Flexibilizing epoxy resins with low molecular weight acrylate copolymers

Flexible epoxy resins are made by curing the epoxy with an amine curing agent in the presence of a low molecular weight acrylate copolymer made from a major amount of a lower aliphatic ester or amide of acrylic or methacrylic acid and a minor amount of an ethylenically unsaturated monomer having functionality reactive with functional groups present in the epoxy resin or its curing agent. The acrylate copolymer has a number average molecular weight in the range of 1000 to 6000, preferably 2000 to 3000, and a ratio of weight average to number average molecular weight in the range of 1 to 3.5. Copolymers of butylacrylate and acrylic acid or maleic anhydride are favored. Further advantages are realized by including in the cure formulation a monofunctional diluent reactive with the curative.

FIELD OF THE INVENTION 
This invention relates to a method of making flexible epoxy resins using 
low molecular weight acrylate copolymers. In another aspect it relates to 
a cured epoxy resin which has been formulated with a low molecular weight 
acrylate copolymer as a flexibilizer. 
BACKGROUND OF THE INVENTION 
Polymeric epoxy resins have been widely used as coatings in both industrial 
and civil engineering applications because they can be made to adhere well 
to a substrate and provide good protection from moisture and chemicals. 
For some uses, however, such as in coatings for concrete structures, it 
has been difficult to develop resins having sufficient flexibility and 
elongation to withstand impact and cover shrinkage-induced cracks. 
Additives to the resin formulations or structural modifications of the 
polymer to improve elongation properties frequently result in loss of 
moisture and chemical resistance or compatibility problems which adversely 
affect strength and appearance. 
One of the earliest methods of improving flexibility in epoxy resins was 
the addition of coal tar or similar material to the formulation. More, 
recently the use of long chain modifiers or flexibilizers in the form of 
resins, curatives or reactive materials has been favored, partially 
because of concerns about the carcinogenicity of coal tar materials. 
Changes in epoxy resin properties have been effected by increasing the 
aliphatic character of the resin, lowering its crosslink density through 
election of curative or modifier, and by adding flexibilizers. 
U.S. Pat. No. 3,567,677, Donaetz et al. (1971) discusses the need to 
improve the flexibility of epoxy potting compounds and addresses the 
problem by formulating diglycidyl ether of bisphenol A with diepoxide of 
polyglycol using a curative such as N-aminoethylpiperazine or its adduct 
with allylglycidyl ether. 
U.S. Pat. No. 5,098,780, Nemunaitis et al. (1992) discusses the need for 
crack-bridging properties in concrete coatings and sets forth a solution 
by formulating an epoxy base coat having 50 to 400 percent elongation 
using a flexibilizing agent, e.g. a phenol blocked isocyanate. The 
curatives are modified cycloaliphatic amines and aliphatic polyamines. 
U.S. Pat. No. 4,521,490, Pocius et al. (1985) and U.S. Pat. No. 4,524,181, 
Adam et al. (1985) describe reducing brittleness in epoxy resins by 
incorporating colloidally dispersed elastomeric particles, such as 
polymers of hexyl acrylate, formed by in-situ polymerization. The '181 
patent describes adding a stabilizer which is partially soluble in the 
epoxy resin and partially soluble in the elastomeric particles. 
Canadian Patent No. 1,216,385, Kim (1987) discloses epoxy adhesive modified 
by in-situ polymerization with the epoxy resin of an alkyl acrylate, such 
as butyl acrylate, and a grafting agent such as an ethylenically 
unsaturated carboxylic acid, for example, acrylic acid. U.S. Pat. No. 
4,565,853, Herscovici et al. (1986) improves on this approach by adding a 
chain transfer agent, such as bromotrichloromethane, to allow for higher 
amounts of rubber to be present with less chance of gelation. Both of 
these approaches, however, suffer from the necessity of workers handling 
volatile and toxic acrylate monomers during the preparation of the cured 
epoxy. In addition, the in-situ polymerization method suffers from a lack 
of control of the polymer Mw when compared to polymer prepared in a plant 
prior to incorporation into the cured epoxy. 
