Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Reexamination Certificate
2001-02-14
2003-03-04
Sellers, Robert E. L. (Department: 1712)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C106S764000
Reexamination Certificate
active
06528593
ABSTRACT:
This invention relates to novel copolymers containing structural units derived from olefins, &agr;,&bgr;-unsaturated mono- or dicarboxylic acids or derivatives thereof and a hydrophobic moiety that is incorporated into the copolymer chain, as well as to a process for preparing these hydrophobically modified copolymers. These polymers are especially useful as additives in cementitious compositions to enhance their flowability and processability. According to a second aspect, the present invention refers to the use of these copolymers as cement additives and to cementitious compositions comprising the copolymer of the present invention.
Surface-active dispersions are commonly used as additives in cementitious mixtures, for example, in mortar or concrete mixtures in order to enhance their flowability and processability. Well-known dispersions in the art are lignosulfonates, naphthalene- or formaldehyde-condensates. However, lignosulfonates show a non-satisfactory performance and naphthalene- or formaldehyde-condensates have come under environmental pressure since they contain residual toxic amounts of free formaldehyde.
Therefore, synthetic water-soluble acrylate-based superplasticizers have been introduced into the market. Among others, they are particularly produced from styrene/(meth)acrylic acid monomers. Typical products and processes for the preparation of such copolymers are disclosed in U.S. Pat. No. 5,138,004, JP-A 62-187152 (“Cement Additives”, Production And Use Of Styrene/(Meth)Acrylic Acid And Styrene/Maleic-Anhydride-Copolymers), GB-A-2 221 673 (Use Of Olefin/&agr;,&bgr;Unsaturated Dicarboxylic Acid Copolymers), and JP-A 84-62137 (“Low Molecular Weight StyrenelMaleic-Anhydride-Copolymers”).
These polymers have, however, in common that they are of very hydrophilic nature due to their higher level of carboxylic acid groups in the polymer backbone. As a consequence, these polymers are very surface-active and promote an air entrainment into the cement/mortar mixtures. Usually, if no defoamers are added to the mortar, the air content can add up to 15 percent or more. The high air content negatively influences other properties of the hardened cement, such as its mechanical strength. Additionally, defoamers, which are added to reduce the air content, separate from the aqueous polymer solution within a very short time, usually within a couple of days only.
Therefore, and because of other reasons, that is, to enhance the performance of such synthetic polymers, these polymers have been modified.
EP-A-736553 discloses a copolymer composed of at least 3 different structural units a), b) and c). Structural unit a) is derived from an unsaturated dicarboxylic acid derivative or cyclic anhydrides and imides of these dicarboxylic acids. Preferred units are derived from maleic acid derivatives. The structural unit b) is derived from an oxyalkyleneglycol-alkenylether, preferably polyethylene oxide-vinyl ether, and, finally structural unit c) is derived from a monomer selected from a wide range of ethylenically unsaturated monomers. However, in general, oxyalkyleneglycol ethers are difficult to produce and they are obtained in lower yields. Therefore, these polymers are rather expensive. Furthermore, they are susceptible to hydrolysis in acidic environments that may occur during preparation of the polymers.
From DE-A-37 28 786 a copolymer comprising styrenic units and units derived from maleic anhydride esterified with a polyalkylene glycol is known wherein only esterification with polyethylene glycols is explicitly disclosed. The used polyethylene glycols still render the copolymer hydrophilic. It is further disclosed that, due to their surface-activity, these copolymers can be used as emulsifiers to improve dispersibility of cement in water. However, the high surface-activity also leads to an undesired high foam level.
EP-A-306 449 discloses copolymers of styrene and maleic acid half-esters. These copolymers are prepared by copolymerization of maleic anhydride and styrene, followed by esterification of the maleic anhydride units with polyalkylene glycols and subsequent neutralization with sodium hydroxide solution. Due to steric hindrance, a minor portion of the maleic anhydride units remains unreacted. However, according to the teaching of this reference, it is preferred to esterify as many maleic anhydride units as possible, although a 100 percent conversion, as envisaged by the teaching of this reference, is in practice, not possible. The preferred polyalkylene glycol is polyethylene glycol. These copolymers are suitable as emulsifiers and increase the flowability of cementitious compositions. It is also mentioned that these copolymers show a reduced level of air entrainment in comparison to comparable copolymers with a lower molecular weight. However, no data are disclosed to enable verification of this statement.
DE-A-41 42 388 discloses copolymers composed of random units represented by the following formula
wherein M is hydrogen or the residue of a hydrophobic polyalkylene glycol, for example polypropylene glycol or of a polysiloxane; R is a C
2
-C
6
-alkylene residue; R
1
is a C
1
-C
20
-alkyl, C
5
-C
9
-cycloalkyl or a phenyl group; x, y and z are integers of 1 to 100; m is an integer of 1 to 100, and n is an integer of 10 to 100, wherein the ratio of x:(y+z) is from 10:1 to 1:10; the ratio of y:z is from 1:5 to 1:100, and m+n equals 15 to 100.
In a preferred embodiment, R is a C
2
-C
3
-alkylene group. These copolymers are useful as emulsifiers and plasticizers in cementitious compositions. It is also described that these copolymers do not have the same air entraining properties as comparable copolymers without providing any data.
DE-A-44 45 569 discloses a similar copolymer for the same purpose wherein the styrene moiety is substituted by a moiety derived from an ethylenically unsaturated monomer selected from a wide range of monomers.
In the preferred embodiments of both German applications, R is preferably ethylene, resulting in a hydrophilic polymer still showing high foam levels.
From WO 97/39037 random styrene-maleic anhydride copolymers are known. In one specific embodiment, these copolymers contain hydrophobic polyalkylene glycol and hydrophilic polyethylene glycol residues bonded to the polymeric backbone via an ester linkage.
EP-A 0 930 321 which constitutes prior art according to Article 54(3) and 54(4) EPC, discloses a copolymer comprising:
a) structural units derived from ethylenically unsaturated hydrocarbons;
b) structural units derived from ethylenically unsaturated monomers selected from monocarboxylic acids as well as salts and amides thereof, dicarboxylic acids as well as salts, amides and half-amides thereof and cyclic anhydrides and imides of dicarboxylic acids and mixtures thereof; and
c) structural units derived from monomers selected from esters of ethylenically unsaturated monocarboxylic acids, half esters of ethylenically unsaturated dicarboxylic acids, allyl ethers and vinyl ethers and mixtures thereof having a substituent R linked to the oxygen atom of either the ester groups or the ether group that is selected from:
(i) polyalkylene oxide groups corresponding to the formula
wherein R
1
is independently at each occurrence selected from hydrogen and C
1
-C
4
alkyl, R
2
is C
1
-C
44
hydrocarbyl, t is 0 or 1 and m is an integer in the range of 5-200, with the proviso that if R
2
is C
1
-C
5
alkyl, the polyalkylene oxide group does not contain more than 50 weight percent ethylene oxide moieties, based on the weight of the polyalkylene oxide group; and
(ii) groups corresponding to the formula
wherein t is 0 or 1 and Q is a polysiloxane residue;
wherein the molar ratio of units b) to units c) in the copolymer is in the range of 1000:1 to 5:1.
The polymers described in this European Patent Application combine high plasticity of the cementitious composition with a low air entrainment due to the incorporation of certain specified hydrophobic residue wherein already a very low level of hydrophobic residues exhibits a very h
Eiffler Juergen
Froehlich Christoph
Stranimaier Kerstin
Sellers Robert E. L.
The Dow Chemical Company
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