EPOXY RESINS This product can then further react bifunctionally, giving cross-linked materials. U p to 30 mole % of maleic anhydride has been incorporated by keeping the reaction temperature below
90' C. and adding maleic anhydride in the later reaction stages.
(2) Shechter, L., W~nstra,J., CHEM.48, 86 ( 1 9 5 6 ) .
literature Cited (1)Fontana, c, M., Kidder, G. A.,
R. F. FISCHER: Shell Development Co., Emeryville, Calif.
J.
Am.
Chem. Sod. 70, 3748 (1948).
Epoxy Resin Hardeners
Epoxy Resin Systems Based on Epoxidized Soybean Oil and HET Anhydride T H E RELATIVELY HIGH cost of conventional epoxy resins has frequently stimulated searches for lower cost systems containing inexpensive epoxidized derivatives. The current use of epoxidized vinyl plasticizers, compounded with poly(viny1 chloride) resins and selected epoxy hardeners, represents one procedure by which the low cost epoxycontaining plasticizers can perform the dual function of a vinyl plasticizer and an epoxy resin. The work presented herein provides a system by which homogeneous epoxy resin formulations can be derived from epoxidized plasticizers and the epoxy resin hardener, chlorendic anhydride (HET; Hooker Chemical Corp.)
These Are Typical Properties for Solutions of Bisphenol A in Epoxidized Soybean Oil Cured with HETAnhydride" Specific gravity Water absorption (24 hr.), % Fire resistance, in./ min. Heat distortion temp., O C., 264 p.8.i. Flexural strength, p.s.i. Flexural modulus, p.s.i. Tensile strength, psi. Tensile modulus, p.s.i. Compressive strength, p.s.i. Hardness
Plasticizers
?.
I n a typical epoxidized vinyl plasticizer, based on soybean oil, the unsaturated components are epoxidized to an average of about 3.6 equivalents of epoxy oxygen out of a theoretical of about 4.6 equivalents. Materials of this type have an average molecular weight of about 1000, an epoxide number of about 260, and an epoxide content of about 6.0%. These epoxidized soybean oils can be considered as potential epoxy resins which are somewhat similar in basic structure to those derived from glycerol and epichlorohydrin ; however, these
Table 1. Y
Hardening Agent Diethylenetriamine m-Phenylenediamine HET anhydride
Dielectric
ASTM Method 0-792 D-570
1.340
D-635
0.09 0.26 Self-ext.
D-648
85
0-790
11,320
D-790
3 . 0 X 106
D-638
6,390
D-638
4 . 3 X IO6
D-695 9,630 Rockwell M-66 Barcol 10 D-149
(WT) (WS)
Table I shows that typical amine hardeners, when compounded with epoxidized soybean oil, do not yield materials of sufficient rigidity for most epoxy applications. O n the other hand, H E T anhydride provides compositions having a linear increase in heat distortion from 45' to 63' C. as its content is reduced from 200 to 100 parts per hundred of resin (p.h.r.). As the H E T content is reduced further to 80 and to 6 0 p.h.r., brittleness and excessive shrinkage become apparent.
Modifler Additives
strength
Volts/mil
I N D . END.
410 3 94
Dielectric constant D-149 (IMC) (Cond A) 2.87 (D48-50) 2.96 " H E T anhydride (100 p.h.r.) 1:2 molar ratio of bisphenol A in epoxidized soybean oil, cured for 24 hours at 140° C.
materials have less epoxy oxygen for a given molecular weight and more of a long chained plasticizing-type structure.
I n an attempt to reduce the brittleness and shrinkage of the H E T anhydrideepoxidized soybean oil systems, the difunctional coreactants listed in Table I1 were evaluated for their effect on the heat distortion characteristics of the system. These studies suggested that bisphenol A is one of the better modifiers, in that it afforded an optimum heat distortion of 91' C. us. 63' C. for the nonmodified system. This optimum heat distortion was obtained at a 1 to 2 molar ratio of bisphenol A to epoxidized soybean oil and 100 p.h.r. H E T anhydride at a cure temperature of 140" C. (Table 111). The viscosity stability characteristics of various solutions of bisphenol A in an epoxidized soybean oil indicate that the systems are quite stable at moderate temperatures-Le., 24' to 60' C. However, their general stability decreases as the temperature of the system is increased and the molar ratio of bisphenol A is increased.
Epoxidized Soybean Oil with Epoxy Resin Hardeners
Quantity, P.H.R. 7.8" 10.2" 60 80 100 120 140 160 180 200
Gel Time, Hr.
... ...
3 . 5 -4.0 2 . 0 -2.5 2 . 0 -2.5 1.0 0.75-1.0 0.75 0.75 0.5
Control (Araldite 6020)f 100 0.5 HET anhydride e Ratio of amine hydrogen equivalents to epoxy equivalents, 1:l. Rubbery. 180' C. Hard, cracked. e Cracked. I Ciba Co., Inc.
Temp.,
... ... 120
120 120 140 140 140 140 140
C.
