NOVEL HIGH-PERFORMANCE EPOXY RESINS A. C. SOLDATOS A N D A. S. B U R H A N S Union Carbide Corp., Bound Brook, ‘V. J .
The chemistry involved in the preparation of high performance cycloaliphatic epoxy resins b y reaction of bis(2,3-epoxycyclopentyl) ether with hydroxy compounds, catalyzed by tertiary amines, is described. These resins showed substantial improvement in cast resin properties and reinforced composites performance over conventional epoxies.
HE
development of high-strength filaments in recent years
Tfor use in reinforced structures has increased the need for
epoxy resins of improved strength. T o realize the maximum potential of the newest higher strength glass, boron, and carbon filaments, substantial improvements in the performance of epoxy matrices are indicated. T h e major objectives of this investigation, which was conducted under contracts sponsored by the Air Force Materials Laboratory, were: T h e development of new types of epoxy resins with cast properties-namely, compressive, flexural, and tensile-substantially higher than those of the state-of-the-art materials. T h e development of resin-hardener systems which can be used for the fabrication of practical reinforced structures. T h e reinforcements, pre-impregnated with these systems, should be storage-stable “prepregs” which would remain soft and tacky prior to curing. These objectives have been met to a very large extent. Several resins with outstanding performance, both in cast properties and in composites, have been developed, and significant progress has been made toward the development of stable prepregs. Some understanding of the chemistry of these resins has also been developed. T h e chemistry and the cast and composite properties of the three resins, ERLA-4305, ERLA-4300, and ERLA-4617, which exhibited high performance, are discussed and these resins are compared with two commercial state-of-the-art resins, ERLA2772 and Epon 828/1031.
and this product, which contains a small amount (approximately 10%) of liquid isomers, is designated ERRA-0300. No attempt has been made to separate the individual isomers. ERLA-4617 is the copolymer of bis(2,3-epoxycyclopentyl) ether (ERNA-4205) and ethylene glycol, catalyzed with benzyldimethylamine. The state-of-the-art epoxy resins used for comparison purposes in this study are ERL-2772 and Epon 828/Epon 1031. ERL-2772 is essentially the diglycidyl ether of bisphenol A. This liquid resin is used in “wet-lay-up’’ techniques which consist of impregnating the reinforcement immediately prior to assembling the composite to be cured.
/O\
CH2-CH-CH2-0-
Epon 828jEpon 1031 is a mixture of equal parts of Epon 828 and Epon 1031. Epon 828 is essentially the diglycidyl ether of bisphenol A, and Epon 1031 (which is solid) is the tetraglycidyl ether of tetrakis(hydroxypheny1) ether. This resin is used in prepreg systems, by impregnating various types of substrates which are wound on spools and stored for subsequent composite preparation. EPON 828lEPON 1031
0 / \
0 / \
CH2 -CH-CHz-O-
0-1-
Epoxy Resins
ERLA-4300 and ERLA-4305 are the “homopolymers” of bis(2,3-epoxycyclopentyl) ether produced by reaction with water in the presence of a tertiary amine. ERLA-4300 was produced from essentially all solid isomers (ERRA-0300) and ERLA-4305 was produced from a mixture of about 2 parts of solids to 1 part of liquid isomers (ERNA-4205). 0
CHz-CH-CHz- 0\ /
Q-O-CH2-CH
‘0’
H
0
- CHz
EPON 1031
CH3
n
EPON 8 2 8 Experimental
ERRA-0300
90%SOLlDS-IO% LlOUlD ISOMERS
ERNA-4205
65°hSOLlDS-35%L10UlD
ISOMERS
