Process for stabilizing polyester compositions

The present invention provides an improved process for reducing the premature gelation during esterification of epoxy compounds containing tertiary, allylic or benzylic hydrogens (e.g., saturated epoxy resins) with ethylenically unsaturated monocarboxylic acids (e.g., acrylic acid) wherein the epoxy compound in pre-reacted with a trialkylphosphite (e.g., triethylphosphite) prior to the esterification.

BACKGROUND OF THE INVENTION 
Hydroxy-containing ethylenically unsaturated polyesters prepared from 
glycidyl polyethers of polyhydric phenols and ethylenically unsaturated 
monocarboxylic acids tend toward premature gellation. In other words, the 
polyesters, if stored for long periods of time before use, will increase 
in viscosity (gel) to a value which severely limits their use for many 
applications where low viscosity is important. 
Such premature gelation is significantly reduced by the addition of a 
dialkylhydroxylamine. See, for example, U.S. Pat. No. 3,408,422, issued 
Oct. 29, 1968. 
When, however, the epoxy compound contains tertiary, allylic or benzylic 
hydrogens, such as the so-called saturated epoxy resins and epoxidized 
novolac resins, there appears to be a propensity toward auto-oxidation and 
peroxide formation. Accordingly, when such epoxy compounds are esterified 
with ethylenically unsaturated acids, the reaction mixture gels during the 
esterification step. It has now been found that if the saturated epoxy 
resin or epoxidized novolac resin is pretreated with a trialkylphosphite 
before the esterification, the esterification can be effected without 
premature gelation to produce unsaturated vinyl esters exhibiting 
excellent stability. 
SUMMARY OF THE INVENTION 
This invention provides an improved process for preparing unsaturated 
polyesters from epoxy compounds containing tertiary, allylic or benzylic 
hydrogens. More particularly, the invention is directed to an improved 
process for reducing gelation during the esterification of saturated 
polyepoxides and epoxidized novolac resins with ethylenically unsaturated 
monocarboxylic acids which comprises pre-reacting the saturated 
polyepoxide or epoxidized novolac resin with a trialkylphosphite. 
DESCRIPTION OF PREFERRED EMBODIMENTS 
As a special embodiment, the invention provides a process for reducing 
premature gelation during the esterification of saturated epoxy resins and 
glycidyl resins derived from novolac resins with ethylenically unsaturated 
monocarboxylic acids which comprises pre-reacting the unsaturated epoxy 
resin or glycidyl novolac resin with a trialkylphosphite. Epoxy compounds 
which contain a number of tertiary hydrogens and therefore have a high 
peroxide level include the saturated epoxy resins. Accordingly, these 
saturated epoxides are extremely useful in the present process and include 
those compounds derived from polyhydric phenols and having at least one 
vicinal epoxy group wherein the carbon-to-carbon bonds within the 
six-membered ring are saturated. Such epoxy resins may be obtained by two 
well-known techniques, i.e., (1) by the hydrogenation of glycidyl 
polyethers of polyhydric phenols or (2) by the reaction of hydrogenated 
polyhydric phenols with epichlorohydrin in the presence of suitable 
catalysts such as the Lewis acids and subsequent dehydrochlorination in an 
alkaline medium. The methods of preparation form no part of the present 
invention and the resulting saturated epoxy resins derived by either 
method are suitable in the present compositions. 
Briefly, the first method comprises the hydrogenation of glycidyl 
polyethers of polyhydric phenols with hydrogen in the presence of a 
catalyst consisting of rhodium or ruthenium supported on an inert carrier 
at a temperature below about 50.degree. C. This method is thoroughly 
disclosed and described in U.S. Pat. No. 3,336,241, issued Aug. 15, 1967. 
The hydrogenated epoxy compounds prepared by the process disclosed in U.S. 
Pat. No. 3,336,241 are suitable for use in the present compositions. 
Accordingly, the relevant disclosure of U.S. Pat. No. 3,336,241 is 
incorporated herein by reference. 
The second method comprises the condensation of a hydrogenated polyphenol 
with an epihalohydrin, such as epichlorohydrin, in the presence of a 
suitable catalyst such as BF.sub.3, followed by the dehydrohalogenation in 
the presence of caustic. When the phenol is bisphenol A, the resulting 
saturated epoxy compound is sometimes referred to as "diepoxidized 
hydrogenated bisphenol A", or more properly as the diglycidyl ether of 
2,2-bis(4-cyclohexanol)propane. 
