Curable crosslinking system with monobenzaldimine as crosslinker

This invention relates to improved crosslinking systems for polymeric dispersions and solutions having suitability for coatings, adhesives and use in many other applications. These systems are based upon crosslinkable polymers having a plurality of activated keto methylene groups, e.g., a beta diketone such as an acetoacetate or a keto cyano methylene functional groups and a crosslinkable component comprising an aldimine. A sufficient amount of the aldimine curing agent is used to effect reaction with the polymer containing the activated keto methylene groups and cure thereof. The improvement in the crosslinking system resides in the utilization of a monoaldimine having only one aldimine group and no other methylene reactive group as a crosslinking agent. Another improvement variation to that previously suggested comprises a redispersible polymer(s) containing activated methylene functionality and combined with the monoaldimine and the use of heterocyclic aldimine.

TECHNICAL FIELD OF THE INVENTION 
The present invention relates to a new crosslinking reaction system for 
polymer systems containing activated methylene functionality, e.g., 
acetoacetate groups. The crosslinker is a monoaldimine. 
BACKGROUND OF THE INVENTION 
Solvent and water-based crosslinkable polymers have wide utility in 
industry as coatings and adhesives. Current and proposed environmental 
regulations have been instrumental in the development of formaldehyde- and 
isocyanate-free coatings in an effort to reduce health hazard materials 
used in coatings. One relatively new type of water-borne system is based 
upon a polymeric system having a plurality of acetoacetate groups and a 
crosslinker system of blocked polyamines which is capable of reacting with 
the acetoacetate groups. Recently developed blocked polyamine crosslinkers 
for acetoacetate coatings are based upon benzaldimine chemistry. 
Publications describing acetoacetate chemistry as well as that associated 
with benzaldimine crosslinking systems are as follows: 
European Patent EP 0 552 469 discloses polyacetoacetate resins curable with 
a crosslinker comprising a multifunctional benzaldimine. In the background 
of EP '469, the patentees point out that U.S. Pat. No. 3,668,183 discloses 
the use of a blocked aldimine or ketimine generated by the reaction of 
polyamine and an aliphatic ketone or aliphatic aldehyde as a curative for 
polyacetoacetate resins to form polyenamine resins. The patentees of '469 
point out the aliphatic aldimine crosslinking system is moisture 
intolerant and that gloss and solvent resistance are not as high as 
desired. European '469 suggests the formation of a two component coating 
composition comprising a polymer containing a plurality of acetoacetate 
functional groups as a first component and a second component consisting 
of an aromatic aldimine having the structure: 
##STR1## 
where R.sub.1 is an aryl group, R.sub.2 is a hydrocarbon, a 
polyalkylether, an oligomeric adduct or an acrylic polymer which may 
contain at least one group, such as a secondary amine which will react 
with the acetoacetate groups, and n is greater than 2 unless another 
acetoacetate reactive group is present. Both solvent and water-borne 
coatings are prepared. 
An article by Kim, et al., Utilization of the Novel Acetoacetate Chemistry 
and Solvent and Water Borne Coatings, presented at the Water Borne, 
Higher-Solids and Powder Coating Symposium, Feb. 24-26, 1993, supplements 
European '469 EPO. Two component coating systems based upon acetoacetate 
functional polymers employing an aromatic aldimine as the crosslinker are 
described. Again, at least two aldimine groups or an aldimine and at least 
one other acetoacetate reactive group are present in the crosslinker. 
U.S. Pat. No. 5,288,804 is the U.S. companion to European '469 and to the 
article by Kim, et al.. It too, pertains to curable polyacetoacetate 
resins having low solvent loading using a multifunctional benzaldimine as 
the curing agent. 
U.S. Pat. No. 4,743,668 discloses vinyl polymers containing polymerized 
N-acetoacetylacrylamide units which are found useful for effecting 
coagulation, flocculation and dewatering of wet slurries. One of the 
monomer structures is represented by the formula: 
##STR2## 
wherein R is H or CH.sub.3. This monomer then is polymerized with a 
variety of other ethylenically unsaturated monomers, e.g., vinyl acetate, 
acrylic acid, acrylamide, vinylethers, maleic anhydride and so forth. 
Other monomers include acrylonitrile, various acrylic and methacrylic acid 
esters and the like. These polymers then are contacted with a bisulfite 
salt to form a sulfonate substituted material. 
U.S. Pat. No. 4,908,403 discloses the production of pressure sensitive 
adhesives from acetoacetoxy-alkylacrylate polymers by emulsion 
polymerization. The monomers are generally defined by the formula: 
##STR3## 
wherein R.sub.1 is a divalent organic radical and X is an organoacyl or 
cyano group. The monomer is polymerized with other ethylenically 
unsaturated monomers, e.g., vinyl esters of carboxylic acids which include 
vinyl acetate and vinyl propionate; alpha-beta-unsaturated hydrocarbons, 
such as ethylene and propylene, and other monomers, e.g., vinyl chloride 
and alkyl esters of acrylic and methacrylic acid, as well as acrylic and 
methacrylic acid. The resultant polymers have acceptable adhesive strength 
without crosslinkers such as N-methylolamides. 
In one effort (U.S. Pat. No. 5,214,086), a crosslinking system containing a 
hydroxyl functional resin, at least one isocyanate functional resin and a 
di- or multi-aldimine or ketimine functional moiety was described. The 
crosslinking occurred at either ambient temperature or a higher 
temperature, the aldimine being used to accelerate the cure rate of the 
hydroxyl-containing polymer with the polyisocyanate. 
U.S. Pat. No. 5,332,785 discloses liquid coating compositions comprising 
acetoacetate modified epoxy resins and blocked polyamines, e.g., 
aldimines. Hydroxyl-containing polyepoxides are converted to 
acetoacetate-modified resins through transesterification using alkylesters 
of acetoacetic acid. 
SUMMARY OF THE INVENTION 
This invention relates to improved crosslinking systems for polymeric 
dispersions having suitability for coatings, adhesives and use in many 
other applications. These dispersions are based upon crosslinkable 
polymers having a plurality of activated keto methylene groups, e.g., a 
beta diketone such as an acetoacetate or keto cyano methylene functional 
groups, and a crosslinkable component comprising an aldimine. In effecting 
crosslinking, a sufficient amount of the aldimine curing agent is used to 
effect reaction with the polymer containing the activated keto methylene 
groups and cure thereof. The improvement in the crosslinking system 
resides in the utilization of a monoaldimine having no other activated 
methylene reactive group present as a crosslinking agent. Another 
improvement variation to that previously suggested comprises a 
redispersible polymer(s) containing activated methylene functionality 
combined with the monoaldimine. 
The polymeric component can be in the form of a solution or as a dispersion 
in water. Examples of polymeric components include addition polymers 
formed by the polymerization of ethylenically unsaturated monomers, 
condensation polymers such as polyurethane, epoxy and polyester resins and 
combinations of condensation and addition polymers, e.g., 
polyurethane/acrylate hybrids. The crosslinker utilized is one having only 
one aldimine group and no other activated keto methylene reactive group. 
