Polyfunctional amine crosslinker, process for making same, and compositions containing same

A sterically unhindered, trifunctional primary amine is provided. This compound is useful as a crosslinking agent for a composition containing an amine-reactive polymer. Also provided is a low temperature cure composition containing the amine-reactive polymer and the trifunctional primary amine, and a crosslinked coating obtained by curing such a composition. Additionally, there is provided a process of synthesizing the novel trifunctional primary amine.

TECHNICAL FIELD 
This invention relates to low temperature curing thermoset resins. More 
particularly, this invention relates to a novel crosslinking agent for an 
amine-reactive polymer, to a process for synthesizing the crosslinking 
agent, to a composition containing the crosslinking agent, and to a 
crosslinked coating formed from the composition. 
BACKGROUND ART 
The reaction of maleic diesters with certain diamines is known, as 
illustrated by the work of Yu. T. Tanckuk and I. A. Ral'chuk, J. Organic 
Chem. U.S.S.R., Vol. 14, pp. 2083-2088 (1978). In this work, the reported 
reaction products are a polyamide that retains the maleic acid double 
bond, an addition product in which each amine group of the diamine has 
added by Michael reaction to the double bond of a maleic diester, and a 
maleic diester derivative in which one of the ester groups has been 
replaced by an amide group (an amic ester). 
Low temperature cure coating compositions based on amine-reactive polymers, 
as illustrated by U.S. patent application Ser. No. 346,329, filed Feb. 5, 
1982, and now abandoned, and U.S. patent application Ser. No. 377,504, 
filed May 12, 1982, now U.S. Pat. No. 4,446,280, are known to me. These 
coating compositions are based upon solvent borne, solution polymers 
containing activated ester groups. In Ser. No. 377,504, the polymer 
thereof is crosslinked by the use of an amine-terminated triazine resin, 
to give a film with good resistance properties. However, the coatings are 
often rather brittle. In Ser. No. 346,329, the crosslinking agent may be a 
long chain diamine such as 4,7-dioxo-1,10-decanediamine (DODA) or a 
shorter aliphatic diamine such as 1,6-hexanediamine. Flexibility can be 
obtained by using a long chain diamine such as DODA, but at the expense of 
hardness. In fact, it is difficult to prepare films with a Knoop hardness 
over 3 when using DODA. Moreover, when a shorter aliphatic diamine is 
used, it is difficult to obtain an acceptable crosslink density. The six 
carbon chain of 1,6-hexanediamine is too short to provide efficient 
utilization of the activated ester groups. Therefore, there has existed an 
urgent need for a crosslinking agent that makes possible low temperature 
cure, that yields a hard yet flexible film having good resistance 
properties, and that provides efficient utilization of the amine-reactive 
groups of the crosslinkable polymer. Hence, the provision of such a 
crosslinking agent and of compositions based thereon useful, for example, 
for coatings and adhesive applications, would constitute a significant 
advance in the art. 
SUMMARY OF THE INVENTION 
It is accordingly one object of the present invention to provide a 
crosslinking agent that makes possible low temperature cure, that yields a 
hard yet flexible film having good resistance properties, and that 
provides efficient utilization of the amine-reactive groups of a 
crosslinkable polymer. 
A further object is to provide a composition based on such a crosslinking 
agent. 
A still further object is to provide a crosslinked coating obtained by 
curing this composition. 
An even further object is to provide a process for synthesizing the 
crosslinking agent. 
Additional objects, advantages and novel features of the invention will be 
set forth in the description which follows, and in part will become 
apparent to those skilled in the art upon examination of the following or 
may be learned by practice of the invention. 
To achieve the foregoing objects and in accordance with the purpose of the 
present invention, as embodied and broadly described herein, there is 
provided a novel crosslinking agent. This crosslinking agent is a 
sterically unhindered, trifunctional primary amine of the formula 
##STR1## 
in which n=4-8. Also provided is a process for making the crosslinking 
agent that includes the steps of (a) reacting an unsaturated diester of 
the formula 
##STR2## 
in which R is an alkyl of 1-4 carbon atoms, with a diamine of the formula 
EQU NH.sub.2 (CH.sub.2).sub.n NH.sub.2 
in which n=4-8, and (b) recovering the trifunctional amine. The reaction is 
carried out at a temperature sufficient to remove ROH byproduct by 
distillation, and the diamine/diester molar ratio is at least about 3:1. 
