EPOXY R E S I N S The proportion of fatty acid and diepoxide charged in the adduct preparation was significant in determining molecular weight of the polymer. The optimum formulation was derived from a carboxyl-epoxide ratio ranging between 0.40 and 0.55. Lower proportions of
Table 1.
EP-201 Varnishes Have Good Resistance to Caustic, Boiling Water, and Ultraviolet
% Acid On Solids
Flexibility; In. Lb. Impact
45 45 45 45 53
108 80 100 88 108
Exc. Exc. Exc. Exc. Exc.
Exc. Good Good Exc. Exc.
87 90 90 85 66
40 40 45
108 108 108
Exc. Exc. Exc.
Exc.
69 73 87
i.
F a t t y Acid
x
fatty acid tended to give gelled products, whereas higher proportions led to polymers which had unnecessarily low molecular weights. A small quantity of water added to the product decreased solution viscosity significantly. Where a semigelled poly-
D Ca Linseed Soya bean Soya beanb Tung
them. Resistance M'ater Caustic
Hardness; U.V. Sward Resistance
Formulation Conventional epoxided Alkyds EP-20la
x
Exc.
Poor Good Good
Dehydrated castor. Varnish contained 10% of butylated melamine resin (American Cyanamid Co., Cyme1 Resin 448-8. 0 Varnish prepared from 0.55 adduct and final viscosity was 1070 cp. at 50% solids. Care was necessary t o avoid premature gelation. d Epoxide equivalent weight of about 1000 plus dehydrated castor oil acid. e From American Cyanamid Co., Rezyl Resin 330-5.
C. W. McGARY, Jr., C. T. PATRICK, Jr., and RALPH STICKLE, Jr.
An Epoxy Resin from Phenolphthalein
designed. Phenolphthalein and epichlorohydrin were allowed to react with 2 or 3 moles of sodium hydroxide in the presence of a limited amount of water. The resin was isolated without being washed with water or dilute acid. A large ash content would have indicated the presence of an organic acid salt. The low ash content found experimentally eliminates structure VII. Comparing the theoretical epoxy equivalents of mono-, di-, and triglycidyl phenolphthaleins with the experimental values, it appears that the glycidyl product of phenolphthalein has approximately two epoxy groups per molecule. The saponification value indicates that the second
Dmiw
+
Poor
mer formed, 1% of water based on solids, converted the gel to a mobile solution. One explanation for this is that the inorganic initiator entered into the polymer chain by forming inorganic ether linkages, e.g., if boron trifluoride were used, the borate should have been easily hydrolyzed. Adding water to the polymer mixtures could also reduce viscosity by reducing interpolymer hydrogen bonding. The polymerization reaction was carried out in enough solvent, usually xylene, to give a polymer concentration of about 50 to 55%. The varnishes also had a high tolerance for aliphatic solvents. Film properties were determined using conventional dip-coating and testing methods. T o obtain optimum properties by air-drying or baking at 160' C., dryers such as cobalt and lead naphthenate were used (Table I). The coatings had excellent resistance to caustic (20% sodium hydroxide for 24 hours), boiling water (1 hour), and ultraviolet light (2 weeks at 60' C.).
THE PAST 20 years a considerable quantity of literature has appeared on epoxy resins related to their synthesis, formulation, and application. The major portion of this literature is concerned with the resinous materials prepared from epichlorohydrin and bis-(4hydroxyphenyl)-dimethylmethane (bisphenol A). These resins also make up the bulk of the commercial market. Recently more interest has been shown in the synthesis of new epoxy resins, including glycidyl derivatives of other phenols and epoxides from the peroxide epoxidation of olefins. The purpose of the research reported here is to synthesize a new epoxy resin with higher heat distortion temperature and better solvent resistance than that obtainable from resins based on bisphenol A.
The condensation with 2 moles of epichlorohydrin could conceivably give any or all of the three structures V, VI, or VII. Of these three possibilities, V would be formed from I, V I from 111, or VI1 from either I1 or IV. If 3 moles of epichlorohydrin condense then only structure VI11 is possible, and could be formed from either I1 or IV. To determine which of these four structures is predominant in the resin, the experiments shown in Table I were
Table 1.
The epoxy resin of phenolphthalein can be prepared by condensing phenolphthalein with epichlorohydrin in the presence of alkali at 105' to 115' C. for 2 or 3 hours. According to the literature (7) the reaction between an alkali and phenolphthalein is shown by the equation on the following page.
Epoxy Resin of Phenolphthalein Prepared by Using Different Amounts of Sodium Hydroxide No.
69-1 16-1 84-1 91-1 110-1
Structure Study
Research Department, Union Carbide Chemicals Co., South Charleston, W. Va.