There are several advantages associated with these crosslinkable 
dispersions and these include: 
an ability to produce a low volatile organic content, formaldehyde- and 
isocyanate-free, crosslinkable polymeric dispersion and have excellent 
physical properties, e.g., solvent and water resistance; 
an ability to form clear solvent and water-borne dispersions which are 
curable at ambient and elevated temperatures; 
an ability to form solvent and water based premium hybrid urethane/acrylic 
coatings which are crosslinkable; 
an ability to produce a crosslinkable polymeric dispersion which has 
sufficient potlife and low viscosity to permit ease of processing; 
an ability to produce crosslinked polymers at reduced aldimine crosslinker 
levels; and, 
an ability to use monoaldimines of greater availability as compared to 
their multifunctional analogs. 
DETAILED DESCRIPTION OF THE INVENTION 
One of the components making up the polymeric dispersions or solutions 
having application in coatings, etc., is a solvent or water based 
dispersion comprising a polymeric component having pendant activated keto 
methylene functionality, preferably acetoacetate functionality. By 
activated it is meant that the proton(s) on the methylene group adjacent 
the carbonyl group is sufficiently reactive with the monoaldimine 
component to effect reaction and crosslinking. 
Two types of techniques have been generally utilized in preparing polymeric 
components having activated keto methylene functionality, particularly 
acetoacetate functionality. One technique involves the addition 
polymerization of a monomer having an activated keto methylene group, 
e.g., a monomer containing at least one acetoacetate group via solution, 
emulsion or suspension polymerization. (For purposes herein suspension 
polymerization is equivalent to and incorporated by reference within the 
term emulsion polymerization.) Another technique for preparing the 
polymeric component involves the solution or emulsion polymerization of 
monomers capable of forming polymers having pendant functional groups 
convertible to activated keto methylene groups. The use of hydroxyl 
functional monomers, e.g., hydroxy acrylates, is one way of forming these 
polymers. These hydroxyl groups then can be converted to activated keto 
methylene groups via transesterification. Transesterification can be 
effected by reacting an alkyl acetoacetate, e.g., t-butyl acetoacetate 
with the hydroxy functional polymer. Other monomers having functional 
groups convertible to hydroxyl groups, for example, allyl chloride can 
also be used as a monomer for forming the acetoacetate containing polymer. 
Broadly, the polymeric components useful herein are represented by the 
formulas: 
##STR4## 
wherein R is hydrogen or methyl, preferably hydrogen and R.sub.1 is 
C.sub.1-4 alkyl. 
Generally, the polymeric component described above containing the activated 
keto methylene group have polymerized unsaturation units as follows: 
##STR5## 
wherein R.sub.1 is C.sub.1-20 alkyl, C.sub.1-20 alkoxy, and hydroxyalkyl 
where the alkyl group has from 1-20 carbon atoms; R.sub.2 is C.sub.1-20 
alkyl, C.sub.1-20 alkoxy, and hydroxyalkyl where the alkyl group has from 
1-20 carbon atoms; and R.sub.3 is hydrogen or methyl. Preferably, the 
polymer is an acrylate-containing polymer having the general structure: 
##STR6## 
where R.sub.1 is pendent from an ethylenically unsaturated monomer capable 
of copolymerization with another monomer such as C.sub.1-8 alkyl esters of 
acrylic and methacrylic acid, styrene, vinyl chloride, vinyl acetate, 
ethylene, maleic and fumaric anhydride, butadiene, acrylonitrile, etc.; 
R.sub.2 is hydrogen, C.sub.1 -C.sub.20 alkyl, preferably C.sub.1-8 alkyl, 
C.sub.2-8 alkylene oxide, aryl; R.sub.3 is hydrogen or methyl, X=C.sub.1 
-C.sub.20 alkylene, preferably C.sub.1-4 alkyl, C.sub.2-4 alkylene oxide, 
arylene, secondary or tertiary alkylene amine; and Y is a unit having the 
structure: 
##STR7## 
m is 0-100, n is 1-100, p is 1-50. Preferably the alkyl functionality 
R.sub.2 has from 1-8 carbon atoms, X is C.sub.1-6.alkyleneoxy, m is 0-30, 
n is 40-50 and p is 5-40. 
Examples of preferred ethylenically unsaturated monomers are those having 
acetoacetate functionality. Specific examples include acetoacetoxyethyl 
methacrylate and N-acetoacetylacrylamide. 
The active keto methylene, e.g., acetoacetate-functional group generally 
comprises from about 10 to 80 weight percent of the total polymer. 
Preferably from about 20-60% of acetoacetate functionality based upon the 
total weight of the polymer is used. Generally, it takes a moderate amount 
of cross-linking to produce desired results, e.g., solvent and water 
resistance with modest flexibility. High levels of activated keto 
methylene functionality may reduce stability and one should consider the 
polymer system and degree of cross-linking desired. In addition these 
polymers should have a molecular weight of at least 2,000. Preferably, the 
molecular weight of the addition polymer will be from about 2,000 to 
15,000. 
Addition polymers generally are copolymers of the monomers having keto 
methylene functionality or groups convertible to acetoacetate 
functionality. The monomers containing activated methylene functionality 
can be reacted with other ethylenically unsaturated monomers containing 
reactive functional groups to form copolymers containing appropriate 
levels of keto methylene functionality. These monomers include 
epoxy-containing monomers and carboxylic acid-containing monomers. 
Representative epoxy-containing functional monomers are glycidyl acrylate, 
glycidyl methacrylate, N-glycidylacrylamide and allylglycidyl ether, while 
the carboxylic acid containing monomers include acrylic and methacrylic 
acid, crotonic and itaconic acid and anhydrides such as maleic anhydride, 
phthalic anhydride, itaconic anhydride, etc.. Carboxylic acid amides 
include acrylamide and N-methylol acrylamide, etc. 
The acetoacetate functional monomers also can be polymerized with a variety 
of ethylenically unsaturated monomers having limited to no reactive 
functionality. These monomers include C.sub.1 -C.sub.8 alkyl esters of 
acrylic and methacrylic acid, vinyl esters such as vinyl acetate and vinyl 
propionate, vinyl chloride, acrylonitrile, butadiene, styrene, etc. 
Preferred ethylenically unsaturated monomers copolymerizable with the 
monomers containing activated keto methylene functionality include alkyl 
(meth)acrylates and specifically methyl methacrylate, 2-ethylhexyl 
acrylate and butyl acrylate. 
Dispersions of condensation polymers containing acetoacetate functionality 
also are known and can also be used in forming the first polymeric 
dispersions. These systems can be derived from polyurethanes, polyepoxides 
and polyesters having pendent hydroxyl groups. Generally, they will have a 
molecular weight of from 1,000 to 200,000 and will contain from 25 to 50% 
acetoacetate by weight of the total polymer. Water dispersible 
polyurethane condensation polymers can be prepared by reacting 
polyisocyanates with polyhydric compounds incorporating functionality 
suited for effecting dispersibility in water or through the use of 
surfactants. Examples of polyisocyanates include the aromatic, aliphatic, 
and cycloaliphatic isocyanates, such as toluenediisocyanate, 
m-phenylenediisocyanate, isophoronediisocyanate, methylene 
di(phenylisocyanate) and methylene-di(cyclohexylisocyanate). Polyhydric 
compounds suited for reaction with the polyisocyanates to form the 
polyurethanes typically include both short-chain or long-chain polyols. 