Also provided is a low temperature cure composition containing an 
amine-reactive polymer, and the crosslinking agent described above. The 
crosslinking agent is present in an amount sufficient to form a 
crosslinked polymer. The presence of the crosslinking agent in the 
composition makes possible low temperature cure, results in a hard yet 
flexible film having good resistance properties, and provides efficient 
utilization of the amine-reactive groups of the crosslinkable polymer. 
Also provided by the present invention is a crosslinked coating obtained 
by curing this composition. 
DETAILED DESCRIPTION 
In the present invention, crosslinking utilizes the reaction between a 
polymer bearing amine-reactive groups and a crosslinking agent containing 
primary amine groups. This reaction takes place under low temperature 
conditions. I have unexpectedly found that the inclusion of an amide 
functionality in the middle of a long chain polyamine provides harder 
films while retaining flexibility. More complete conversion of the 
amine-reactive groups is made possible by the presence of at least 12, 
preferably at least 16, carbon and/or nitrogen atoms in the linking chains 
between primary amine groups. 
The novel crosslinking agent of this invention is a sterically unhindered, 
trifunctional primary amine of the formula 
##STR3## 
in which n=4-8. The preferred trifunctional primary amine is 
N,N'-bis(6-aminohexyl)-2-[(6-aminohexyl)amino]butanediamide, in which n in 
the above formula is 6. 
The trifunctional amine can be used as a crosslinking agent for an 
amine-reactive polymer such as in epoxy systems. The polymer is curable by 
reaction with a crosslinking agent having a plurality of primary amine 
groups. Applications of the resulting composition include coatings and 
adhesives. Conveniently, the amine-reactive polymer contains repeating 
units derived from an activated ester-containing vinyl monomer of the 
formula 
##STR4## 
in which the R.sup.1 group is selected from H and Me, the R.sup.2 group is 
selected from alkyls of 1-6 carbon atoms, cycloalkyls of 5-6 carbon atoms, 
and 2-hydroxyalkyls of 2-6 carbon atoms, and the R.sup.3 group is selected 
from alkyls of 1-6 carbon atoms, cycloalkyls of 5-6 carbon atoms, and 
2-hydroxyalkyls of 2-6 carbon atoms. Suitable vinyl monomers include 
methyl acrylamidoglycolate methyl ether (MAGME), ethyl acrylamidoglycolate 
ethyl ether, butyl acrylamidoglycolate butyl ether, methyl 
acrylamidoglycolate ethyl ether and ethyl acrylamidoglycolate methyl 
ether, with MAGME being preferred. 
These vinyl monomers are suitably formed by the procedures set forth in 
U.S. patent application Ser. No. 346,329, which is discussed earlier, the 
relevant portions of the disclosure of which are hereby incorporated by 
reference into this description. Additionally, attention is invited to two 
illustrative procedures set forth later in this description of the present 
invention. 
The activated ester group-containing polymer may contain repeating units 
derived from one or more copolymerizable ethylenically unsaturated 
monomers. Useful comonomers include, but are not limited to, C.sub.1 
-C.sub.18, preferably C.sub.1 -C.sub.8, alkyl esters of acrylic acid, 
C.sub.1 -C.sub.18, preferably C.sub.1 -C.sub.8, alkyl esters of 
methacrylic acid, hydroxy-containing monomers such as hydroxyethyl 
acrylate, hydroxypropyl acrylate, hydroxyethyl methacrylate and 
hydroxypropyl methacrylate, styrene, alpha-methyl styrene, acrylonitrile, 
acrylamide, acrylic acid, methacrylic acid and vinyl acetate. 
The polymer containing activated ester groups may be polymerized, or more 
preferably copolymerized with these other monomers, according to 
conventional polymerization techniques. No special precautions are 
required. However, for viscosity control in solution polymers, a hydrogen 
bonding solvent should be included in the polymerization solvent mixture. 
