Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Polymers from only ethylenic monomers or processes of...
Reexamination Certificate
2002-04-15
2004-01-06
Pezzuto, Helen L. (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Polymers from only ethylenic monomers or processes of...
C526S318400, C526S320000, C526S328500, C526S932000
Reexamination Certificate
active
06673885
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a process for preparing a (meth)acrylic acid-based polymer being useful as a dispersant for cement so as to improve the dispersibility of cement particles in a hydraulic composition such as cement paste, mortar, concrete or the like.
TECHNICAL FIELD
A polycarboxylic acid-based polymer is useful as a dispersant for cement and various techniques in this regard have been proposed. As such dispersants for cement, JP-B 59-18338 discloses a substance comprising a copolymer prepared by reacting a polyalkylene glycol mono (meth)acrylate-based monomer, a (meth)acrylic acid-based monomer, and a monomer capable of reacting with these monomers in specific proportions; JP-A 5-238795 discloses a substance comprising a copolymer prepared by polymerizing an unsaturated bond-bearing polyalkylene glycol diester-based monomer and a monomer having a dissociative group; and JP-A 8-12396 discloses a substance comprising a copolymer of an unsaturated bond-bearing polyalkylene glycol ester monomer and a specific monomer. However, no specific condition for polymerization is described in the above-mentioned prior art and, for example, in JP-A 8-12396, column 4, there is the description that the polymer in this invention can be prepared according to a known process.
DISCLOSURE OF THE INVENTION
The object of the present invention is to provide a process for preparing a (meth)acrylic acid-based polymer which makes it possible to obtain a (meth)acrylic acid-based polymer having a stable quality and suitable as a dispersant for cement by setting the condition for polymerization specifically.
The present inventors have established the invention based on the discovery that the above-mentioned object can be achieved by adding an alkaline agent to an esterification reaction product containing an acid catalyst and a polymerization inhibitor so that the acid catalyst is deactivated and further carrying out a polymerization reaction at a pH value in a specific range.
The invention is a process for preparing a (meth)acrylic acid-based polymer, comprising the steps of the stage 1 of introducing (meth)acrylic acid and a polyalkylene glycol monoalkyl ether at a molar ratio in the range of 3:1 to 50:1, subjecting them to an esterification reaction in the presence of an acid catalyst and a polymerization inhibitor and deactivating the acid catalyst with an alkaline agent in order to obtain an esterification product containing a (meth)acrylate and (meth)acrylic acid residues and the stage 2 of copolymerizing the (meth)acrylate and the (meth)acrylic acid residues at a pH value in the range of 1.5 to 3.5.
A monomer copolymerizable with these monomers may also be present. The (meth)acrylic acid residues include (meth)acrylic acid, an alkali metal salt of (meth)acrylic acid, and an alkaline earth metal salt of (meth)acrylic acid. These salt are formed by the alkaline agent and (meth)acrylic acid when the deactivation by the alkaline agent is carried out.
The monomers at the stage 2 may include the reaction product of the stage 1, the (meth)acrylic acid residues and a newly added monomer. The (meth)acrylate monomer at the stage 2 includes the reaction product of the stage 1 and may further include a newly added monomer. The (meth)acrylic acid may include the residues of the stage 1 and a newly added monomer.
The reaction product of the stage 1 may be subjected directly to the polymerization or may be subjected to the polymerization after the remaining (meth)acrylic acid is distilled off. The polymerization may be carried out by the addition of a monomer. Alternatively, the polymerization may be a combination of these polymerizations. The polymerization is carried out at a pH value in the range of 1.5 to 3.5. The polymerization may be carried out without the addition of acid.