T h e bis(2,3-epoxycyclopentyl)ether, ERNA-4205, theoretically consists of ten liquid and solid isomers. T h e ratio of solid to liquid isomers is approximately 65 to 35. T h e solid isomers are physically separated by distillation from the ERNA-4205
Preparation of ERLA-4300 and ERLA-4305. These resins were prepared by reaction of 1 mole of bis(2,3-epoxycyclopentyl) ether with 1 mole of water for 7 hours a t 100’ C. in the presence of 3.9Yo by weight of the tertiary amine, benzyldimethylamine (BDMA). T h e unreacted water, tert-amine, and a portion of the monomer are removed by distilling to 150’ C. under 8 mm. of pressure. T h e distilled product is dissolved with toluene and the solution is then purified by water extraction. Finally, the toluene and the residual water are removed by vacuum stripping. Both resins are low viscosity liquids (approximately 3500 centipoises), VOL. 6
NO. 4
DECEMBER 1967
205
Table 1. Cast Resin Properties ERLA-2772 EPON 82811037 ERLA-4300 ERLA-4305 MNAa 1BDMA m-PDAb m-PDA m-PDA Compressive modulus, p.s.i.< 441 ,000 551,000 985,000 987,500 Compressive strength, p.s.i. 19,200 21,600 37,150 35,650 Tensile modulus, p.s.i.d 458,000 507,000 842,000 871,500 Tensile strength, p.s.i. 12,900 9,100 13,650 15,650 Flexural modulus, p.s.i.e 462,000 597,000 870,000 910,000 Flexural strength, p.s.i. 23,250 23,800 17,500 16,400 Heat distortion temp., O C.f 158 143 115 115 ERLA-4305, ERLA-4617 cure cycle. 4 hours at 85' C . 3 hours at 120' C . 16 hours at 160' C . a Methyl nadic anhydride. m-Phenylenediamine. C ASTM D 695-63T. d ASTM D 638-64T. e ASTM D 790-66.
+
ERLA-4300
"HOMOPOLYMER" FROM ERRA-0300
ERLA- 43 05
'I
HOMOPOLYMER" FROM ERNA-420 5
Preparation of ERLA-4617. This very low viscosity liquid (70 centipoises) copolymer was prepared in the same way as the above homopolymers. I n this case 1 mole of ERNA-4205 reacted with 0.5 mole of ethylene glycol and 3.9% by weight of benzyldimethylamine. n
n
+
ERLA-467 7 m-PDA 890,000 32,800 783,000 19,200 815,000 31,000 175 ASTIM D 648-56.
the-art materials, except that ERLA-4300 and ERLA-4305 are lower in heat distortion temperatures. The improvements over the state-of-the-art resins in compressive, flexural, and tensile properties range from approximately 25 to 110%. ERLA-4305 and ERLA-4300 are the first :'prepregable" resins to exhibit 1,000,000-p.s.i. compressive moduli and greater than 37,000-p.s.i. compressive strengths. ERLA-4617 exhibited somewhat lower, but still very high, modulus and strength under compression (890,000 and 32,800 p.s.i., respectively), outstanding tensile strength (19,200 p s i . ) , and substantially higher heat distortion (175' C. us. 115' C.). The flexural strength of this resin is 31,000 p s i . , the highest observed for any epoxy cast resin. Reaction Mechanism
Cast Resin Properties. T h e typical cast properties of the above resins are shown in Table I. ERLA-4300, ERLA-4305, and ERLA-4617 are all significantly superior to the state-of-
i2000
ERNA-4205:H20-I:I MOLE BDMA 2 % BY WT, BDMA 3.9% BY W L BDMA 0.0 % BY WT.,--,--
In view of the large number of intermediate products formed in the course of this reaction, it is difficult to show the exact mechanism. However, we postulate a probable mechanism, based on our experimental data and those previously reported by others on the reactions of glycidyl ethers (Narracott, 1953; Shechter and Wynstra, 1953). I t is believed that the reaction is essentially ionic and during the initial stages of the reaction the tert-amine reacts with the bis(2,3-epoxycyclopentyl) ether to form the alkoxide ion.
--/.
