SYNTHESIS AND PROPERTIES OF TETRAPOLYETHER ELASTOMERS Z. T. OSSEFORT, R. R. F R E E M A N , A N D F. B. TESTROET
Rock Island Arsenal Research Laboratories, C . S Arm?' W e a p o n s C o m m a n d , Rock I s l a n d , Ill 61201
Tetrapolyether elastomeric gums were prepared from various ratios of epichlorohydrin, ethylene oxide, propylene oxide, and allyl glycidyl ether in a solution polymerization using water-modified trialkyl aluminum catalysts. The high molecular weight gums were essentially linear and amorphous, as indicated by their solubility in acetone. Carbon black-reinforced vulcanizates were prepared from these gums using peroxide and sulfur cures. The low temperature properties were better than those of a commercial epichlorohydrin-ethylene oxide-based elastomer. However, this improvement w a s achieved only through some sacrifice in resistance to hot water and petroleum lubricants.
HIGHmolecular weight alkylene oxide polymers are of comparatively recent origin, the first being polypropylene oxide reported by Pruitt and Baggett (1955). Sumerous low molecular weight polymers of this type have been described, among the earliest of which are polyethylene oxide (Wurtz, 1863) and polymethylene oxide (Butlerov, 1859). Since 1952 a great many high molecular weight polymers have been reported. The success of these polymerizations is due to the discovery of new catalysts which are believed to function through a coordinate anionic mechanism. Monomeric alkylene oxide is coordinated to the catalyst through an unshared electron pair of the epoxy oxygen atom, thereby activating the monomer toward polymerization and providing an orientation of reacting molecules leading to stereospecific polymerization. Furukawa and Saegusa (1963) have given a classification and tabular summary of these catalyst systems which excellently illustrate their extensive application. Price and Osgan (1956) and St. Pierre and Price (1956) have described some of the basic chemistry involved and showed that the epoxide polymers are stereoregular, consisting of a mixture of solid and liquid polymer. The solid fraction is stereoregular and crystalline and may comprise 20 to 65% of the total, depending on catalyst system and epoxide. Other workers reported the use of metal carbonates (Hill et al., 1958), metal sulfates (Bressler and Gurgiolo, 19591, metal salts of organic acids (Gurgiolo, 1960a) and stannous salts (Gurgiolo, 1960b) as catalysts in forming high polymers from alkylene oxides. For reasons previously cited (Ossefort and Veroeven, 1967) the polyether structure appears to offer the best potential for obtaining an elastomer having good properties a t temperatures down to -67" F. along with adequate resistance to petroleum lubricants and fuels. An elastomer of this type is needed for use in military and civilian equipment operating in cold climates. The work of Hendrickson, Gurgiolo, and Prescott (1963) revealed that copolymers of propylene oxide (PO) and allyl glycidyl ether (AGE) prepared using an iron alkoxide catalyst gave vulcanizates with good low temperature flexibility but high swell in oils. Gruber et al. (1964) reported on similar copolymers which also had high oil
swell. Initial efforts in our laboratory (Spearman, 1967) were directed toward improvement of oil resistance by inclusion of a polar monomer in this system. Among those tried, a terpolymer of 861618 mole ratio PO-AGEepichlorohydrin (ECH) gave vulcanizates having the best balance between oil resistance and flexibility a t low temperatures. Oil resistance, however, was still not adequate for many military needs. Recently, E C H elastomers (Willis et al., 1965) prepared using a water-modified alkylaluminum catalyst (Vandenberg, 1960, 1964) have been described: the