Cationic acrylate or methacrylate polymer admixtures.

0001The storage life of cationic acrylate polymers, particularly emulsions, is short due to the lack of hydrolytic stability. These polymers are also found to be degraded during dilution, especially in a neutral or alkaline aqueous solution. A long storage life and good hydrolytic stability is desired to maintain the product quality, i.e. activity.

0002It has now been unexpectedly found that acidic buffering compounds improve the stability of these polymers.

0003The present invention provides an admixture comprising a cationic acrylate of methacrylate polymer and 0.1 to 5.0% by weight, based on the weight of the said polymer, of an acidic buffering compound.

0004Also in accordance with the present invention, the stability of a cationic acrylate or methacrylate polymer is improved by adding to it 0.1 to 5.0% by weight, based on the weight of the polymer, of an acidic buffering compound.

0005The stability of any cationic (meth)acrylate polymer is enhanced by the addition of an acidic buffering compound. Specific examples of such polymers include homopolymers of methacryloyloxyethyl trimethyl ammonium methosulfate (METAMS), methacryloyloxyethyl trimethyl ammonium chloride (METAC), acryloyloxyethyl trimethyl ammonium chloride (AETAC), and copolymers of the above monomers with acrylamide. The preferred polymers are copolymers of acrylamide and 2-­methacryloyloxyethyl trimethyl ammonium chloride (AM/METAC) and copolymers of acrylamide and methacryloyloxyethyl trimethyl ammonium methosulfate (AM/METAMS).

0006Although the stability of any cationic (meth)acrylate polymer may be enhanced by the addition of the acid buffer, those having an intrinsic viscosity of at least 2.0 (MWT greater than 1,000,000) in 1.0 <u style="single">M</u> sodium chloride are more prone to stability problems.

0007Any acidic buffering compound may be used. The preferred acidic buffering compounds are polycarboxylic acids with a pK₁ of 1.19 to 3.08 and a pK₂ of 4.72 to 13.0. Examples include citric acid, phthalic acid, succinic acid, adipic acid, tartaric acid and malic acid. The most preferred acidic buffering compound is citric acid.

0008The acidic buffering agent is used in a dosage range of 0.1 to 5.0%, by weight, based on the weight of the polymer.

0009The stability of the polymer is enhanced in all forms, e.g. emulsion, solution, and dry.

0010The admixtures of the present invention may be used as dewatering and paper retention aids.

EXAMPLES 1 through 8

0011A set of water-in-oil emulsion copolymers of acrylamide and 2-methacryloyloxyethyl trimethyl ammonium chloride (40/60 w/w, 37.5% active) was pre­pared. After polymerization, a citric acid solution was slowly added in before addition of the inverting surfactant. This set of emulsions, containing differing levels of citric acid, was stored at both 50°C and room temperature for four weeks. The polymer reduced viscosity (0.05% in lN NaCl at 30°C), the net cationic unit on the polymer, and the polymer performance as a sludge dewatering aid, were compared to a control. The results are shown in Table I below. <tables id="tabl0001" num="0001"><img file="EP0222579A2_D0001.tif" /></tables>

EXAMPLES 9 through 11

0012A commercial AM/METAMS dry polymer (Calgon K-400) was blended with both 2.5% and 4.0% citric acid (anhydrous). Next, these polymer blends, as well as the original polymer, were dissolved in tap water to make a 0.1% solution. The % net cationic unit (as METAMS) pm polymer was determined initially and after 24 hours. The polymers with citric acid were stable. The results are summarized in Table II. <tables id="tabl0002" num="0002"><img file="EP0222579A2_D0002.tif" /></tables>

EXAMPLE 12

0013The emulsion polymers of Example 1 through 8 were diluted down to 0.1% concentration in three different industrial waters. The polymers with citric acid were more stable than the one without citric acid as indicated in Table III. <tables id="tabl0003" num="0003"><img file="EP0222579A2_D0003.tif" /></tables>