and b) 0 - 1 mol-% of the at least one cationic monomer unit MC, c) 0 - 1 mol-% of the at least one anionic monomer unit MA, d) 30 - 70 mol-% of the at least one non-ionic monomer unit M3.

23. The method according to claim 16, wherein the comb polymer, with respect to the total number of monomer units present in the comb polymer, comprises: a) 10 - 99 mol-% of the at least one poly(alkylene oxide) side chain-bearing monomer unit Ml, and b) 1-90 mol-% of the at least one cationic monomer unit MC, c) 0 - 1 mol-% of the at least one anionic monomer unit MA, d) 0 - 75 mol-% of the at least one non-ionic monomer unit M3.

24. The method according to claim 16, wherein the comb polymer consists essentially of the at least one poly(alkylene oxide) side chain-bearing monomer unit Ml and, optionally, the non-ionic monomer unit M3.

25. The method according to claim 16, wherein the comb polymer consists of the at least one poly(alkylene oxide) side chain-bearing monomer unit Ml and the at least one cationic monomer unit MC.

26. The method according to claim 16, wherein the comb polymer is a block polymer, wherein, at least 75 mol-% of the total number of the at least one side chain-bearing monomer units Ml are arranged in a first block of the block copolymer and wherein the block copolymer comprises a second block in which at least 75 mol-% of the total number of the at least one cationic monomer units MC are arranged.

27. The method according to claim 16, wherein the plasticizer for gypsum compositions is a polycarboxylate ether which is chemically and/or structurally different from the comb polymer.

28. A gypsum composition comprising gypsum as a binder and optionally, one or more additional binders, (i) a comb polymer as an inerting agent and (ii) a plasticizer for gypsum compositions, wherein the comb polymer comprises: a) at least one poly(alkylene oxide) side chain-bearing monomer unit Ml without ionic groups, b) optionally at least one cationic monomer unit MC, wherein the molar ratio of the cationic monomer units MC to the side chain-bearing monomer units Ml is equal to or less than 10, c) optionally at least one anionic monomer unit MA, wherein the molar ratio of the anionic monomer units MA to the side chain-bearing monomer units Ml is less than 1, preferably equal to or less than 0.5, d) optionally, at least one non-ionic monomer unit M3, wherein the molar ratio of the non-ionic monomer units M3 to the side chain-bearing monomer units M1 is less than 5.

29. The gypsum composition according to claim 28, comprising at least 30 wt.-% of gypsum, and 0.01 - 10 wt.-% of the comb polymer, each relative to the weight of a total amount of binders in the gypsum composition.

30. The gypsum composition according to claim 28, wherein the side chain-bearing monomer unit Ml includes a structure of the formula I ##STR00019## wherein R.sup.1, and R.sup.2, in each case independently, are H or an alkyl group having 1 to 5 carbon atoms, R.sup.3, in each case independently, is H, an alkyl group having 1 to 5 carbon atoms, or a group with formula ##STR00020## m = 0, 1 or 2, p = 0 or 1, X, in each case independently, is —O— or —NH—, R.sup.4 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, a cycloalkyl group or an alkylaryl group, and n = 2-250.

31. The gypsum composition according to claim 28, wherein the cationic monomer unit MC is present in the polymer and includes a monomer which has a structure of the formula II, ##STR00021## wherein R.sup.5, in each case independently, is —[D].sub.d—[E].sub.e—F, with D = -(COO)- and/or -(CONH)-, E = an alkylene group having 1 to 5 carbon atoms, F = -N.sup.+R.sup.10R.sup.11R.sup.12, -S.sup.+R.sup.10R.sup.11R.sup.12 and/or -P.sup.+R.sup.10R.sup.11R.sup.12, wherein R.sup.10, R.sup.11 and R.sup.12 are independently of one another H, an aliphatic hydrocarbon moiety having 1 to 20 C atoms, a cycloaliphatic hydrocarbon moiety having 5 to 8 C atoms and/or an aryl moiety having 6 to 14 C atoms; wherein d = 0 or 1, e = 0 or 1, R.sup.6, R.sup.7 and R.sup.8, in each case independently, are H or an alkyl group having 1 to 5 carbon atoms.

32. The gypsum composition according to claim 28, wherein the anionic monomer unit MA is present in the polymer and includes a monomer which has a structure of the formula III, ##STR00022## wherein R.sup.13, in each case independently, is -COOM, —SO.sub.2—OM, —O—PO(OM).sub.2 and/or —PO(OM).sub.2, R.sup.14 and R.sup.15, in each case independently, are H or an alkyl group having 1 to 5 carbon atoms, R.sup.16, in each case independently, are H, -COOM or an alkyl group having 1 to 5 carbon atoms, or where R.sup.13 forms a ring together with R.sup.16 to give —CO—O—CO—, M independently from each other is 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.

33. The gypsum composition according to claim 28, wherein the non-ionic monomer M3 is present in the polymer and has a structure of the formula IV, ##STR00023## wherein R.sup.5′, R.sup.6′, R.sup.7′ in each case independently, are H or an alkyl group having 1 to 5 carbon atoms, and 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.20, 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.

34. The gypsum composition according to claim 28, wherein the comb polymer, with respect to the total number of monomer units present in the comb polymer, comprises: a) 95 - 100 mol-% of the at least one poly(alkylene oxide) side chain-bearing monomer unit Ml, b) 0 - 1 mol-% of the at least one cationic monomer unit MC, c) 0 - 1 mol-% of the at least one anionic monomer unit MA, d) 0 - 1 mol-% of the at least one non-ionic monomer unit M3.

35. The gypsum composition according to claim 28, wherein the comb polymer, with respect to the total number of monomer units present in the comb polymer, comprises: a) 30 - 70 mol-% of the at least one poly(alkylene oxide) side chain-bearing monomer unit Ml, and b) 0 - 1 mol-% of the at least one cationic monomer unit MC, c) 0 - 1 mol-% of the at least one anionic monomer unit MA, d) 30 - 70 mol-% of the at least one non-ionic monomer unit M3.

36. The gypsum composition according to claim 28, wherein the comb polymer, with respect to the total number of monomer units present in the comb polymer, comprises: a) 10 - 99 mol-% of the at least one poly(alkylene oxide) side chain-bearing monomer unit Ml, and b) 1-90 mol-% of the at least one cationic monomer unit MC, c) 0 - 1 mol-% of the at least one anionic monomer unit MA, d) 0 - 75 mol-% of the at least one non-ionic monomer unit M3.

37. The gypsum composition according to claim 28, wherein the comb polymer consists essentially of the at least one poly(alkylene oxide) side chain-bearing monomer unit Ml and, optionally, the non-ionic monomer unit M3.

38. The gypsum composition according to claim 28, wherein the comb polymer consists of the at least one poly(alkylene oxide) side chain-bearing monomer unit Ml and the at least one cationic monomer unit MC.

39. The gypsum composition according to claim 28, wherein the comb polymer is a block polymer, wherein, at least 75 mol-% of the total number of the at least one side chain-bearing monomer units Ml are arranged in a first block of the block copolymer and wherein the block copolymer comprises a second block in which at least 75 mol-% of the total number of the at least one cationic monomer units MC are arranged.

40. The gypsum composition according to claim 28, wherein the plasticizer for gypsum compositions is a polycarboxylate ether which is chemically and/or structurally different from the comb polymer.

Description

[0077] In a further advantageous embodiment, m = 0, p = 1 and preferably X = -O-. In this case it is possible to prepare the copolymer on the basis of (meth)acrylic esters which are commercially available.

[0078] In another advantageous embodiment, m = 0 - 2, p = 0 and preferably X = -O-. Thereby, it is possible to prepare the copolymer on the basis of vinyl ether, (meth)allyl ether or isoprenyl ether monomers which are commercially available.