amorphous homopolymer of ECH and a 1 to 1 mole ratio copolymer of E C H and ethylene oxide (EO). Vulcanizates based on these elastomers offer an excellent combination of properties, including resistance to hot petroleum fluids, but do not have adequate elasticity and flexibility a t temperatures below about -40°F. They are being offered commercially and many of their potential automotive applications have been described (Leach, 1966). The present writing covers structural variations in this polymer system made in an effort to improve the low temperature properties without unduly sacrificing other desirable characteristics. A secondary objective was to obtain both a sulfur- and a peroxide-curable system. T o these ends, various co-, ter-, and tetrapolyether elastomers were prepared using a triethylaluminum-acetylacetonewater complex catalyst. These were compounded and vulcanized, and properties determined. Desired properties for vulcanizates of elastomers synthesized are shown in Table I. An elastomer exhibiting such properties should find wide military application. I n accordance with common usage (but not exact definition) copolymer is used to describe a polymer formed by the reaction of two monomers. Dipolymer or bipolymer would be more accurate but these terms are rarely used. Experimental
Catalyst Preparation. The n-heptane and ether were purified when gas-liquid chromatography indicated it to be necessary. The acetylacetone (AA) and triethylaluminum (TEA1) were used as received from the commercial supplier. VOL. 7
N O . 1 MARCH 1968
17
Table I. Desired Properties of Tetrapolyether Vulcanizates
Propeey or Characteristic
Goal
Tensile, p.s.i. Elongation, Hardness, Shore A Compression set ASTM D 395, Method B, 70 hours at
2000 min. 300 min. 50 to 80
(;
212" F., "b
ASTM D 1229, 70 hours at -67O F., C; Volume change ASTM 3 oil, 70 hours at 212" F., % M'ater. 70 hours at 212' F., ' C Isooctane-toluene. $0 30. i days at RT. ' c Tensile change, 30 days over water at 158O F., % 30 days, ozone cabinet, 50 pphm 0 3 , bent loop specimen 30 days, humidity cabinet, 90% RH, 100"F., bent loop specimen Tensile change, 70 hours at 212" F., air oven, 5 Elongation change, 70 hours at 212" F., air oven, Temperature at which Young's modulus (torsion) is 10,000 p.s.i., ASTM D 1053, Brittleness, ASTM D 746 (nonfailure temp.), ' F. TR50, ASTM D 1329 at 5 0 5 elongation, " F. Processing type Cure types I
(;
O F .
50 max. 50 max. 0 to 20 0 to 5 0 t o 30 -30 max.
No cracks No cracks -15 max. -15 max. -67 max. -67 max.
bottle was removed from the cabinet and cooled, and 60 ml. of ethanol added t o deactivate the catalyst. The polymer was precipitated in n-heptane (4 volumes), and washed with fresh n-heptane and then with fresh n-heptane containing 0 . 2 5 4,4'-thiobis(6-tert-butyl-o-cresol).The polymer was dried in a vacuum oven a t 122°F. for 24 hours. The amorphous content of the polymer was determined by placing 0.2 gram of polymer. in 100 ml. of acetone and allowing to stand for 48 hours with occasional agitation a t room temperature. The amount dissolved was considered the amorphous portion (Kutner, 1962). Solubility and inherent viscosity (based on soluble polymer) were determined from a benzene polymer solution (0.2 gram per 100 ml.). Infrared spectra and elemental analyses were performed on the polymers obtained. The type reaction may be summarized as follows:
A
H r C CH
-,
+
CHZCl
-40 max. Millable Sulfur and
/9 + HZC-CH~
P,
to\
HZC-CH t HC-CHZ I
CH3
5t3A1-CH2( C O C H 3 ) z - H 2 0
1
CHZOCHZCH=CHZ
7 2 hr
at
'
peroxide
The catalyst solution was prepared according to the following recipe: Triethylaluminum (0.1 mole), g. n-Heptane, ml. Ether, ml. Acetylacetone (0.5 mole/mole of Al), g. Water (distilled) (0.5 mole/mole of Al), g.