In any event, the term "saturated epoxy resin", as used herein shall be 
deemed to mean the glycidyl ethers of polyhydric phenols wherein the 
aromatic ring structure of the phenols has been saturated. 
An ideal structural formula representing the preferred saturated epoxy 
compounds is as follows: 
##STR1## 
wherein n has a value so that the average molecular weight of the 
saturated polyepoxide is from about 350 to about 3000. 
Preferred saturated epoxy resins are the hydrogenated resins prepared by 
the process described in U.S. Pat. No. 3,336,241. More preferred are the 
hydrogenated glycidyl ethers of 2,2-bis(4-hydroxylphenyl)propane, 
sometimes called the diglycidyl ethers of 2,2-bis(4-cyclohexanol)propane. 
As noted hereinbefore, equally suitable saturated epoxy resins include the 
saturated resins prepared by reacting the saturated (hydrogenated) 
polyhydric phenol with epichlorohydrin in the presence of BF.sub.3, 
followed by dehydrochlorination in the presence of caustic. 
Other suitable epoxy compounds containing tertiary, alkylic or benzylic 
hydrogens include the glycidyl polyethers of bisphenol F and hydrogenated 
bisphenol F; as well as the acrylate and methacrylate esters of fusion 
reaction products of liquid epoxy resins and glycidyl phenolic novolac 
resins. Preferred resins of this type are those of the general formula: 
##STR2## 
wherein R is hydrogen or an alkyl radical and n is an integer of 1 to 
about 10. Preparation of these polyepoxides is illustrated in U.S. Pat. 
No. 2,658,885. 
The above-noted epoxy resin is pre-reacted with a trialkylphosphite of the 
formula: 
##STR3## 
wherein R.sub.1, R.sub.2 and R.sub.3 are each an alkyl group of up to 
about 10 carbon atoms. 
Suitable such trialkyl phosphites are trimethylphosphite, 
triethylphosphite, tripropylphosphite, triisopropylphosphite, 
methyldiethylphosphite and the like. Very preferred is triethylphosphite. 
The amount of trialkylphosphite pre-reacted with the saturated polyepoxide 
or glycidyl novolac will vary widely depending upon the particular 
trialkylphosphite, saturated epoxide or glycidyl novolac and the time and 
temperature. In general, the amount of the trialkylphosphite will vary 
from as little as 0.001 to 10 parts by weight based on the one hundred 
parts by weight (pbw) of epoxide. Preferred amounts will vary from about 
0.01 to 3 phr. 
The trialkylphosphite compound is pre-reacted with the epoxide compound at 
a temperature from about room temperature (20.degree. C.) to about 
100.degree. C. for a period from about 1 minute to about 40 minutes. A 
very desirable temperature period is 90.degree. C. for 30 minutes. 
After this prereaction time, the epoxy compound is esterified with an 
ethylenically unsaturated organic carboxylic acid which may be aliphatic, 
cycloaliphatic or aromatic, and may be monocarboxylic or polycarboxylic. 
Examples of the acids to be utilized include acrylic acid, methacrylic 
acid, cyclohexene carboxylic acid, maleic acid, crotonic acid, 
alpha-phenylacrylic acid, tetrahydrophthalic acid, 
2,4-octadienedicarboxylic acid, dodecadienoic acid and the like. 
Particularly preferred acids to be utilized comprise the ethylenically 
unsaturated acids such as, for example, acrylic acid, methacrylic acid, 
crotonic acid, alpha-phenylacrylic acid, alpha cyclohexylacrylic acid, 
maleic acid, alpha-chloromaleic acid, tetrahydrophehalic acid, itaconic 
acid, fumaric acid, cyanoacrylic acid, methoxyacrylic acid, and the like. 
Also particularly preferred are the partial esters of polycarboxylic acids, 
and particularly the alkyl, alkenyl, cycloalkyl and cycloalkenyl esters of 
polycarboxylic acids such as, for example, allyl hydrogen maleate, butyl 
hydrogen maleate, allyl hydrogen, tetrahydrophthalate, allyl hydrogen 
succinate, allyl hydrogen furmarate, butenyl hydrogen tetrahydrophthalate, 
cyclohexenyl hydrogen maleate, cyclohexyl hydrogen tetrahydrophthalate, 
and the like, and mixtures thereof. 