Ochi and Bell, J. Applied Polymer Science, 29, pp 1381-1391 (1984) report a 
study of the effect of functionality of a n-butylacrylate/acrylic acid 
copolymer when reacted with an epoxy resin before curing on the impact 
strength of the epoxy product. The copolymers studied were of moderate 
molecular weight (M.sub.n of 6070 to 7570; M.sub.w of 31,700 to 40,600 by 
GPC) and served to increase the toughness of the epoxy resin with an 
optimum functionality. The copolymer prepared by bulk polymerization was 
first reacted with the epoxy resin in the presence of a catalyst for the 
epoxy-carboxyl reaction, proceeding until practically no carboxyl groups 
remained, and then the modified epoxy resin was cured with an amine curing 
agent, methylenedianiline. 
U.S. Pat. No. 5,334,654, Starher et al. (1994) discloses increasing 
elasticity of epoxy resins with an acrylate terminated urethane prepolymer 
and a monofunctional aliphatic ether or ester amine-reactive component, 
such as an aliphatic glycidyl ether or ester or a C.sub.1 to C18 alkyl 
ester of acrylic or methacrylic acid. 
SUMMARY OF THE INVENTION 
It has been found that low molecular weight acrylate copolymers having 
functionality reactive with functional groups present in the epoxy resin 
or its curative can be added to the curing formulation of the epoxy resin 
to provide a flexible resin. In this way epoxy resins exhibiting 
elongation values on the order of 20 to 200 percent can be obtained. The 
acrylate copolymers are formed by copolymerizing a major amount of a lower 
aliphatic ester or amide of acrylic or methacrylic acid with a minor 
amount of an ethylenically unsaturated monomer containing the functional 
groups required in the copolymer. This copolymerization is carried out in 
such a way that the copolymer has a number average molecular weight 
(M.sub.n) of 1000 to 6000 daltons, preferably in the range of 2000 to 
3000, and typically a ratio of weight average to number average molecular 
weight (M.sub.w /M.sub.n) in the range of 1 to 3.5. Curing the uncured 
epoxy resin with an amine curing agent in carried out in the presence of a 
flexibilizing amount of the functional acrylate copolymer. 
It is further advantageous to carry out the curing step in the presence of 
an amine-reactive monofunctional diluent in an amount sufficient to reduce 
the crosslink density in the cured epoxy resin. This is the monofunctional 
diluent disclosed by Starher et al. in the '654 patent cited above. 
DETAILED DESCRIPTION OF THE INVENTION 
The epoxy resins which are formulated and cured according to the invention 
are polyepoxides having a 1,2-epoxy equivalence greater than one. A number 
of examples of suitable epoxy resins are given by Lee and Neville, 
Handbook of Epoxy Resins, McGraw-Hill, New York, 1967. The preferred 
polyepoxides are polyglycidylethers, particularly polyglycidylethers of 
bisphenol A. Other useful epoxy resins include 1,4-butanediol diepoxide as 
well as cycloaliphatic polyepoxides which are prepared by epoxidation of 
cyclic olefins. The preferred epoxy resin or resin mixture has an epoxide 
equivalent weight (EEW) in the range of 150 to 2500, and in the case of 
hisphenol A resins, it is particularly convenient to use a resin having an 
EEW of 150 to 250, and preferably 190, which allows the resin to be in the 
liquid form. Liquid resins are preferred for formulation according to the 
invention since curing can occur without formation of volatile organic 
compounds which raise environmental and safety concerns. 
The epoxy resin is generally present in the curable formulation in from 20 
to 80 percent, preferably 25 to 75 percent based on the total weight of 
the cured product, depending upon the specific use intended. The specific 
amine compound selected as the curative depends upon the desired 
flexibility of the cured product and the nature of other additives in the 
composition, such as added flexibilizers or reactive diluents. The 
functionality of the amine curing agent is determined by the number of 
active hydrogen atoms present in the curative, and the specific curative 
chosen will determine the level of flexibilizer and monofunctional diluent 
needed to obtain a given elongation in the cured epoxy resin. Generally, 
as the functionality of the curative is lowered, the amount of added 
flexibilizer or reactive diluent can also be lowered to maintain a desired 
percent elongation. In this way one can obtain better control of the epoxy 
resin properties. To obtain higher elongations, one can decrease the 
curative functionality and increase the level of added flexibilizer and/or 
reactive diluent. 
