CS219801B1 - A method for removing residual amounts of acrylic monomers - Google Patents

Abstract

Method for removing residual amounts of acrylic monomers from acrylate or acrylic monomer-containing aqueous dispersions. First, the pH of the dispersion is adjusted to a value of 6.0 to 7.5 with an aqueous solution of sodium, potassium, ammonium or secondary amine hydroxide. At a temperature of 20 to 70 °C, the dispersion thus adjusted is mixed with a secondary amine, or its aqueous solution, in an amount equivalent to the content of free acrylic monomers in the dispersion, optionally in the presence of acetic acid. Then, the dispersion is left to react at the indicated temperatures for at least 24 hours. Substances from the group including morpholine, diethanolamine and piperidine are used as secondary amines.

Description

The invention relates to a process for removing residual amounts of acrylic monomers from acrylate or acrylic monomers containing aqueous dispersions. By removing these monomers, the processability of these dispersions is improved and their ecological properties are greatly improved.

Dispersions of acrylic or methacrylic compounds, prepared by emulsion copolymerization of acrylic and methacrylic monomers, such as esters, nitriles, amides or acrylic and methacrylic acids, optionally with other monomers such as vinyl acetate, styrene and the like, serve as an intermediate for the preparation of paints, adhesives or sealants. Although the copolymerization reaction proceeds very rapidly to high conversion, the dispersions obtained contain certain amounts - less than 1% by weight of the monomers used - of free, unreacted monomers ......

These free monomers are then a source of difficulties in the further processing of the acrylate dispersions. By evaporating, they contaminate the work environment with their typical and characteristic odor, prevent allergic persons from working and can also cause injury (J. Sokal et al. Occupational Medicine 29, 1977, 157; M. Kuželová, Occupational Medicine, 33, 1981, 95) . For these reasons, efforts are made to minimize the amount of residual monomers in the acrylate dispersions. This can be achieved either by carrying out the conversion of the monomers in the copolymerization process up to 100 percent, which is usually very time and energy consuming, or by chemical reaction, in particular residual acrylic monomers, to saturated, non-volatile and therefore odorless compounds.

There are a number of reactions that can be applied to convert an acrylate double bond into a single bond, thereby forming an acrylate compound, a volatile and typically odorous compound, a saturated compound, a non-volatile compound, and thus a non-odorous compound. These include, for example, the reactions of α, (S-unsaturated bonds with ozone, sulfites, halogens and hydrogen halides, nucleophilic addition of dodecanethiol, catalytic hydrogenation, and also reactions with amines. Most of these possible reactions prevent their practical application for technical or economic reasons.

The reaction of primary and secondary amines with α, β-unsaturated bonds has long been known (JH Ford et al., J. Am. Chem. Soc. 69, 1974, 844; FC Whitmore et al., J. Am. Chem. Soc., 66 , 1944, 725). Recently, the use of primary amines for this purpose, for the disposal of residual monomers in acrylic dispersions, has been discovered by the action of ethanolamine (Jpn. Kokai Tokkyo Koho 80151 015 (1980); C. A. 94-16-122 266c).

For the disposal of residual monomers in acrylate dispersions, it is advantageous to use high boiling amines which do not smell and do not create unfavorable conditions for further processing or use of the treated dispersion. Reaction of both primary and secondary amines with esters of acrylic acid easily results in esters of .beta.-alkylaminopropionic acid, respectively. β-dialkylaminopropionic acids, or β, β-alkyliminodipropionic esters (Methode der org. Chem., 11/1, 277).

The aforementioned disadvantages are overcome by the invention which is concerned with a process for removing residual amounts of acrylic monomers from acrylate or acrylic monomers containing aqueous dispersions. SUMMARY OF THE INVENTION The pH of this dispersion is first adjusted to a pH of 6.0 to 7.5 with a 10- to 55% aqueous solution of sodium, potassium, ammonium or secondary amine; then the dispersion thus treated is stirred at a temperature of 20 to 70 ° C with the secondary amine or its 10 to 55% aqueous solution, in an amount equivalent to the free acrylic monomer content of the dispersion, optionally in the presence of catalytic acetic acid in an amount of up to 20% by weight to the amount of secondary amine, after which the dispersion is allowed to react for at least 12 hours at the indicated temperatures. As secondary amines, they are used ^; morpholine, diethanolamine and plperidine.