11.4 140 60 5.01
0.90
The n-heptane was added to a three-necked, 500-ml. flask equipped with a stirrer, nitrogen inlet-outlet, thermometer, and dropping funnel. Prior to the n-heptane addition, the reaction apparatus was flamed under vacuum, and alternately flushed with nitrogen, and exhausted three or four times to remove absorbed moisture and oxygen. The TEA1 was added, followed by ether (slowly), and the mixture was stirred. I t was equilibrated a t 86°F. and acetylacetone added a t a rate to maintain this temperature. Water was then added, and the reaction mixture agitated for 4 hours and stored under nitrogen for 24 hours prior to use. Polymer Preparation. The copolymerizations and tetrapolymerizations were conducted in citrate of magnesia bottles (350-ml.) or 30-ounce pressure bottles that could be fitted with a crown cap. The bottles were baked 24 hours a t 302°F. prior to use. They were cooled under vacuum, and alternately exhausted and flushed (three times) with nitrogen. The bottle was blanketed with nitrogen during all subsequent filling operations. A typical polymerization recipe is: ECH, g. EO, g. PO, g. AGE, g. Toluene, g. Catalyst (1.5 g. TEAl), ml.
42 9 6 3 240 26
The catalyst was added last and the bottle capped. The polymerization was induced by tumbling the bottles in a bottle polymerizer for 24 to 72 hours a t 86°F. Upon completion of the polymerization reaction, the 18
I & E C P R O D U C T RESEARCH A N D D E V E L O P M E N T
l L
A
Tetrapolyether Gun
Conclusive evidence that the four-membered interpolymers are formed rather than mixtures of homo-, co-, or terpolymers has not as yet been obtained. However, infrared spectra of the gums differ from those of homopolymers based on a, b , or c moieties in the above polymer structure and from copolymers of those with d. Formation of the random tetrapolymer may also be inferred from properties of the gums and vulcanizates resulting therefrom, similarity in reactivity of the monomers, and reaction conditions used. Pendant unsaturation in the d moiety provides a site for sulfur and peroxide crosslinking without adversely affecting ozone resistance of the vulcanizates. Results and Discussion
The properties of raw and vulcanized samples of the ECH homopolymer and copolymers based on varying ratios of ECH and EO are given in Table 11. The ratios were calculated from the ECH content determined by analysis for chlorine. Compounding recipes are given in Table 111. I t is evident that the EO concentration may be varied within wide limits without affecting oil resistance. Flexibility a t low temperatures is greatly improved as the EO concentration is increased, but no further improvement is noted beyond 58% by weight EO. The temperature a t which Young's modulus is 10,000 p s i . was chosen as a limiting value, since experience has shown that a t greater stiffness values, a polymer loses its elastic characteristics and becomes unsuitable for use in flexing applications. For most elastomers, this is close to the secondorder transition or glass temperature (T,) (Liska, 1946). The yields of high polymer were poor for all cases except that of the homopolymer (this was the general result throughout this work). The high solubility in acetone indicates that these elastomers are probably essentially amorphous.
Table II. Raw and Vulcanizate Properties of Epichlorohydrin and Epichlorohydrin-Ethylene Oxide Elastomers
ECH EO Composition, Wt. ( (
100 0 88: 12 73/27 72/28 48152 45/55 42 i 58 28 I72
Si Conuersion 95 36 23 12 17 17 11 27
Acetone bility,
Benzene Solubility,
5
CIC
Solu-
100 95 97 96 94 98 97 90
100 88 93 90 97 97 100 89
Fiesibility A S ?'!VI D1053. Young's Benzene" 1.58 1.92 1.81
Vulc. Formulab A B B
1.54 1.61 2.94 1.54
B B B B B
*17inh,
...
TenE, P.S.I. sile, P . S . I . I O E C 3OOCc 1000 170 780 1830 170 760 1270 200 960 1440 420 1300 1300 240 1000 1470 240 $10 820 220 ... 380 ... 160
Elongation,
5; 370 560 340 340 430 640 250 820
Hard- Modulus ness, 10,000 Shore A P . S . I . , F . 60 -2 54 -20 59 -38 64 -36 64 -56 63 -56 63 -58 63 -54
Oil Aging, A S T M 3 Oil, 70 Hours at 212" F .