A copolymer having a desired monomer ratio can be obtained by distilling off all or part of unreacted (meth)acrylic acid after the stage 1, but before the stage 2, and/or by copolymerizing a monomer copolymerizable with the (meth) acrylate and/or (meth)acrylic acid residues at the stage 2 wherein two or more kinds of the monomers may be added. That is, the monomers of the polymer include the reaction product of the stage 1 and the monomer added at the stage 2. In the case where unreacted (meth)acrylic acid is distilled off, the (meth)acrylic acid residue after the distillation is taken as the (meth)acrylic acid residue.
At the stage 2, the pH may be adjusted to a value in the range of 1.5 to 3.5 by adding an acid to the esterification reaction product.
At the stage 2, it is preferable that the monomer intended for copolymerization and copolymerizable with the (meth)acrylate and/or (meth)acrylic acid residues is (meth)acrylic acid, methyl (meth)acrylate, or methoxypolyethylene glycol mono (meth)acrylate.
In the present invention, “(meth)acrylic acid” means both acrylic acid and methacrylic acid.
Embodiments of the Implementation of the Invention
At the stage 1, (meth)acrylic acid and a polyalkylene glycol monoalkyl ether are subjected to an esterification reaction in the presence of an acid catalyst and a polymerization inhibitor.
The (meth)acrylic acid for use in the esterification reaction is not particularly limited and, therefore, commercially available (meth)acrylic acid, for example, (meth)acrylic acid containing a polymerization inhibitor, can also be used.
Examples of the polyalkylene glycol monoalkyl ether for use in the esterification reaction include a polyalkylene glycol monoalkyl ether whose polyalkylene portion comprises an alkylene oxide addition product of ethylene oxide alone and a polyalkylene glycol monoalkyl ether whose polyalkylene portion comprises an alkylene oxide addition product of a mixture of ethylene oxide and propylene oxide. The total number of the moles of the alkylene oxide added is preferably 1 to 300. The alkyl group constituting the monoalkyl ether portion is preferably an alkyl group having 1 to 3 carbon atoms. It is possible to use one kind of polyalkylene glycol monoalkyl ether or to use two or more kinds of polyalkylene glycol monoalkyl ethers in which the numbers of moles of alkylene oxide added differ and/or the numbers of the carbon atoms of the alkyl groups differ.
The molar ratio between (meth)acrylic acid and the polyalkylene glycol monoalkyl ether in the reaction system is in the range of 3:1 to 50:1, preferably in the range of 10:1 to 40:1, in order to raise the rate of the esterification reaction.
Examples of the acid catalyst for use in the esterification reaction include sulfonic acids such as p-toluenesulfonic acid, methanesulfonic acid, and benzenesulfonic acid and mineral acids such as sulfuric acid and phosphoric acid.
The amount of the acid catalyst to be used is preferably in the range of 0.1 to 10 parts by weight based on 100 parts by weight of the polyalkylene glycol monoalkyl ether. An amount of 0.1 parts by weight or more makes it possible to maintain a proper reaction rate and an amount of 10 parts by weight or less is economical. Accordingly, the amount's range is preferable because the reaction can be carried out smoothly without cleavage of the alkylene oxide chain of the polyalkylene glycol monoalkyl ether.
Examples of the polymerization inhibitor for use in the esterification reaction include one or a combination in arbitrary ratio of those selected from hydroquinone, benzoquinone, methoquinone, BHT, etc. It is also possible to further raise the effect of polymerization inhibition by the introduction of a gas containing oxygen into the reaction system.
The amount of the polymerization inhibitor to be used is preferably in the range of 0.001 to 1 part by weight based on 100 parts by weight of the polyalkylene glycol monoalkyl ether.
The reaction temperature in the esterification reaction is preferably in the range of 80 to 130° C. A temperature of 80° C. or above makes it possible to maintain a proper reaction rate. A temperature of 130° C. or below makes it possible to prevent the deterioration of the quality of the polyalkylene
Kono Yoshinao
Minou Haruya
Sato Haruyuki
Shibata Kengo
Ukena Toshinao
Kao Corporation
Pezzuto Helen L.
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