Procedures for forming solvent borne, solution polymers are set forth in 
U.S. patent application Ser. No. 377,504, now U.S. Pat. No. 4,446,280, 
which is discussed earlier, and the relevant portions of the description 
of this patent application are hereby incorporated by reference into this 
description. Attention is also invited to the illustrative polymerization 
procedures set forth below in the description of the present invention. 
The amount of the trifunctional amine used in a composition containing a 
primary amine-reactive polymer, may vary widely and is generally 
determined by a number of factors such as the extent of crosslinking 
desired and the particular reactants employed. In any event, the 
crosslinker is used in a sufficient amount to form a crosslinked polymer. 
Generally, the functional groups of the amine crosslinker in the 
composition will range from about 0.5 to 10 equivalents based on the 
primary amine-reactive functionality of the polymer employed. Preferably, 
about 0.8 to 1.2 equivalents of the primary amine groups are used. 
When the composition is based upon an activated ester group-containing 
polymer, the polymer should contain from about 2-35 weight percent of 
repeating units derived from the activated ester-containing vinyl monomer. 
In the case of a solvent borne, solution polymer, optimum properties are 
obtained when about 20-35 weight percent of the repeating units are 
derived from this monomer. 
A later invention of which I am aware is disclosed and claimed in copending 
application U.S. Ser. No. 529,237 filed Sept. 6, 1983, in the names of D. 
A. Ley and H. Burkhard, now U.S. Pat. No. 4,522,973, relates to a low 
temperature crosslinkable emulsion containing an emulsified polymer 
bearing activated ester groups. In the activated ester-containing vinyl 
monomer thereof, R.sup.1 is H or methyl, and the R.sup.2 and R.sup.3 
groups are independently selected from alkyls of 1-4 carbon atoms. For 
these emulsions, it is preferred that the polymer contain about 2-10 
weight percent of repeating units derived from the activated 
ester-containing vinyl monomer thereof. Except for these distinctions, the 
disclosure set forth above pertains to this type of low temperature 
crosslinkable composition. 
The crosslinkable, amine-reactive polymer used in the present invention, is 
cured by reaction with the trifunctional primary amine, at low 
temperature. By "low temperature" is meant from about ambient temperature 
up to and including about 50.degree. C., and, in certain instances, up to 
and including about 100.degree. C. When MAGME is used as the activated 
ester-containing vinyl monomer, crosslinking can occur at room 
temperature. When higher alkyl esters are used, such as the butyl ester, 
heating is required to obtain the crosslinked film. 
The composition of the present invention is readily cured by exposure to an 
appropriate low temperature for an adequate period of time. The speed of 
curing depends upon factors including the particular temperature at which 
curing is carried out, the components forming the composition, and the 
presence or absence of an accelerator. 
The composition may contain such other ingredients as are customarily 
employed in coating compositions. Such ingredients include pigments, and 
flow additives and modifiers. Compositions of the present invention based 
upon solvent borne, solution polymers bearing activated ester groups, are 
useful as general purpose coatings, as well as coatings in automotive, 
wood, decorative, textile and paper applications. 
The novel crosslinking agent of the present invention is synthesized by 
heating an unsaturated diester of the formula 
##STR5## 
in which R is an alkyl of 1-4 carbon atoms, with a diamine of the formula 
EQU NH.sub.2 (CH.sub.2).sub.n NH.sub.2 
in which n=4-8, and collecting an alcohol such as methanol in the case 
where R is methyl, as the byproduct. The diester is an ester of either 
maleic or fumaric acid, with a convenient diester being dimethyl maleate. 
The preferred diamine is 1,6-hexanediamine. 
The amount of heat applied to the reaction vessel is selected to give a pot 
temperature at which distillation of the alcohol byproduct occurs. The 
reactants are combined in a molar ratio of at least about 3:1 
(diamine:diester). A molar ratio of about 3:1 is convenient. If a molar 
ratio of more than about 3:1 is used, typically the molar ratio will be 
only slightly more than 3:1, with about 5:1 being a practical upper limit 
because of difficulty in removing the unreacted excess of diamine. 