Vol. su'ell, '1 9 12 10 9 10 8 12 27
Hardness. Shore A 55 48 52 63 56 49 59 34
"Measured at 0.2 gram in 100 ml. based on soluble polymer. bSee Table I I I for curing conditions and formulations of uulcanizates.
Table 111. Formulations and Curing Conditions Parts by Weight A Compound zng Ingredients 100 E C H homopolymer ... ECH/EO copolymers E C H / EO:PO/AGE tetrapoll'mer 1 Agerite Resin D ... Neozone D ... NBC 5 Red lead 1.5 Na-22 ... DiCup 40C (40% active) ... Sulfur ... Zinc oxide ... Methyl Tuads ... Captax ... Stearic acid Lanolin ... FEF black 50 45 Cure test pads, min. a t 310" F. Cure compression set buttons, 60 min. a t 310" F.
B
... 100
... ... ... 1
5 1.5
... ...
... ... ... ... 2 30 45 60
C
D
. . . . . . . . . . . . 100
100
. . . . . . 2
...
. . . . . . . . . . . . . . . . . . ... 5 5 10 2 2 2
... 5
... ...
...
. . . . . . 30 45 60
30 45 60
Properties of raw polymers as well as vulcanizates based on tetrapolyethers prepared from various ratios of E C H / EO/PO/AGE are presented in Table IV. The PO level is shown to be extremely critical in so far as oil resistance is concerned. When one quarter of the monomer charge is PO, oil swell is in the 50'; range, while with onefifth PO it drops to 11%. Further reduction produces little effect. As in the case of the copolymers, the relative proportion of E C H to EO has little effect on oil resistance. However, in contrast t o the copolymers, reduction of the ECH in favor of EO does not improve the flexibility a t low temperatures. The polymerization of the tetrapolyether based on the 4 2 / 9 / 6 / 3 monomer charge was repeated three separate times to establish reproducibility. Results indicate that in batches of similar size, properties of the polymers and their vulcanizates were fairly reproducible. The unsaturation was determined using the method described by Steyermark (1961). Using this unsaturation value, the amount of AGE incorporated into the polymer was calculated and found to compare favorably with the amount charged. The weight per cent of ECH in the tetrapolyethers was calculated from chlorine
Table IV. Raw and Vulcanizate Properties (Sulfur-Cure) of Tetrapolyethers Flexibility ECH,'EOl PO;AGE, Monomer Charge
7; ECH in Acetone Con- PolySoluuermer, bility, sion W t . Y; CiC
Benzene Solubility, R
42/0/15/3 39/3!15/3 42/3/1213 42/6/9/3 42191613 42/9/6/3 42/9/6/3 42/12/3/3 42/15/0/3 311201613 45/6/6/3 48161313 Measured
14 27 55 51 2.13 2050 60 55 1.96 1870 18 28 62 1.84 1850 17 23 68 18 30 91 90 1.50 1730 100 2.09 1220 18 31 100 18 29 92 98 1.50 1260 17 30 100 100 1.86 1540 17 23 53 58 1.16 2010 17 25 77 75 1.30 1930 23 16 81 82 1.96 2040 21 40 82 80 1.91 1350 12 48 93 90 1.88 1400 at 0 . 2 gram in 100 ml. based on soluble polymer.
qrnh,
Benzene'
Tensile, P.S.1.
E, P.S.I. 100'E 30051 960 770 610 600 340 430 390 640 370 390 400 170
1950 1370 1320
...
1220
...
1270 1510 790 920
..
,
460
Elongation, %;
310 290 480 280 300 280 390 480 710 780 250 860
Hardness, Shore A
D1053' Young's Modulus 10,000 P.S.I.,
87 78 56 77 62 71 69 81 70 72 71 55
-20 -35 -54 -54 -62 -62 -60 -54 -53 -62 -49 -54
O F .