Examples of short-chain polyols are the lower aliphatic C.sub.1-6 
aliphatic glycols, such as ethylene glycol, butanediol, hexanediol, 
glycerine, trimethylolpropane and pentaerythritol. Long-chain polyols can 
be used for preparing polyurethane prepolymers and these include 
poly(tetramethylene glycol) and polyethylene and polypropylene oxide 
adducts of ethylene glycol, propylene glycol, butanediol, etc. Molecular 
weights of these long chain polyols range typically from about 300 to 
3000. 
Polyepoxide resin dispersions containing pendant hydroxyl groups also are 
known and can be formed by the reaction of bridged phenols with 
epichlorohydrin. Typically, the bridging group is a propylidine or 
methylene group. Examples of polyepoxides include dispersions of a 
polyglycidyl or diglycidyl ether of polyhydric phenols such as bisphenol A 
and bisphenol F. Typically, they are in the form of adducts derived by 
reacting a polyamine with the epoxy group. Residual hydroxyls can be 
converted to acetoacetate containing polymers by transesterification of 
pendant hydroxyl groups with, e.g. t-butyl acetoacetate or diketene. A 
combination of condensation polymers can be formed into water borne 
dispersions and appropriate functionality applied thereto. Polyurethane 
resins can be combined with an epoxy component as for example as described 
in U.S. Pat. No. 4,772,643 which is incorporated by reference. 
A combination of condensation/addition polymerization methods can be used 
to form the polymeric component having acetoacetate functionality, e.g., a 
polyurethane/acrylate hybrid, one containing acetoacetate functionality. 
Because of the importance of polyurethane/acrylate hybrids, particularly 
in water-borne coating applications, such water based polymers are 
described further. 
Water dispersible polyurethane/acrylate hybrids are the preferred form of 
crosslinkable polymeric dispersions and this preparation is more fully 
described. In producing the water dispersible hybrids, the acrylate 
monomer containing the activated methylene functionality is addition 
polymerized onto the polyurethane prepolymer backbone. These polyurethanes 
typically incorporate acid functionality in order to enhance water 
dispersibility and water resistance. Acid functional compounds which may 
be used in the preparation of the anionic water-dispersible prepolymers 
include carboxy group containing diols and triols, for example 
dihydroxyalkanoic acids of the formula: 
##STR8## 
wherein R is hydrogen or a C.sub.1 -C.sub.10 alkyl group. The preferred 
carboxy-containing diol is 2,2-dimethylolpropionic acid. If desired, the 
carboxy-containing diol or triol may be incorporated into a polyester by 
reaction with a dicarboxylic acid before being incorporated into the 
prepolymer. Useful acid group containing compounds include aminocarboxylic 
acids, for example lysine, cystine and 3,5-diaminobenzoic acid. 
The anionic water-dispersible isocyanate-terminated polyurethane prepolymer 
may be prepared in conventional manner by reacting a stoichiometric excess 
of the organic polyisocyanate with the polymeric polyol and any other 
required isocyanate-reactive compounds under substantially anhydrous 
conditions at a temperature between about 30.degree. C. and 130.degree. C. 
until the reaction between the isocyanate groups and the hydroxyl groups 
is substantially complete. A polyisocyanate and the active hydrogen 
containing components are suitably reacted in such proportions that the 
ratio of number of isocyanate groups to the number of hydroxyl groups is 
in the range from about 1.1:1 to about 6:1, preferably within the range of 
from 1.5:1 to 3:1. If desired, tin catalysts may be used to assist 
prepolymer formation. 
To disperse the prepolymer in water, a tertiary amine is added to the 
mixture in an amount sufficient to quaternize the carboxylic acid groups 
therein and to render the prepolymer water dispersible. Typically this is 
at a level of 65-100% amine equivalents per carboxyl equivalent. Tertiary 
amines that may be used in the practice of the invention are relatively 
volatile so that they evaporate from the coating upon curing. Examples of 
suitable amines are represented by the formula: 
##STR9## 
where R, R.sub.1 and R.sub.2 are independently C.sub.1 -C.sub.6, 
preferably C.sub.2 -C.sub.4 alkyl groups. Illustrative of such tertiary 
amines are trimethylamine, triethylamine, tri-n-butylamine, 
tricyclohexylamine, dimethylethylamine, and methyldiethylamine. To enhance 
the compatibility of the organic and aqueous phases, a small quantity of a 
polar organic liquid such as N-methylpyrrolidone can be added in amounts 
ranging from 1 to 12 wt %, preferably 3 to 6 wt %, of the final polymer 
dispersion. The prepolymer may be dispersed in water using techniques well 
known in the art. Preferably, the prepolymer is added to the water with 
agitation, or, alternatively, water may be stirred into the mixture. 
To increase the molecular weight of the polyurethane, optionally a chain 
extender containing active hydrogen atoms is added. The active 
hydrogen-containing chain extender which is reacted with the prepolymer is 
suitably a polyol, an amino alcohol, ammonia, a primary or a secondary 
aliphatic, alicyclic, aromatic, araliphatic or heterocyclic amine, 
especially a diamine. The amount of chain extender employed should be 
approximately equivalent to the free isocyanate groups in the prepolymer, 
the ratio of active hydrogens in the chain extender to isocyanate groups 
in the prepolymer preferably being in the range from 0.7 to 1.3:1. Of 
course when water is employed as the chain extender, these ratios will not 
be applicable since the water, functioning as both a chain extender and 
dispersing medium, will be present in a gross excess relative to the free 
isocyanate groups. 
Examples of suitable chain extenders include polyethylene polyamines such 
as ethylenediamine, diethylenetriamine, triethylenetetramine, 
propylenediamine, isobutylenediamine, hexamethylenediamine, 
cyclohexylenediamine; polyoxyalkylene polyamines such as 
polyethyleneoxypolyamine and polypropyleneoxypolyamine, piperazine, 
2-methylpiperazine, phenylenediamine, toluenediamine, 
tris(2-aminoethyl)amine, 2,6-diaminopyridine, 
4,4'-methylenebis(2-chloraniline), 3,3'-dichloro-4,4'diphenyldiamine, 
4,4'-diaminodiphenyl methane, isophoronediamine, and adducts of 
diethylenetriamine. 
Solution and emulsion polymerization of the activated methylene group 
containing monomer to form crosslinkable polymeric dispersions and 
solutions can be effected by conventional procedures using a free radical 
polymerization catalyst. Examples of free radical generating catalysts 
include hydrogen peroxide, t-butylhydroperoxide and 
azobisisobutyronitrile. Conventional surfactants, emulsifiers and 
protective colloids may be utilized as stabilizer for the emulsion 
polymerization. By appropriate selection of stabilizer, one can alter the 
water sensitivity of the resulting polymer. Selection and adjustment of 
concentration are at the discretion of the formulator. With regard to the 
preparation of polyurethane/acrylate hybrids having acetoacetate 
functionality, a monomer containing acetoacetate functionality is 
polymerized onto the polyacrylic backbone. Polymerization is effected in 
conventional manner generally using an oil soluble initiator. 
Alternatively, another method for forming self-crosslinking polymeric 
dispersions is through redispersion of polymers containing acetoacetate 
functionality. These polymers typically are formed through emulsion 
polymerization followed by spray drying. Reemulsification can be effected 
by adding the polymer(s) singly or in combination to water and agitating. 