[0079] In a particularly advantageous embodiment, R.sup.1 is a mixture of 40-60 mol% of H and 40-60 mol% of —CH.sub.3.

[0080] The R.sup.4 moiety in the side chain-bearing monomer units M1, based on the total number of R.sup.4 moieties in the monomer units, in particular consists of a poly(ethylene oxide), especially to an extent of at least 50 mol%, especially at least 75 mol%, preferably at least 95 mol% or at least 99 mol%.

[0081] The proportion of ethylene oxide units, based on the total number of alkylene oxide units in the copolymer, is especially more than 75 mol%, especially more than 90 mol%, preferably more than 95 mol% and specifically 100 mol%.

[0082] More particularly, R.sup.4 has essentially no hydrophobic groups, especially no alkylene oxides having three or more carbon atoms. This especially means that the proportion of alkylene oxides having three or more carbon atoms based on the total number of alkylene oxides is less than 5 mol%, especially less than 2 mol%, preferably less than 1 mol% or less than 0.1 mol%. In particular, there are no alkylene oxides having three or more carbon atoms present, i.e. the proportion thereof is 0 mol%.

[0083] R.sup.a is advantageously H and/or a methyl group. Particularly advantageously, A = C.sub.2-alkylene and R.sup.a is H or a methyl group.

[0084] More particularly, n = 10-150, especially n = 15-100, preferably n = 17-70, specifically n = 19-45 or n = 20-25. In particular, this achieves excellent blocking effects.

[0085] Particular preference is given to copolymers in which R.sup.1 is selected from the group consisting of H, -CH.sub.3, and mixtures thereof; R.sup.2 and R.sup.3 = H; R.sup.4, based on the total number of R.sup.4 moieties in the monomer units, consists of a poly(ethylene oxide) especially to an extent of at least 50 mol%, especially at least 75 mol%, preferably at least 95 mol% or at least 99 mol%; and X in at least 75 mol%, particularly in at least 90 mol%, especially in at least 99 mol%, of the total number of monomer units M1 is —O—.

[0086] According to a preferred embodiment, the cationic group of the cationic monomer unit MC in the comb polymer includes or consists of an ammonium group, a sulfonium group and/or or a phosphonium group, in particular a quaternary ammonium group.

[0087] In a preferred embodiment of the invention, the cationic group is an ammonium group. Particularly preferably it is a quaternary ammonium group. In this case, a positively charged nitrogen atom is substituted with four organic groups Preferably, the cationic group has formula -N.sup.+R.sup.10R.sup.11 R.sup.12, wherein R.sup.10, R.sup.11 and R.sup.12 are independently of one another H, an aliphatic hydrocarbon moiety having 1 to 20 C atoms, a cycloaliphatic hydrocarbon moiety having 5 to 8 C atoms and/or an aryl moiety having 6 to 14 C atoms. As indicated by the hyphen, the positively charged nitrogen atom in the group of formula -N.sup.+R.sup.10R.sup.11R.sup.12 is chemically or covalently bonded, optionally via a chemical linker group, to the cationic monomer. Preferably, R.sup.10, R.sup.11 and R.sup.12 are not H, particularly preferably selected from methyl and ethyl.

[0088] Especially, the cationic monomer unit MC in the polymer includes or consists of a cationic monomer which has a structure of the formula II:

##STR00003##

where [0089] R.sup.5, in each case independently, is —[D].sub.d—[E].sub.e—F, with [0090] D = —(COO)— and/or —(CONH)—, [0091] E = an alkylene group having 1 to 5 carbon atoms, [0092] F = —N.sup.+R.sup.10R.sup.11R.sup.12, —S.sup.+R.sup.10R.sup.11R.sup.12 and/or —P.sup.+R.sup.10R.sup.11R.sup.12, [0093] wherein R.sup.10, R.sup.11 and R.sup.12 are independently of one another H, an aliphatic hydrocarbon moiety having 1 to 20 C atoms, a cycloaliphatic hydrocarbon moiety having 5 to 8 C atoms and/or an aryl moiety having 6 to 14 C atoms; whereby [0094] d = 0 or 1, [0095] e = 0 or 1, [0096] R.sup.6, R.sup.7 and R.sup.8, in each case independently, are H or an alkyl group having 1 to 5 carbon atoms.

[0097] Thereby, preferably, R.sup.6 = H or CH.sub.3, R.sup.7 = R.sup.8 = H, d = 1 and, especially D = -(COO)-.

[0098] According to a preferred embodiment, F = —N.sup.+R.sup.10R.sup.11R.sup.12, e = 1 and, preferably E = an alkylene group having 2 to 3 carbon atoms.

[0099] In a preferred embodiment of the invention, the ionic monomer is selected from [2-(acryloyloxy)-ethyl]trimethylammonium chloride, [2-(acryloylamino)-ethyl]trimethylammonium chloride, [2-(acryloyloxy)-ethyl]trimethy-lammoniummethosulfate, [2-(methacryloyloxy)-ethyl]trimethylammonium chloride or methosulfate, [3-(acryloylamino)-propyl]trimethylammonium chloride, [3-(methacryloylamino)-propyl]trimethylammonium chloride.

[0100] Particularly advantageous according to the invention proved to be the use of [2-(methacryloyloxy)-ethyl]trimethylammonium salts, in particular the chloride. The use is commercially available from Evonik Industries, DE (under the brand name “Visiomer TMAEMC”) or from Sigma-Aldrich, DE.

[0101] In a further preferred embodiment, an anionic group of the anionic monomer unit MA in the comb polymer includes or consists of a carboxylic acid, sulfonic acid, phosphoric acid and/or phosphonic acid group.

[0102] Preferably, the anionic monomer unit MA in the polymer includes or consists of an anionic monomer which has a structure of the formula III

##STR00004##

where [0103] R.sup.13, in each case independently, is —COOM, —SO.sub.2—OM, —O—PO(OM).sub.2 and/or —PO(OM).sub.2, [0104] R.sup.14 and R.sup.15, in each case independently, are H or an alkyl group having 1 to 5 carbon atoms, [0105] R.sup.16, in each case independently, are H, —COOM or an alkyl group having 1 to 5 carbon atoms, [0106] or where R.sup.13 forms a ring together with R.sup.16 to give —CO—O—CO—, [0107] M independently from each other is H.sup.+, an alkali metal ion, an alkaline earth metal ion, a di- or trivalent metal ion, an ammonium ion and an organic ammonium group.

[0108] More particularly, R.sup.13 = COOM, R.sup.14 = H or CH.sub.3, R.sup.15 = R.sup.16 = H. It is thus possible to prepare the copolymer on the basis of acrylic or methacrylic acid monomers, which is of interest from an economic point of view.

[0109] Likewise advantageously, R.sup.13 = COOM, R.sup.14 = H, R.sup.15 = H and R.sup.16 = COOM. Corresponding comb polymers can be prepared on the basis of maleic acid monomers.

[0110] It may further be advantageous if the comb polymer comprises at least one further non-ionic monomer unit M3 which especially differs chemically and/or structurally from the monomer units M1, MC and MA. In particular, multiple different further monomer units M3 may be present. In this way, it is possible to further modify the properties of the comb polymer and to adjust them, for example, with regard to specific applications.

[0111] Particularly advantageously, the non-ionic monomer unit M3 a monomer unit of the formula IV:

##STR00005##

where R.sup.5′, R.sup.6′, R.sup.7′ in each case independently, are H or an alkyl group having 1 to 5 carbon atoms, and m′ and p′ are the same as defined for m and p as described above in the context of the copolymer; [0112] Y, in each case independently, is a chemical bond or —O—; [0113] Z, in each case independently, is a chemical bond, —O— or —NH—; [0114] R.sup.20, 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.