Oil Aging, A S T M 3 Oil, 70 Hours at 212" F . Hardness Vol. Shore A swell, SC 73 58 53 67 57 63 54 72 65 61 61 52
VOL. 7 N O . 1 M A R C H 1 9 6 3
52 43 11 19 12 19 15 11 6 10 12 12
19
analyses. I n all cases it was considerably lower than the amount charged, in contrast to results obtained with the copolymers (Table 111, in which E C H uptake was proportional to the charge. The acetone solubilities indicate relatively high degrees of crystallinity in several of these polymers, based on the criteria established by Kutner (1962). Ash content was very low, in most cases less than 0.2% by weight. With the objective of improving low temperature properties, monomers which would provide bulky pendant groups to reduce chain packing were incorporated in place of the PO. No improvement was obtained by using 1,2epoxyethylbenzene. 1,2-epoxy-3-phenoxypropane,glycidoxyphenyldimethylsilane, or glycidoxydimethylchloromethylsilane. To make a more extensive property evaluation, two of the tetrapolyethers which looked most promising were
selected and designated tetrapolyether I (ECH 42/EO 9/ PO 6IAGE 3) and tetrapolyether I1 (ECH 31/EO 20/PO 6/AGE 3), the numbers referring t o monomer charges in grams. Two hundred grams of each were prepared by combining several polymerization runs. The polymers were pale yellow tough rubbery gums, tetrapolyether I having a specific gravity of 1.16. Their high solubility (over 90% in benzene and acetone) indicated that they were essentially uncrosslinked and predominantly amorphous. They banded well on the mill (6 x 12 inches) and showed satisfactory processing characteristics. Attempts to determine the number-average molecular weight (membrane osmometer) gave strong solventpolymer interaction and a reliable value could not be obtained. However, estimations from this work and the inherent viscosity (1.98) would place the molecular weight in the 1.5 to 2.5 x lo5 range.
Table V. Physical Properties of Tetrapolyether-Based Vulcanizates Tetrapolyether 11'
Tetrapol yetherb Control"
Sulfur cured
Peroxide cure'
Sulfur cure'
Peroxide curee
2000
1920
1000
2530
1140
380 1460 440 66
830
730
...
250 70
125 61
380 1240 670 69
530
...
48 70 100 -51
93 34 100 -54
30 26 80 -60
100 96 100 -67
47 94 100 -70
-33
-22 -15
-58 -51 -47 -38
-67 -60 -53 -44
-69 -5 1 -8 +19
-74 -60 -26 +18
-45
-60
-54
-62
-59
1840 400 64 5
1620 210 67 11
820 110 60 15
2630 765 53 4
710 140 47 7
1740 370 53 10
1080 230 53 33
510 125 51 22
780 350 55 36
380 110 40 32
1740 390 56 12
1430 240 65 21
750 140 58 24
...
... ... ...
53 22
63 25
57 28
55 20
52 23
2000 310 66
1940 170 75
1030 115 65
2360 500 68
1170 160 65
OK 30 days
OK 30 days
OK 30 days OK 30 days
OK 30 days
OK 30 days
OK 30 days
OK 30 days OK 30 days
OK 30 days
ECH EO Property Measured Tensile, p.s.i. Modulus, p.s.i. At 100% elongation At 300% elongation Elongation, % Hardness, Shore A Compression set ASTM D 395, Method B, 70 hr. a t 212O F. ASTM D 1229, 70 hr. at -40°F., Ts0,5% ASTM D 1229, 70 hr. a t -67"F., T,,, 5% Brittleness, ASTM i l 746 (nonfailure temp.), F. Temperature retraction, ASTM D 1329, a t 50% elongation T R 10, F. T R 30, F. T R 50, O F. T R 70, F. Flexibility, ASTM D 1053, 10,000 p.s.i., Young's modulus, O F. Immersion ASTM 3 oil, 70 hours a t 212" F. Tensile, p.s.i. Elongation, "c Hardness, Shore A Volume change, % Water immersion, 70 hours a t 212" F. Tensile, p.s.i. Elongation 5% Hardness, Shore A Volume change, % Water immersion, 70 hours a t 158" F. Tensile, p.s.i. ' Elongation, % Hardness, Shore A Volume change, % Immersion, isooctane-toluene, 70130, 7 days a t R T Hardness, Shore A Volume change, ' C Air-oven aging, TO hours at 2 1 2 F . Tensile, p.s.i. Elongation, % Hardness, Shore A Ozone resistance 50 pphm 0 1, bent loop specimen, time to 1st crack, 7X 30 days, humidity cabinet, 9 0 5 R H , 100" F., bent loop specimen, time to 1st crack, 7X
...
