A PROCESS FOR PREPARING A POLYMERISABLE LATEX-FORMING SOLUTION INCORPORATING UNSATURATED NITROGEN-CONTAINING ACID

Abstract: A process for preparing unsaturated nitrogen containing acids such as acrylamidoglycolic acid utilizes a catayst free route and low pH conditions. An unsaturated amide such as acrylamide is reacted with an aldehyde acid such as glycolic acid in an aqueous environment. The unsaturated nitrogen containing acids are typically produced in solution form and can be utilized as such.

Description: The present invention relates to the preparation of polymerisable solutions incorporating unsaturated nitrogen-containing acid. Heretofore, unsaturated nitrogen-containing acids have been prepared using alkali compounds as catalyst. The end product was generally therefore a basic salt which required purification e.g. using an acid such as hydrochloric, to neutralize the solution containing the end product which was thus precipitated. In the prior art, US-A-3,422,139 relates to the preparation of acrylamidoglycolic acid using an alkali carbonate catalyst, and describes the need to crystallize the product before use. The problem addressed herein is to provide a new preparation of a polymerisable latex-forming solution, which may provide improved latex properties. The invention provides a process for preparing a polymerisable latex-forming solution, characterised in that an unsaturated nitrogen-containing acid of the formula in which R¹ is H or an alkyl having from 1 to 3 carbon atoms, and R² is CH₂, C₂H₄ or absent, is prepared by reacting an unsaturated amide of the formula with an aldehyde acid of the formula in the absence of basic catalyst in an aqueous medium having a pH of from about 1.2 to about 7.0, in the proportion of 1.2-2.4 equivalents of the unsaturated amide to one equivalent of the aldehyde acid, to produce the nitrogen-containing acid in a salt-free form which is incorporated in the polymerisable latex-forming solution. In another aspect the invention provides polymerisable latex-forming solutions obtainable by the above process. The excess of amide over aldehyde acid in the reaction is desirable inasmuch as it speeds up the reaction rate. As stated, from about 1.2 to about 2.4, preferably from about 1.7 to about 2.0, equivalents of amide are used for each equivalent of aldehyde acid. Also, improved latex properties can result from the presence of an unsaturated amide such as acrylamide. Such amide can conveniently be introduced as excess in the preparation of the unsaturated nitrogen-containing acid. The reaction of the reactants is generally carried out in the aqueous reaction medium so that a solution is produced. Although the solution can contain generally any amount of solid, unsaturated nitrogen-containing acid therein, it may be from about 25% to about 70% by weight of solids, desirably from about 30% to about 60% by weight, and most preferably from about 40% to about 55% by weight based upon the total weight of the solution, that is the weight of the solid acid product and the liquid. The reaction is generally carried out at elevated temperatures with higher temperatures yielding faster reaction rates of the reactants. Generally, the reaction temperature is at least 40°C. Since water is generally used, as the reaction medium, the maximum temperature will be 100°C unless the reaction is carried out under pressure. A desirable reaction temperature range is from about 60°C to about 100°C, with from about 70°C to about 100°C being preferred. The reaction is generally carried out at atmospheric pressure because of convenience although either subatmospheric or superatmospheric pressures can also be utilized. As noted above, the reaction is conducted without the use of any salt-forming basic catalyst, and preferably without buffer systems and the like, such that a salt-free unsaturated nitrogen containing acid is produced. This method not only produces a product having low impurities, but is also relatively inexpensive since purification is not required. Inasmuch as a basic catalyst and the like are not utilized the pH of the reaction as well as of the slurry is relatively low or acidic and is from about 1.2 to about 7.0, and preferably from about 1.4 to about 4.0. An advantage of the present invention is that since the unsaturated nitrogen-containing acid is produced in a relatively pure solution, it can be utilized as it is, without any purification of the solution, in various latex polymerization reactions well known to the art and to the literature. The reaction between the unsaturated amide and the aldehyde acid produces an unsaturated nitrogen-containing acid of the following formulation; wherein R¹ and R² are as set forth hereinabove. Examples of suitable products include methacrylamidoglycolic acid, acrylamido lactic acid, with acrylamidoglycolic acid being preferred. Various conventional additives e.g. inhibitors, can be utilized during the reaction as known to the art and to the literature. Inhibitors are utilized