The use of secondary amines has an advantage over the use of ethanolamine and other primary amines, especially in significantly higher reactivity, further extending the choice of a suitable reagent to remove residual amounts of unreacted monomers in acrylate dispersions with respect to influencing the final dispersion or copolymer film properties, e.g. mechanical or thermal stress, resistance to low temperatures ^of adhesion, cohesion, hygroscopicity and the like.

It has also proven to be advantageous in some cases to combine individual secondary amines, for example, neutralize to a pH of about 7.0 with diethanolamine and then add an equivalent amount to the free acrylic monomers of morpholine or piperidine, or add an additional amount of diethanolamine.

For the disposal of residual amounts of acrylic monomers in the acrylate dispersions according to the invention, it is suitable to use a secondary amine of sufficiently high boiling point which does not significantly affect the properties of the dispersion or copolymer film after evaporation of water from the dispersion or it will at least increase. Such secondary amines according to the invention are:

M. hm.

mp ° C sp. hm.

morpholine 87.12 diethanolamine 105.14 piperidine 85.15

128

270

106.3

0.9994

1,0966

0.8606

Acrylate dispersions prepared using a redox initiation system (NH 2) 2 S 2 O 3 / K 2 S 2 O 5 have an acidic reaction at about pH = 2.5 to 3.0 when the polymerization is complete, or are formed by the decomposition of acid sulphate initiators. ammonium, incapable of nucleophilic addition to the double bond

I \ /

R-NH + C = C

I / \

H

R X = I-R-N-C-C

I H

X

AND

N-C-C, the pH of the dispersion must be adjusted to a value of about 7.0 prior to application of the secondary amine with a sodium, potassium or ammonium hydroxide solution; or an excess of amine can be advantageously used to neutralize the acidic components of the dispersion, which may have other advantageous consequences for the dispersion.

The application of the secondary amine in the disposal of residual amounts of acrylic monomers can be accomplished in two ways. Depending on the free residual monomer content of the neutralized dispersion to pH 6-7, an equivalent amount of secondary amine or amine mixture is added, or a small excess is added and the dispersion is thoroughly mixed at normal or elevated temperature and then left to stand for 12 to 24 hours. all monomers reacted with amines to form a nonvolatile and therefore odorless dialkylaminopropionic acid ester. Alternatively, the required amount of amine is added to the acid dispersion at pH 2.5 to 3.0 for both neutralization and reaction with the free residual monomers, possibly higher amounts, for example diethanolamine, which is non-volatile but lowers the freezing point of the aqueous phase. or by altering the morphology of the ice crystals to such an extent that the freezing resistance of the dispersion is increased.

The amines, or mixtures thereof, may, of course, be applied either alone or, if desired, aqueous solutions of appropriate concentration. The substitution of alkyl groups and / or β carbon of acrylic compounds (CH3- in methacrylates) has a pronounced retarding effect for the reaction of secondary amines - apparently due to electron releasing effects - so it is advisable to use elevated temperatures or small amounts of acetic acid as catalyst.

The invention is illustrated by the following non-limiting examples.

Example 1

950 g of an aqueous dispersion of butyl acrylate, ethyl acrylate and acrylic acid copolymer had 62.5 percent by weight of solids after copolymerization. and pH 2.95. The pH of the dispersion was adjusted to 6.8 by the slow dropwise addition of 10% aqueous NaOH. According to gas chromatography, the content of free monomers was 0.45% by weight of butyl acrylate, 0.18% by weight of ethyl acrylate, and acrylic acid was not found in the dispersion. While stirring, 4 g of morpholine were slowly added dropwise to the dispersion at 32 ° C, and the dispersion was allowed to stand overnight after stirring. After 15 hours, 0.01 wt. butyl acrylate and no free ethyl acrylate or acrylic acid.

Example 2

1200 g of the aqueous dispersion of the copolymer of 2-ethylhexyl acrylate, butyl acrylate, ethyl acrylate, acrylonitrile and acrylic acid after copolymerization had a pH of 3.1; % dry matter 55.2 wt. and residual monomer content after 3 hours after completion of the emulsion polymerization: butyl acrylate 0.22 wt%, ethyl acrylate 0.12 wt%, 2-ethylhexyl acrylate 0.32 wt%. and 0.0 wt. acrylic acid. After adjusting the pH of the dispersion to 6.2 with 12% ammonium hydroxide solution, the dispersion was stirred at 28 ° C for 2 hours after the dropwise addition of 6.5 g piperidine and then left at room temperature for 22 hours at room temperature for 16 hours. The dispersion sample was then found by gas chromatography:

0.015 wt. (based on the dispersion mass) of 2-ethylhexyl acrylate, traces of butyl acrylate. The other monomers used: ethyl acrylate, acrylonitrile and acrylic acid were no longer detected in the dispersion.