Coming under special consideration, particularly because of the superior 
coating properties of the resulting prepolymers, are the ethylenically 
unsaturated monocarboxylic acids and unsaturated partial estes, and 
especially the unsaturated aliphatic monocarboxylic acids containing 3 to 
10 carbon atoms, and the alkenyl and alkyl esters of alkenedioic acids 
containing up to 12 carbon atoms. 
Although an esterification catalyst is not required, such a catalyst is 
usually employed and any known esterification catalyst can be utilized to 
make the instant composition. 
Very suitable catalysts include the metal hydroxides such as sodium 
hydroxide; tin salts such as stannous octoate; phosphines such as 
triphenyl phosphine; the onium salts such as the phosphonium salts, 
including the phosphonium halides and the ammonium halides. 
Preferred catalysts to be utilized in the process comprise the onium salts, 
and preferably those containing phosphorus, sulfur or nitrogen, such as, 
for example, the phosphonium, sulfonium and ammonium salts of inorganic 
acids. Examples of these include, among others, benzyltrimethylammonium 
sulfate, tetramethylammonium chloride, benzyltrimethylammonium nitrate, 
diphenyldimethylammonium chloride, benzyltrimethylammonium chloride, 
diphenyldimethylammonium nitrate, diphenylmethylsulfonium chloride, 
tricyclohexylsulfonium bromide, triphenylmethylphosphonium iodide, 
diethyldibutylphosphonium nitrate, trimethyl sulfonium chloride, 
dicyclohexyldiphenylphosphonium iodide, benzyltrimethylammonium 
thiocyanate, and the like, and mixtures thereof. 
Preferred onium salts to be employed include those of the formula: 
##STR4## 
wherein R is a hydrogen radical, and preferably an aryl, alkyl, alkenyl, 
cycloalkyl, cycloalkenyl or alkaryl radical containing up to 12 carbon 
atoms, X is an ion or inorganic acid, and particularly a halogen atom, 
nitrate, sulfate or phosphate radical, m is the valency of the X ion and 
n=m. 
The amount of the pre-reacted polyepoxide and the ethylenically unsaturated 
monocarboxylic acid used in the esterification reaction will vary over a 
wide range. In general, these reactants are used in approximately chemical 
equivalent amounts. As used herein and in the appended claims, a chemical 
equivalent amount of the polyepoxide refers to that amount needed to 
furnish one epoxy group per carboxyl group. Under some circumstances, 
excess amounts of either reactant can be used. Preferred amounts range 
from about 0.5 to 2 equivalents of epoxide per equivalent of 
monocarboxylic acid. 
The amount of the catalyst employed may also vary over a considerable 
range. In general, the amount of the catalyst will vary from about 0.05% 
to about 3% by weight, and more preferably from 0.1% to 2% by weight of 
the reactants. 
The reaction may be conducted in the presence or absence of solvents or 
diluents. In most cases, the reactants will be liquid and the reaction may 
be easily effected without the addition of solvents or diluents. However, 
in some cases, whether either or both reactants are solids or viscous 
liquids it may be desirable to add diluents to assist in effecting the 
reaction. Examples of such materials include the inert liquids, such as 
inert hydrocarbons as xylene, toluene, cyclohexane and the like. 
If solvents are employed in the reaction and the resulting product is to be 
used for coating purposes, the solvent may be retained in the reaction 
mixture. Otherwise, the solvent may be removed by any suitable method such 
as by distillation and the like. If the product is not to be used for 
sometime after its formation, it may also be desirable to remove the 
catalyst used in the preparation, such as by stripping and the like. 
Temperatures employed in the reaction will generally vary from about 
50.degree. C. to about 150.degree. C. In most cases, the reactants will 
combine in the presence of the catalysts at a very rapid rate and lower 
temperatures will be satisfactory. Particularly preferred temperatures 
range from about 50.degree. C. to 120.degree. C. 
The reaction will be preferably conducted under atmospheric pressure, but 
it may be advantageous in some cases to employ subatmospheric or 
superatmospheric pressure. 
The polyester products obtained by the above process will vary from liquids 
to solid resins and will possess a plurality of ethylenic groups. The 
products will be of higher molecular weight than the basic polyepoxide 
from which they are formed and will possess at least two acid groups per 
polyepoxide unit. 