Any aliphatic or cycloaliphatic amine compound known to be an epoxy 
curative can be used in practicing this invention, but preferred curatives 
include 1-(2-aminoethyl)piperazine (AEP) and bis(p-aminocyclohexyl)methane 
(M). Especially preferred are the alkylated diamines made by reductive 
alkylation of alkylene diamines with aldehydes or ketones of moderate 
chain length, as disclosed in the copending patent application cross 
referenced above. Favored among such curing agents are the monoalkylated 
adducts of 2-methyl-1,5-pentanediamine and methyl isobutyl ketone, 
acetophenone, benzaldehyde, 2-ethylhexanal, or 2-tridecanone. These 
adducts can be prepared by reductive alkylation in the liquid phase under 
hydrogen pressure and at elevated temperature using conventional 
hydrogenation catalysts, such as palladium or rhodium on carbon. The 
catalyst is filtered out and the adducts recovered by fractional 
distillation. 
The acrylate copolymers used as epoxy resin flexibilizers according to our 
invention are low molecular weight poly(acrylate) compositions in which 
esters or amides of acrylic or methacrylic acid make up the major 
component with the minor component being epoxy, amine or alcohol reactive, 
ethylenically unsaturated comohomers. By "low molecular weight" is meant 
having a number average molecular weight (M.sub.n) in the range of 1000 to 
6000 daltons, preferably 2000 to 3000 daltons, and a weight average to 
number average ratio of molecular weights (M.sub.w /M.sub.n) in the range 
of 1 to 3.5. Acrylate modifiers which are higher or lower in molecular 
weight than indicated result in decreased performance and compatibility. 
Also, acrylate flexibilizers which are higher in molecular weight than 
indicated will increase formulation viscosity making mixing more difficult 
and may result in phase separation prior to epoxy curing which is not 
desired. 
The term "acrylate copolymer" as used herein is meant to include both 
esters and amides of acrylic or methacrylic acid. Examples of acrylic acid 
esters and amides which can be used to make the acrylate copolymer include 
lower aliphatic esters and amides, preferably C.sub.1 to C.sub.7 alkyl 
acrylates and methacrylates, such as ethylacrylate, n-butylacrylate, 
n-hexylacrylate, 2-methyl-n-hexylacrylate, and the like, acrylamide and 
methacrylamide, C.sub.1 to C.sub.7 alkyl acrylamides and methacrylamides, 
N-vinylformamide, polyether esters of acrylic acid and methacrylic acid, 
hydroxyl and tertiary amine functional esters of acrylic acid and 
methacrylic acid such as 2-(N,N-diethylamino) ethyl(meth)acrylate, 
triethylene glycolmono(meth)acrylate monomethyl ether, diethylene 
glycolmono(meth)acrylate monomethyl ether, hydroxypropyl(meth) acrylate, 
and the like. Mixtures of monomers can also be used to form the base 
monomer package. In such mixtures, any desirable termonomer, such as 
styrene, alpha-methyl styrene, vinyl esters, dialkyl maleates, and the 
like, can be included in minor amounts. The most preferred monomers are 
the lower alkyl acrylates and more specifically, the C.sub.2 to C.sub.6 
alkyl acrylates. By this it is meant alkyl esters or amides in which the 
alkyl group has 2 to 6 carbons. In general, however, any combination of 
such monomers which produces a copolymer with a T.sub.g less than about 
25.degree. C. can be used. 
The comonomer used in forming the acrylate flexibilizer is an ethylenically 
unsaturated monomer which has epoxy or amine or alcohol reactive 
functional groups. Examples of such functional groups include carboxylic 
acid groups, carboxylic anhydride, isocyanato, hydroxyl, epoxy, siloxyl, 
halogen, and the like. Examples of hydroxyl group containing monomers 
include hydroxyethyl acrylate and methacrylate and hydroxybutylacrylate. 
Examples of acid containing functional monomers include acrylic and 
methacrylic acid, maleic acid, crotonic acid, itaconic acid, and the like. 
Examples of anhydride group containing monomers include maleic anhydride 
and analogous compounds. Examples of other possible comonomers include 
trimethoxysilylpropylmethacrylate, chloroethylacrylate, glycidyl acrylate 
and methacrylate, isocyanatoethylmethacrylate, chloromethylstyrene, and 
the like. The preferred functional comohomers are acrylic acid and maleic 
anhydride. The preferred amount of functional comohomer in the 
flexibilizer is from 1 to 15 percent, most preferably 3 to 12 percent by 
weight of the acrylate copolymer. It is also preferred that the alkyl 
acrylate make up the balance of the copolymer. Polymerization methods for 
such copolymers are well known in the art. 