Moles NaOHa
Epoxy Equiv./ 100 G.
3 3
0.36 0.40 0.42 0.35 0.38
2 2 2
Sapon. Value
... 135
Ash,
%
132 128
0.04 0.06 0.00 0.00 0.02
150 130 111
0 0 0
..I
Theor. Value
a
Monoglycidylb Diglycidylb Triglycidyla Per mole of phenolphthalein.
0.267 0.465 0.595
Phenolphthalein. ~~~~~
VOL. 52, NO. 4
APRIL 1960
31 9
Table II.
Heat Distortion Temperature and Solvent Resistance of Cured Phenolphthalein Resins Compared with Those of Bisphenol A Resin Heat Distortion Temp., C.
Curing Agent Menthanediamine
+20
120 160
2 16
120 150
+
P h om n 1. II”’AyI-
phthalein resin
Bisphenol A resin 137
161
m-t.
Solvents
Days
CHCls
4.2
7
116
175
200
150
Acetone 10% NaOH 3oyo HsSOi 5 % HAC Hz0 CHCli
11
GI. HAC 16
180
207
170
...
8
7
0.41
7
7 7
0 0
7
7
0.53 0.55 0.85
...
...
0.6 0.6 1.9 2.0 ~.
0.3 0.7
..
...
epoxy resin shows a distinct shift of the 1725 to 1730 ern.-' band of phenolphthalein to 1750 to 1760 cm.-’ in the resin, indicating the change of a ketonic carbonyl to an ester carbonyl. II the resin had the lactoid structure, the carbonyl absorption of phenolphthalein should have been retained. Also the 0-Ka
0-h’a
OH
0-Ka
I
I
33
0.77 0 0.4
2. Phenolphthalein did not give a saponification value under the same condition used to hydrolyze the resin. The disubstitution on the two phenol groups, however, may influence reactivity of the lactoid carbonyl. 3. A comparison of the infrared spectra of phenolphthalein and its
glycidyl group is combined as an ester. Of the two remaining possible structures, (V) and (VI), the quinoid structure is favored because : 1. The resin is distinctly yellow, which is in agreement with the dimethyland the diethylphenolphthalein (2, 3 ) of the quinoid structure.
Bisphenol A Resin_ ~ Days Wt. % incr. 7 Partially soluble
7 7 30 70 30 70 30 70
HzO
Dianiline sulfone
70
incr.
150
3
m-Phenylenediamine
~
90
2 + 4
Methylnadic anhydride
Solvent Resistance, Room Temp. Phenolnhthalein Resin
O
Conditions Temp., Hr. O c.
0-Na
I
I
00 \/
NaOH
-HzO
NaOH
I__)
___f
COONa
L
0
1
Phenol hthalein
Colorless
PI)
0
0
/ \
/ \
CH ZCH CH 2
0
Colorless
Red (111)
(11)
(IV)
OCH2CHCH2
6
OCH 2CH CH 2
0
0
O ‘’
/ \
/ \
(111) 2CH2CHCHZCl
( I ) 2CHzCHCHzCl
____)
____+
Quinoid (VI)
Lactoid ( V )
0 I
/ \
CHZCHCHZO OCH2dHbH2
OCHzCHCHz I
\i
0
0 / \
0
/ \
CHzCHCHzO
0 / \
3CH gCH CHzCl
03
$tCH 2CHCHz /0\
COONa
(VIII)
320
INDUSTRIAL AND ENGINEERING CHEMISTRY
EPOXY R E S I N S band at about 1300 cm.-’ which appears in all simple quinones is present in the resin, but not in Phenolphthalein. Curing
The epoxy resin of phenolphthalein can be cured by conventional hardeners such as the anhydrides or the amines. The values of heat distortion temperature, measured according to ASTM-D648, and solvent resistance are described in Table 11. Co-epoxy Resin
One method of modifying the properties of phenolphthalein resin is preparation of its co-epoxy resins. T h a t is, instead of phenolphthalein, a mixture of phenolphthalein with another phenol is used. Bisphenol A, phenol, resorcinol, diphenol sulfone, chlorinated phenols, or the like, may be used in combination with phenolphthalein. By varying the amount of these phenols, resins from
viscous liquids to high melting solids were obtained. These can also be cured by amines or anhydrides. Coating
A high molecular weight phenolphthalein epoxy resin was reacted with soybean oil acid at 235” to 240” C. for 3’/z hours. The ester formed (acid value about 10) was mixed with a small amount of cobalt naphthenate in xylene, coated on a glass plate, and baked at 150” C. for ‘/z hour. A hard, tough and continuous film was obtained. Experimental
Phenolphthalein (318 grams), epichlorohydrin (925 grams) and isopropanol (100 grams) were placed in a flask and brought to reflux with stirring. Sodium hydroxide pellets (81 g r a m ) were added slowly to the solution and followed by 12 grams of water. Reflux
Polyesters from Epoxides and Anhydrides
*
E