Optionally, a surfactant, e.g., ethoxylated nonyl phenol or protective 
colloids such as polyvinyl alcohol and hydroxy ethyl cellulose can be 
added to the aqueous medium to facilitate redispersion. Examples of 
redispersible powders are spray dried emulsions of vinyl acetate, vinyl 
acetate/acrylic; vinyl acetate-ethylene, vinyl acetate-styrene/maleic 
anhydride polymers, etc. The polyvinyl acetate may be partially hydrolyzed 
to convert the acetate groups to hydroxyl groups which then can be 
converted to acetoacetate groups via transesterification. 
Polyurethane, polyurethane/polyacrylate, or polyurethane/polyester hybrid 
solution polymers can be prepared by the following general method. In this 
method, one needs to functionalize the isocyanate functional urethane 
oligomer or polymers. This can be accomplished by capping NCO terminated 
urethanes with acetoacetate functional hydroxyl moieties, such as: 
monoacetoacetylated ethylene glycol, diacetoacetylated 1,1,1 
-tris(hydroxylmethyl)ethane, and triacetoacetylated pentaerythritol. The 
functionalized hydroxyl moieties are reacted then with an NCO terminated 
urethane to give acetoacetylated urethanes. 
The aldimine crosslinkers used in effecting crosslinking of the polymers 
containing activated methylene functionality are formed by reacting a 
multitude of aromatic aldehydes or heterocyclic aldehydes with a 
monofunctional aliphatic, aromatic or heterocyclic primary amine. These 
aldehydes may be reacted in conventional manner with the amine 
functionality to form the aldimine complex. Representative aromatic and 
heterocyclic aldehydes are represented by the structures: 
##STR10## 
wherein Y represents hydrogen or methyl. Of course, isomers of the above 
are included within the above structures. Open bonds represent hydrogen or 
a substituent such as a (C.sub.1-6) alkyl group, C.sub.1-6 alkoxy, halogen 
acetamide sulfonyl, cyano, hydroxyl, trifluoromethyl, amine where the 
hydrogen atoms have been replaced by organo groups and nitro groups. Such 
groups are characterized in the fact that they do not interfere with the 
formation of the aldimine or react with the activated keto methylene group 
present in the polymer. Specific aldehydes include benzaldehydes and 
substituted derivatives, e.g., C.sub.1-6 alkyl and alkoxy substituted 
derivatives such as methyl and methoxy benzaldehyde, halogenated 
benzaldehydes, etc. and bridged and fused aromatic aldehydes such as 
napthaldehyde. Heterocylic aldehydes include furfural, 
thiophenecarboxaldehyde, pyrrolecarboxyaldehyde, pyridinecarboxaldehyde, 
etc. For preferred results 3-pyridinecarboxaldimine is one of the 
preferred aldehydes to be employed for forming the monoaldimine structure. 
A wide variety of monoprimary amines may be used in preparing the 
monoaldimine crosslinking agent. The amines play little role in the 
crosslinking reaction and are liberated on cure. Primary amines include 
aliphatic, cycloaliphatic, aromatic, and heterocyclic amines. These amines 
also include substituted amines so long as they do not have a group 
reactive with the acetoacetate group. Such amines include alkyl amines 
hydroxyalkylamines and hydroxyalkyletheramines. Typically, the alkyl 
portions of such amines will have from 1-8 carbon atoms. Specific examples 
of suitable amines include methylamine, ethylamine, n and i-propylamine, 
n, i and t,-butylamine, ethoxyethylamine dimethoxyethylamine, 
ethoxyethanolamine, hydroxyethylpiperazine, cyclohexylamine, aniline and 
so forth. 
By and large the amines used in preparing the aldimine do not participate 
materially in the reaction. Thus, the rate and performance of the 
resulting crosslinked polymer is not affected by the amine. The rate of 
crosslinking is influenced more by the aldehyde used in forming the 
aldimine; the extent of cure is controlled by the crosslink density. 
Surprisingly, the heterocyclic aldimines, for example, are faster reacting 
than the benzaldehydes. 
Broadly, then,, the aldimines suited for practicing the process are 
represented by the structures: 
##STR11## 
wherein, R is C.sub.1-10 aliphatic, alkylene oxide (C.sub.1-10), aryl, or 
a substituted derivative. Open bonds represent hydrogen or a substituent 
such as a (C.sub.1-6) alkyl group, C.sub.1-6 alkoxy, halogen acetamide 
sulfonyl, cyano, hydroxyl, trifluoromethyl, amine where the hydrogen atoms 
have been replaced by organo groups and nitro groups which do not 
interfere with the formation of the aldimine or react with the activated 
keto methylene group present in the polymer. The key is that the 
substituent have no other acetoacetate reactive group; the monoaldimine is 
the only reactive group. 
The polymeric dispersion having keto methylene functionality and the 
monoaldimine then are blended to form the crosslinkable polymeric 
dispersion. The polymeric dispersions typically will contain about 10 to 
60% polymer or solids, preferably 45 to 60% by weight. The polymeric 
dispersion and monoaldimine are blended in a ratio such that there is 
sufficient monoaldimine present to effect reaction and cure with the 
polymer containing activated keto methylene groups, e.g., acetoacetate 
groups contained in the dispersion. Generally, the stoichiometry is such 
that from about 0.1 to 10 moles activated keto methylene group containing 
two protons per mole of monoaldimine is employed. Preferably, the 
stoichiometry is from 0.25 to 1.5 moles activated methylene group per mole 
of monoaldimine. Aldimine levels slightly above stoichiometric are 
preferred to insure crosslinking. The second proton on the acetoacetate is 
relatively unreactive as is a hydrocarbyl group, e.g., an active methylene 
containing a methyl group and the stoichiometry is adjusted accordingly. 
Without meaning to limit the scope of this invention, the crosslinking 
mechanism is proposed to be as follows: 
##STR12## 
In the above described mechanism NH.sub.2 R represents the amine portion of 
the aldimine. If a polyaldimine were used to effect crosslinking, R could 
possibly include the amine and residual aldimine moiety. The most striking 
difference between aldimine crosslinking options proposed herein and the 
previous art is that this invention recognizes that a monoaldimine 
functionality is necessary to achieve crosslinking. Through this 
recognition one can reduce the level of crosslinking agent added to the 
polymeric dispersion for cure. To execute crosslinking, a mixture of the 
polymer, which can be either in solution or in emulsion form, and 
monoaldimine is cast and cured within a time period ranging from one day 
to three weeks, depending upon the composition of the polymers and 
structure of the aldimine. 
The following examples are intended to represent various embodiments of the 
invention and are not intended to limit the scope. The examples are set 
forth in the following sequence: aromatic monoaldimine synthesis, polymer 
containing acetoacetate syntheses, and coating property evaluations of 
polymer crosslinked with aromatic aldimine. Another series involves 
heterocyclic monoaldimine synthesis, gel time to determine reaction rate, 
polymer synthesis and coating property evaluations of polymer crosslinked 
with heterocyclic aldimine. 
The following examples are provided to illustrate various embodiments of 
the invention and are not intended to restrict the scope thereof.