In addition to the flexibilizing copolymer, a reactive diluent can be 
included in the epoxy cure formulation. These diluents can be 
monofunctional epoxy or acrylate compounds as described in U.S. Pat. No. 
5,334,654 of Starner et al., cited above. Broadly, the reactive diluent 
can be any compatible amine-reactive monofunctional material since its 
function in the curing step is to react with the curative and, being 
monofunctional, reduce crosslink density. Generally this compound is 
aliphatic in character, having a substituent which is reactive with amine 
hydrogen. Preferably such a diluent is a monofunctional epoxide, such as a 
C.sub.12 to C.sub.14 alkyl glycidyl ether, or a monofunctional acrylate, 
such as 2-ethylhexylacrylate. Other monofunctional glycidyl ethers or 
acrylates or methacrylates, such as those disclosed by Starner et al., can 
also be used to dilute the crosslinking potential of the epoxy resin. 
The relative amounts of polyepoxy compound, monofunctional diluent and 
flexibilizer can vary broadly, depending upon the specific compounds 
selected, and Generally follow recipes well known in the art, for example 
as set forth in the Starher et al. patent. As a Guide, one can expect to 
use about 50 to 100 parts by weight of polyepoxy compound, 0 to 50 parts 
of reactive diluent, and 40 to 400 parts of flexibilizer per 100 parts of 
the epoxy resin/diluent components. The amount of curative is generally 
the stoichiometric quantity, more or less, required to react with the 
amine hydrogen reactive functions present in the formulation. This is in 
accordance with standard epoxy resin recipes. Also, the curing procedure 
can follow any of a number of methods known in the art for epoxies 
involving mixing and curing at ambient or elevated temperatures. 
The combination of the curative with the flexibilizing acrylate copolymer 
and a reactive monofunctional diluent in epoxy resin formulations provides 
a very potent tool for tailoring epoxy resin properties to suit a given 
use. The flexibilizing agent supplies a resin segment which assists in 
developing the desired elongation property, while the amine curative and 
reactive diluent combine to control crosslink density in the cured epoxy 
resin.

In order to illustrate further the invention and its advantages, the 
following Examples are Given, the specific nature of which should not be 
construed to limit the invention unduly. 
EXAMPLES 1-7 
These Examples illustrate the preparation of the acrylate copolymer. 
Diluent, either 800 g of isopropanol (IP) or 400 g of tetrahydrofuran 
(THF) were charged to a 2000 mL three-neck round bottomed flask equipped 
with a mechanical stirrer, condenser, nitrogen line and thermometer. After 
purging for 10 to 15 minutes, butylacrylate (BA) and either acrylic acid 
(AA), acrolein (An) or maleic anhydride (MA) in the weight ratios Given in 
Table 1 were added followed by azobisisobutyronitrile (AIBN) initiator and 
dodecyl mercaptan (DDM) at the levels indicated in Table 1. Table 1 also 
shows the solids level for each run based on the monomers used. The 
reaction mixture was then heated to reflux with mechanical stirring using 
an oil bath. As the mixture approached reflux temperature, heating was 
discontinued until the initial exotherm dissipated, then heating was 
resumed such that reflux was continued for seven hours. After cooling, the 
reaction mixture was evaporated in vacuo and dried for 16 hours at 
74.degree. C. to leave a clear, colorless or slightly yellow viscous 
liquid in about 95 percent yield. The number and weight average molecular 
weights were determined by GPC for each copolymer and are reported in 
Table 1. 
TABLE 1 
__________________________________________________________________________ 
Example 
Monomer 
Wt. Ratio 
Diluent 
% Solids 
Wt. % AIBN 
mL DDM 
M.sub.n 
M.sub.w 
__________________________________________________________________________ 
1 BA/AA 90/10 IP 29 4% 4.3 2493 5457 
2 BA/AA 90/10 IP 29 1% none 5006 15702 
3 BA/AA 90/10 IP 44 4% 4.3 &gt;3300 
&gt;7000 
4 BA/AA 90/10 IP 10 4% 4.3 1500 2770 
5 BA/An 90/10 IP 29 4% 4.3 2340 5280 
6 BA/MA 90/10 THF 33 4% 5.0 2186 6219 
7 BA/MA 95/5 THF 32 4% 5.0 2560 5756 
__________________________________________________________________________ 
In Example 2 higher molecular weight polymer was obtained by reducing the 
initiator level and eliminating the chain transfer agent (DDM). In Example 
3 the molecular weight of the polymer was increased by increasing the 
solids level. The molecular weight was lowered by reducing the solids 
level in Example 4. Although the polymers from all seven runs are within 
the scope of the invention, the polymers of Examples 1 and 5-7 represent 
preferred embodiments of the flexibilizing additive. 