[0115] Advantageous examples of non-ionic monomer units M3 are those where m′ = 0, p′ = 0, Z and Y represent a chemical bond and R.sup.20 is an alkylaryl group having 6-10 carbon atoms.

[0116] Also suitable are especially further monomer units M3 in which m′ = 0, p′ = 1, Y is —O—, Z represents a chemical bond and R.sup.20 is an alkyl group having 1-4 carbon atoms.

[0117] Further suitable are further monomer units M3 where m′ = 0, p′ = 1, Y is a chemical bond, Z is —O— and R.sup.20 is an alkyl group and/or a hydroxyalkyl group having 1-6 carbon atoms.

[0118] Particularly advantageously, the non-ionic monomer unit M3 consists of polymerized vinyl acetate, styrene and/or hydroxyalkyl (meth)acrylate, especially styrene.

[0119] According to a preferred embodiment, the comb polymer, with respect to the total number of monomer units present in the comb polymer, comprises 20 - 100 mol-%, in particular 50 - 100 mol-%, especially 65 - 100 mol-%, for example 80 - 100 mol-% or 95 - 100 mol-%, of the at least one poly(alkylene oxide) side chain-bearing monomer unit M1.

[0120] Especially, a preferred comb polymer, with respect to the total number of monomer units present in the comb polymer, comprises: [0121] a) 95 - 100 mol-%, especially 97 - 100 mol-%, particularly or 98 - 100 mol-%, preferably 99.5 mol-%, of the at least one poly(alkylene oxide) side chain-bearing monomer unit M1, [0122] b) 0 - 1 mol-%, especially 0 - 0.1 mol-%, preferably 0 mol-%, of the at least one cationic monomer unit MC, [0123] c) 0 - 1 mol-%, especially 0 - 0.1 mol-%, preferably 0 mol-%, of the at least one anionic monomer unit MA, [0124] d) 0 - 1 mol-%, especially 0 - 0.1 mol-%, preferably 0 mol-%, of the at least one non-ionic monomer unit M3.

[0125] In such or other preferred comb polymers, [0126] the molar ratio of the cationic monomer units MC to the side chain-bearing monomer units M1 is equal to or less than 0.5, especially less than or equal to 0.1, in particular less than or equal to 0.01 or 0. [0127] the molar ratio of the anionic monomer units MA to the side chain-bearing monomer units M1 is equal to or less than 0.5, especially less than or equal to 0.1, in particular less than or equal to 0.01 or 0. [0128] the molar ratio of the non-ionic monomer units M3 to the side chain-bearing monomer units M1 is equal to or less than 0.5, especially less than or equal to 0.1, in particular less than or equal to 0.01 or 0.

[0129] In particular, the comb polymer, with respect to the total number of monomer units present in the comb polymer, comprises 100 mol-% of the at least one poly(alkylene oxide) side chain-bearing monomer unit M1. In this case, the comb polymer can be a homopolymer of identical side chain-bearing monomeric units M1 or a copolymer of at least two different side chain-bearing monomeric units M1.

[0130] Such comb polymers are for example preferred if the comb polymer comprises side chain-bearing monomer units M1 including or consisting of a structure of formula I as shown above wherein parameter p is equal to 1. These are for example poly(alkylene oxide) (meth)acrylate based monomer units M1.

[0131] According to another preferred embodiment, the comb polymer essentially consists of the at least one poly(alkylene oxide) side chain-bearing monomer unit M1 and the non-ionic monomer unit M3. In this case the comb polymer is a copolymer based on the at least one side chain-bearing monomeric units M1 and the non-ionic monomer unit M3.

[0132] Such comb polymers are for example preferred if the comb polymer comprises side chain-bearing monomer units M1 including or consisting of a structure of formula I as shown above wherein parameter p is equal to 0. These are for example poly(alkylene oxide) alkenyl ether-based monomer units M1.

[0133] For example, a preferred comb polymer, with respect to the total number of monomer units present in the comb polymer, comprises: [0134] a) 30 - 70 mol-%, especially 40 - 60 mol-%, particularly or 40 - 50 mol-%, of the at least one poly(alkylene oxide) side chain-bearing monomer unit M1, and [0135] b) 0 - 1 mol-%, especially 0 - 0.1 mol-%, preferably 0 mol-%, of the at least one cationic monomer unit MC, [0136] c) 0 - 1 mol-%, especially 0 - 0.1 mol-%, preferably 0 mol-%, of the at least one anionic monomer unit MA, [0137] d) 30 - 70 mol-%, especially 40 - 60 mol-%, particularly or 40 - 50 mol-%, of the at least one non-ionic monomer unit M3.

[0138] In such or other preferred comb polymers, [0139] the molar ratio of the cationic monomer units MC to the side chain-bearing monomer units M1 is equal to or less than 0.5, especially less than or equal to 0.1, in particular less than or equal to 0.01 or 0. [0140] the molar ratio of the anionic monomer units MA to the side chain-bearing monomer units M1 is equal to or less than 0.5, especially less than or equal to 0.1, in particular less than or equal to 0.01 or 0. [0141] the molar ratio of the non-ionic monomer units M3 to the side chain-bearing monomer units M1 is 0.1 - 5, especially 0.5 - 2.5, in particular 0.8 - 2 or 1 - 1.5.

[0142] In a further preferred embodiment, the comb polymer comprises the at least one cationic monomer MC. Thereby, preferably, the comb polymer consists to an extent of at least 30 mol%, particularly at least 50 mol%, in particular at least 65 mol%, especially at least 90 mol% or 95 mol%, of side chain-bearing monomer units M1 and the cationic monomer units MC, with respect to the total number of monomer units present in the comb polymer. The remaining monomer units can e.g. be the non-ionic monomer units M3. Especially, the comb polymer consists of the at least one poly(alkylene oxide) side chain-bearing monomer units M1 and the at least one cationic monomer units MC.

[0143] For example, a further preferred comb polymer, with respect to the total number of monomer units present in the comb polymer, comprises: [0144] a) 10 - 99 mol-%, especially 40 - 95 mol-%, particularly or 50 - 75 mol-%, of the at least one poly(alkylene oxide) side chain-bearing monomer unit M1, and [0145] b) 1 - 90 mol-%, especially 5 - 60 mol-%, preferably 25 - 50 mol-%, of the at least one cationic monomer unit MC, [0146] c) 0 - 1 mol-%, especially 0 - 0.1 mol-%, preferably 0 mol-%, of the at least one anionic monomer unit MA, [0147] d) 0 - 75 mol-%, especially 5 - 60 mol-%, particularly 25 - 50 mol-% or 0 mol-%, of the at least one non-ionic monomer unit M3.

[0148] In such or other preferred comb polymers, [0149] the molar ratio of the cationic monomer units MC to the side chain-bearing monomer units M1 is 0.1 - 5, especially 0.5 - 2.5, in particular 0.8 - 2 or 1 - 1.5, [0150] the molar ratio of the anionic monomer units MA to the side chain-bearing monomer units M1 is equal to or less than 0.5, especially less than or equal to 0.1, in particular less than or equal to 0.01 or 0, [0151] the molar ratio of the non-ionic monomer units M3 to the side chain-bearing monomer units M1 is 0 5, especially 0.1 - 2.5, in particular 0.5 - 2 or 0.8-1.5.

[0152] Thereby, in particular, the molar ratio of the anionic monomer units MA to the cationic monomer units MC is in the range of 0 - 1, especially 0 - 0.9, in particular 0 - 0.5 or 0 - 0.05.

[0153] In an especially preferred embodiment, the comb polymer is a block copolymer, whereby at least 75 mol-%, especially at least 90 mol-%, preferably at least 99 mol-%, of the total number of at least one side chain-bearing monomer units M1 are arranged in a first block of the block copolymer.