Cure Temp, a C. 180 1so 150 18OC 150 18OC 150 180c 150 180c 150 18OC 150 180c 150 18OC 150 f 180°
+ + +
+ +
+ +
Heat Distortion, 'c . h b
b d
63 58 55 a
48 45
120 180 196 Stage cured for 24 hours at 150' C. followed by 24 hours a t
VOL. 52, NO. 4
APRIL 1960
323
~
~~
~
~
~
_
_
_
_
Table II. Bisphenol A Is the Best Modifier for Epoxidized Soybean Oil Hardened with HET Anhydride Chemical Formula ClbH1602 CiaH~zOiClr CizHiiO4S CeHsOz CSHIBOZ CEHIlO4 CsHaO4Cls
Molar Ratio Modifier/ Modifier Molecular Epoxidized Soh. Weight 011 Temp., C. 228 1/2 80-90 3 66 1/2 100 250 1/4a 80-90 110 1/2 115-120 104 1/2 90-100 146 1/ 2 130-140 389 1/2
Modifier Bisphenol A Tetrachlorobisphenol A Dihydroxydiphenylsulfone Hydroquinone Neopentgl glycol Adipic acid HET acid Control (none) a Reactivity of the 1:2 ratio was excessively fast.
...
Table 111. HET Anhydride Content, P.H.R. 80 100 120 140 a
...
HET Content, P.H.R.
... ...
...
100 100 120 100 120 100 120 100
120OC. Gel Time, M in. 30 60 14 11 9
...
...
24-Hr Cure Temp., O C. 140 120 120 150 150 150
130
150
... + 180
Heat Distortion Temp., O C. 91 49
55 68 69 59
..
63
Bisphenol A in Epoxidized Soybean Oil Cured with HET Anhydride
1 :2a Cure Temp., O C. 120 140 160 180 120 140 160 b 61 57 62 70 62 73 77 63 81 91 73 75 h 66 73 58 81 88 54 62 60 53 75 80 70 Molar ratio of bisphenol A in epoxidized soybean oil. * Fissures would not permit determination of 1 :4"
sf
Modifier Reactants The successful use of solutions of bisphenol A in an epoxidized soybean oil suggested that a useful epoxy resin might be prepared from the reaction product of these two materials. The reaction characteristics of an epoxidized soybean oil, with sufficient
bisphenol A to react with 1M equivalent of epoxy oxygen were determined and evaluated in the same manner as previously described for the solutions. I t was found that this reaction product yielded only rubbery products with conventional amine type . _ epoxy hardeners and excessively fast systems when used with HET anhydride.
-
I
1: l a
120 62 73 76 75
140 63 67 69 74
160 56 70 67 69
180 51 55 58 58
heat distortion temperature.
These studies indicate that solutions of bisphenol A in epoxidized soybean oil are more suitably hardened with H E T anhydride than are the reaction products of the two materials.
C. S. ILARDO and 9. 0.SCHOEPFLE Hooker Chemical Corp., Niagara Falls, N. Y.
Epoxy Resins from Resorcinol-Acetone Condensation Pro P H Y S I C A L AND CHEMICAL properties of cured epoxy resins improve, within limits, as the number of reactive groups per unit weight of resin (functionality) increases and as length of the polymer chain (molecular weight) increases. Increased chain length and functionality have been obtained in phenol-aldehyde epoxy resins, the so-called hTovolak epoxies (7, 3, 5). Increased functionality has also been obtained in resorcinol epoxy resins (4, 7, 8 ) . The object of the investigation described here was to demonstrate that epoxy resins could be prepared from mononuclear polyhydric phenol-ketone resins (2, 6 , 9 ) and thereby take advantage of both the Novolak and resorcinol structures. A series of resorcinol-acetone resins was prepared (Table I) by heating resorcinol and acetone to 70' C. in a round-bottomed flask equipped with a stirrer, condenser, and addition funnel. Concentrated hydrochloric acid was added slowly and the reaction was maintained at between 70' and 100' C., depending on the amount of acetone added, for 4 to 8 hours.
324
Table 1. A Series of Resins Was Prepared b y Heating Acetone and Resorcinol Resorcinol/ Acetone Mole Ratio 1 :I 1 :2 1 :3 1 :4 1 :8
Resulting Intermediate M.P., C. Mol. V't.a 108-110 175-180 218-220 210-220 200-205
1200 1700
3700 3000 3600
a Apparent weight-average molecular weight from light scattering measurements of polymer in methyl ethyl ketone solution.
When the molar ratio of resorcinol to acetone was 1 to 3 or greater, the reaction mixture slowly changed to a light amber color; when the resorcinol-acetone ratio was less than 1 to 3, the reaction mixture became dark red in color. The excess of either acetone or resorcinol and acid catalyst was removed by repeated flocculation-precipitation of an acetone
INDUSTRIAL AND ENGINEERING CHEMISTRY
solution of the resin in violently agitated water. The resinous material was isolated, dried, and characterized. The resulting resins were white powdery solids. The melting points of the resins increased from approximately 100' C. with a 1 to 1 reaction ratio of resorcinol to acetone to approximately 170' C. with a ratio of 1 to 2 and finally to above 200' C. for ratios of 1 to 3 or greater. The resins were fusible and soluble in ketones and aromatic hydrocarbons. Ilard, transparent yellow films could be formed from the melted resin or from the resin solution by evaporation of the solvent. Weight average molecular weights, as determined from light scattering measurements of the resin in methyl ethyl ketone solution, increased from approximately 1200 for the 1 to 1 ratio to approximately 3600 for the 1 to 8 ratio. Infrared spectra indicated the presence of multiple hydroxy groups (3.0 microns) and also the presence of five- or six-membered oxygen-containing cyclics (9.3 to 9.5 microns). Yields were high, 80 to 90%, based on model structure (I).