These unsaturated polyesters prepared as hereinbefore described may be 
further modified by reacting the polyesters prepared by the esterification 
of polyepoxides with ethylenically unsaturated carboxylic acids, with a 
polycarboxylic acid anhydride such as maleic anhydride. Typical examples 
of such modified polyesters (partial half esters) and their method of 
preparation s disclosed in U.S. Pat. No. 3,634,542, issued Jan. 11, 1972, 
and the disclosure relevant to their preparation is incorporated herein by 
reference. 
The stable polyesters will be compatible and soluble in a great variety of 
different materials. They will be compatible, for example, with various 
oils, tars, resins and the like, and with a great variety of different 
types of unsaturated monomers. Examples of such compatible monomers 
include, among others, aromatic compounds such as styrene, 
alpha-methylstyrene, dichlorostyrene, vinyl naphthalene, vinyl phenol and 
the like, unsaturated esters, such as acrylic and methacrylic esters, 
vinyl acetate, vinyl benzoate, vinyl chloroacetate, vinyl laurate, and the 
like, unsaturated acids, such as acrylic and alpha-alkylacrylic acid, 
butenoic acid, allylbenzoic acid, vinylbenzoic acid, and the like, 
halides, such as vinyl chloride, vinylidene chloride, nitriles, such as 
acrylonitrile, methacrylonitrile, diolefins, such as butadiene, isoprene, 
methylpentadiene, esters of polycarboxylic acids, such as diallyl 
phthalate, divinyl succinate, diallyl maleate, divinyl adipate, 
dichloroallyl tetrahydrophthalate, and the like, and mixtures thereof. 
The instant hydroxy-substituted polyesters may be polymerized, either 
alone, or in combination with any of the above-noted unsaturated mononers, 
to form valuable polymeric products. When used in combination with the 
above components, the amount of the other component may vary over a wide 
range, but it is generally preferred to have at least 15% by weight of the 
polyester present. In working with components, such as the aromatic 
unsaturated monomers, such as styrene, it is preferred to utilize from 1% 
to about 65% of the dissimilar monomer and from 99% to 35% of the present 
polyester. 
The polymerization of the above-noted polyesters or mixtures of monomers 
may be accomplished by any suitable method. The preferred method comprises 
heating the monomer or mixture of monomers in the presence of a free 
radical yielding catalyst. Examples of such catalysts includes the 
peroxides, such as benzoyl peroxide, tertiary butyl hydroperoxide, 
ditertiary butyl peroxide, hydrogen peroxide, potassium persulfate, methyl 
cyclohexyl peroxide, cumene hydroperoxide, actyl benzoyl peroxide, 
Tetralin hydroperoxide, phenylcyclohexane hydroperoxide, tertiary 
butylisopropylbenzene hydroperoxide, tertiary butyl peracetate, tertiary 
butylacetate, tertiary butyl perbenzoate, ditertiary butyl peradipate, 
tertiary amyl percarbonate, and the like, and mixtures thereof; azo 
compounds such as 2,2'-azobisisobutyronitrile dimethyl 
2,2-azobisisobutyrate, 2,2'-azobis(2,4-dimethylvaleronitrile, 
2,2'-azobisisotulyamide, and the like. Particularly preferred catalysts 
include the diaryl peroxide, tertiary alkyl hydroperoxides, alkyl 
peresters of percarboxylic acids and particularly those of the above-noted 
groups which contain no more than 18 carbon atoms per molecule and have a 
decomposition temperature below 125.degree. C. 
Other materials may also be added to the mixtures before or during 
polymerization. These include plasticizers, stabilizers, extenders, oils, 
resins, tars, asphalts and the like, as well as all types of coloring or 
pigments to give the material the desired color. 
The above-noted components may be mixed in any order and then the combined 
mixture heated to the desired temperature. Temperatures employed in the 
polymerization will vary depending upon the reactants and catalyst 
selected. In general, polymerization temperatures may vary from about 
20.degree. C. to 200.degree. C. and more preferably from 20.degree. C. to 
125.degree. C. 
The unsaturated polyesters and their above-noted mixtures with other 
monomers may be utilized in a wide variety of different applications. They 
may be utilized in the preparation of coatings and impregnating 
compositions, in the preparation of adhesives for metals, wood, cement and 
the like, and in the preparation of reinforced composite products, such as 
laminated products, filament windings and the like. In this latter 
application, the polyester compositions are applied to the fibrous 
products, such as glass fibers or sheets, the material formed into the 
desired object and heated to effect cure of the polyester composition.