EXAMPLES 8-25 
These Examples present evaluation of specimens of epoxy resins cured in the 
presence of acrylate copolymer in accordance with the invention. The 
specimens were prepared by thoroughly mixing the uncured epoxy resin with 
the acrylate copolymer from one of the seven Examples given above, and, 
when used, with a monofunctional epoxide diluent. Addition of the amine 
curative was followed by additional thorough mixing and degassing at 10 mm 
Hg. The mixtures were then cured at either 70.degree. C. for 16 hours or, 
in the case of Examples 23-25, for 14 days at room temperature, while 
molded in the desired shape of test plaques. Specimens were die cut from 
the plaques and tensile properties were measured according to ASTM D-638 
protocol. 
The epoxy resin used in each case was a diglycidyl ether of bisphenol A 
having an epoxy equivalent weight of 190. The monofunctional diluent which 
was used in every Example except Example 9 was a C.sub.12 to C.sub.14 
monoglycidyl ether, and the acrylate copolymer and curative used for each 
Example were as given in Table 2. In Table 2 all parts given are parts by 
weight. The curatives used were either 4,4'-diaminodicyclohexylmethane 
(M 20) which is tetrafunctional, 1-(2-aminoethyl)piperazine (AEP) which 
is trifunctional, diethylenetriamine (DETA) which is pentafunctional, 
dimethylethylenediamine (DMEDA) which is bifunctional, or Ancamine.RTM. 
epoxy curative which is an aliphatic amine-based mixture. The appearance 
of the plaques are given in Table 2 as either clear and colorless, opaque, 
yellow or light brown. Tensile values at yield and at break were 
essentially identical for all specimens. This value and percent elongation 
for each specimen are given in Table 2. 
TABLE 2 
__________________________________________________________________________ 
Elongation 
Epoxy/MGE 
Acrylate Curative Appear. 
Tensile 
Example 
(parts) 
Exam. 
Parts 
Type parts 
(a) (psi) 
(%) 
__________________________________________________________________________ 
8 80/20 1 124 M 24 c, co 
1715 46.3 
9 100/0 1 378 M 26 c, co (b) 
324 57.8 
10 80/20 7 124 M 24 -- 665 63.8 
11 80/20 3 124 M 24 c 1715 25.7 
12 80/20 4 124 M 24 c 1093 53.1 
13 80/20 2 124 M 24 o 1623 28.1 
14 80/20 3 124 AEP 24 c, y 1190 57.0 
15 70/30 3 124 M 24 c, co 
504 46.7 
16 60/40 3 124 M 24 c, co 
288 83.8 
17 50/50 3 124 M 24 c, co 
103 104.4 
18 80/20 1 53 DETA (c) c, y 2733 9.3 
19 80/20 1 53 AEP (c) o, y 2836 51.1 
20 100/0 1 53 DMEDA (c) c, y 2280 179.4 
21 80/20 6 124 AEP (c) c, lb 
1734 61.0 
22 80/20 5 53 AEP (c) o, y 2191 64.2 
23 80/20 7 79 M 19 -- 1250 26.7 
24 75/25 1 79 AEP 21 -- 1700 82.2 
25 75/25 1 50 Anc. (d) 
43 -- 1264 71.3 
__________________________________________________________________________ 
(a) Appearance code: c -- clear; co -- colorless; o -- opaque; y -- 
yellow; lb -- light brown. 
(b) Contained a number of voids. 
(c) Stoichiometric amount of curative. 
(d) Mixture of Ancamine .RTM. 1784 and 2205, products of Air Products and 
Chemicals, Inc. 
A comparison of Examples 8 and 9 shows that omitting the monofunctional 
diluent, MGE, and increasing the acrylate level resulted in a product 
having good elongation but reduced tensile. These examples support the 
preference for using the combination of the acrylate copolymer 
flexibilizer and the monofunctional diluent. 