AROMATIC MONOALDIMINE SYNTHESIS 
EXAMPLE 1 
Preparation of Benzylidene i-Propylamine 
To a three neck round bottom flask, equipped with a cold water condenser, 
30 g of water and 26.5 g of benzaldehyde were added. The mixture was mixed 
using a magnetic stirrer for 3 minutes at room temperature. i-Propylamine 
(17.7 g) was added to the reaction flask in one portion, followed by 
vigorous stirring for 40 minutes. The agitation was stopped and the 
reaction mixture was allowed to stand for at least 15 minutes. The lower 
aqueous layer was separated from the reaction mixture. The upper layer was 
collected and dried over magnesium sulfate to give 38.9 g of product. This 
crude product could be further purified by distillation, collecting the 
fraction between 94.degree.-95.degree. C./18 mmHg. .sup.1 H NMR (300 Hz, 
CDCl.sub.3, ppm): 8.29 (1H, s), 7.70 (2H, m), 7.38 (3H, m), 3.53 (hep. 
J=6.3 Hz), 1.27 (9H, d, J=6.3 Hz); IR (NaCl film, cm.sup.-1): 3061, 3026, 
2930, 2835, 1647, 1581, 1450, 1382, 1306, 1141,967, 755, 693. 
EXAMPLE 2 
Preparation of Benzylidene Butylamine 
To a stirred mixture of 20 g of water and 21.2 g of benzaldehyde, 
butylamine (14.6 g) was added under an nitrogen atmosphere. After being 
stirred for 45 minutes at room temperature, the agitation was stopped and 
the reaction mixture was allowed to stand for at least 15 minutes. The 
lower aqueous layer was then separated from the reaction mixture. The 
upper layer was collected and dried over anhydrous magnesium sulfate to 
give 22.0 g of product. .sup.1 H NMR (300 Hz, CDCl.sub.3, ppm): 8.25 (1H, 
s), 7.69 (2H, m), 7.39 (3H, m), 3.60 (2H, t, J=7.0 Hz), 1.68 (2H, p, J=7.3 
Hz), 1.39 (2H, hex. J=7.7 Hz), 0.94 (3H, t, J=7.3 Hz)). 
EXAMPLE 3 
Preparation of Benzylidene t-Butylamine 
To a three neck round bottom flask, equipped with a cold water condenser, 
30 g of water and 26.5 g of benzaldehyde were added. The mixture was mixed 
with a magnetic stirrer at room temperature for 3 minutes. t-Butyl amine 
(22.1 g) was added to the reaction flask in one portion, followed by 
vigorous stirring for 15 hours. The agitation was stopped and the reaction 
mixture was allowed to stand for at least 15 minutes. The lower aqueous 
layer was separated from the reaction mixture. The upper layer was 
collected and dried over magnesium sulfate to give 35.5 g of product. 
.sup.1 H NMR (300 Hz, CDCl.sub.3, ppm): 8.29 (1H, s), 7.77 (2H, m), 7.40 
(3H, m), 1.33 (9H, s). 
EXAMPLE 4 
Preparation Benzylidene of 3-Hydroxypropylamine 
To a three neck round bottom flask, equipped with a cold water condenser, 
50 g of water and 25 g of benzaldehyde was added. All reactants were mixed 
with a magnetic stirrer at room temperature for 3 minutes. 
3-Amino-1-propanol (17.8 g) was added to the reaction flask in one 
portion, followed by vigorous stirring for 2.5 hours. The agitation was 
stopped and the reaction mixture was allowed to stand for at least 15 
minutes. The lower aqueous layer was separated and discarded. The upper 
layer was collected and washed with saturated sodium chloride solution. 
The organic layer was collected and dried over magnesium sulfate to give 
26.1 g of product. .sup.1 H NMR (300 Hz, CDCl.sub.3, ppm): 8.24 (1H, s), 
7.65 (2H, m), 7.40 (3H, m), 3.83 (2H, t, J=5.6 Hz), 3.77 (2H, t, J=6.1 
Hz), 1.92 (2H, p, J=5.6 Hz). 
EXAMPLE 5 
Preparation of Benzylidene 2,2-Dimethoxyethylamine 
To a three neck round bottom flask, equipped with a cold water condenser, 
20 g of water and 21.2 g of benzaldehyde were added. The reactants were 
mixed using a magnetic stirrer at room temperature for 3 minutes. 
Aminoacetaldehyde dimethyl acetal (21 g) was added to the reaction flask 
in one portion, followed by vigorous stirring for 2.5 hours. The agitation 
was stopped and the reaction mixture was allowed to stand for at least 15 
minutes. The lower aqueous layer was separated and discard. The upper 
layer was collected and washed with saturated sodium chloride solution. 
The organic layer was collected and dried over magnesium sulfate to give 
20.4 g of product. .sup.1 H NMR (300 Hz, CDCl.sub.3, ppm): 8.26 (1H, s), 
7.65 (2H, m), 7.40 (3H, m), 4.66 (1H, t, J=5.3 Hz), 3.77 (2H, d,d, J=5.3 
Hz, J=1.5 Hz), 3.39 (6H, s). 
EXAMPLE 6 
Preparation of Benzylidene 2-(2-Hydroxyethoxyl)ethylamine. 
A three neck round bottom flask, equipped with a gas inlet/outlet tube and 
a cold water condenser, was charged with 106 g (0.5 mol) of benzaldehyde, 
200 ml of tetrahydrofuran and 105 g (0.5 mol) of 2(2-aminoethoxy)ethanol 
in that sequence. The room temperature reaction was allowed to proceed 
under a nitrogen atmosphere for 18 hours. The solvent was then removed 
using a rotary evaporator and the residual was distilled at a reduced 
pressure (120.degree.-123 .degree. C./1 mmHg) to give a colorless liquid 
170.3 g (88%). .sup.1 H NMR (300 Hz, CDCl.sub.3, ppm): 8.24 (1H, s), 7.68 
(2H, m), 7.36 (3H, m), 3.75 (4H, m), 3.64 (2H, m), 3.57 (2H, m); IR (NaCl 
film, cm.sup.-1): 3384, 2863, 1646, 1451, 1127, 1067, 756, 694. 
POLYMER SYNTHESES 
EXAMPLE 7 
Preparation of Butyl acrylate/Methyl Methacrylate/2-Acetoacetoxyethyl 
Methacrylate Terpolymer 
A three neck round bottom flask was charged with 27.3 g of butyl acrylate, 
5.8 g of methyl methacrylate, 11.9 g of 2-acetoacetoxyethyl methacrylate, 
0.45 g of dodecanethiol and 45 g of propylene glycol methyl ether acetate. 
This mixture was heated to 80.degree. C. with vigorous mechanical 
stirring, under a nitrogen atmosphere. 2,2'-Azobis(2-methylbutanenitrile), 
0.23 g, was added in one portion to the reaction mixture and the reaction 
was stirred at that temperature for 22 hours. A clear solution of the 
terpolymer was obtained and used without further purification. The 
resulting polymer had 0.62 milliequivalents acetoacetate per gram of 
polymer. 
EXAMPLE 8 
Preparation of Butyl acrylate/Methyl Methacrylate 2-Acetoacetoxyethyl 
Methacrylate Terpolymer 
A three neck round bottom flask was charged with 15.3 g of butyl acrylate, 
7.9 g of methyl methacrylate, 17.7 g of 2-acetoacetoxyethyl methacrylate, 
and 49.5 g of propylene glycol methyl ether acetate. This mixture was 
heated to 80.degree. C. with vigorous mechanical stirring, under a 
nitrogen atmosphere. 2,2'-Azobis(2-methylbutanenitrile), 0.20 g, was added 
in one portion to the reaction mixture and the reaction was stirred at 
that temperature for 22 hours. A clear solution of the terpolymer was 
obtained and used without further purification. The resulting polymer had 
0.91 milliequivalents acetoacetate per gram of polymer. 