[0154] In particular, the block copolymer comprises a second block in which at least 75 mol-%, especially at least 90 mol-%, preferably at least 99 mol-%, of the total number of at least one cationic monomer units MC are arranged.

[0155] In a further preferred embodiment, between the first block and the second block, there is a third block comprising at least one side chain-bearing monomer unit M1, at least one cationic monomer unit MC and/or at least one non-ionic monomer unit M3. Especially, the third block has a non-random distribution of the monomer units M1 and/or the cationic monomer units MC in a direction along the polymer backbone.

[0156] A “non-random distribution” is understood in the present case to mean a non-statistical distribution of the monomer units M1 and/or the monomer units MC. This means that the side chain-bearing monomer units M1 and/or the ionic units MC are arranged in the third block, for example, in an alternating manner and/or in a gradient structure.

[0157] The structure of the copolymers can be analyzed and determined, for example, by nuclear magnetic resonance spectroscopy (NMR spectroscopy). By .sup.13C and.sup.1H NMR spectroscopy in particular, the sequence of the monomer units in the copolymer can be determined on the basis of neighboring group effects in the copolymer and by using statistical evaluations.

[0158] In all of the structures described above, non-ionic monomer units M3 may be added, for example in order to control the density of the other monomeric units in the comb polymer and/or in order to adjust the comb polymer for specific needs.

[0159] Preferably, if used, the molar proportion of the non-ionic monomer units M3, with respect to the total number of the monomeric units in the comb polymer, is from 0.0001 - 50 mol-%, in particular 0.0002 - 30 mol-%, especially 0.001 - 25 mol-%, advantageously 0.1 -10 mol-% or 1 - 9 mol-%. This is in particular valid for block copolymers.

[0160] The comb polymer is especially prepared by free-radical polymerization, e.g. by conventional free-radical polymerization or by controlled free-radical polymerization (also called living free-radical polymerization). These polymerization techniques are well known to the skilled person.

[0161] Thereby, unilaterally ethylenically unsaturated poly(alkylene oxide) side chain-bearing monomer units M1′ according to formula V, optionally at least one unilaterally ethylenically unsaturated ionic monomer unit MC′ and/or MA′ according to formula VI and/or VII and, optionally, at least one unilaterally ethylenically unsaturated non-ionic monomer unit M3′ according to formula VIII, are polymerized together such that the molar ratio of the cationic monomer units MC to the side chain-bearing monomer units M1 is equal to or less than 10, especially less than 5, the molar ratio of the anionic monomer units MA to the side chain-bearing monomer units M1 is less than 1, preferably equal to or less than 0.5, and the molar ratio of the non-ionic monomer units M3 to the side chain-bearing monomer units M1 is less than 5.

##STR00006##

##STR00007##

##STR00008##

##STR00009##

[0162] Thereby, R.sup.1 - R.sup.16, R.sup.5′ - R.sup.7′, R.sup.20, X, Y, Z, m, m′, n and p, p′ are defined as described above.

[0163] According to a highly preferred embodiment, the comb polymer is a comb polymer which is obtainable or obtained by conventional free-radical polymerization.

[0164] Among controlled free-radical polymerization techniques, reversible addition-fragmentation chain-transfer polymerization (RAFT), nitroxide-mediated polymerization (NMP) and/or atom transfer radical polymerization (ATRP) can be used.

[0165] In reversible addition-fragmentation chain-transfer polymerization, control over the polymerization is achieved by a reversible chain transfer reaction. Specifically, a growing free-radical chain adds to what is called a RAFT agent, which leads to formation of an intermediate free radical. The RAFT agent then fragments, in such a way as to reform another RAFT agent and a free radical available for propagation. In this way, the probability of propagation is distributed uniformly over all chains. The average chain length of the polymer formed is proportional to the RAFT agent concentration and to the reaction conversion. RAFT agents used are especially organic sulfur compounds. Particularly suitable are dithioesters, dithiocarbamates, trithiocarbonates and/or xanthates. The polymerization can be initiated in a conventional manner by means of initiators or thermal self-initiation.

[0166] In nitroxide-mediated polymerization, nitroxides react reversibly with the active chain end to form what is called a dormant species. The equilibrium between active and inactive chain ends is strongly to the side of the dormant species, which means that the concentration of active species is very low. The probability of two active chains meeting and terminating is thus minimized. An example of a suitable NMP agent is the substance with Chemical Abstract number 654636-62-1, commercially available e.g. under the tradename “Blockbuilder MA”.

[0167] In atom transfer radical polymerization (ATRP), the concentration of free radicals is lowered by addition of a transition metal complex and a controlling agent (halogen-based) to such an extent that chain termination reactions, such as disproportionation or recombination, are very substantially suppressed.

[0168] In the present context, reversible addition-fragmentation chain-transfer polymerization (RAFT) has been found to be particularly preferable, especially if block copolymers are to be produced.

[0169] The initiator used for the polymerization is more preferably an azo compound and/or a peroxide as free-radical initiator, which is at least one representative selected from the group consisting of dibenzoyl peroxide (DBPO), di-tert-butyl peroxide, diacetyl peroxide, azobisisobutyronitrile (AIBN), α,α′-azodiisobutyramidine dihydrochloride (AAPH) and/or azobisisobutyramidine (AIBA).

[0170] If the polymerization is effected in an aqueous solution or in water, α,α′-azodiisobutyramidine dihydrochloride (AAPH) is advantageously used as initiator.

[0171] For control of the polymerization, in particular, one or more representatives from the group consisting of dithioesters, dithiocarbamates, trithiocarbonates and/or xanthates are used.

[0172] It has additionally been found to be advantageous if the polymerization is effected at least partly, preferably fully, in an aqueous solution.

[0173] In a second method known as polymer-analogous reaction, a polycarboxylic acid backbone is synthesized in a first step. Subsequently, side chains are attached to the polycarboxylic acid backbone, for example by esterification, amidation or etherisation reactions with alcohols, amines and the like. Such polymer-analogous reactions, as well as resulting comb polymers, are described, for example, in WO 97/35814, WO 95/09821, DE 100 15 135 A1, EP 1 138 697 A1, EP 1 348 729 A1 and WO 2005/090416. Details about the polymer-analogous reaction are disclosed, for example, in EP 1 138 697 B1 on page 7, line 20 to page 8, line 50, as well as in its Examples, or in EP 1 061 089 B1 on page 4, line 54 to page 5, line 38 as well as in its Examples.

[0174] For formation of copolymers having block and/or gradient structures, unilaterally ethylenically unsaturated poly(alkylene oxide) side chain-bearing monomer units M1′ and ethylenically unsaturated ionic monomer units MC′ and/or MA′ and/or the ethylenically unsaturated non-ionic monomer units M3′ are preferably at least partly added at different times.

[0175] In a further preferred embodiment, in the polymerization, in a first step a), a portion of the monomer units M1′ is converted or polymerized and, after reaching a predetermined conversion, in a second step b), the as yet unconverted monomer units M1′ (if present) are polymerized together with ionic monomer unit MC′ and/or MA′ and/or the non-ionic monomer unit M3′. Step a) is especially effected essentially in the absence of ionic monomer units MC′ and/or MA′ and M3′.

[0176] In this way, in a simple and inexpensive manner, a copolymer having a section consisting essentially of polymerized monomer units M1′ followed by a section having a gradient structure is preparable.

[0177] It is advantageous here to conduct steps a) and b) in immediate succession. In this way, it is possible to maintain the polymerization reaction in steps a) and b) to the best possible degree.