/ I /
We believe that this alkoxide is not capable of opening a new epoxy group and therefore propagates the polymerization in a sort of epoxy-epoxy reaction. This conclusion is supported by the following facts:
HOURS
Figure 1. ERLA-4305 epoxy assay vs. reaction time at various BDMA concentrations 206
l & E C P R O D U C T RESEARCH A N D D E V E L O P M E N T
Heating 100 grams of ERNA-4205 with 3.9 grams of anhydrous benzyldimethylamine (BDMA) for 20 hours a t 150' C. did not change the composition of the reaction mixture, as shown by the lack of any appreciable change in epoxy assay. When ERNA-4205 reacted with water in the presence of BDMA, approximately 59% of the tert-amine catalyst was found chemically bound in the final product. The rate of polymerization increases significantly with a n increase of BMDA concentration. This effect was studied in three experiments which consisted of reaction of equimolar amounts of ERNA-4205 and water in the presence of 2.0, 3.9, and 8.0% of BDMA. When epoxy assay values were plotted against reaction time (Figure 1) the rate of reaction increased
as the concentration of the amine increased from 2.0 to 3.9 to 8.0%. We postulate that the quaternary base formed by the reaction of the BDMA and bis(2,3-epoxycyclopentyl) ether (reaction step I, Figure 2) is not a polymerization catalyst because of the insufficient separation of the charges. Addition of water results in increasingly faster rates of reaction, suggesting reaction step I1 (Figure 2) which separates the charges and thereby produces the reactive hydroxyl ion, OH-. This ion will add to an epoxide group and thus propagate the polymerization (reaction step 111, Figure 2). More water can also react with the polymer chain or the intermediate alkoxide (reaction step IV, Figure 2). T h e importance of the water in this reaction was substantiated in three experiments. ERNA-4205 reacted with water a t the molar ratios of 1 to 0.5, 1 to I , and 1 to 2 in the presence of 3,9y0by weight of BDMA. T h e epoxy content of the reaction mixture was plotted against reaction time (Figure 3 ) . I t is evident from the slopes of the three curves that the rate of reaction increases with increasing water concentration. Further support for the water-epoxy reaction is shown in Figure 4, which is based on the equimolar ERNA-4205-rvater reaction catalyzed with 3.9% BDMA. T h e moles of water reacted per mole of the diepoxide, and the calculated epoxy assay based on the amount of water reacted, as well as the actual experimentally determined epoxy assay values, were plotted against reaction time. T h e actual assay is much higher than the calculated value, indicating that the alkoxides and hydroxyls generated by the reaction with water reacted with epoxy groups.
‘The above mechanism indicates that during the polymerization various molecular species must be formed, which vary greatly in reactivity with the m-phenylenediamine (m-PDA) hardener. From the analytical evidence shown in Tables I1 and I11 we further postulated that in addition to the reactive dimer and higher molecular weight homologs. monofunctional (monoepoxide) and nonfunctional cyclic and linear polymers are also formed. The bulk of these compounds is removed by the water extraction of the resin, but undoubtedly the final product will retain some of these impurities. O u r analytical data indicate high hydroxyl content and low epoxy functionality for these impurities, which are consistent with their high solubility in water and low degree of reactivity with m-PDA. We suggest that some of these compounds have the molecular configurations shown in Figure 5.
- - --
ERNA-4205: H20,1:0.5 E R N A - 4 2 0 5 : H20, I:I ERNA-4205: H20.1:2-.--BDMA 3 . 9 %
5000 400C
/ / ’
3000
2 3
$ z
200c
a a
0
>
1000
a a
0
i
I
/ / / /
/ m,,
2
i
>
8n W
I.
/
/
/
/
./,
200
’4
It.
2
6
4
8
IO 12 14 16 I6 20 22 24 26 HOURS
+
Figure 3. ERLA-4305 epoxy assay vs. reaction time a t various water concentrations
m.
E,
+OH0 0 +H20--i,
OH
O@
0
D O - ( J OH OH
+OH@
0
Figure 2. Reaction of bis(2,3-epoxycyclopentyl)ether with BDMA and water
.I
.p ,
,
I
,
2
4
6
8
,
,
I O 12
,
,
Figure 4. ERNA-4205-water 3.9% BDMA VOL. 6
,
,
,
,
,
14 16 18 20 22 24 26 HOURS
NO. 4
reaction catalyzed
with
DECEMBER 1967
207
Sample 1 2 3 Table 111.