Conveniently, the reaction is a solventless reaction, i.e., no solvent is 
added to the reactants, the reactants are mixed with stirring during the 
course of the reaction, and the reaction is carried out under ambient 
atmosphere. The reaction is continued until no more alcohol byproduct is 
evolved. The desired product is recovered, for example, by pouring the 
reaction mixture into a large excess of toluene, and separating as the 
product, the material that is insoluble in toluene and more dense than 
toluene. 
A later invention of which I am aware, which is disclosed and claimed in 
copending application U.S. Ser. No. 529,233, filed Sept. 6, 1983, now U.S. 
Pat. No. 4,495,366, in the names of D. A. Ley and H. Burkhard, relates to 
an improved process for forming the trifunctional amine. This process is 
illustrated as follows: 
Dimethyl maleate (72 g, 0.5 moles) is added over a 2-3 hour period to a 
solution of 1,6-hexanediamine (174 g, 1.5 moles) in toluene (360 g) at 
75.degree.-80.degree. C. The reaction temperature rises from 80.degree. to 
110.degree. C. under reflux conditions. After the addition is completed, 
methanol is distilled at a reaction temperature of 120.degree.-125.degree. 
C. Additional toluene (320 g) is added to maintain reaction volume. The 
reaction may be followed by amine titration or by disappearance of the 
methyl ester in the .sup.1 H NMR spectrum. After the reaction is complete, 
toluene is removed under vacuum (50.degree.-70.degree. C., 15-20 mm Hg) to 
give N,N'-bis(6-aminohexyl)-2-[(6-aminohexyl)amino]butanediamide as a 
viscous liquid which solidifies on standing. 
In the illustrative procedures which follow, all parts and percentages are 
by weight unless otherwise specified.

EXAMPLE 1 
A reaction vessel containing dimethyl maleate (43.2 g, 0.3 moles) and 
hexamethylenediamine (175 g, 1.5 moles) is heated under ambient atmosphere 
with stirring, so as to remove by distillation, methanol as the byproduct. 
After 90 minutes, the pot temperature increases to 170.degree. C., and the 
reaction is terminated since no more methanol byproduct is being evolved. 
The reaction mixture is poured into a large excess of toluene, and a 
product is separated that is insoluble in toluene and more dense than 
toluene. IR and NMR spectra are consistent with the desired 
N,N'-bis(6-aminohexyl)-2-[(6-aminohexyl)amino]butanediamide structure. The 
product yield is 50.0 g. The product is insoluble is toluene, 
chlorobenzene and carbon tetrachloride, and soluble in methylene 
dichloride, cellosolve, methanol, chloroform and water. 
EXAMPLE 2 
A reaction vessel containing dimethyl maleate (72 g, 0.5 moles) and 
hexamethylenediamine (197 g, 1.7 moles) is heated under ambient 
atmosphere, and methanol is collected as the byproduct of the reaction. 
The reaction is continued for 3 hours 35 minutes by which time the pot 
temperature has increased to 170.degree. C. The reaction mixture is 
extracted with approximately 1000 ml toluene using approximately 200 ml 
portions. The toluene is separated, and the remaining product is dissolved 
in methylene dichloride and filtered through a medium glass filter. The 
yield is 76%. 
Preparation of Methyl Acrylamidoglycolate Methyl Ether (MAGME) 
To a three-necked flask equipped with a stirrer and an extractor filled 
with a molecular sieve drying agent is added 300 parts acrylamidoglycolic 
acid, 3000 parts parts methanol, 0.05 parts phenothiazine, 4.5 parts 98% 
sulfuric acid and 200 parts chloroform. The mixture is heated to reflux 
and the distillate is allowed to pass through the extractor for 61/2 
hours. The mixture is cooled and allowed to stand for 16 hours at which 
point the mixture is warmed to about 40.degree. C., 19 g of sodium 
carbonate is added, and the solution is stirred for 21/2 hours. The 
mixture is filtered and vacuum stripped of solvent. The solid residue is 
extracted with chloroform. Diethyl ether is added to the extract and a 
polymeric mass precipitates which is discarded. The remaining extract is 
stripped of solvent to yield 264.2 parts of crude MAGME. 