[0178] The polymerization in step a) is especially conducted until 0.1 - 100 mol%, especially 1 - 95 mol%, preferably 10 - 90 mol%, in particular 25 - 85 mol%, especially 60 - 85 mol% of monomer units M1′ have been converted or polymerized.

[0179] The conversion of the monomers or the progress of the polymerization can be monitored in a manner known per se, for example, with the aid of liquid chromatography, especially high-performance liquid chromatography (HPLC).

[0180] Preferably, the comb polymer is used with a proportion of 0.01 - 10 wt.-%, preferably 0.05 - 5 wt.-%, more preferably 0.1 - 2 wt.-%, especially 0.25 - 1 wt.-%, with respect to the weight of the binder in the gypsum composition.

[0181] In a further preferred embodiment, the comb polymer is used in combination with a plasticizer for mineral binder compositions. Thereby, plasticizer and comb polymer differ from a chemical and/or structural point of view. The comb polymer and the plasticizer can for example be provided as a kit of parts or in the form of a premixed composition.

[0182] What is meant by the term “plasticizer” in the present context is especially a substance which is capable of improving the flowability of a gypsum composition which has been mixed with water, and/or of reducing the water requirement of such compositions. Substances of this kind are also referred to as “superplasticizers”.

[0183] More particularly, the plasticizer comprises at least one representative from the group consisting of lignosulfonates, gluconates, naphthalenesulfonates, sulfonated naphthalene-formaldehyde condensates, melamine sulfonates, vinyl copolymers, sulfonated vinyl copolymers, polycarboxylates, especially polycarboxylate ethers, or mixtures thereof.

[0184] More particularly, the plasticizer is a polycarboxylate, especially a polycarboxylate ether. It is more preferably a comb polymer having a polycarboxylate backbone and polyether side chains, where the polyether side chains are bonded to the polycarboxylate backbone via ester, ether, amide and/or imide groups. More particularly, the polycarboxylate has a random, statistical, blockwise, alternating or gradient-like monomer distribution.

[0185] More preferably, the plasticizer is a polymer P having or consisting of the following substructure units: [0186] a) a molar parts of a substructure unit S1 of the formula X [0187] b) b molar parts of a substructure unit S2 of the formula XI [0188] c) c molar parts of a substructure unit S3 of the formula (XII) [0189] d) d molar parts of a substructure unit S4 of the formula (XIII) where [0190] L independently represents H.sup.+, an alkali metal ion, alkaline earth metal ion, a di- or trivalent metal ion, an ammonium ion or an organic ammonium group, [0191] each R.sup.u independently of the others is hydrogen or a methyl group, [0192] each R.sup.v independently of the others is hydrogen or COOM, [0193] r = 0, 1 or 2, [0194] t = 0 or 1, [0195] G.sup.1 and G.sup.2 is independently a C.sub.1- to C.sub.20-alkyl group, -cycloalkyl group, -alkylaryl group or is -[A′O].sub.s-G.sup.4 [0196] where A′ = C.sub.2- to C.sub.4-alkylene, G.sup.4 is H, a C.sub.1- to C.sub.20-alkyl group, -cycloalkyl group or -alkylaryl group, [0197] and s = 2-250, [0198] G.sup.3 is independently NH.sub.2, —NG.sup.5G.sup.6, —OG.sup.7NG.sup.8G.sup.9,and where a, b, c and d represent molar proportions of the respective substructure units S1, S2, S3 and S4, with a/b/c/d = (0.1-0.9) / (0.1-0.9) / (0-0.8) / (0-0.8), especially a/b/c/d = (0.3-0.9) / (0.1-0.7) / (0-0.6) / (0-0.4), preferably a/b/c/d = (0.5-0.8) / (0.2-0.4) / (0.001-0.005) / 0 and with the proviso that a + b + c + d = 1. [0199] where G.sup.5 and G.sup.6 are independently [0200] a C.sub.1- to C.sub.20-alkyl group, -cycloalkyl group, -alkylaryl group or -aryl group, [0201] or are a hydroxyalkyl group or are an acetoxyethyl group (CH.sub.3—CO—O—CH.sub.2—CH.sub.2—) or a hydroxyisopropyl group (HO—CH(CH.sub.3)—CH.sub.2—) or an acetoxyisopropyl group (CH.sub.3—CO—O—CH(CH.sub.3)—CH.sub.2—); [0202] or G.sup.5 and G.sup.6 together form a ring of which the nitrogen is part, in order to construct a morpholine or imidazoline ring; [0203] G.sup.7 is a C.sub.2-C.sub.4-alkylene group, [0204] G.sup.8 and G.sup.9 each independently represent a C.sub.1- to C.sub.20-alkyl group, -cycloalkyl group, -alkylaryl group, -aryl group or a hydroxyalkyl group,

[0205] The sequence of the substructure units S1, S2, S3 and S4 may be alternating, blockwise or random. It is also possible that the one or more substructure units S1, S2, S3 and S4 form a gradient structure. In principle, it is also possible that further structural units are present in addition to the substructure units S1, S2, S3 and S4. In particular, the sequences of the substructure units S1, S2, S3 and S4 in the polymer P are random or statistical.

[0206] Preferably, the substructure units S1, S2, S3, and S4 together have a proportion of at least 50% by weight, especially at least 90% by weight, most preferably at least 95% by weight, of the total weight of the polymer P.

[0207] In the polymer P, R.sup.v especially represents hydrogen and R.sup.u is preferably hydrogen and/or a methyl group.

[0208] Preferably, in the polymer P, r = 0 and t = 1. Also advantageously, r = 1-2 and t = 0.

[0209] More particularly, in the polymer P, R.sup.v is hydrogen, R.sup.u is a methyl group, r = 1-2 and t = 0.

[0210] G.sup.1 and/or G.sup.2 in the polymer P, in each case independently, are advantageously -[A′O].sub.s-G.sup.4 with s = 8-200, especially 20-70, and A′ is a C.sub.2- to C.sub.4-alkylene.

[0211] In the polymer P, G.sup.4, in each case independently, is preferably hydrogen or a methyl group.

[0212] Especially, a ratio a/b in polymer P is greater than the ratio of monomeric units MC/M1 and/or a ratio of MA/M1 in the comb polymer described above. In particular the ratio a/b in polymer P is in the range of 1 - 10, in particular 1.5 - 5, especially 2-4.

[0213] Very particularly advantageous polymers P are those where [0214] a) the R.sup.u and R.sup.v moieties are hydrogen, [0215] b) r = 0, [0216] c) t = 1, [0217] d) G.sup.1 and G.sup.2, in each case independently, are -[A′O].sub.s-G.sup.4 with s = 20-70 and A′ = C.sub.2-alkylene, [0218] e) G.sup.4 represents a methyl group and/or [0219] f) a/b/c/d = (0.5-0.8) / (0.2-0.4) / (0.001-0.005) / 0

[0220] Likewise advantageous polymers P are those where [0221] a) t = 0 and r = 1-2, [0222] b) G.sup.1, in each case independently, is -[A′O].sub.s-G.sup.4 with s = 8-200, especially 20-70, [0223] c) G.sup.4 represents hydrogen or a methyl group, especially hydrogen, [0224] d) and/or A′ is a C.sub.2- to C.sub.4-alkylene, especially a C.sub.2-alkylene.

[0225] A weight-average molecular weight (Mw) of the polymer P is particularly in the range of 5′000-150 ′000 g/mol, preferably 10′000-100 ′000 g/mol, especially 20′000-90 ′000 g/mol. The weight-average molecular weight (Mw) is determined by gel permeation chromatography (GPC), using polyethylene glycol (PEG) as standard.

[0226] The preparation of polymers P is known per se to the person skilled in the art. Corresponding superplasticizers or polymers P are also commercially supplied by Sika Schweiz AG under the ViscoCrete® trade name series.

