Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Polymers from only ethylenic monomers or processes of...
Reexamination Certificate
2003-02-24
2004-05-25
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...
C526S220000, C526S236000, C526S303100, C526S317100, C526S318500
Reexamination Certificate
active
06740720
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to water-soluble homopolymers and copolymers having an E
b
C
50
value of more than 10 mg/l in the algae toxicity test on
Scenedesmus subspicatus
. The present invention further relates to the preparation of these polymers and to their use as flocculation aids or thickeners and as constituents of plant protection agents or erosion protection agents.
2. Description of the Background
Water-soluble homopolymers and copolymers are currently widely used inter alia as constituents of plant protection or erosion protection agents. As these polymers are frequently used in the open countryside, their toxicological properties are becoming increasingly important. In particular, polymers based on acrylic acid, methacrylic acid or their derivatives have a toxic effect on humans and other mammals, as well as on microorganisms such as algae. Because of their toxic effect on microorganisms, the use of these polymers in the open countryside, for example in soils, is not completely harmless, so there has been no lack of attempts in the past to develop polymers with a smaller toxic effect.
In a number of known processes, the residual monomer content is reduced by aftertreating the polymers with amines. Thus DE-AS 1 041 248 describes a process for reducing the residual content of monomeric acrylamide in acrylamide-containing water-soluble copolymers by treating the polymers with ammonia or a primary or secondary amine. The residual content of monomeric acrylamide can be reduced to approx. 0.1% by weight using this process. The copolymers obtainable in this way are said to have a lower toxicity to rats and cats than the untreated polymers.
DE 35 39 385 A1 discloses a process for the production of polymer gel particles in which the polymer gel is fed through a special roller device. To reduce the content of acrylamide monomer in acrylamide-containing homopolymers and copolymers, alkaline compounds, substances containing active hydrogen or compounds capable of forming active hydrogen are added to the cutting mechanism of this roller device. Examples of such compounds are alkali metal and alkaline earth metal hydroxides, sulphites and amines, inter alia.
To reduce the residual acrylamide monomers, DE 197 52 127 and DE 197 52 128 teach the addition of ammonia and amines or ammonium salts to the monomer solution before polymerization. To achieve the desired effect, the products have to be dried at more than 120° C. Crosslinking reactions occur at these high temperatures and lead to a marked decrease in the solubility of the polymers. This applies especially to copolymers which, in addition to acrylamide, also contain ionic comonomers such as sodium acrylate.
Such partial insolubilities due to the aftertreatment, whether it be because of the chosen aftertreatment reagents or because of the high aftertreatment temperature, are described in JP 56-103207 using copolymers of sodium acrylate and acrylamide as an example. According to said disclosure, aftertreatment of the appropriate polymers with 1% by weight of ammonia, amines or thiosulphates, based in each case on the polymer, followed by drying at a temperature of 150° C., leads to insolubility of almost all the polymer. Aftertreatment with ammonia or an amine leads to partial insolubility of the polymers, even at a low drying temperature of 50° C. To reduce the residual monomer content without affecting the solubility of the corresponding polymers, said disclosure describes a process in which at least 1% by weight of sulphites, bisulphites or pyrosulphites is added to the acrylamide-containing polymers, which are then dried at 50 to 100° C.
A similar process for the preparation of acrylamide-containing copolymers is described in DE 1 070 377. In this process the polymer is aftertreated with an aqueous solution of sodium bisulphite or sodium metabisulphite, the sulphites being used in amounts of at least 1 mol of sulphite per mol of residual acrylamide. A reduction in the residual monomer content to about 0.01% is achieved using this process.
U.S. Pat. No. 3,780,006 discloses the use of gaseous sulphur dioxide for the same purpose.
EP 0 505 163 A1 describes a process in which superabsorbent polymers are treated with surface-active compounds and substances capable of reacting with a vinyl double bond, for example sulphites, bisulphites, sulphinic acids, cysteine or lysine. The residual monomer content of (meth)acrylic acid can be reduced to less than 10 ppm by this process. However, the process gives rise to a comparatively high degree of secondary crosslinking in the case of non-crosslinked polymers.
Many of the processes known in the state of the art for reducing the residual monomer content have the disadvantage that the substances used to aftertreat the polymers, optionally in combination with the temperatures applied during the aftertreatment, impair the solubility or other engineering properties of the polymers. Moreover, the majority of known processes are restricted to acrylamide-containing polymers. Furthermore, insufficient attention has been paid to the aspect of the toxicity of the known polymers to microorganisms. However, a sufficiently low toxicity of the polymers to microorganisms, for example algae, is particularly desirable from the ecological point of view for their use in the open countryside.
SUMMARY OF THE INVENTION
The object of the present invention is therefore to provide water-soluble polymers which, compared with polymers of the state of the art, have an improved environmental compatibility coupled with otherwise at least equivalent product properties, especially at least the same water solubility.
The object is achieved according to the invention by the provision of water-soluble polymer particles having an E
b
C
50
value of more than 10 mg/l in the algae toxicity test on
Scenedesmus subspicatus.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The present invention relates to both homopolymer and copolymer particles. The monomers used are preferably acrylic acid and methacrylic acid, acrylic acid derivatives such as salts of acrylic acid and methacrylic acid, acrylamide, methacrylamide, acrylonitrile, methacrylonitrile, N,N-dimethylacrylamide, vinyl-pyridine, vinyl acetate, water-soluble, ethylenically unsaturated organic acids such as maleic acid, fumaric acid, itaconic acid, vinylsulphonic acid and acrylamido-methylpropanesulphonic acid, and salts thereof, hydroxyl group-containing esters of polymerizable acids, such as hydroxyethyl and hydroxypropyl esters of acrylic acid and methacrylic acid, and amino group-containing esters of polymerizable acids, such as dimethylaminoalkyl and diethylaminoalkyl esters and amides of acrylic acid and methacrylic acid. It is also possible to modify the copolymers by using monomers containing sulpho groups and sulphate groups, such as (meth)allylsulphonic acid, vinylsulphonic acid, styrenesulphonic acid and acrylamidomethylpropanesulphonic acid, monomers containing phospho groups, such as vinylphosphonic acid, allylphosphoric acid, acrylamidomethylpropanephosphonic acid and salts thereof, hydroxyethyl (meth)acrylate sulphates, allyl alcohol sulphates and phosphates, polyalkylene glycol esters of (meth)acrylic acid and polyalkylene glycol ethers with (meth)allyl alcohol. If an acid is used as the monomer, this can be in the form of the free acid, neutralized or partially neutralized. The neutralization or partial neutralization can be carried out with any base or any mixture of suitable bases that form a water-soluble salt with the acid, especially alkali metal hydroxides, alkaline earth metal hydroxides and/or ammonia.
The polymer particles preferably contain at least one acrylic acid derivative/methacrylic acid derivative or acrylic acid/methacrylic acid as the monomer.
Particularly preferably, the polymer particles additionally contain at least one other polymerized monomer from the group comprising monoethylenically unsaturated C
3-10
monocarboxylic acids and their alkali metal, ammonium and amine
Herth Gregor
Mertens Richard
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Pezzuto Helen L.
Stockhausen GmbH & Co. KG
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