Preparation of Butyl Acrylamidoglycolate Butyl Ether 
One hundred parts of acrylamidoglycolic acid, 517 parts butanol, 1 part 
conc. sulfuric acid and 0.1 part monomethyl ether of hydroquinone are 
mixed in a flask equipped with a Dean Stark water trap and a stirrer. The 
mixture is heated until homogeneous. After 5-10 minutes, 100 ml of toluene 
is added and the mixture is brought to reflux and held 5 hours until the 
theoretical amount of water is collected by azeotrope. The toluene and 
excess butanol are removed under vacuum to yield 173 parts of the crude 
product. 
Preparation of Polymer A 
Methyl acrylamidoglycolate methyl ether (33.2 parts) is dissolved in 59.8 
parts absolute ethanol and 89.6 parts toluene. To this are added 66.4 
parts butyl acrylate, 42.6 parts methyl methacrylate, 16.6 parts styrene, 
4.2 parts acrylic acid, 1.7 parts n-dodecyl mercaptan, and 3.3 parts 
t-butylperoxyisobutyrate. Toluene (10 parts) and 6.6 parts ethanol are 
placed in a flask and heated to 82.degree. C. under a N.sub.2 purge. The 
monomer mixture is slowly added over a 6.5 hour period. The reaction 
mixture is held at 82.degree. C. for an additional 12 hours. 
The polymer has the following characteristics: clear yellow color, dish 
solids (2 hrs. at 105.degree. C.) 52.9%, non-volatiles, theoretical Tg of 
polymer, 16.degree. C. 
Preparation of Polymer B 
The procedure used for Polymer A is again followed except that the 
reactants are as follows: 
______________________________________ 
methyl acrylamidoglycolate methyl ether 
34.0 parts 
butyl acrylate 53.1 parts 
methyl methacrylate 49.7 parts 
styrene 28.9 parts 
acrylic acid 4.3 parts 
n-dodecyl mercaptan 1.7 parts 
t-butylperoxyisobutyrate 3.4 parts 
abs. ethanol 68.0 parts 
toluene 102.0 parts 
______________________________________ 
The resulting polymer is a clear yellow liquid, dish solids of 52.5%, and a 
theoretical Tg of 30.degree. C. 
Preparation of Polymer C 
Polymer C is prepared by in situ formation of high and low Tg polymer 
fractions. 
______________________________________ 
Parts by Weight 
Component Charge 1 Charge 2 
______________________________________ 
abs. ethanol 20.4 47.6 
toluene 30.6 71.4 
methyl acrylamidoglycolate methyl ether 
12.8 29.8 
butyl acrylate 27.8 24.4 
methyl methacrylate 4.6 21.4 
styrene 4.6 40.5 
acrylic acid 1.3 3.0 
n-dodecyl mercaptan 0.1 1.2 
t-butyl peroctoate 0.2 2.4 
______________________________________ 
Charge 1 is placed in a flask and heated to 82.degree. C. under a N.sub.2 
purge. A slight exotherm is noticed. The solution is held at 82.degree. C. 
for 4 hrs. Charge 2 is slowly added over a 3 hr. period. The reaction 
mixture is held an additional 12 hrs. at 82.degree. C. The polymer has the 
following characteristics: clear yellow solution, dish solids 52.0%, 
Brookfield viscosity, 1700 centipoises. 
EXAMPLE 3 
1.6 Parts of N,N'-bis(6-aminohexyl)-2-[(6-aminohexyl)amino]butanediamide in 
1.2 parts of toluene is blended with 20 parts of Polymer A, and 0.2 parts 
2-hydroxypyridine in 1.0 part ethanol is added as catalyst. The mixture is 
cast into films on pretreated aluminum panels and cured at the 
temperatures shown in the Table. A 20 minute cure time is used for 
100.degree. C., and a 14 day cure time is used at room temperature. 
Properties are given in the Table. 
EXAMPLE 4 
The procedure of Example 3 is followed except that Polymer B is used. 
Properties are set forth in the Table. 
EXAMPLE 5 
The procedure of Example 3 is followed except that 3.4 parts of the amine 
crosslinker is added to 20 parts of Polymer C. Properties are given in the 
Table. 