[0227] Preferably, the plasticizer is used with a proportion of 0.01 - 10 wt.-%, preferably 0.05 - 5 wt.-%, more preferably 0.1 - 2 wt.-%, especially 0.25 - 1 wt.-%, with respect to the weight of the binder in the gypsum composition.

[0228] A further aspect of the present invention is a gypsum composition, especially a gypsum composition containing swelling and/or non-swelling clays, comprising a comb polymer as described above. In particular, the gypsum composition, the swelling clays and the non-swelling clays are the same as described above in connection with the use of the comb polymer.

[0229] If present, the total amount of clays, especially the total amount of swellable and non-swellable clays, in the gypsum composition is 0.01 - 5 wt.-%, especially 0.1 -2 wt.-%, with respect to the dry weight of the gypsum composition.

[0230] Especially, the gypsum composition may additionally comprise another binder, aggregates, and/or a plasticizer as described above. As explained above, the plasticizer and the comb polymer are chemically and/or structurally different.

[0231] The plasticizer preferably is a polycarboxylate, especially a polycarboxylate ether, most preferably a polymer P as described above.

[0232] Especially, the gypsum composition comprises the comb polymer as described above, swelling clays and/or non-swelling clays, and a plasticizer.

[0233] According to a preferred embodiment, the gypsum composition, with respect to the weight of the binder in the gypsum composition, comprises at least 30 wt.-%, preferably at least 50 wt.-%, especially at least 70 wt.-% or 100 wt.-%, of gypsum, and 0.01 - 10 wt.-%, preferably 0.05 - 5 wt.-%, more preferably 0.1 - 2 wt.-%, especially 0.25 - 1 wt.-%, of the comb polymer as described above. Preferably, the gypsum composition, with respect to the weight of the binder in the gypsum composition, additionally comprises 0.01 - 10 wt.-%, preferably 0.05 - 5 wt.-%, more preferably 0.1 - 2 wt.-%, especially 0.25 - 1 wt.-%, of the plasticizer as described above.

[0234] The gypsum composition can furthermore contain other additives such as, for example, fibers, as well as additives of conventional components such as, for example, other plasticizers, for example, lignosulfonates, sulfonated naphthalene/formaldehyde condensates, sulfonated melamine/formaldehyde condensates, accelerators, retarders, starch, sugar, silicones, shrinkage reducers, defoamers, or foaming agents.

[0235] Preferably, in the gypsum composition a proportion of binders other than gypsum, especially cement, is below 30 wt.-%, especially below 10 wt.-%, preferably below 5 wt.-%, in each case with respect to the total weight of the binder in the gypsum composition. Most preferred the gypsum composition is cement-free.

[0236] Moreover, the present invention is concerned with a method comprising the steps of adding to a gypsum composition comprising swelling clays and/or non-swelling clays: [0237] (i) a comb polymer as described above, and [0238] (ii) a plasticizer as described above.

[0239] The method is in particular suitable for plasticizing a gypsum composition comprising swelling and/or non-swelling clays. The method is also suitable for retarding said composition and/or for increasing the compressive strength of said composition. The plasticizer preferably is a polycarboxylate, especially a polycarboxylate ether, most preferably a polymer P as described above. The plasticizer is chemically and/or structurally different from the comb polymer.

[0240] Preferably, the comb polymer is added before the addition of the plasticizer. However, it is for example also possible to add the comb polymer and the plasticizer simultaneously.

[0241] Preferably, the gypsum composition, with respect to the weight of all binders in the gypsum composition, comprises at least 30 wt.-%, preferably at least 50 wt.-%, especially at least 70 wt.-% or 100 wt.-%, of gypsum.

[0242] According to a preferred embodiment, the comb polymer of the present invention is added to the gypsum composition in an amount of 0.01 - 10 wt.-%, preferably 0.05 - 5 wt.-%, more preferably 0.1 - 2 wt.-%, especially 0.25 - 1 wt.-%, each relative to the weight of the binder in the gypsum composition. A further aspect of the present invention is related to the use of a comb polymer as described above as a clay-inerting agent and/or for reducing or inhibiting adverse effects of swelling clays and/or non-swelling clays on the effectiveness of dispersants, in particular of PCE-based dispersants, in gypsum compositions comprising swelling clays and/or non-swelling clays. Thereby, the comb polymer can e.g. be used to increase the flowability and/or the processing time of mineral binder compositions comprising swellable clays and a dispersant, in particular a PCE-based dispersant.

[0243] Further advantageous embodiments and combinations of features of the invention will emerge from the following exemplary embodiments and the totality of the patent claims.

EXEMPLARY EMBODIMENTS

1. Preparation Examples of Comb Polymers

1.1 Comb Polymer P1 (Non-Ionic Homopolymer Produced by RAFT Polymerization)

[0244] For the preparation of a non-ionic homopolymer by means of controlled free-radical polymerization, a round-bottom flask equipped with a reflux condenser, stirrer system, thermometer and a gas inlet tube was initially charged with 57.4 g of 50% methoxy polyethylene glycol.sub.1000 methacrylate (0.027 mol; average molecular weight: 1 ′000 g/mol; ~ 20 ethylene oxide units per molecule) and 18 g of deionized water. The reaction mixture was heated to 80° C. with vigorous stirring. A gentle inert N.sub.2 gas stream is passed through the solution during the whole reaction time. 378 mg of 4-cyano-4-(thiobenzoylthio)pentanoic acid (1.35 mmol) were then added to the mixture. Once the substance had fully dissolved, 67 mg of AIBN (0.41 mmol) were added. From then on, the conversion was regularly checked by means of HPLC.

[0245] When the conversion, based on methoxy polyethylene glycol methacrylate, had reached 90%, the reaction was stopped. A clear, reddish, aqueous solution was obtained having a solids content of around 40 wt.% which was diluted with water to obtain a solids content of around 30 wt. %.

[0246] The comb polymer thus obtained is a homopolymer comprising about 20 side chain-nearing monomeric units and is referred to as comb polymer P1.

1.2 Comb Polymer P2 (Non-Ionic Homopolymer Produced by Conventional Polymerization)

[0247] For the preparation of a non-ionic homopolymer by conventional free-radical polymerization, a round-bottom flask equipped with a reflux condenser, stirrer system, thermometer and a gas inlet tube was initially charged with 186 g of deionized water. At a temperature of 100° C., 796 g of 50% methoxy polyethylene glycol.sub.1000 methacrylate (0.37 mol, average molecular weight: 1 ′000 g/mol; ~ 20 ethylene oxide units per molecule) was added within 180 minutes. Additionally a solution of 4.5 g sodium hypophosphite and 6.7 g of water was added within 175 minutes and a solution of 0.93 g sodium persulfate and 5.0 g water was added within 190 minutes. Once all the solutions were added, the reaction mixture was cooled down. A clear, colorless solution was obtained having a solids content of around 40 wt.% which was diluted with water to obtain a solids content of around 30 wt. %.

[0248] This polymer is referred to as comb polymer P2.

2. Gypsum Compositions

[0249] Clay-free gypsum slurries were produced by mixing 106 g water with a PCE based plasticizer and/or clay-blocking additive (if used). The nature and proportions of the PCE based plasticizer and the clay-blocking additive are given in the tables in the results section. Then 200 g calcium sulfate β-hemihydrate (Bau- und Elektrikergips, Knauf), containing 0.4 g (= 0.2 wt.%, relative to the total weight of the calcium sulfate β-hemihydrate) of a calcium sulfate dihydrate accelerator was sprinkled into the water over a 15 second period, and the gypsum slurry was allowed to soak for 15 seconds. Then it was vigorously stirred by hand for 30 seconds. These gypsum slurries are referred to as SL0.

