Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Treating polymer containing material or treating a solid...
Reexamination Certificate
2001-03-02
2002-04-02
Boykin, Terressa M. (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Treating polymer containing material or treating a solid...
Reexamination Certificate
active
06365709
ABSTRACT:
The invention relates to a process for reducing the amount of residual monomer in aqueous polymer dispersions by chemical aftertreatment with a specific redox initiator system.
Following their preparation by free-radical polymerization or copolymerization, aqueous polymer dispersions include not only a polymer solids fraction of from 30 to 75% by weight but also, owing to the incomplete polymerization of the monomers employed in the free-radical main polymerization, which is usually carried out to a monomer conversion of 95 and preferably 98 to 99% by weight, an unwanted fraction of unpolymerized free monomers (residual monomers). On mainly toxicological grounds the market Far requires aqueous polymer systems having a low residual monomer content with no change in processing and use properties.
In addition to the nonchemical methods such as stripping with inert gas or steam, a wide variety of chemical methods, such as described, for example, in EP-B 003 957, EP-B 028 348, EP-B 563 726, EP-A 764 699, U.S. Pat. No. 4,529,753, DE-A 37 18 520, DE-A 38 34 734, DE-A 42 32 194 and DE-A 195 29 599, is available for lowering residual monomer contents of aqueous polymer dispersions.
For the use of carbonyl compounds and/or their reaction products in the aftertreatment of aqueous polymer dispersions it is necessary to start from the following prior art.
According to WO 95/33775, aqueous polymer dispersions can be aftertreated using redox systems whose reducing agent comprises an adduct of hydrogen sulfite anion and a ketone of 3 to 8 carbon atoms, and/or the conjugate acid of said adduct. Aftertreatment is performed in the presence of metal compounds that are soluble in the aqueous medium.
For the reduction of residual monomer contents, EP-A 767 180 advises a redox initiator system comprising organic hydroperoxides whose solubility in water is, at best, poor and, inter alia, adducts of aldehydes having a carbon chain of 4 to 6 carbon atoms with bisulfites.
The German patent application with the file reference 197 411 87.8, unpublished at the priority date of the present application, discloses using a system comprising an oxidizing agent and an organic &agr;-hydroxy carboxylic acid for chemical removal of residual monomers.
In the German patent application with the file reference 198 391 99.4, likewise unpublished at the priority date of the present application, the use of oxidizing agents in combination with a redox system consisting of an aldehyde and an inorganic dithionite is disclosed for bringing about depletion of residual monomers.
It is an object of the present invention to provide a new and effective process for reducing the amount of residual monomer in aqueous polymer dispersions. The intention is also that the reducing of the amount of residual monomer should be easy to utilize industrially without the formation of microcoagulum.
We have found that this object is achieved and thus that the amount of residual monomers in aqueous polymer dispersions can be effectively reduced if the aftertreatment of the aqueous polymer dispersions comprising residual monomers is accompanied by the addition of a redox initiator system comprising essentially
a) from 0.001 to 5% by weight, based on the total monomer amount used to prepare the polymer dispersion,
a
1
) of an oxidizing agent
R
1
OOH,
where R
1
is hydrogen or a C
1
-C
8
-alkyl or a C
6
-C
12
-aryl group, and/or
a
2
) of a compound which in aqueous medium releases hydrogen peroxide, and
b) from 0.005 to 5% by weight, based on the total monomer amount used to prepare the polymer dispersion,
b
1
) of an &agr;-hydroxycarbonyl compound
where R
2
and R
3
independently of one another are hydrogen and/or a C
1
-C
12
-alkyl group which may contain functional groups and/or may be olefinically unsaturated, or R
2
and R
3
optionally, by way of methylene groups, form a ring structure which may contain functional groups and/or may be olefinically unsaturated, and/or
b
2
) of a compound which in aqueous medium releases such &agr;-hydroxycarbonyl compounds, and
c) advantageously, catalytic amounts of a polyvalent metal ion which is able to exist in a plurality of valence states.