to prevent polymerization of the vinyl group in the unsaturated amide. Generally, free radical inhibitors are utilized such as hydroquinone, para-methoxy phenol, and t-butyl catechol. When utilized, the amount of the inhibitors is generally from about 10 to about 1,000 parts by weight, desirably from about 20 to about 500 parts by weight and preferably from about 5 to about 150 parts by weight for each 1 million parts by weight of the reactants. The unsaturated nitrogen-containing acids are generally prepared in a suitable vessel, such as a reactor, etc., and subsequently utilized in solution form and added to a solution containing latex forming monomers. Alternatively, the reactants can be reacted in-situ in a latex forming vessel. That is, the unsaturated amide and the aldehyde acid can be added to a vessel containing a latex forming monomer solution as the reaction medium and reacted therein while the latex monomers are being polymerized. Upon formation of the unsaturated nitrogen-containing acid it will generally react with the latex forming monomers. It is thus to be understood that such in situ preparation is within the scope of the present invention. The latex-forming monomers can be any conventional monomers known to the art as well as to the literature and include monomers such as the various conjugated dienes containing from 4 to 10 carbon atoms, the various vinyl substituted aromatics containing from 8 to 12 carbon atoms, such as styrene, and the like. The invention will be better understood by reference to the following Examples: EXAMPLE I This example illustrates the effect of pH of the reaction media on rate of disappearance of glyoxylic acid and the subsequent effect on cure rate of the saturated Whatman paper. Three reactions were carried out at 50°C using the following formulations: The samples were tested for residual glyoxylic acid each hour with results as follows: It is apparent that the test method should have been recalibrated since A after 1 hour is still greater than 100%. However, it is clear that the reaction is accelerated at higher pH's. The test method utilized in the examples for measuring wet tensile strength is as follows: Whatman #4 chromatographic paper die-cut to 10 x 25cm (8" x 10") is used with a tolerance of ±5.0% in an untreated weight basis. The sheets are saturated with the latex using a laboratory padder at a binder add-on target of 20 ± 1.5% based on the finished sheet weight. The saturated sheets are air dried at n room temperature and then duplicate sheets are cured on the steam heated drier can at 157°C (315°F) for 15, 30, 60, and 300 seconds. All sheets are conditioned in accordance with TAPPI test method T402 before testing. Then they are immersed in distilled water until they are completely wetted. The tensile is then determined on four test strips in both the machine direction (MD) and in the cross direction (CD) for each cured sheet. The average of the eight results in each direction and the total tensile is reported as the sum of the CD and MD averages. This result is normalized to a basis weight of 33kg/91m (73.0 lbs./300 ft.) and a binder add on of 20%. EXAMPLE II Each of the products in Example 1 was used at 7 PHM in polymerization of latexes in bottles as detailed below. In each case an initial charge was made to the bottles using the ingredients in the order listed in the table. The bottles were flushed with nitrogen, capped, and allowed to react 45 minutes at 65°C. The bottles were opened, recharged with the appropriate amount of styrene, Sulfole 120, and butadiene as listed in the table. This charge was reacted until the bottles were under vacuum as a result of most of the monomers having reacted. The bottles were opened a second time and further monomers, Sulfole 120, and the experimental activated acids added as listed. This charge was also reacted to vacuum. The latexes obtained were tested without stripping. Solution A - 0.5% (W/V) Hampene Na-3, 0.9% (W/V) Dowfax 2A-1, 5.0% (W/V) Sipex BOS, and 3.0% (W/V) Aerosol MA in deionized water Solution B - 5.0% (W/V) Itaconic acid in deionized water Solution C - 5.0% (W/V) Sodium persulfate in deionized water Solution D - 3.8% (W/W) Sulfole 120 in styrene Solution E - 15.0% (W/W) A from Example 1 in deionized water Solution F - Product B from Example 1 in deionized water Solution G - Product C from Example 1 in deionized water It is evident that the three latexes have different pH's as a result of the differences in pH of the r eaction to form the products as shown in Example 1. Each of the latexes were tested in Whatman #4 paper with the following results: Example A relates to the present invention in that no basic catalyst such as sodium hydroxide was utilized. In contrast, Examples B and C relate to the prior art method of utilizing a basic catalyst. Even though the reaction between glyoxylic acid and acrylamide is promoted by a high pH, the above data indicates that such increased pH results in poor latex performance. Thus, the product