Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Polymers from only ethylenic monomers or processes of...
Reexamination Certificate
2002-09-12
2004-11-30
Egwim, Kelechi C. (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Polymers from only ethylenic monomers or processes of...
C525S423000, C526S204000
Reexamination Certificate
active
06825301
ABSTRACT:
The present invention relates to a water-in-oil polymer emulsion containing, in a continuous and virtually water-immiscible organic phase, finely divided water-swellable or water-soluble polymers, a water-in-oil emulsifier and optionally wetting agents. The invention also relates to a process for preparing said emulsion.
Water-in-oil polymer emulsions of water-soluble polymers are known. Processes for preparing them by reverse emulsion polymerization are also known. Reference may be made to document U.S. Pat. No. 3,284,393, which is the reference patent in this field.
The process as described in U.S. Pat. No. 3,284,393 consists of emulsifying, in an organic phase, one or more water-soluble ethylenically unsaturated monomer(s), optionally in aqueous solution, using a water-in-oil emulsifier, and then in performing emulsion polymerization in the presence of an initiator. Benzoyl peroxide, lauroyl peroxide and potassium persulfate are mentioned as free-radical initiators. These peroxides have also been mentioned in U.S. Pat. No. 3,920,599.
U.S. Pat. No. 4,059,552 describes finely divided water-swellable polymers and mentions tert-butyl hydroperoxide, dimethane sulfonyl peroxide and ammonium persulfates as polymerization initiators.
It is found, however, that, in the most recent processes, azobisisobutylronitrile is most commonly used (See U.S. Pat. Nos. 4,024,097, 4,713,431, and 4,419,344) as a reverse emulsion polymerization initiator.
Moreover, U.S. Pat. No. 5,292,800 discloses water-in-oil polymer emulsion, in which the organic phase consists of at least 50% plant or animal oils. Comparative Example 1 of said patent shows that, by polymerizing at 55° C., 250 g of an aqueous 50% solution of acrylamide in 250 g of rapeseed oil in the presence of dimethyl 2,2′-azobis (isobutyrate) as initiator and using a commercial sorbitan monooleate as an emulsifier, a granular and unfiltrable water-in-oil polymer emulsion is formed.
Applicants have now developed a process for preparing a stable reverse emulsion having an organic phase of less than 50% by weight. In addition, it makes it possible to reduce or even eliminate the problems of formation of coagulates or of grains that are encountered during the polymerization. This process also makes it possible to prepare polymers with high molecular masses, this property being particularly advantageous for increasing their efficacy in applications such as flocculation, etc.
The process, according to the present invention, comprises emulsifying, in an organic phase, one or more ethylenically unsaturated monomer(s), using a water-in-oil emulsifier and then performing an emulsion polymerization, wherein the polymerization is performed in the presence of one or more initiator(s) belonging to the family of azocarboxylic acid esters, represented by formula (I).
in which:
R
1
, R
2
, R
3
and R
4
, which may be identical or different, are selected independently from the group consisting of linear or branched-alkyls containing from 1 to 9 carbon atoms are preferably from 1 to 4 carbon atoms, optionally substituted with one or more substituents selected from hydroxyl, C
1
to C
6
alkoxy and halogen substituents; C
3
to C
12
-cycloalkyls, optionally substituted with one or more substituents selected from C
1
to C
6
alkyl, C
1
to C
6
alkoxy, hydroxyl and halo groups;
-aralkyls optionally substituted with one or more C
1
to C
6
alkyl, C
1
to C
6
alkoxy, hydroxyl and halo groups;
-aryls optionally substituted with one or more substituents selected from C
1
to C
6
alkyl, C
1
to C
6
alkoxy, hydroxyl and halo groups;
with at least one of the combinations R
1
-R
2
and R
3
-R
4
possibly forming an aliphatic ring; R″ and R′ are identical to or different than each other and are selected independently from the group consisting of linear or branched C
1
to C
10
and preferably C
1
to C
4
aliphatic radicals.
The advantage of these azocarboxylic acid esters is their low melting point, which is generally less than 27° C. The preferred azocarboxylic acid esters are those in which R″ and R′ represent methyl or ethyl and in which R
1
, R
2
, R
3
and R
4
advantageously represent C
1
to C
4
alkyl groups.