EXAMPLE 9 
Preparation of Butyl Acrylate/Methyl Methacrylate/2-Acetoacetoxyethyl 
Methacrylate Terpolymer. 
A three neck round bottom flask was charged with 8.4 g of butyl acrylate, 
7.6 g of methyl methacrylate, 24.3 g of 2-acetoacetoxyethyl methacrylate, 
1.3 g of dodecanethiol and 52 g of butyl acetate. This mixture was heated 
to 70.degree. C. with vigorous mechanical stirring, under a nitrogen 
atmosphere. 2,2'-Azobis(2-methylbutanenitrile), 0.62 g, was added in one 
portion to the reaction mixture and the reaction was stirred at that 
temperature for 22 hours. A clear solution of the terpolymer was obtained 
and used without further purification. The resulting polymer had 1.23 
milliequivalents acetoacetate per gram of polymer. 
EXAMPLE 10 
Preparation Of AAEM Containing Emulsion Polymer 
Into a clean, dry reactor equipped with heating, cooling, stirring and a 
nitrogen blanket capability was charged 96 g of polyester polyol 
[poly(neopentyl adipate) MW .about.2,000, followed by 87 g of methylene 
dicyclohexyl diisocyanate and 0.2 g of dibutyltin dilaurate. With 
agitation, the reaction mixture was brought to 94.degree. C. and held for 
0.5 hour. At this point, 25 g of N-methylpyrrolidone solvent was added 
followed by titration for % NCO (theoretical NCO equals 11.6%). When the 
NCO value was met, 14 g of dimethylolpropionic acid powder was added 
followed by 27 g of N-methylpyrrolidone and reaction maintained at 
94.degree. C. for 2.5 hours. 
The mixture was cooled to 25.degree. C. while adding 168 g of butyl 
methacrylate, then 30 g of acetoacetoxyethylmethacrylate followed by 0.9 g 
of hexanediol diacrylate. To the prepolymer-monomer solution at 25.degree. 
C. was added 11 of triethylamine with agitation to dissolve. 
A second reactor was charged with 502 of distilled water under a nitrogen 
blanket and held at 25.degree. C. The water was agitated and the 
prepolymer-monomer solution was added at a rate of 6.7% of the prepolymer 
solution per minute to form an aqueous dispersion. Catalyst VAZO 64 (AIBN 
from Dupont), 0.9 g in 8.4 of N-methylpyrrolidone, was slowly charged and 
mixed for 5 minutes. 
Ethylenediamine (10) was dissolved in 20 of water and added immediately 
after the initiator. The dispersion was heated to 60.degree.-65.degree. 
C., allowed to exotherm to 75.degree. C. during the course of 
polymerization and maintained until the residual monomers were less than 
1,000 ppm. 
The resulting aqueous polymer dispersion had a solid content of 43%, a pH 
of about 8 and a viscosity of 50 cps (with #2 spindle at 30 rpm on LTV). 
EXAMPLE 11 
Preparation of Triacetoacetylated Pentaerythritol 
A mixture of t-butyl acetoacetate (158 g) and pentaerythritol (45 g) was 
heated at 140.degree. C. in the presence of Ti(Oi-Pr).sub.4 (0.5 mL). The 
generated t-butanol was collected during the reaction. After one hour, the 
reaction was complete and a pale yellow (Gardner 1 ) viscous liquid was 
obtained (.about.96%). 
EXAMPLE 12 
Preparation of Acetoacetylate Terminated Polyurethane 
To a mixture of triacetoacetylated pentaerythritol of Example 10 (13.85 g) 
and a commercial isophoronedisocyanate--polyether NCO terminated 
polyurethane prepolymer having an equivalent weight of 500 and a 
functionality of 2.3 (20.0 g) in butyl acetate (22.6 g), was added T-12, a 
dibutyltin dilaurate catalyst (0.1 g). The mixture was heated to 
80.degree. C. and stirred at that temperature for 18 hours. By that time 
there were no NCO functional groups left in the reaction mixture 
(indicated by IR). This polymer was used for film casting without further 
purification. 
COATINGS PROPERTY EVALUATION 
In general the properties of coatings were determined by mixing terpolymer 
A (40% solid) and preselected aldimines at ambient temperature. Films 
(from this mixture) were cast on steel plates in such a way that the 
resulting dry films had a thickness of between 1.3.about.2.7 mils. Films 
were dried in a static air atmosphere at room temperature. Film solvent 
resistance properties were used as the criterion to determine the extent 
of crosslinking reaction in the system. The major solvent resistance 
properties tested were: 
1. ) Swell index, which is defined as 
##EQU1## 
(1) where W.sub.wet is the weight of a free film soaked in solvent for &gt;72 
hours and W.sub.cure is the weight of the cured film before soaking. 
(2). Soluble percentage, which is defined as 
##EQU2## 
where W.sub.baked is the weight of a film baked at 100.degree. C. in a 
vacuum oven for two hours. 
Ethyl acetate was used as the solvent for swell index and percentage 
soluble tests and ethyl acetate, toluene and/or methylethyl ketone were 
used for double rub resistance test. A swell index of below 2 is 
considered excellent. A percent insoluble fraction of below 20 and 
preferably below 10 is considered good. Double rub resistance values of 
100 or greater are considered good. 
EXAMPLE 13 
Films Prepared From AAEM Terpolymer and Benzylidene i-Propylamine 
An unpigmented coating composition was prepared with the acetoacetate 
containing acrylate terpolymer of Example 7 (A, 5.90 g) and the 
benzaldehyde/i-propylamine aldimine of Example 1 (B, 0.50 g). The 
stoichiometry was 1 mole equivalent acetoacetate (2 protons) per 
equivalent monoaldimine. The solvent resistance properties of the films 
are listed in Table 1. 
TABLE 1 
______________________________________ 
Double Rub Resistance 
Swell % (Ethyl 
Film Index Soluble acetate) 
(Toluene) 
______________________________________ 
A + B (3 week) 
1.0 10 &gt;200 179 
A (3 week) dissolved 
100 41 34 
______________________________________ 
These results show that the monoaldimine of Example 1 was effective as a 
crosslinker in that the double rub resistance of the coating formed from 
polymeric dispersion (A) and the monoaldimine (B) was much higher and the 
percent solubles lower than the non-crosslinked polymer (A) above. 
EXAMPLE 14 
Films Prepared From AAEM Terpolymer and Benzylidene Butylamine 
An unpigmented coating composition was prepared with the acetoacetate 
containing terpolymer of Example 7 (A, 5.90 g) and the 
benzaldehyde/butylamine benzaldimine of Example 2 (B, 0.54 g). The 
stoichiometry was 1 equivalent acetoacetate (2 protons) per equivalent 
aldimine. The solvent resistance properties of the films are listed in 
Table 2. 
TABLE 2 
______________________________________ 
Double Rub Resistance 
Swell % (Ethyl 
Film Index Soluble acetate) 
(Toluene) 
______________________________________ 
A + B (1 week) 
2.4 10 -- -- 
A + B (3 week) 
1.0 9 &gt;200 &gt;200 
A (3 week) dissolved 
100 41 34 
______________________________________ 
The results show that the crosslinked polymer, A+B, had less solubles and 
was more resistant to the double rub test than noncrosslinked terpolymer A 
above. 
