Organic compounds -- part of the class 532-570 series – Organic compounds – Heterocyclic carbon compounds containing a hetero ring...
Reexamination Certificate
2002-05-03
2003-12-23
McKane, Joseph K. (Department: 1626)
Organic compounds -- part of the class 532-570 series
Organic compounds
Heterocyclic carbon compounds containing a hetero ring...
C524S430000
Reexamination Certificate
active
06667407
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a process for reducing monomeric aziridines in a polyaziridine reaction by adding an isocyanate as a scavenger, the products obtained by that process and coating compositions prepared from these products.
Polyfunctional aziridines have been shown to be useful as crosslinking agents in various types of waterborne and solventborne coating systems such as carboxylated acrylics, vinyl-acetate, carboxylated urethanes such as polyurethane dispersions (PUDs), styrene acrylics or mixtures thereof.
One important subclass of commercially available polyfunctional aziridines includes reaction products of ethylene imine (EI, aziridine) or propylene imine (PI, methyl aziridine) with trimethylol propane triacrylate (described for example in U.S. Pat. No. 2,596,299 to Bastian). Other commercially important polyfunctional aziridines can be prepared from ethylene imine or propylene imine and pentaerythritol triacrylate. Other polyfunctional aziridines are based on alkoxylated polyols.
Another method of preparing polyfunctional aziridines includes the transesterification of methyl(1-aziridinyl)propionates with polyols catalyzed with tertiary amines (as described in DE 2334656 to Miksovsky), whereby the methyl(1-aziridinyl)propionates are prepared from monomeric aziridines.
Ethylene imine and propylene imine are volatile low molecular weight toxic compounds which are undesired residuals in the processes to form polyfunctional aziridines. The residual monomeric aziridine compound has to be removed sometimes tediously by elaborate distillation methods or lengthy aging processes. This is especially true, if the reaction temperature is low, which is sometimes necessary to avoid discoloration or viscosity problems. Sometimes the residue can exceed 1000 ppm in raw reaction mixtures. It is very desirable to reduce this amount for a commercial product below 500 ppm and even more preferred to reduce it below 100 ppm or ultimately below 10 ppm.
To drive the Michael-type addition reaction of the aziridine and the acrylate to completion, it is possible to use an excess of aziridine. A disadvantage of this approach is the amount of aziridine to be removed from the reaction product under vacuum. With a simple distillation column and a vacuum of about 50 mm Hg it is usually not possible to remove the aziridine level to below 300 ppm on a commercial time scale, for example in a day. To achieve an aziridine level below that, it is necessary to use refined equipment, like an expensive falling-film or wiping-film evaporator, or longer distillation times which is economically unfavorable. Another method to drive the Michael addition uses an excess of acrylate. The residual aziridine levels can thereby be reduced to less than 10 ppm, which sometimes require considerable aging times up to several months, which again is economically unfavorable.
It is an object of the present invention to provide an easy process for making polyfunctional aziridines without advanced and expensive distillation or cleaning steps. It is another object of the invention to obtain these polyfunctional polyaziridines rheological stable and with a low color. It is another object of the invention to develop a process that results in less than 10 ppm of monomeric aziridine without incurring elaborate vacuum steps or long batch or aging times.
The present invention uses a scavenger. The reactions between electrophiles and aziridines have been described in detail in the literature. One example of a suitable electrophile is an isocyanate.
U.S. Pat. No. 3,789,034 to Wismer et al discloses the preparation of aziridine-functional polymers by preparing an aziridine-diisocyanate adduct and then reacting such adduct with hydroxy-bearing polymers. The aziridine-diisocyanate adduct is prepared, for example, by reacting a diisocyanate with 1,2-propylene imine in such a ratio so as to “half-block” the diisocyanate. Such a reaction does not lead solely to half-blocked products but also to full-blocked products and residual unreacted diisocyanate.
U.S. Pat. No. 4,563,307 to Briden discloses the preparation of aziridine polymers involving the reaction of an isocyanate with an active hydrogen-containing aziridine.
U.S. Pat. No. 5,106,993 to Kania discloses specific aziridine compounds which can be prepared, for example, by reacting a monoisocyanate with an aziridine.