Comparing Examples 8 and 11 shows how higher molecular weight for the 
acrylate copolymer provides a lower elongation value than obtained with a 
copolymer having a molecular weight within the preferred range. Example 11 
used the copolymer of Example 3 prepared at a higher solids level and 
having a higher molecular weight than the copolymer of Example 1 used for 
the plaque of Example 8. On the other hand, Example 12 used the copolymer 
of Example 4 which had a lower solids level and produced a copolymer 
having a molecular weight lower than the preferred range. The result in 
the plague was a higher elongation but lower tensile strength. Example 13 
used the copolymer of Example 2 which obtained a higher molecular weight 
product by reducing the initiator level and eliminating the chain transfer 
agent, dodecylmercaptan. As with Example 11, the elongation of the cured 
epoxy was lower than for Example 8. Additionally, the specimen of Example 
13 was phase separated as evidenced by the opaque nature of the plaque. 
Thus, Examples 8, 11, 12 and 13 show the effect of molecular weight on the 
cured epoxy product. Example 14, however, shows how changing the curative 
from that used in Example 11 to a trifunctional curative, AEP, can 
increase elongation, but with a sacrifice in tensile strength. These 
Examples illustrate how it is possible to obtain a variety of physical 
property combinations in the epoxy product by adjusting the nature of the 
acrylate copolymer, the curative, and different levels of monofunctional 
diluent. Indeed, an epoxy with both high tensile and very high elongation 
was obtained in Example 20 using a lower level of acrylate copolymer than 
in Example 8 and a different curative. 
COMATIVE EXAMPLE 26 
Five epoxy plaques were prepared using M curative, two with and three 
without the monoglycidyl ether monofunctional diluent, using polyacrylates 
not within the scope of the invention, namely, ethylhexylacrylate 
homopolymer, 90/10 ethylhexylacrylate/acrylic acid copolymer, 
ethylacrylate homopolymer, 90/10 butylacrylate/N,N-dimethylacrylamide 
copolymer, and 90/10 copolymer of butylacrylate and acrylamide. Both the 
N,N-dimethylacrylamide and acrylamide are nonfunctional with respect to 
the epoxy resin and curative. In each case the epoxy compositions were too 
severely phase-separated to have any utility. It is concluded that such 
acrylate homopolymers and copolymers are not useful in the invention even 
though they had molecular weights within the operative range. 
EXAMPLE 27 
An epoxy resin formulation was prepared by thoroughly mixing 80 parts by 
weight of polyepoxide, diglycidyl ether of bisphenol A having an EEW of 
190, 20 parts of a C.sub.12 to C.sub.14 monoglycidyl ether as a reactive 
diluent, and 53 parts of a 90/10 copolymer of butylacrylate and acrylic 
acid. A curative which was an adduct of 2-methyl-1,5-pentanediamine and 
methyl isobutyl ketone was then added, 33.2 parts, followed by additional 
thorough mixing and degassing at 10 mm Hg. 
The amine/ketone adduct curing agent was trifunctional and made by 
combining 2.3 gram mol each of the diamine and MIBK in a reactor in the 
presence of 10 g of 5% palladium on carbon. The reactor was purged with 
nitrogen, pressurized to 800 psig with hydrogen, and heated to 120.degree. 
C. The reactor pressure was stabilized at 770 psig and maintained at these 
conditions for 72 hours, after which gas uptake was complete. The reactor 
was vented, purged with nitrogen, the catalyst filtered out, and the 
product recovered by fractional vacuum distillation. The fraction boiling 
at 98.degree. to 106.degree. C. at 2 mm Hg was 98 percent monoalkylate 
adduct and this product was used as the trifunctional curative. 
The cure of the epoxy mixture was carried out at 70.degree. C. for 20 hours 
in a plaque-forming mold. Test specimens die cut from the plaque were 
found to have a tensile strength (at both yield and break) of 1158 psi and 
an elongation of 121 percent. 
In addition to the advantages involving the physical properties of the 
cured epoxy resin, the invention provides other benefits related to ease 
of handling of the acrylate flexibilizer in the epoxy cure recipe, low 
toxicity, absence of volatile organic compounds, and no use of initiators 
or chain transfer agents in the cure process such as is the case with the 
in-situ polymerizations of the prior art. 
Other advantages, features and embodiments of our invention will be 
apparent to those skilled in the art from the foregoing disclosure without 
departing from the spirit or scope of the invention.