The azocarboxylic acid ester that is particularly preferred is diethyl 2,2′-azobisisobutyrate, that is to say with R
1
, R
2
, R
3
and R
4
representing methyl and R′ and R″ representing ethyl. DEAB may also be used as a mixture with other azocarboxylic acid esters. Mention may be made, for example, of mixtures of diethyl 2,2′-azobisisobutyrate (DEAB) and of dimethyl 2,2′-azobisisobutyrate (DMAB) with a mass content of DEAB of greater than 50%, and mixtures of DEAB, DMAB and 2-methyl 2′-ethyl azobisisobutyrate with a COOCH
3
/COOC
2
H
5
molar ratio ≦10.
The azocarboxylic acid esters of formula (I) may be prepared by a standard two-step process comprising a first step of converting the azonitrile, by reaction with an alcohol, in the presence of HCl, according to the Pinner reaction, leading to the corresponding azoimino ether hydrochloride, and a second step of hydrolysis in the presence of the hydrochloride thus obtained. They may also be prepared by the improved processes as described in documents DE 2 254 575, EP 80 275 and EP 230 586.
In addition, these esters may be prepared by reacting an azonitrile with an alcohol and hydrochloric acid in an aromatic solvent, with an HCl/azonitrile molar ratio >2 when the alcohol is methanol and >3 when the alcohol is ethanol or a higher alcohol.
The amount of azocarboxylic acid esters used in the process according to the present invention represents about 0.01 to 1% by weight of the ethylenically unsaturated monomer(s) used and preferably 0.02% to 0.5% by weight.
The water-soluble ethylenically unsaturated monomers or the mixtures of water-soluble monomers, comprising water-soluble ethylenically unsaturated monomers and water-insoluble ethylenically unsaturated monomers, are preferred.
Water-soluble ethylenically unsaturated monomers that may especially be mentioned include unsaturated monoethylenic carboxylic acids, for instance acrylic acid, methacrylic acid, maleic acid, itaconic acid, and salts of the abovementioned carboxylic acids, for example the sodium, potassium or ammonium salts, esters or acrylic acid and methacrylic acid and of amino alcohols such as, for example, dimethylaminoethyl acrylate, in protonated or quaternized form, for example dimethylaminoethyl acrylate hydrochloride, dimethylaminoethyl acrylate hydrogen sulfate or bisulfate, dimethylaminoethyl acrylate methyl chloride, dimethylaminoethyl acrylate methyl sulfate, dimethylaminoethyl methacrylate hydrochloride, dimethylaminoethyl methacrylate hydrogen sulfate or bisulfate, dimethylaminoethyl methacrylate methyl chloride, dimethylaminoethyl methacrylate methyl sulfate, acrylamide, methacrylamide, N-alkyl(meth)acrylamides, methacrylamidopropyltrimethylammonium chloride, acrylamidopropyltrimethylammonium chloride, methacrylamidopropyltrimethylammonium methyl sulfate, acrylamidopropyltrimethylammonium methyl sulfate, acrylamido- and methacrylamidoalkylsulfonic acids and salts thereof, such as 2-acrylamido-2-methylpropanesulfonic acid, hydroxyalkyl acrylates and hydroxyalkyl methacrylates, vinylsulfonic acid, vinylphosphonic acid, N-vinylamides such as, for example, N-vinyl-formamide, N-vinylacetamide, N-vinyl-N-methylacetamide and N-vinyl-N-methylformamide, diallyldimethylammonium chloride, N-vinylpyrrolidone, N-vinylimidazole, N-vinylimidazoline, 2-methyl-1-vinylimidazoline, 2-ethylsulfonic methacrylic acid, styrenephosphonic acid and styrene sulfonic acid. Mention may also be made of N-methylolacryamide and N-methylolmethacrylamide, and also of N-methylol(meth)acrylamides which are partially or totally etherified with monohydroxylated C
1
to C
4
alcohols.
These monomers may be cationic or anionic and, in certain cases, the ionic charges are small enough for the monomers to be considered as nonionic.
The cationic monomers are, for example, allylic amines or diall
Benard Françoise
Cerf Martine
Triballier Karine
ATOFINA, Elf Atochem, S.A.
Egwim Kelechi C.
Hunton & Williams LLP
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