Example 3

980 g of an aqueous dispersion of a copolymer of butyl acrylate, ethyl acrylate, acrylic acid and acrylonitrile having a dry weight of 59.5% by weight. and pH 2.85 at 15 hours after completion of the emulsion copolymerization (based on the dispersion mass): 0.42 wt. butyl acrylate; 0.12% wt. ethyl acrylate and no free acrylonitrile and acrylic acid. 11 g of diethanolamine in 12 g of water and 2 g of glacial acetic acid were added to the stirred dispersion at 45 ° C, and the dispersion was stirred at this temperature for 2 hours. The dispersion was then allowed to stand for 24 hours. A dispersion sample was found. 0.02 wt. butylacrylate and traces of ethyl acrylate. The dispersion had a pH of 7.4 and showed no changes after two cycles of temperature variation of -10 ° C and 20 ° C.

Example 4

1100 g of an aqueous dispersion of a copolymer of 2-ethylhexyl acrylate, methyl methacrylate, acrylonitrile and methacrylic acid, containing 55.5% by weight of a copolymer; 12 hours after the end of the emulsion copolymerization, it contained 0.62 wt. 2-ethylhexyl acrylate; 0.19 wt. % methyl acrylate, traces of acrylonitrile and 0.1 wt. methacrylic acid (based on the dispersion mass). After adjusting the pH dropwise to a pH of 6.8 with a 55% solution of diethanolamine, a mixture of 3.4 g of morpholine and 3.4 g of piperidine was added dropwise at 60 ° C. The dispersion was further stirred at this temperature for 2 hours. After cooling the dispersion to 20 ° C, only 0.03% by weight was found in the dispersion sample after 24 hours. 2-ethylhexyl acrylate and traces of methyl methacrylate. The pH of the dispersion was 7.65 and its viscosity increased from the original 80 to 90 mPa · s prior to amine treatment to 130 to 150 mPa · s after treatment.

Example 5

880 g of an aqueous dispersion of vinyl acetate, butyl acrylate and methacrylic acid copolymer contained 0.24 wt. % butyl acrylate and 0.1 wt. methacrylic acid, based on the dispersion mass. At 45 ° C, the pH of the dispersion was adjusted to 7.2 by dropwise addition of a 33% solution of diethanolamine and then a 50% solution of morpholine equivalent to free acrylic monomers (2.5 g morpholine and 2.5 g water) was added under stirring at the same temperature. ). The dispersion was stirred at this temperature for a further 3 hours and then allowed to stand for 12 hours. The dispersion contains only trace amounts of free acrylic monomers. Example 6

1000 g of an aqueous dispersion of a copolymer of styrene, vinyl acetate, 2-ethylhexyl acrylate and acrylic acid contains 0.32 wt. 2-ethylhexyl acrylate based on the weight of the dispersion. The dispersion, which was adjusted to pH 6.0 with 12% NaOH, was stirred at 35 ° C after a gradual dropwise addition of 0.1 g of acetic acid and a solution of 1.5 g of morpholine and 3.0 g of water for 2 hours. After standing the dispersion for 15 hours at rest, 0.05% wt. 2-ethylhexyl acrylate per dispersion mass, after 30 hours only traces of this monomer were detected by gas chromatography.

Claims (2)

Subject A process for removing residual amounts of acrylic monomers from acrylate or acrylic monomers containing aqueous dispersions, characterized in that the pH of the dispersion is first adjusted to a value of 6.0 to 6.0 to an aqueous solution of sodium, potassium, ammonium or secondary amine with a 10- to 55% aqueous solution. 7.5, then the dispersion thus treated is stirred at a temperature of 20 to 70 ° C with the secondary amine or a 10- to 55% aqueous solution thereof, in an equilibrium amount to the free acrylic monomer content of the dispersion, optionally in the presence of catalytic acetic acid. in an amount of up to 20 wt. based on the amount of secondary amine, after which the dispersion is allowed to react for at least 12 hours at said temperatures. 2. The process of claim 1 wherein the secondary amines are morpholine, diethanolamine and piperidine.