Sample 1 2 3
I
Table II. Material Analysis Epoxide E uivalent, G.lEguivalent N o , Av. of Epoxide Mol. W t . % IV 262 374 0.4 400 393 0.4 888 477 0.6
I-
OH
o/
P-( I w
o OH
%O
26.70 50.26 28.96
I
2
Number of Functional Groups and Dicyclopentyl Ether Units per Molecule
Total 6.23 7.42 8.63
Hydroxy 1.30 2.83 3.66
Oxygen Epoxy 1.27 0.98 0.54
Dicvclope& Ether Units 1.945 1.924 2.410
N's*
Ether. 3.66 3.61 4.43
0.10 0.11
0.20
+
Determined by dtyerence, ether 0 = total 0-(hydroxy epoxy 0 ) . b Because of low nitrogen content, confrgurations involving this atom were ignored. 0
Table IV. ERLA-4300 m-PDAa
3
4
Figure 5. Cyclic and noncyclic species of reduced functionality
Properties of laminates, 18 1-S-994-HTS Cloth ERL A-4305 ERLA-4617 ERLA-4617 m-PDA" m-PDA m-PDA
ERLA-2774 m-PDAb
Edgewise compressiveC strength, p.s.i. 79,900 83,600 85,400 84,000 56,000 Modulus, p.s.i. 4,320,000 4,540,000 4,350,000 4,130,000 3,980,000 Flexural. strength at 75" p.s.1. 125,000 ... 134,000 ... ... Flexural. modulus at 75" p.s.1. 4,090,000 ... 4,390,000 ... ... Cure cycle. 5 hours at 105' C. 16 hours at 120' C. f 16 hours at 160' C. E R L A - 2 7 7 4 is very similar to ERLA-2772. A S T M D 695-65 with rectangular specimen. Test specimensprepared from prepreg.
+
The analytical evidence was obtained from the following experiment. Formulation Bis(2,3-epoxycyclopentyl)ether, ERNA4205 J$7aier, distilled Benzyldimethylamine
Weight, Grams
3990 378 i 5 5 . 6 (3.9% wt. on ERNA-4205 )
The reaction mechanism and molecular structure proposed for ERLA-4617 are similar to those of ERLA-4305. The only obvious, major, expected difference is that some ERNA-4205 molecules are connected with ethylene glycol ( - O C H r CHz0-) units instead of oxygen. This configuration would also decrease the probability of cyclic formations, which is probably reflected by the higher heat distortion and higher flexural strength of the resin.
Procedure
T h e reactants reacted for 7 hours a t 100-09.5' C. in a 5liter flask equipped with an agitator, thermometer, and reflux condenser. The reaction mixture was then distilled to 150' C. under 8-mm. pressure. T h e residue was designated specimen 2. A portion of specimen 2 was dissolved in toluene and the solution was then extracted with water. The toluene and the residual water were removed by vacuum distillation to 130' C. under 50-mm. pressure. T h e residual material was designated specimen 1. T h e water wash was subjected to flash evaporation using a rotary film evaporator (130' C. and 50mm. pressure) for recovery of the removed water-soluble organic material. This residue was designated specimen 3. The above samples were subjected to further analysis employing nuclear magnetic resonance (NMR) techniques. Our primary objective was the characterization of the oxygen (type of oxygen) of the various samples. This analytical tool enabled us to determine the oxygen of the hydroxyl groups. With this additional information a t hand, we then calculated the number of functional groups and dicyclopentyl ether units in each of the three specimens (Table 111). 208
l & E C P R O D U C T RESEARCH A N D DEVELOPMENT
Table V.
Properties of Unidirectional Flat laminates EPON ERLA8281 1031 ERLA-4300 4617 MNAIBDMA m-PDA m-PDA
Interlaminar shear strength, p.s.i. 11,600 Edgewise compressive strength (NASL), p s i . 192,000 Modulus, p.s.i. 8,200,000 Flexural-3 point loading strength, p.s.i. 344,000 8,350,000 Modulus, p.s.i. Tensile-90' to fibers 6,100 strength, p.s.i. Modulus, p.s.i. 2,410,000 Resin content, wt. 70 23.0 Void content, vol. 70 1 .o Cure cycle. 5 hours at 105' C. hours at 160' C.
+
12,900
15,000
228,000 8,333,000
246,000
...
380,700 8,620,000
...
8,000
...
3,570,000 22.0
... I
.
.
23.0 1 .o 0.5 16 hours at 120' C. 4- 16
Composite Properties
or ethylene glycol in the presence of benzyldimethylamine, we have produced novel epoxy resins of greatly improved performance over the state-of-the-art resins, ranging from 25 to 110% in compressive, flexural, and tensile cast properties. Improvements in the corresponding composite properties ranged from 11 to 53% and it is expected that even better over-all performance can be realized by improved cure and handling techniques. These resins can be used as practical prepreg systems.