I N THE PRESENCE of a tertiary amine, a terminal epoxide such as allyl glycidyl ether (AGE), reacts cleanly at 70’ to 100’ C . with an acid anhydride (such as phthalic) giving a linear polyester. If equimolar quantities are used, residual activity at the end of the reaction is generally less than 1% of the starting value, proving that the reaction is at least 99% specific-Le., that at least 99% of the epoxide molecules react with anhydride molecules rather than with each other.’ The anhydride requirement with terminal epoxides is 99%; with vinylcyclohexene and cyclohexene oxides the requirement is 75 to SO%, and with such internal epoxides as the alkyl epoxy stearates it is only 60 to 65%. This means that 20 to 40% of these epoxides are unavailable for anhydride reaction, due to homopolymerization, isomerization, or other side reactions. This decreasing order of anhydride demand somewhat parallels the decreasing quality of cure obtained with polyepoxides containing these types of epoxides. Even with terminal epoxides not all catalysts are specific. Tetrabutyl titanate for example, gave 40% homopolymerization of AGE in a phthalate esterification. The reaction has several features which result in important advantages over conventional polyester formation :
1. Volatile products are not formed, eliminating the need for distillation during the reaction. 2. Molecular weights, at least to 12,000, are controlled by the presence of
active hydrogen impurities (alcohol, carboxyl, or water). Agreement between molecular weights by end-group and ebullioscopic analyses is very good to about 12,000. Above this value the discrepancy ranges to 30 to 40%. However, in this region both ebullioscopy and conventional end-group analysis are approaching their detection limits. I t is possible, therefore, that chain termination is largely or even completely caused by stray active hydrogen impurities in the reaction mixture. 3. Within certain limits the reaction is zero order-Le., is independent of monomer concentration. The zero order portion of the curves at 1 to 1 mole ratios persists to about 60% conversion. At this level, the excess of monomers is no longer large, and the over-all rate drops as the growing chain must alternately seek anhydride and epoxide molecules. If an excess of one reagent is present, the rate remains zero order with respect to the other monomer to 8O+Y0 reaction. 4. The zero order rate persists over a wide range of catalyst concentrations, and this rate is proportional to the catalyst concentration. Mathematically the equation takes the form:
R,
= u
+ k 5 (R, -
u)
CY
where R, and R, represent the rates a t catalyst concentrations x and y , respectively; a is the intercept a t 0 catalyst concentration; k is a constant Practically, a may be taken as the rate of the uncatalyzed reaction and k an efficiency factor representing the portion of the amine which is catalytically effective. For the system studied in
was continued for an additional hour. The solution turned from deep purple to pale yellow, indicating the end of the reaction. The resin solution was filtered to separate sodium chloride. Isopropanol and excess epichlorohydrin were removed by vacuum distillation. A pale yellow resin (about 400 grams) left in the flask had an epoxy equivalent of about 0.42 per 100 grams of resin (4). literature Cited
(1) Fieser, L. F., Fieser, M., “Organic Chemistry,” 3rd ed., p. 896, Reinhold,
New Ynrk. (2) Green, A. G., King, P. E., Ber. 40, 3724-35 (1907). (3) Meyer, R., Marx, K., Ibid., ai, 2446-53 (1908). (4) Mitchell, J., Jr., “Organic Analysis,” vol. I, p. 136, Interscience, New York.
ELIZABETH S. LO Exploratory Research Department, Permacel, New Brunswick, N.J.
detail (AGE-phthalic anhydride a t 100’ C . ) , a = 0.0770 reaction per minute and k = 96y0. T h a t is, doubling the catalyst concentration increases the rate by a factor of 1.92, taking into account a small constant uncatalyzed rate. 5. The reaction is so specific that an excess of epoxide may be used. I t serves merely as a solvent, and when the anhydride has been consumed, the excess epoxide may be distilled quantitatively. Within the limits of the analyses, the products are indistinguishable from those in which the reagents are carefully calculated at l to lM, both in structure and molecular weight. The use of excess epoxide has the advantage that the rate remains high to the last removal of anhydride. With 1 to 1 M mixtures the rate becomes very low as both anhydride and epoxide concentrations become low. 6. Another difference from conventional esterification is that end-groups tend to be the same-Le., with excess epoxide, the polymers can be better than 90% hydroxyl terminated, and with a slight excess of anhydride, carboxyl termination predominates. Mecha niIm
The following mechanism is consistent with the facts previously described. 1. Activation of anhydride by the amine : 0
VOL. 52, NO. 4
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321