[0250] As a model system for argillaceous gypsum compositions, gypsum slurries similar to the gypsum slurries SL0 have been produced whereby, instead of 200 g calcium sulfate β-hemihydrate, a mix of (200 — x) g calcium sulfate β-hemihydrate and x g of a swelling clay or x g of a non-swelling clay was used. The nature and proportions of the clays used are given below in the results section. These clay containing gypsum slurries are referred to as SL1.

3. Testing Procedures

[0251] To determine the effectiveness of the clay-blocking comb polymers in the gypsum compositions, the dispersing effect of the plasticizer was determined as follows:

[0252] Directly after producing the gypsum slurries, a mini-cone of diameter 50 mm and height 51 mm was filled, and after 75 seconds (total time) the spread diameter was determined in millimeters. The diameter of the gypsum cake formed was measured as soon as flow was no longer observed. The diameter in mm was called the spread diameter.

[0253] The beginning of stiffening (VB) and the end of stiffening (VE) were determined by the knife-cut method according to DIN EN 13279-2:2014 and the thumb pressure method. The beginning of stiffening is reached if after a knife cut through the gypsum cake, the edges of the cut no longer heal. The end of stiffening occurs when water no longer escapes from the gypsum cake when finger pressure of about 5 kg is applied.

4. Results

[0254] Table 1 gives an overview of a first series of tests conducted and the results achieved. Experiments EA1 to EA9 are experiments conducted for comparative purposes with clay-free gypsum compositions SL0.

TABLE-US-00001 all wt.-% are given with respect to the gypsum content in the gypsum composition Experiment .fwdarw. EA1 EA2 EA3 EA4 EA5 EA6 EA7 EA8 EA9 ↓ Components Base composition SL0 SL0 SL0 SL0 SL0 SL0 SL0 SL0 SL0 Clays [wt.%] - - - - - - - - - Clay blocker - - B1 P1 P2 B2 M1 M2 M3 - Proportion [wt.-%] 0.2 0.2 0.2 0.2 0.2 0.2 0.2 PCE plasticizer [wt.- %] - 0.2 - - - - - - - w/c 0.53 0.53 0.53 0.53 0.53 0.53 0.53 0.53 0.53 Slump flow [mm] 89 210 192 105 112 89 88 89 87 VB [sec] 115 190 380 115 120 125 120 115 120 VE [sec] 355 545 652 395 410 370 370 360 365 Plasticizer = Sika® ViscoCrete® G-2 (Sika Deutschland GmbH) B1 = MasterSuna SBS 3890 (BASF) B2 = Floset EVA 250 L (SNF Floerger, polycation) M1 = MPEG 1′000 (methyl polyethylene glycol with M.sub.w = 1 ′000 g/mol) M2 = MPEG 3′000 (methyl polyethylene glycol with M.sub.w = 3 ′000 g/mol) M3 = MPGE 5′000 (methyl polyethylene glycol with M.sub.w = 5 ′000 g/mol)

[0255] The data in table 1 shows that with respect to the reference example EA1 without any plasticizer, the PCE based plasticizer (Sika® ViscoCrete® G-2) has a strong plasticizing effect in clay-free gypsum compositions SL0 (example EA2). Likewise, the product MasterSuna B1 (example EA3), a commercial product with clay-blocking properties, gives rise to a strong water-reducing effect. However, both, the PCE based plasticizer as well as the product MasterSuna have a strong retarding effect on the setting of the gypsum composition.

[0256] In contrast, inventive comb polymers P1 and P2 (examples EA4 and EA5) show relatively small plasticizing effects, whereas the plasticizing effects of the polycation B2 (example EA6) and MPEG polymers (M1, M2 and M3) is even lower (examples EA7 — EA9). Nevertheless, none of these compounds shows a significant retarding effect.

[0257] Table 2 gives an overview of a second series of tests conducted and the results achieved. Experiments EB1 and EB2 are reference examples whereas, experiments EB3 to EB8 are experiments conducted with gypsum compositions based on formulation SL1 comprising swelling clays (bentonite). In this set of examples, the dosage of the clay blocker was adjusted to achieve a slump flow as close as possible to the reference experiment EB2 (plasticizer in clay-free gypsum composition SL0).

TABLE-US-00002 Results for gypsum composition comprising swelling clays (all wt.-% are given with respect to the gypsum content in the gypsum composition) Experiment .fwdarw. EB1 EB2 EB3 EB4 EB5 EB6 EB7 EB8 ↓ Components Gypsum composition SL0 SL0 SL1 SL1 SL1 SL1 SL1 SL1 Bentonite [wt.%] - - 1.0 1.0 1.0 1.0 1.0 1.0 Clay blocker - - - B1 P1 M1 M2 M3 - Proportion [wt.-%] 0.2 0.1 0.8 0.8 0.8 PCE plasticizer [wt.- %] - 0.2 0.2 0.2 0.2 0.2 0.2 0.2 w/c 0.53 0.53 0.53 0.53 0.53 0.53 0.53 0.53 Slump flow [mm] 87 232 204 237 235 226 231 238 VB [sec] 110 245 180 930 225 200 245 310 VE [sec] 350 540 465 1150 535 460 505 610 Plasticizer = Sika® ViscoCrete® G-2 B1 = MasterSuna SBS 3890 (BASF) M1 = MPEG 1′000 (methyl polyethylene glycol with M.sub.w = 1 ′000 g/mol) M2 = MPEG 3′000 (methyl polyethylene glycol with M.sub.w = 3 ′000 g/mol) M3 = MPGE 5′000 (methyl polyethylene glycol with M.sub.w = 5 ′000 g/mol)

[0258] As evident from the data shown in table 2, without clay blocking additives and compared to the situation in clay-free gypsum compositions (experiment EB2), the effectivity of the PCE based plasticizer is reduced when used in clay containing gypsum composition (experiment EB3). Specifically, the slump flow decreases from 232 mm to 204 mm (- 12%).

[0259] Although with a prior art clay blocker B1 the reduction of the slump flow can be compensated with a dosage of 0.2 wt.-%, a strong retarding of the setting of the gypsum composition is observed. In contrast, with the inventive comb polymer P1, the loss in slump flow can be compensated with a lower dosage of only 0.1 wt.-% without any significant effect on the setting times of the gypsum composition.

[0260] With MPEG polymers M1, M2 and M3, similar results are observed as with inventive comb polymer P1, however, a significantly higher dosage is needed (0.8 wt.-%). Thus, the inventive comb polymers clearly show the best performance.

[0261] Table 3 gives an overview of a third series of tests conducted and the results achieved. Experiments EC1 and EC2 are reference examples whereas, experiments EC3 to EC8 are experiments conducted with gypsum compositions based on formulation SL1 comprising non-swelling clays (kaolinite). In this set of examples, the dosage of the clay blocker was adjusted to achieve a slump flow as close as possible to the reference experiment EC2 (plasticizer in clay-free gypsum composition SL0).

