Preparing aqueous polymer dispersions

Details Preparing aqueous polymer dispersions Preparing aqueous polymer dispersions

1999-12-08

2002-09-03

Wu, David W. (Department: 1713)

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

At least one aryl ring which is part of a fused or bridged...

C524S802000, C524S804000, C526S348200, C526S348500, C526S348600, C526S319000, C526S328000

Reexamination Certificate

active

06444748

ABSTRACT:

The invention relates to a process for preparing aqueous polymer dispersions and to their use as auxiliaries for pharmaceutical administration forms.
A host of publications deal with the investigation of processes for preparing aqueous polymer dispersions; these include H. Fikentscher et al., Angew. Chem. 72 (1960) 856; A. Alexander, Prog. Polym. Sci. 3 (1971) 145; G. Markert, Angew. Makromol. Chem. 123/124 (1984) 285; Houben-Weyl, 4th ed., E20/2, 1150; EP-A-0 450 437 and EP-A-0 627 450.
Depending on the field of use, such polymer dispersions are frequently employed in fully or partly neutralized form. In this case, the dispersion can be neutralized either during or after the polymerization.
In this regard it is frequently observed that the storage stability, especially the pH stability, of neutralized, aqueous polymer dispersions is not always satisfactory. For instance, there may be unwanted drops in pH in the course of storage, as a result of which the properties of such dispersions may be drastically impaired.
As is known, furthermore, from the literature [Friedrich Höscher, Dispersionen synthetischer Hochpolymerer, Part I (Springer Verlag Berlin, 1969), page 77], the pH of the reaction system in polymerization plays an important part in respect of the polymerization rate, the residual monomer content after polymerization, and the colloidal stability of the system. For example, pH regulation by means of buffers may result in the formation of considerable amounts of electrolytes, which may lead to unwanted coagulation of the system.
It is an object of the present invention to provide a process for preparing storage-stable aqueous polymer dispersions of low monomer content without the abovementioned disadvantages.
We have found that this object is achieved in accordance with the invention by a process for preparing an aqueous polymer dispersion by polymerizing at least one free-radically polymerizable, ethylenically unsaturated monomer in an aqueous system in the presence of a polymerization initiator, which comprises adjusting the pH of the aqueous dispersion during the preparation process by adding at least two different, basic reagents, at least one of the basic reagents being added in a plurality of stages.
The free-radically polymerizable ethylenically unsaturated monomers employed in the process of the invention comprise compounds from the group consisting of C
1
-C
24
alkyl esters of monoethylenically unsaturated C
3
-C
8
carboxylic acids, C
1
-C
24
alkyl esters of monoethylenically unsaturated C
4
-C
8
dicarboxylic acids, vinyl esters of aliphatic C
1
-C
24
carboxylic acids, amides of monoethylenically unsaturated C
3
-C
8
carboxylic acids, C
1
-C
24
alkyl vinyl ethers, N—C
1
-C
24
alkyl-substituted amides of monoethylenically unsaturated C
3
-C
8
carboxylic acids, N,N—C
1
-C
24
dialkyl-substituted amides of monoethylenically unsaturated C
3
-C
8
-carboxylic acids, N-vinyllactams, N-vinylamines, styrene and butadiene.
Alkyl esters of monoethylenically unsaturated C
3
-C
8
carboxylic acids and of monoethylenically unsaturated C
4
-C
8
dicarboxylic acids include branched or unbranched C
1
-C
24
alkyl esters, preferably methyl, ethyl, n-propyl, 1-methylethyl, n-butyl, 1-methylpropyl, 2-methylpropyl, 1,1-dimethylethyl, n-pentyl, 1-methylbutyl, 2-methylbutyl, 3-methylbutyl, 2,2-dimethylpropyl, 1-ethylpropyl, n-hexyl, 1,1-dimethylpropyl, 1,2-dimethylpropyl, 1-methylpentyl, 2-methylpentyl, 3-methylpentyl, 4-methylpentyl, 1,1-dimethylbutyl, 1,2-dimethylbutyl, 1,3-dimethylbutyl, 2,2-dimethylbutyl, 2,3-dimethylbutyl, 3,3-dimethylbutyl, 1-ethylbutyl, 2-ethylbutyl, 1,1,2-trimethylpropyl, 1,2,2-trimethylpropyl, 1-ethyl-1-methylpropyl, 1-ethyl-2-methylpropyl, n-heptyl, 2-ethylhexyl, n-octyl, n-nonyl, n-decyl, n-undecyl, n-dodecyl, n-tridecyl, n-tetradecyl, n-pentadecyl, n-hexadecyl, n-heptadecyl, n-octadecyl, n-nonadecyl, n-eicosyl, n-docosyl- or n-tetracosyl esters.