None of the above disclosures however describes the present invention
SUMMARY OF THE INVENTION
The invention relates to a process for reducing monomeric aziridines in a polyaziridine forming reaction mixture by adding to the polyaziridine forming reaction mixture an excess of a isocyanate scavenger, wherein the excess is based on the equivalent ratio of scavenger to monomeric aziridine.
The invention also relates to a product obtained by that process and a coating composition containing the product obtained by the claimed process.
DETAILED DESCRIPTION OF THE INVENTION
Various aziridines and substituted aziridines can be used to form polyfunctional aziridines. The suitable aziridines are well known in the art and generally correspond to the formula
where R
1
, R
2
, R
3
, and R
4
independently represent hydrogen; alkyl with up to about 20 carbon atoms, preferably methyl, ethyl, or propyl; aryl, preferably phenyl; alkaryl, preferably tolyl or xylyl; or aralkyl, preferably benzyl or phenethyl.
The groups R
1
-R
4
may represent substituted radicals wherein the substituents include cyano, halo, amino, hydroxy, alkoxy, carbalkoxy, and nitrile. Suitable examples of substituted groups R
1
, R
2
, R
3
, and R
4
thus include cyanoalkyl, haloalkyl, aminoalkyl, hydroxyalkyl alkoxyalkyl, carbalkoxyalkyl, and similar substituted derivatives of aryl, alkaryl and aralkyl groups.
Specific examples of suitable aziridines include ethylenimine (aziridine), 1,2-propylenimine (2-methyl aziridine), 2-ethyl aziridine, 1,2-dodecylenimine (2-decyl aziridine), 1,1-dimethyl ethylenimine (2,2-dimethyl aziridine), phenyl ethylenimine (2-phenyl aziridine), tolyl ethylenimine (2-(4-methylphenyl)aziridine), benzyl ethylenimine (2-phenylmethyl aziridine), 1,2-diphenyl ethylenimine (2,3-diphenyl aziridine), hydroxyethyl ethylenimine (2-(2-hydroxyethyl)aziridine), aminoethyl ethylenimine (2-(2-aminoethyl)aziridine), 3-chloropropyl ethylenimine (2-(3-chloropropyl)aziridine), p-chlorophenyl ethylenimine (2-(4-chlorophenyl)aziridine), methoxyethyl ethylenimine (2-(2-methoxyethyl)aziridine), dodecyl aziridinyl formate(dodecyl 1-aziridinyl carboxylate), carbethoxyethyl ethylenimine (2-(2-carbethoxyethyl)aziridine).
Because of their availability and because they have been found to be among the most effective, the preferred aziridines are ethylenimine, 1,2-propylenimine and 2 ethylaziridine.
The suitable aziridines are usually reacted with acrylates.
Preferred acrylates are polyacrylates having a functionality f≧2, which can be synthesized e.g. by an esterification reaction between a polyol and acrylic acid. However, other methods are also possible to synthesize those polyfuctional acrylates. Examples of polyols used in this kind of polyacrylate synthesis include neopentyl glycol, 2,2′-bis(p-hydroxy-phenyl)propane (bis-phenol A), bis(p-hydroxyphenyl)methane (bis-phenol F), glycerol, trimethylolpropane, pentaerythritol and others. It is also possible to use diols commonly used in polyester synthesis. Examples of these diols include ethylene and propylene glycol, butandiol, hexanediol and others.
It is also possible but less preferred to react the monomeric aziridine with monoacylates e.g. esters of acrylic and methacrylic acid and subsequently perform an optionally base catalyzed transesterification reaction.
The reaction temperature in the Michael-addition between the acrylate and the aziridine is above the melting point of the components and below 100° C. Reactions at room temperature will usually work well. It is preferred to react between 0 and 60° C., more preferred between 25 and 50° C. Theoretically higher temperatures can be applied, but are not preferred. It is also po
Danielmeier Karsten
Mandara Joseph P.
Venham Lanny D.
Wicks Douglas A.
Bayer Polymers LLC
Gil Joseph C.
McKane Joseph K.
Roy Thomas W.
Saeed Kamal
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