EXAMPLE 15 
Films Prepared From AAEM Terpolymer and Benzylidene i-Propylamine 
An unpigmented coating composition was prepared with the acetoacetate 
containing terpolymer of Example 7 (A, 5.90 g) and the monobenzaldimine of 
Example 3 benzaldehyde (t-butylamine) (B, 0.54 g). The solvent resistance 
properties of the films are listed in Table 3. 
TABLE 3 
______________________________________ 
Double Rub Resistance 
Swell % (Ethyl 
Film Index Soluble acetate) 
(Toluene) 
______________________________________ 
A + B (1 week) 
2.7 10 -- -- 
A + B (3 week) 
1.0 11 &gt;200 &gt;166 
A (3 week) dissolved 
100 41 34 
______________________________________ 
As in the previous examples, the crosslinked polymer formed on cure with 
the monoaldimine was more resistant to solvent than the non-crosslinked 
terpolymer (A) above. 
EXAMPLE 16 
Films Prepared From AAEM Terpolymer and Benzylidene 3-Hydroxypropylamine 
An unpigmented coating composition was prepared with the acetoacetate 
containing terpolymer of Example 7 (A, 5.90 g) and the monobenzaldimine 
(benzaldehyde/hydroxypropylamine) of Example 4 (B, 0.55 g, one equivalent 
aldimine/2 protons). The solvent resistance properties of the films are 
listed in Table 4. 
TABLE 4 
______________________________________ 
Double Rub Resistance 
Swell % (Ethyl 
Film Index Soluble acetate) 
(Toluene) 
______________________________________ 
A + B (1 week) 
2.3 12 -- -- 
A + B (3 week) 
1.0 11 &gt;200 &gt;200 
A (3 week) dissolved 
100 41 34 
______________________________________ 
The results show an acceptable cure was achieved within one week with 
better solvent resistance at the 3-week cure. Again, the non-crosslinked 
polymer had poor solvent resistance. 
EXAMPLE 17 
Films Prepared From AAEM Terpolymer and Benzylidene i-Propylamine 
An unpigmented coating composition was prepared with the acetoacetate 
containing terpolymer of Example 8 (A, 7.00 g) and the monobenzaldimine of 
Example 1 (B, 1.00 g). The stoichiometry was 1 mole acetoacetate (2 
protons) per 1 mole aldimine. The solvent resistance properties of the 
films are listed in Table 5. 
TABLE 5 
__________________________________________________________________________ 
7 days cure 
1 day cure Double rub resistance 
Film 
Swell index 
% Soluble 
Swell index 
% Soluble 
(Ethyl acetate/Toluene) 
__________________________________________________________________________ 
A + B 
2.8 11 2.1 12 &gt;200/&gt;200 
A dissolved 
dissolved 
dissolved 
dissolved 
21/61 
__________________________________________________________________________ 
The results show the monobenzaldimine effected cure of the polymer rather 
quickly. 
EXAMPLE 18 
Films Prepared From AAEM Terpolymer and Benzylidene 
2-(2-Hydroxyethoxyl)ethylamine 
An unpigmented coating composition was prepared with the acetoacetate 
containing terpolymer of Example 8 (A, 4.00 g) and the 
benzaldehyde/2-(2-hydroxyethyl)ethylamine aldimine of Example 6 (B.sub.1, 
0.35 g or B.sub.2, 0.70 g). Films were allowed to stand at ambient 
temperature for 5 days. The solvent resistance properties of the films are 
listed in Table 6. 
TABLE 6 
______________________________________ 
Swell % Double Rub Resistance 
Film Index Soluble (Ethyl acetate) 
(Toluene) 
______________________________________ 
A + B.sub.1 
1.5 7 &gt;200 &gt;200 
A + B.sub.2 
1.7 16 &gt;200 &gt;200 
A dissolved 100 21 61 
______________________________________ 
The hydroxyethyl aldimine of Example 6 was effective in producing resulted 
in crosslinked systems. Double rub resistance was excellent. Films cast 
with the theoretical stoichiometry exhibited substantially lower percent 
solubles and slightly lower swell index. 
EXAMPLE 19 
Films Prepared From AAEM Containing Emulsion Polymer 
An unpigmented coating composition was prepared with the AAEM containing 
urethane/acrylate emulsion polymer of Example 10 (4.0) and the benzylidene 
i-propylamine of Example 1 (0.082 g). After mixing the two components and 
allowing the system to settle down for about 5-10 minutes, a very good 
dispersion system was obtained. Films cast with this emulsion were allowed 
to stand at ambient temperature for 2 days. The solvent resistance 
properties of the films are listed in Table 7. 
TABLE 7 
______________________________________ 
[AAEM]/[Aldimine] 
EtOH Rub MEK Rub 
______________________________________ 
2:1 54 &gt;200 
1:1 45 &gt;200 
1:0 34 69 
______________________________________ 
The film performance showed that with the addition of aldimine, the 
methylethylketone resistance property of the films was significantly 
improved, although the resistance to ethanol only marginally improved, 
compared to the film which was not cured with the aldimine. 
To summarize, the results of Examples 13-19 show all of the monoaldimines 
were effective in crosslinking the polymer containing acetoacetate groups. 
Little difference between the various amines used to form the benzaldimine 
was noticed in performance. 
HETEROCYCLIC MONOALDIMINE SYNTHESES 
EXAMPLE 20 
Preparation of N-i-propylfurfurylidene 
To a three neck round bottom flask equipped with a cold water condenser 
were added 38.4 g of furfural, 50 g of toluene and 28.0 g of 
i-propylamine, in that order. The mixture was mixed with vigorous stirring 
for 12 hours. The agitation was stopped and the reaction mixture was 
allowed to stand for at least 15 minutes. The lower aqueous layer was 
separated from the reaction mixture. The upper layer was collected, washed 
with brine and dried over magnesium sulfate. After the drying agent was 
removed from the mixture, the toluene was removed on a rotary evaporator. 
The residual was distilled under reduced pressure. The fraction at 
81.degree.-82.degree. C./26 mmHg was collected to give 59.2 g of colorless 
product. 
EXAMPLE 21 
Preparation of 2-Thiophenylidene i-Propylamine 
The same procedure as that of Example 16 was employed. 
2-Thiophenecarboxaldehyde, 22.4 g, and 13 g of i-propylamine in 20 ml of 
toluene gave the desired product (30.4 g, almost quantitative). 
EXAMPLE 22 
Preparation of 3-Thiophenylidene i-Propylamine 
The same procedure as that of Example 16 was employed. 
3-thiophenecarboxaldehyde, 10.0 g, and 5.5 g of i-propylamine in 10 ml of 
toluene gave 14.5 g of the desired product. 
EXAMPLE 23 
Preparation of N-Methyl-2-Pyrrolidene i-Propylamine 
To a three neck round bottom flask, equipped with a cold water condenser 
were added 21.8 g of 1-methyl-2-pyrrolecarboxaldehyde, 13 g of 
i-propylamine and 20 ml of toluene. The reaction mixture was stirred at 
70.degree. C. for three hours to give a cloudy solution. The agitation was 
stopped and the reaction mixture was allowed to stand for at least 15 
minutes. The upper layer was collected and washed with saturated sodium 
chloride solution. The organic layer was collected and dried over 
magnesium sulfate. Solvent was removed using a rotary evaporator to give 
29.3 g of crude product containing 84% of the desired aldimine and 16% of 
the starting material (aldehyde). 