TABLE-US-00003 Results for gypsum composition comprising non-swelling clays (all wt.-% are given with respect to the gypsum content in the gypsum composition) Experiment .fwdarw. EC1 EC2 EC3 EC4 EC5 EC6 EC7 EC8 ↓ Components Gypsum composition SL0 SL0 SL1 SL1 SL1 SL1 SL1 SL1 Kaolinite [wt.%] - - 6.0 6.0 6.0 6.0 6.0 6.0 Clay blocker - - - B1 P1 M1 M2 M3 - Proportion [wt.-%] 0.2 0.2 0.2 0.2 0.2 PCE plasticizer [wt.-%] - 0.2 0.2 0.2 0.2 0.2 0.2 0.2 w/c 0.53 0.53 0.53 0.53 0.53 0.53 0.53 0.53 Slump flow [mm] 91 228 190 227 216 188 197 204 VB [sec] 110 270 235 1510 300 255 285 305 VE [sec] 365 590 580 1820 630 560 585 615 Plasticizer = Sika® ViscoCrete® G-2 B1 = MasterSuna SBS 3890 (BASF) M1 = MPEG 1′000 (methyl polyethylene glycol with M.sub.w = 1 ′000 g/mol) M2 = MPEG 3′000 (methyl polyethylene glycol with M.sub.w = 3 ′000 g/mol) M3 = MPGE 5′000 (methyl polyethylene glycol with M.sub.w = 5 ′000 g/mol)

[0262] In gypsum compositions comprising non-swelling clays, similar results are observed as with gypsum compositions comprising swelling clays (cf. table 2). The prior art clay blocker B1 gives rise to a very strong retarding effect, whereas the inventive comb polymer P1 is essentially as effective in compensating the loss in slump flow without any significant effect on the setting times of the gypsum composition. Also with non-swelling clays, lower performance is obtained to compensate the loss in slump flow for MPEG polymers M1, M2 and M3. Thus, the inventive comb polymers clearly show the best performance in gypsum compositions comprising non-swelling clays.

[0263] Table 4 gives an overview of a fourth series of tests in which the effectivity of polymers P1 and P2 are compared in gypsum compositions comprising swelling clays. Experiments ED1 and ED2 are reference examples whereas, experiments ED3 to ED5 are experiments conducted with gypsum compositions based on formulation SL1 comprising swelling clays (bentonite). In this set of examples, the dosage of the clay blocker was adjusted to achieve a slump flow as close as possible to the reference experiment ED2 (plasticizer in clay-free gypsum composition SL0).

TABLE-US-00004 Comparison of effectivity of polymers P1 and P2 in gypsum composition comprising swelling clays (all wt.-% are given with respect to the gypsum content in the gypsum composition) Experiment .fwdarw. ED1 ED2 ED3 ED4 ED5 ↓ Components Gypsum composition SL0 SL0 SL1 SL1 SL1 Bentonite [wt.%] - - 1.0 1.0 1.0 Clay blocker - - - P1 P2 - Proportion [wt.-%] 0.1 0.05 PCE plasticizer [wt.- %] - 0.2 0.2 0.2 0.2 w/c 0.53 0.53 0.53 0.53 0.53 Slump flow [mm] 87 232 204 235 235 VB [sec] 110 245 180 225 210 VE [sec] 350 540 465 535 430 Plasticizer = Sika® ViscoCrete® G-2

[0264] As evident, with both polymers P1 and P2, the slump loss caused by swelling clays can be compensated similarly with rather small dosages. Thereby, polymer P2 is somewhat more effective than polymer P1 since the dosage, needed to obtain the same slump loss compensation, is lower.

[0265] Table 5 gives an overview of a fifth series of tests in which the effectivity of polymers P1 and P2 are compared in gypsum compositions comprising non-swelling clays. Experiments EE1 and EE2 are reference examples whereas, experiments EE3 to EE5 are experiments conducted with gypsum compositions based on formulation SL1 comprising non-swelling clays (kaolinite). In this set of examples, the dosage of the clay blocker was adjusted to achieve a slump flow as close as possible to the reference experiment EE2 (plasticizer in clay-free gypsum composition SL0).

TABLE-US-00005 Comparison of effectivity of polymers P1 and P2 in gypsum composition comprising non-swelling clays (all wt.-% are given with respect to the gypsum content in the gypsum composition) Experiment .fwdarw. EE1 EE2 EE3 EE4 EE5 ↓ Components Gypsum composition SL0 SL0 SL1 SL1 SL1 Kaolinite [wt.0/o] - - 6.0 6.0 6.0 Clay blocker - - - P1 P2 - Proportion [wt.-%] 0.2 0.2 PCE plasticizer [wt.- %] - 0.2 0.2 0.2 0.2 w/c 0.53 0.53 0.53 0.53 0.53 Slump flow [mm] 91 228 190 216 230 VB [sec] 110 270 235 300 210 VE [sec] 365 590 580 630 590 Plasticizer = Sika® ViscoCrete® G-2

[0266] Also with non-swelling clays, with both polymers P1 and P2, the slump loss can be compensated with rather small dosages. Thereby, polymer P2 is somewhat more effective than polymer P1 since the slump compensation at the same dosage is higher.

[0267] Table 6 gives an overview of a sixth series of tests in which the effectivity of polymer P2 and a polycationic clay blocker is compared in gypsum compositions comprising swelling clays. Experiments EF1 and EF2 are reference examples whereas, experiments EF3 to EF5 are experiments conducted with gypsum compositions based on formulation SL1 comprising swelling clays (bentonite). The dosage of the clay blocker was adjusted to achieve a slump flow as close as possible to the reference experiment EF2 (plasticizer in clay-free gypsum composition SL0).

TABLE-US-00006 Comparison of effectivity of polymer P2 and a polycationic clay blocker in gypsum composition comprising swelling clays (all wt.-% are given with respect to the gypsum content in the gypsum composition) Experiment .fwdarw. ↓ Components EF1 EF2 EF3 EF4 EF5 Gypsum composition SL0 SL0 SL1 SL1 SL1 Bentonite [wt.%] - - 1.0 1.0 1.0 Clay blocker - - - P2 B2 - Proportion [wt.-%] 0.05 0.05 PCE plasticizer [wt.- %] - 0.2 0.2 0.2 0.2 w/c 0.53 0.53 0.53 0.53 0.53 Slump flow [mm] 87 232 204 235 228 VB [sec] 110 245 180 210 195 VE [sec] 350 540 465 430 460 Plasticizer = Sika® ViscoCrete® G-2 B2 = Floset EVA 250 L (SNF Floerger, polycation)

[0268] From the results of table 6 it follows that in gypsum compositions comprising swelling clays, the inventive comb polymer P2 in terms of effectivity and retarding effects is comparable with polycationic clay blockers. However, the inventive comb polymers do not comprise any chloride.

[0269] Table 7 gives an overview of a seventh series of tests in which the effectivity of polymer P2 and a polycationic clay blocker is compared in gypsum compositions comprising non-swelling clays. Experiments EG1 and EG2 are reference examples whereas, experiments EG3 to EG5 are experiments conducted with gypsum compositions based on formulation SL1 comprising non-swelling clays (kaolinite). The dosage of the clay blocker was adjusted to achieve a slump flow as close as possible to the reference experiment EG2 (plasticizer in clay-free gypsum composition SL0).

TABLE-US-00007 Comparison of effectivity of polymer P2 and a polycationic clay blocker in gypsum composition comprising non-swelling clays (all wt.-% are given with respect to the gypsum content in the gypsum composition) Experiment .fwdarw. ↓ Components EG1 EG2 EG3 EG4 EG5 Gypsum composition SL0 SL0 SL1 SL1 SL1 Kaolinite [wt.0/o] - - 6.0 6.0 6.0 Clay blocker - - - P2 B2 - Proportion [wt.-%] 0.2 0.2 PCE plasticizer [wt.- %] - 0.2 0.2 0.2 0.2 w/c 0.53 0.53 0.53 0.53 0.53 Slump flow [mm] 91 228 190 230 234 VB [sec] 110 270 235 285 335 VE [sec] 365 590 400 410 680 Plasticizer = Sika® ViscoCrete® G-2 B2 = Floset EVA 250 L (SNF Floerger, polycation)

[0270] Thus, also in gypsum compositions comprising non-swelling clays, the inventive comb polymer P2 in terms of effectivity and retarding effects is comparable with polycationic clay blockers.

[0271] It will be appreciated by those skilled in the art that the present invention can be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The presently disclosed embodiments are therefore considered in all respects to be illustrative and not restricting.