To illustrate the manner in which the invention may be carried out, the 
following examples are given. It is to be understood, however, that the 
examples are for the purpose of illustration and the invention is not to 
be regarded as limited to any of the specific materials or conditions 
recited therein. Unless otherwise indicated, parts are parts by weight. 
Saturated Resin A is a diglycidyl ether of hydrogenated 
2,2-bis(4-hydroxyphenyl)propane having a weight per epoxy (WPE) of about 
200-240 and an average molecular weight of about 380. 
Epoxy Resin A is a diglycidyl ether of 2,2-bis(4-hydroxyphenyl)propane 
having a weight per epoxy of about 170-190 and an average molecular weight 
of about 350. 
Phenolic Novolac Resin A is a novolac resin having an average molecular 
weight of 520 and a phenolic functionality of about 5. 
EXAMPLE I 
This example illustrates the preparation of the unsaturated polyesters 
wherein no premature gelation occurs in the esterification group. 
Into a three-liter flask equipped with stirrer, thermometer, N.sub.2 sparge 
tube and condenser were placed 1131.9 grams of Saturated Resin A and 1.13 
grams pf triethylphosphite (TEP) and the mixture heated for one hour at 
82.degree. C. (180.degree. F.). Then 332 grams of glacial acrylic acid, 
1.2 grams of monomethyl ether hydroquinone (MMEH) and 15.45 grams of 
tetramethylammonium chloride (TMAC) in 50% water were added with 
nitrogen/air sparge and the temperature was raised to 115.degree. C. 
(240.degree. F.) for three hours. The mixture was then cooled to about 
107.degree. C. (226.degree. F.) and 15.1 grams of para-toluene sulfuric 
acid (PTSA) and 6.5 grams of water were added and the mixture cooled to 
ambient temperature (20.degree. C.). The resulting unsaturated vinyl ester 
resin had the following properties: 
______________________________________ 
Color (Gardner): 4 
Viscosity, poise @ 25.degree. C.: 
1122 
Acid Value: 0.096 eq./100 gram 
______________________________________ 
This ungelled resin, either neat or in mixtures with styrene, can be cured 
by conventional techniques such as free radical catalysts (peroxides) by 
UV-radiation to produce films exhibiting excellent physical properties. 
EXAMPLE II 
The procedures of Example I were essentially repeated except that 
hydroquinone was used in lieu of MMEH. Related results were obtained. 
EXAMPLE III 
The procedures of Examples I and II were essentially repeated except that 
no TEP was employed. The reaction mixture gelled during the esterificatin 
step and the esterification was terminated. 
EXAMPLE IV 
Into a three-liter flask equipped with stirrer, thermometer, N.sub.2 sparge 
tube and condenser were placed 666 grams of Epoxy Resin A, 52.5 grams of 
Phenolic Novolac Resin A and 0.53 grams of TMAC under N.sub.2 blanket. The 
reaction mixture was heated to 171.degree. C. (340.degree. F.) for 1 hour. 
Then the reaction mixture was cooled to 127.degree. C. (260.degree. F.) 
and 0.48 gram of TEP were added and the temperature held for 30 minutes. 
The temperature was then lowered to 116.degree. C. (240.degree. F.) and 
the following components were added: 
______________________________________ 
Glacial methacrylic acid (GMAA): 
246.3 grams 
25% hydroquinone in methanol 
1.87 grams 
Styrene 160.6 grams 
TMAC 5.54 grams 
______________________________________ 
The resulting mixture was held at 116.degree. C. (240.degree. F.) for three 
hours. The temperature was then lowered to 110.degree. C. (230.degree. F.) 
and 21.7 grams of maleic anhydride was added and the temperature held at 
110.degree. C. for 20 minutes. The mixture was then cooled to 93.degree. 
C. (200.degree. F.) and 384 grams of styrene was added. 
One hundred grams of the resin was cured with 0.2 grams of methyl ethyl 
ketone peroxide and 0.4 grams of 6% cobalt naphthenate. The room 
temperature gel time was 16 to 18 minutes. 
When no TEP was used to pre-react with the epoxy resin, the composition 
gelled during the esterification step.