COMATIVE EXAMPLES 1-3 
The procedures of Examples 3-5 are followed except that an amine terminated 
triazine resin (equivalent weight=262) in methyl cellosolve.RTM. (50% 
solids) is used as a crosslinker. This resin is obtained according to the 
procedures set forth in U.S. patent application Ser. No. 377,504, filed 
May 12, 1982, the relevant portions of which are hereby incorporated by 
reference into this description. In this regard, the resin is obtained by 
either melt condensation of the aminotriazine compound with the amine in 
the presence of an acid catalyst at temperatures of 120.degree. to 
250.degree. C. or by reaction of the chloride (such as cyanuric chloride) 
with the amine in the presence of an acid scavenger. Examples are given in 
U.S. Pat. No. 2,393,755 and in E. M. Smolin and L. Rapport, "s-Triazine 
and Derivatives" in "The Chemistry of Heterocyclic compounds, a series of 
Monographs", A. Weissberger, Editor, Interscience Publishers, Inc., New 
York, 1959. Properties of the three films obtained are given in the Table. 
TABLE 
__________________________________________________________________________ 
Film Properties Using N,N'.about.bis(6-aminohexyl)-2-[(6-aminohexyl)amino] 
butanediamide 
or an Amine-Terminated Triazine Resin as the Crosslinking Agent 
Poly- 
Cure 
Solvent 
Hard- 
Humidity 
Water Impact Resistance.sup. .circle.5 
1 
mer Temp. 
Resistance.sup. .circle.1 
ness.sup. .circle.2 
Resistance.sup. .circle.3 
Resistance.sup. .circle.4 
Front 
Reverse 
Flexibility.sup. 
.circle.6 
__________________________________________________________________________ 
Example 3 
A RT 200+ 1.5 &gt;240 &gt;340 25 25 Pass 
100 200+ 4.3 &gt;240 &gt;340 25 25 Pass 
Example 4 
B RT 200+ 3.4 &gt;240 &gt;340 25 15 Pass 
100 200+ 8.8 &gt;240 &gt;340 &lt;20 5 Pass 
Example 5 
C RT 200+ 2.7 &gt;240 &gt;340 25 10 Pass 
100 200+ 9.0 &gt;240 &gt;340 20 &lt;10 Pass 
Comparative 
A RT 200+ 1.8 24 5 &lt;5 &lt;3 Pass 
Example 1 100 200+ 5.3 &gt;240 &gt;340 &lt;5 &lt;3 Pass 
Comparative 
B RT 200+ 9.2 &gt;240 5 &lt;5 &lt;3 Fail 
Example 2 100 200+ 11.8 
&gt;240 &gt;340 &lt;10 &lt;3 Fail 
Comparative 
C RT 200+ 11.5 
1 24 &lt;5 &lt;3 Fail 
Example 3 100 200+ 14.4 
&gt;240 24 &lt;10 &lt;3 Fail 
__________________________________________________________________________ 
.sup. .circle.1 Methyl ethyl ketone double rubs required to remove 50% of 
film 
.sup. .circle.2 Knoop Hardness 
.sup. .circle.3 38.degree. C. Cleveland .RTM. Humidity Resistance, hours 
to show an effect on the film 
.sup. .circle.4 40.degree. C. Water Immersion, hours to show an effect on 
the film 
.sup. .circle.5 InchPounds Required to cause failure 
.sup. .circle.6 Conical Mandril 
The above examples are illustrative of my invention. It is to be understood 
that these examples are not in any way to be interpreted as limiting the 
scope of the invention. Rather, it is intended that the scope of the 
invention be defined by the claims set forth below. 
When the low temperature cure composition of the present invention is based 
upon an activated ester group-containing polymer, the speed of cure 
provided by my novel trifunctional amine will in certain cases be 
substantially faster than the speed of cure of a diamine such as 
1,6-hexanediamine. Furthermore, in this embodiment of my low temperature 
cure composition, the solution polymer contains from about 1 to 100 wt. % 
of the repeating units derived from the activated ester group-containing 
vinyl monomer.