... ... ...
... 200 65
...
- H j d r i n 200 B F Goodrich Chemical Co (Wzlils et ai 196j), compounded and cured per column B o f Table 111 'Bused on charge ratio of f o l l o i ~ i n gmonomers zn parts by ueight E C H 42 EO 9 PO 6 A G E 3 ipoljmer contams 30'r b i ueight ECHl Bused on charge ratio of follouing monomers in parts b j ueight E C H ,31 EO 20 PO 6 A G E 3 ipolimer contains l d c r bv ueight ECHI 'Compounded and cured per column C o j Table I I I Compounded and cured per column D o j Table I l l
20
I & E C PRODUCT
RESEARCH A N D
DEVELOPMENT
Table VI. Efforts to Improve Yield by Using Tributylaluminum System a
Catalyst (C,Hj) ,Al, 0.5 mole acetylacetone, 0.5 mole H 2 0 (control) (CAH,) IAl, 0.5 mole dimethylglyoxime (C,Hs) ,Al, 0.5 mole H?O (C,H,) ,Al, 0.5 mole acetylacetone. 0.5 mole H?O
Catalyst Concentration, Yield, G. 10 G. Monomer R I
0.25
18
0.69 0.69
7 17
0.69
12
Poi3werization recipe a n d conditions as &en under Experimental.
Properties of vulcanizates of these two polyether elastomers for sulfur and peroxide cures are given in Table V. A commercial epichlorohydrin-ethylene oxide copolymer (Willis et al., 1965) is included for comparison. Monomeric plasticizers which are frequently used to improve properties a t low temperatures, were not used, since they are volatile and extractable by fuels and lubricants. The sulfur-cured rubbers have much better stressstrain properties than peroxide-cured, but less favorable compression set values a t 212°F. The low temperature properties were generally better for the tetrapolymers than for the control. However, the control had much better resistance to hot water and somewhat better oil resistance than tetrapolyether I. The temperature retraction and low temperature compression set data indicate that tetrapolyether I1 crystallizes, which would limit its use in many applications. The experimental elastomers did not meet established goals in several aspects, notable among which were flexibility a t low temperatures, water resistance, elastic recovery, and in some instances tensile strength. Some of these failures might be corrected by compounding changes. Because of the limited samples available, extensive compounding studies were not made. Tetrapolyether I shows favorable elastic recovery a t low temperatures, as indicated by both the temperature retraction and low temperature set a t -40OF. The ethylene oxide content appears to be very critical in this connection, since increasing the EO from 9 t o 20 parts by weight (out of a total of 60) causes poor elastic recovery in tetrapolyether 11. Some loss in elongation was observed after air-oven aging for 70 hours a t 212°F. but the tensile strengths remained relatively close to original. I n view of the low yields obtained in the tetrapolyether synthesis (15 to 20’%), the following efforts were made for improvement: Doubling the catalyst concencration. Using highly purified reagents. Varying monomer-solvent concentration. Varying catalyst system as indicated in Table VI.