This study demonstrated that these novel resins, which have exhibited high cast resin properties, impart high performance to glass-reinforced composites. T h e data reported in Tables IV and V were obtained from composites prepared with S-994-HTS glass cloth or roving. T h e properties shown in Table IV are from cloth composites prepared by both “wet-lay-up” and prepreg techniques. The resin and void contents of the composites were approximately 35 __ to 38% by weight and 1% by volume, respectively. ERLA-4617 and ERLA-4305 exhibited 50 to 537, greater edgewise compressive strength than the state-of-the-art system and good prepreg stability. Prepregs were soft and tacky for 3 days at 77’F. and more than 6 weeks at O’F. I n the case of flat unidirectional laminates (Table V), these novel resins again exhibited significant improvements over the state-of-the-art resins in interlaminar shear, edgewise compressive, flexural, and tensile strengths ranging from 11 to 307,
Acknowledgment
The authors express their appreciation to the Air Force lMaterials Laboratory, Research and Technology Division, Air Force Systems Command, Wright-Patterson Air Force Base, Ohio, for sponsoring the above investigation. They gratefully acknowledge the contributions to this project of C. M. Eichert, J. L. Welch, Jr., W. P. Mulvaney, J. R. Harvey, S. G. Smith, Jr., R. F. Sellers, and L. F. Cole.
improvement. ERLA-4617 and ERLA-4305, particularly the former, represent the resins with the greatest observed and potential performance. By the reaction of bis(2,3-epoxycyclopentyl)ether with water
literature Cited
Narracott, E. s., Brit. PLastjcs26, 120 (1953). Shechter, L., Wynstra, J., Ind. Eng. Chem. 48, 86-93 ( 1 9 5 3 ) . RECEIVED for review March 6 , 1967 ACCEPTED September 8, 1967
PROCESS FOR THE PRODUCTION AND PURIFICATION OF CARBOXY TELECH ELlC POLY M ERS C
. A.
W E
N T Z A N D E. E
.
H0
P P E R , Philli$s Petroleum Co., New
Y o T ~N, .
Y.79995
The polymerization of 1,3-butodiene in the presence of 112-dilithio-1,2-diphenylethane initiator and subsequent carboxylation to yield carboxy telechelic polybutadiene (Butarez CTL, Phillips Petroleum Co.) was studied. The resultant mixture was washed with methanol to remove the lithium chloride catalyst residue from the polymer. Azeotropic distillation and phase separation were employed to separate the methanol from the cyclohexane solvent. The methanol and cyclohexane were recovered.
HE TERM “telechelic polymers” has been used (Wentz and THopper, 1966) to define polymers which are produced from vinylidene-containing monomers and have a reactive group on each end of the polymer molecule. Such polymers can be prepared by polymerization of vinylidene-containing monomers in the presence of a n organo alkali metal catalyst, as illustrated by the following general equation: X
[R,]
+ Y-R2--Y+
Y-
[Ri]-R2n
[Ri]--Y
thus formed is in solution for later treatment by the carboxylating agent, carbon dioxide, according to the following equation : Y-[R1l,-Rz-[R1]-Y z-n
0
/I
Y-0-c-
(1)
z-n
T h e polymer molecular weight will be greatly influenced by the type of monomer and the amount of initiator used in the above reaction. T h e terminally reactive polymers are usually liquids, that have molecular weights in the 1000 to 20,000 range. However, the proper selection of monomer and amount of initiator can result in the production of semisolid and solid terminally reactive polymers with molecular weights as high as 150,000. This polymerization is generally carried out in a suitable polymer solvent-e.g., paraffins or cycloparaffins-that contain four to 10 carbon atoms per molecule. T h e polymer
+ 2 co*+ 0
II
[R,I-c-0-Y
[R+Rz n
(2)
z-n
T h e conversion of the metal salt groups to carboxy groups can be accomplished by the addition of anhydrous hydrogen chloride, 0 /I 11 Y-O-C-[RI]-R~[R~]-C-O-Y
0 II II
+ 2HC1-+
x-n
n
0
0
I/
ll
H-O-C-[[Ri]--R-[[R~]-C.--O-H n
VOL. 6
z-n
NO. 4
+ 2YC1
DECEMBER 1 9 6 7
(3)
209