The oxidizing agent of the redox initiator system should be in a position to form free radicals. Oxidizing agents employed in the redox system are preferably hydrogen peroxide but also include sodium peroxide, potassium peroxide, sodium perborate, and other precursors which in aqueous medium form hydrogen peroxide. It is also possible, for example, to employ ammonium, potassium or sodium persulfate, peroxodisulfuric acid and its salts, ammonium, potassium or sodium perphosphate or diperphosphate, potassium permanganate, and other salts of peracids. Also suitable in principle are organic hydroperoxides, such as tert-butyl hydroperoxide and cumene hydroperoxide. It is, however, also possible to employ mixtures of different oxidizing agents mentioned above.
The amount of added oxidizing agent is usually within a range from 0.001 to 5, preferably from 0.002 to 3, with particular preference from 0.003 to 2, with very particular preference from 0.01 to 1.5 and, preferably, from 0.02 to 1% by weight, based on the total monomer amount.
Suitable reducing agents are generally aliphatic &agr;-hydroxycarbonyl compounds, such as aliphatic &agr;-hydroxy aldehydes and/or aliphatic &agr;-hydroxy ketones, isomeric compounds thereof and/or functional group substituted compounds thereof and/or olefinically unsaturated compounds thereof and mixtures thereof, and also precursors which in aqueous solution release these &agr;-hydroxycarbonyl compounds, examples being acetals and mercaptals. Examples that may be mentioned of &agr;-hydroxycarbonyl compounds are glycol aldehyde and/or its dimer 2,5-dihydroxy-1,4-dioxane, phenyl glycol aldehyde, 2-hydroxy-3-phenylpropionaldehyde, glyceraldehyde and its higher homologous compounds, such as aldotetroses, aldopentoses and aldohexoses, and also &agr;-hydroxyacetone, &agr;,&agr;′-dihydroxyacetone, 1-hydroxy-2-butanone, 1-hydroxy-2-pentanone, 1-hydroxy-2-hexanone, 3-hydroxy-2-butanone (acetoin), 4-hydroxy-2-hepten-5-one, 2-hydroxy-3-pentanone, 3-hydroxy-2-pentanone, 3-hydroxy-4-heptanone, 4-hydroxy-3-heptanone, 4-hydroxy-2,2-dimethyl-3-pentanone, 3-hydroxy-2,2-dimethyl-4-pentanone, 2-hydroxy-1-phenyl-1-propanone, 1-hydroxy-1-phenyl-2-propanone, 1-hydroxy-1-phenyl-2-butanone, 2-hydroxy-1-phenyl-1-butanone, 2-hydroxy-1,2-diphenylethanone (benzoin), 2-hydroxy-1-phenyl-1,4-pentanedione, 1-hydroxy-1-phenyl-2,4-pentanedione, and cyclic &agr;-hydroxy ketones, such as 2-hydroxycyclohexanone (adipoin) and 2-hydroxycyclopentanone (glutaroin). Preference is given to the use of &agr;-hydroxyacetone, &agr;,&agr;′-dihydroxyacetone, 1-hydroxy-2-butanone, 1-hydroxy-2-pentanone and/or 3-hydroxy-2-butanone (acetoin), with particular preference to the use of &agr;-hydroxyacetone and/or &agr;,&agr;′-dihydroxyacetone.
The amount of added reducing agent is customarily within the range from 0.005 to 5, preferably from 0.01 to 3, with particular preference from 0.03 to 2 and, with very particular preference, from 0.05 to 1% by weight, based on the total monomer amount. Higher amounts of reducing agent, although possible, are not generally sensible from the economic standpoint.
The metal compounds advantageous for the aftertreatment are, customarily, completely soluble in the aqueous medium of the polymer dispersion, and their metallic component, moreover, is capable of existing in a plurality of valence states. The dissolved metal ions have a catalytic effect and assist the electron transfer reactions between the actually active oxidizing and reducing agents. Suitable dissolved metal ions are principally iron, copper, manganese, vanadium, nickel, cobalt, titanium, cerium, and chromium ions. It is of course also possible to use mixtures of different, mutually compatible metal ions, such as the system Fe
2/3+
/VSO
4
−
. Preferably, iron ions are employed.
The dissolved metal ions are used in catalytic amounts based on the mass of tota
Baumstark Roland
Heibel Claudia
BASF - Aktiengesellschaft
Boykin Terressa M.
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