EXAMPLE 24 
Preparation of 2-Pyrrolidene i-Propylamine 
The same procedure as that of Example 16 was employed. 
2-pyrrolecarboxaldehyde, 2.85 g, and 1.82 g of i-propylamine in 10 ml of 
toluene gave 3.90 g of the desired product. 
EXAMPLE 25 
Preparation of 2-Pyridylidene i-Propylamine 
The same procedure as that of Example 16 was employed. 
2-pyridinecarboxaldehyde, 3.21 g, and 1.82 g of i-propylamine in 10 ml of 
toluene gave 4.50 g of the desired product. 
EXAMPLE 26 
Preparation of 3-Pyridinylidene i-Propylamine 
The same procedure as that of Example 16 was employed. 
3-pyridinecarboxaldehyde, 3.21 g, and 1.82 g of i-propylamine in 10 ml of 
toluene gave 4.60 g of the desired product. 
COATINGS EVALUATION 
EXAMPLE 27 
Reaction Rate Measurement Between Aldimine and Acetoacetate Group 
Reaction rate measurements for benzaldimine and several heterocyclic 
aldimines with acetoacetate functionality were obtained using model 
systems. This was accomplished by adding the respective aldimine to 
t-butyl acetoacetate in a ratio of 1 mole acetoacetate to 1 mole aldimine 
in tetrahydrofuran at 25.degree. C. The concentration of the reactants was 
measured by GC and the reaction rate determined therefrom. The results are 
shown in Table 7. 
TABLE 7 
______________________________________ 
Aldimine Rate Constant (relative) 
______________________________________ 
5-Nitrothiophene-2-carboxaldimine 
1 
Benzaldimine 3 
Thiophene-2-carboxaldimine 
11 
3-Pyridinecarboxaldimine 
16 
Thiophene-3-carboxaldimine 
29 
N-Methylpyrrole-2-carboxaldimine 
38 
2-Pyridinecarboxaldimine 
73 
2-Furfuraldimine 134 
Pyrrole-2-carboxaldimine 
194 
______________________________________ 
Measurement of the reaction rates of furfuraldimine with t-butyl 
acetoacetate at different temperatures to obtain an Arrhenius relationship 
leads to the prediction that at 47.degree. C., benzaldimine will react 
with acetoacetate functionality at the same rate as that of furfuraldimine 
at 25.degree. C. 
EXAMPLE 28 
Gel Time 
To further confirm the fast reaction of acetoacetate with heterocyclic 
aldimines vis-a-vis benzaldimine, gel time measurements were made. This 
was accomplished by mixing an acetoacetate functional polymer, namely, 
(2-acetoacetoxyethyl methacrylate/methyl methacrylate/butylacrylate 
(50:24:26) with one equivalent of the benzaldimine 
(benzylidene-i-propylamine); gelation occurs after about two hours. When 
the same polymer was mixed with furfuraldimine, gelation occurred in only 
about ten minutes. 
EXAMPLE 29 
Comparison with Polyaldimine Crosslinker 
A comparison of the monaldimine of Example 16 and conventional 
polyaldimines crosslinkers in an acrylic polymer containing 40% of 
acetoacetoxyethyl methacrylate by weight was made. The aldimines tested 
were monobenzaldimine (BENAL), and two dialdimines, 
benzaldehyde/ethylenediamine (EDAL) and hexamethylenedialdimine (HMDAL). 
Table 8 sets forth the results. 
TABLE 8 
______________________________________ 
No crosslinker 
BENAL EDAL HMDAL 
______________________________________ 
MEK Rubs 5 90 30 60 
______________________________________ 
The results show that the monobenzaldimine was highly effective in 
achieving a crosslinked polymer as evidenced by the higher number of 
solvent rubs with methylethyl ketone (MEK) when compared to the results 
for the two dialdimines. 
EXAMPLE 30 
Performance Characteristics of Heterocyclic Aldimines 
The purpose of this example is to provide a comparison in the performance 
between the fast reacting heterocyclic aldimines in their cure of an AAEM 
polyacrylate polymer. An unpigmented coating composition was prepared from 
the acetoacetate containing terpolymer of Example 8 and several of the 
heterocyclic aldimines evaluated in Example 27. The same polymer without 
crosslinker is listed to provide a comparative basis with a noncrosslinked 
polymer. The results are shown in Table 9. 
TABLE 9 
__________________________________________________________________________ 
Solvent 
Solvent 
Swell 
Gloss Pendulum 
Rub Rub Index 
% Soluble 
Rate 
Film 
20.degree./60.degree./85.degree. 
Hardness 
(ETOH) 
(MEK) 
(EA) (EA) Const. 
__________________________________________________________________________ 
A 105/119/99 
71 50 10 -- -- 38 
B 110/129/99 
131 &gt;200 &gt;200 1.1 14 29 
C 114/134/99 
84 &gt;200 50 -- -- 194 
D 107/123/99 
155 &gt;200 &gt;200 1.1 16 73 
E 106/123/99 
141 &gt;200 &gt;200 1.1 17 16 
F 117/134/98 
93 &gt;200 60 1.6 17 134 
G 103/125/98 
16 15 13 dissolved 
100 -- 
__________________________________________________________________________ 
A: 60% AAEM containing polyacrylate:Nmethylpyrrole 2 carboxaldimine (mole 
ratio 100/75) 
B: 60% AAEM containing polyacrylate:3thiophene carboxaldimine (100/75) 
C: 60% AAEM containing polyacrylate:pyrrole2-carboxaldimine (100/75) 
D: 60% AAEM containing polyacrylate:pyridine2-carboxaldimine (100/75) 
E.: 60% AAEM containing polyacrylate:pyridine3-carboxaldimine (100/75) 
F: 60% AAEM containing polyacrylate:furfuraldimine (100/75) 
G: 60% AAEM containing polyacrylate only 
From the above table it can be seen that hard, glossy coatings can be 
obtained with the AAEM containing polyacrylate and monoaldimine 
crosslinking agents. Solvent resistance of the coatings is significantly 
improved compared to film G which does not contain monoaldimine, with some 
exhibiting excellent resistance to both ethanol and methylethyl ketone. At 
this point it is not fully understood why some of the crosslinked systems 
did not cure to a fuller extent. For example, film A showed that cure was 
partial, at best. Such result is not fully understood and it is possible 
that it is not representative. 
EXAMPLE 31 
Films Prepared From Acetoacetylated Urethane Oligomers 
An unpigmented coating composition was prepared from the acetoacetylate 
terminated polyurethane of Example 12 (4.16 g) and the 
3-pyridinecarboxaldimine of Example 26 (0.47 g). Film properties were 
tested after one week. The solvent resistance and the Pendulum hardness of 
the film are listed in Table 10. 
TABLE 10 
______________________________________ 
EtOH Toluene 
Gloss (20.degree./60.degree./85.degree.) 
Hardness MEK Rub Rub Rub 
______________________________________ 
105/122/98 68 -90 -100 -70 
______________________________________