of the present invention produces better properties on the Whatman #4 paper test than the same prior art solution made with sodium hydroxide. EXAMPLE III This example shows the preparation of a product at 49.5 percent total solids and having a mole ratio of 1:1.8 of glyoxylic acid to acrylamide. This product when used in an emulsion polymerization recipe at 7 PHM would be theoretically equivalent to 5 PHM of acrylamidoglycolic acid and 2 PHM of acrylamide. Three (3) polymerization bottles were each charged with 143.5 grams (1.03 moles) of 53.3% (W/W) of glyoxylic acid, 267 grams (1.88 moles) of 50.0% (W/W) of acrylamide, and 17.5 grams (25 PPM on AGA) of a 0.03% (W/V) solution of paramethoxy phenol in deionized water. The bottles were rotated in a polymerization bath at 77°C (170°F) for five (5) hours. Alternate bottles were tested for residual glyoxylic acid at 1 1/2 hour intervals with the results of 34.9, 28.8, and 18.4 percent respectively. The contents of the bottles were blended and stored in a refrigerator. It is noted that the theoretical total solids content of this product is 49.5 percent. The commercial product acrylamidoglycolic acid monohydrate is only soluble at about 13 percent. The reason for this wide discrepancy in solubility is unknown but the greater solubility of the product of the present invention is a significant commercial advantage since it enables preparation of latexes having a high solids content. EXAMPLE IV The product prepared in Example III was used at 3, 5, and 7 PHM, in polymerization of latexes in one gallon reactors equipped with stirrer, heating and cooling means, charging and discharging means, and temperature controller. The reactor was purged with nitrogen before use and the polymerization was conducted under nitrogen. All latexes were stable during polymerization and had the following properties: The latexes were used to saturate Whatman #4 chromatographic paper as described in the Test Method for measuring wet tensile development and the results are set forth in the following table. Results obtained with a conventional commercial latex (D). The superior results for the latexes of this invention are clearly evident by comparing the results for A, B, and C with that of D. Latex C which contains only 3 PHM of the experimental reactive acid gave wet tensiles about 80 percent higher than those with the commercial latex D. Latex A which contains 7 PHM of the experimental reactive acid gave results about 126 percent higher than that of the commercial latex D.

Claims: A process for preparing a polymerisable latex-forming solution, characterised in that an unsaturated nitrogen-containing acid of the formula in which R¹ is H or an alkyl having from 1 to 3 carbon atoms, and R² is CH₂, C₂H₄ or absent, is prepared by reacting an unsaturated amide of the formula with an aldehyde acid of the formula in the absence of basic catalyst, in an aqueous medium having a pH of from about 1.2 to about 7.0, in the proportion of 1.2-2.4 equivalents of the unsaturated amide to one equivalent of the aldehyde acid, to produce the nitrogen-containing acid in a salt-free form which is incorporated in the polymerisable latex-forming solution. A process according to claim 1 in which the prepared nitrogen-containing acid is added to a solution of latex-forming monomers. A process according to claim 1 or claim 2 in which the proportion of the unsaturated amide is from about 1.4 to about 2 equivalents to each equivalent of aldehyde acid. A process according to any one of the preceding claims in which the temperature of the reaction forming the nitrogen-containing acid is from about 60°C to about 100°C. A process according to claim 4 in which said temperature is at least about 70°C. A process according to any one of the preceding claims in which R² is absent. A process according to any one of the preceding claims in which the pH of said aqueous medium is from about 1.4 to about 4.0. A process according to any one of the preceding claims in which R¹ is H. A process according to any one of the preceding claims in which the nitrogen-containing acid forms a solution in the aqueous reaction medium containing from about 25 to about 70 percent by weight of dissolved nitrogen-containing acid based on the weight of said acid and said aqueous medium. A process according to claim 9 in which the solution contains from about 30 to about 60 percent, more preferably from about 40 to about 55 percent, by weight of the nitrogen-containing acid. A process according to any one of the preceding claims in which the polymerisable latex includes conjugated diene monomers of from 4 to 10 carbon atoms, and/or vinyl aromatic monomers of from 8 to 12 carbon atoms. A polymerisable latex-forming solution containing an unsaturated nitrogen-containing acid, obtainable by a process according to any one of claims 1 to 11.

Inventors: WHITE, WOODROW W.
Applicants: GENCORP INC.
Application year: 1987
Main classification: C07C233
IPC codes: C08F20, C07C231, C07C233, C07C67