Preferred representatives of the abovementioned alkyl radicals that may be mentioned are branched or unbranched C
1
-C
2
and, with particular preference, C
1
-C
6
alkyl radicals.
By monoethylenically unsaturated carboxylic acids of 3 to 8 carbon atoms are meant, for example, acrylic acid, methacrylic acid, dimethacrylic acid, ethacrylic acid, allylacetic acid, vinylacetic acid and crotonic acid. Preferred representatives from this group are acrylic acid and methacrylic acid.
By mondethylenically unsaturated dicarboxylic acids of 4 to 8 carbon atoms are meant, for example, representatives from the group consisting of maleic acid, fumaric acid, mesaconic acid and itaconic acid, preferably maleic acid.
By vinyl esters of aliphatic C
1
-C
24
carboxylic acids are meant vinyl esters of aliphatic branched or unbranched, saturated or unsaturated C
1
-C
24
carboxylic acids. Examples that may be mentioned include formic acid, acetic acid, propionic acid, butyric acid, valeric acid, isovaleric acid, caproic acid, caprylic acid, capric acid, undecylenic acid, lauric acid, myristic acid, palmitic acid, palmitoleic acid, stearic acid, oleic acid, arachidic acid, behenic acid, and lignoceric acid.
Preference is given to using vinyl esters of the abovementioned C
1
-C
12
carboxylic acids, especially of the C
1
-C
6
carboxylic acids.
By amides of monoethylenically unsaturated carboxylic acids of 3 to 8 carbon atoms are meant, for example, amides of acrylic acid, methacrylic acid, dimethacrylic acid, ethacrylic acid, allylacetic acid, vinyl acetic acid and crotonic acid. Preferred representatives from this group are acrylamide (H
2
C═CH—CO—NH
2
) and methacrylamide (CH
2
═C(CH
3
)—CO—NH
2
).
It is also possible to polymerize C
1
-C
24
-alkyl vinyl ethers, preferably C
1
-C
12
-alkyl vinyl ethers.
Preferred C
1
-C
12
alkyl radicals of the vinyl ethers that may be mentioned include branched or unbranched alkyl chains such as, for example, methyl, ethyl, n-propyl, 1-methylethyl, n-butyl, 1-methylpropyl, 2-methylpropyl, 1,1-dimethylethyl, n-pentyl, 1-methylbutyl, 2-methylbutyl, 3-methylbutyl, 2,2-dimethylpropyl, 1-ethylpropyl, n-hexyl, 1,1-dimethylpropyl, 1,2-dimethylpropyl, 1-methylpentyl, 2-methylpentyl, 3-methylpentyl, 4-methylpentyl, 1,1-Dimethylbutyl, 1,2-dimethylbutyl, 1,3-dimethylbutyl, 2,2-dimethylbutyl, 2,3-dimethylbutyl, 3,3-dimethylbutyl, 1-ethylbutyl, 2-ethylbutyl, 1,1,2-trimethylpropyl, 1,2,2-trimethylpropyl, 1-ethyl-1-methylpropyl, 1-ethyl-2-methylpropyl, n-heptyl, 2-ethylhexyl, n-octyl, 2-ethylhexyl, n-nonyl, n-decyl, n-undecyl and also n-dodecyl radicals.
Further monomers which can be employed include N—C
1
-C
24
-alkyl- or N,N—C
1
-C
24
-dialkyl-substituted amides of monoethylenically unsaturated C
3
-C
8
carboxylic acids, the alkyl radicals being branched or unbranched aliphatic alkyl radicals of 1 to 24 carbon atoms, examples being methyl, ethyl, n-propyl, 1-methylethyl, n-butyl, 1-methylpropyl, 2-methylpropyl, 1,1-dimethylethyl, n-pentyl, 1-methylbutyl, 2-methylbutyl, 3-methylbutyl, 2,2-dimethylpropyl, 1-ethyipryl, n-hexyl, 1,1-dimethylpropyl 1,2-dimethylpropyl, 1-methylpentyl, 2-methylpentyl, 3-methylpentyl, 4-methylpentyl, 1,1-dimethylbutyl, 1,2-dimethylbutyl, 1,3-dimethylbutyl, 2,2-dimethybuty, 2,3-dimethylbutyl, 3,3-dim thylbutyl, 1-ethylbutyl, 2-ethybutyl 1,1,2-trimethylpropyl, 1,2,2-trimethylpropyl, 1-ethyl-1-methylpropyl, 1-ethyl-2-methylpropyl, n-heptyl, 2-ethylhexyl, n-octyl, n-nonyl, n-decyl, n-undecyl, n-dodecyl, n-tridecyl, n-tetradecyl, n-pentadecyl, n-hexadecyl, n-heptadecyl, n-octadecyl, n-nonadecyl, n-eicosyl, n-docosyl or n-tetracosyl radicals, preferably such alkyl radicals having 1 to 12 and, with particular preference, 1 to 6 carbon atoms.
The amidated monoethylenically unsaturated carboxylic acids of 3 to 8 carbon atoms can, as already specified above, stand, for example, for acrylic acid, methacrylic acid, dimethacrylic acid, ethacrylic acid, allylacetic acid, vinylacetic acid and crotonic acid. Preferred representatives from this group are acrylic acid and methacrylic acid.
From this group of carboxylic acids, preference is likewise given to using acrylic

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