None of these efforts significantly improved yield. Properties of vulcanizates bhsed on elastomers made using the tributylaluminum catalyst were comparable t o properties of those made using the triethylaluminum catalyst. Conclusions
The results presented describe several tetrapolyether elastomers, and vulcanizates prepared therefrom, not
believed to be previously reported. The low temperature properties of these polyethers are considerably better than those of a related commercially available epichlorohydrinethylene oxide copolymer. However, this improvement could be achieved only through some sacrifice in resistance to hot water and hot petroleum oils. The system offers an immense potential for variation and it is possible that other ratios (or monomers) than those selected could lead to an elastomer having the desired properties. The work thus far was not sufficiently definitive to enable an exact choice but only to indicate qualitative future approaches. Acknowledgment
The authors express appreciation to the Army Weapons Command and to the supervisory staff of the Rock Island Arsenal for permission to publish the information given in this paper. literature Cited
Bressler, W. L., Gurgiolo, A. E . (to Dow Chemical Co.), U.S. Patent 2,917,470 (Dec. 15, 1959). Butlerov, A., A n n , 1 1 1 , 245 (1859). Furukawa, J . , Saegusa, T., “Polymerization of Aldehydes and Oxides,” p. 155, Interscience, New York, 1963. Gruber, E . E., Meyer, D. A., Swart, G. H., Weinstock, K. V., IND. ENG. CHEM.PROD.RES. DEVELOP.3, 194 (1964). Gurgiolo, A. E. (to Dow Chemical Co.), U.S. Patent 2,933,459 (April 19, 1960a). Gurgiolo, A. E. (to Dow Chemical Co.), U.S. Patent 2,934,505 (April 26, 1960b). Hendrickson, J. G., Gurgiolo, A. E., Prescott, W. E., IND. ENG. CHEM.PROD. RES. DEVELOP.2, 199 (1963). Hill, F. N., Bailey, F. E., Jr., Fitzpatrick, J. T., Ind. Eng. Chem. 50, 5 (1958). Kutner, A. (to Hercules Powder Co.), U.S.Patent 3,058,923 (Oct. 16, 1962). Leach, W. R., Rubber Age 98, 71-4 (August 1966). Liska, J. W., “Low Temperature Properties of Elastomers,” Symposium on Effects of Low Temperatures on the Properties of Materials, p. 47, ASTM, STP 78 (March 19, 1946). Ossefort, Z, T., Veroeven, W. M., IND.ENG.CHEM.PROD. RES. DEVELOP.6, 12 (1967). Price, C. C., Osgan, M., J . Am. Chem. SOC.78, 4787 (1956). Pruitt, M. E., Baggett, J. M. (to Dow Chemical Co.), U. S. Patents 2,706,181; 2,706,184 (April 12, 1955). St. Pierre, L. E., Price, C. C., J . A m . Chem. SOC.78, 3432 (1956). Spearman, E. J., RIA Techl. Rept., 65-3417, AD627308, Synthesis of Elastomers from Epoxides; CA 66, 10832, 116420d (1967). Steyermark, A., “Quantitative Organic Micro-Analysis,” p. 495, Academic Press, Kew York, 1961. Vandenberg, E . J., J . Polymer Sci. 47, 486-9 (1960). Vandenberg, E. J. (to Hercules Powder Co.), U. S. Patents 3,135,705; 3,135,706 (June 2, 1964); 3,158,580 (1964); 3,158,591 (Nov. 24, 1964). Willis, W. D., Amberg, L. O., Robinson, A. E., Vandenberg, E. J., Rubber World 153, 88-97 (October 1965). Wurtz, A., Ann. Chim. Phys. 69, 330 (1863). RECEIVED for review September 14, 1967 ACCEPTED November 16, 1967 The opinions or assertions contained herein are not to be construed as official or reflecting the views of the Department of the Army. VOL. 7 N O . 1 M A R C H
1968
21
