according to the formulation of Table V I I I . Best results were obtained when the mold was preheated to 130’ to 140’ F. The panels foamed between polyethylene sheeting for effecting release had core densities of about 2 pounds per cubic foot and have been characterized by small uniform cell structure throughout the foam core. Of particular note has been the relatively uniform cell structure adjacent to the foam-mold interface through the height of the panel. Physical properties of molded foam using recipe 9 are summarized in Table I X . The work reported herein is very new and in certain respects incomplete ; however, considerable effort is being extended to improve foams and reduce the cost of this type of foam system. Acknowledgment
The authors are grateful for the physical testing conducted by the Physical Testing Group during the course of this work under the direction of Samuel Steingiser and Harold Staley
and for the assistance of C. D. Ferrell and J. L. Wharton in carrying out the experiments. literature Cited (1) Agnello, L. A., Barnes, E. O., Ind. Eng. Chem. 59, 726 (i960). (2) Am. SOC. Testing Materials, Philadelphia, Pa., ASTM Standards,” 1961. (3) D’Eustachio, D., Schreiner, R. E., A m . Soc. Heating Ventilating Engrs. Trans. 58, 331 (1952). (4) Hoppe, R., tveinbrenner, E., Muhlhauser, C., Breer, K. (to Farbenfabriken Bayer), U. S. Patent 2,764,565 (Sept. 25, 1956). 15) Khawam. A,. Plastics Technol. 5 . No. 6, 31-35 and 50 (1959). ( 6 ) LeBras, L. R.’, S.P.E. Journal 16; 420 (1960). (7) Remington, FV. J., Pariser, R., Rubber World 138, 261 (1958). (8) Rill, J. C., Div. of Chemical Marketing Economics, 139th Meeting, ACS, St. Louis, March 1961. (9) Rill, J. C., Kesling, K. K. (to General Motors Corp.), U. S. Patent 2,962,183 (Nov. 29: 1960). RECEIVED for review October 5, 1961 ACCEPTED February 26, 1962 Division of Organic Coatings and Plastics Chemistry, 140th Meeting, ACS, Chicago, Ill., September 1961. ~I
A R S E N I C PENTOXIDE C U R E OF A N ORGANIC A D H E S I V E f l e w Route to Semi-inorganic Adhesive Polymers HAROLD H . LEVlNE Narmco Research and Development, A Division of Telecomputing Corp., San Diego, Calif.
The reaction of arsenic pentoxide with an epoxy novolak-silicone-phenolic resin system was investigated. The epoxy novolak was polymerized to a polyether, while the silicone-phenolic resin reacted to form a polymer containing Si-O-As+5 linkages. This study points to a new route to semi-inorganic, heat-stable polymers b y reaction of heat-resistant organic polymers with selected inorganic reagents. It may b e possible to avoid difficulties in semi-inorganic polymer synthesis, such as low molecular weight due to insolubilily and hydrolytic instability. Improved adhesive and sealant systems use arsenic trisulfide as the curing agent.
HE major obstacle to achieving a heat-stable adhesive is Toxidation sensitivity. Even at 538’ C. (1000’ F.) the thermal energy input is far below the 80 kcal. per mole required to rupture a carbon-carbon bond. Oxidative degradation of an adhesive is even more severe on stainlesssteel than on aluminum, probably because of iron present in the steel ( 5 ) (Figure 1). This company attempted to find a means of reducing oxidation of adhesives. If some substance could be added to the adhesive which would either act as a catalytic poison or insolubilize iron ions migrating into the adhesive, deterioration of the adhesive would be curtailed or eliminated. The use of arsenic pentoxide was suggested because arsenic compounds were known to act as catalyst inhibitors and because iron arsenate is a n insoluble salt. Effective removal of iron ions from the system was observed in trial experiments. Further work (9) provided the first adhesive containing an arsenic compound in its formulation (Figures 2 and 3). The arsenic pentoxide became an integral part of the adhesive,
96
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
because it was the sole curing agent. Optimum high temperature tensile shear strength was obtained at an arsenic pentoxide concentration of 32 parts per hundred parts of total resin. The most interesting assumption made about this adhesive was : If the arsenic pentoxide was becoming a part of the polymer, this might result in the formation of a semi-inorganic adhesive polymer. Experimental
In addition to arsenic pentoxide, the adhesive consisted of an epoxy novolak, a silicone-phenolic resin synthesized by condensation of bisphenol A with a poly(ethoxyphenylsi1oxane), and aluminum powder. Model compounds were selected to study reactions of the various functional groups. Phenyl glycidyl ether and 1,2epoxydodecane were selected to study the reactions of the oxirane moiety, 1- and 2-octanol and 1,3-diphenoxy-2-propanol to study the reaction of primary and secondary hydroxyl
2000
-
1600
v)
c;
5 1200 0
-c
-.* v)
0 VI
C
-- -Epoxy-phenolic XEpoxy-phenolic ',-e -Modified Epoxy-phenolic
800
400
20 Figure 1.
40
60
80 100 120 140 Time, hours, at 316°C (6OO'F) in Pu'itrogen
160
180
1
m
Relation of exposure time of commercial adhesives a t 316" C. to tensile shear Phosphate etch, 17-7 PH S.S.
Exposure Time, hours
Figure 2.
Tensile shear strength aging and testing at 316" C. (600" F.) in air Phosphate etch, 17-7 PH S.S. Formulation. Epoxy novolak, silicone-phenolic, arsenic pentoxide, aluminum powder
groups, and triphenyle thoxysilane to study the reactions of ethoxy groups present in the silicone-phenolic (page 100). Infrared Spectra. -4 Perkin-Elmer \lode1 21 double-beam recording spectrophotonieter with a sodium chloride prism was used. Liquid and soluble substances were examined in a fixed-thickness sodium chloride cell, while insoluble solids \\'ere examined as mulls in Nujol. Reaction of Epoxy Group. An excess of phenyl glycidyl ether was refluxed for 1.5 hours in the presence of arsenic pentoxide. The infrared spectrum of the brown liquid indicated disappearancr of the oxirane group absorption at 10.95 microns, with the appearance of a hydroxyl group absorption at 2.95 microns. After the excess phenyl glycidyl ether and other low boiling fractions were removed by distillation, attempts to distill the residue appeared to result in some decomposition a t a pot temperature of 210' C. at 0.25 mm. However, about 1 ml. of distillate was collected (b.p. up to 1.5433). Infrared examination of 140' C.10.25 mm., nf
'
this distillate shoived a reversed relationship of the peaks a t 8.70 and 8.90microns when compared to the phenyl glycidyl ether spectrum. The 8.90-micron absorption is assigned to dialkyl ethers-CH2-O-CH2-and it appeared that the distillate was a polyether resulting from polymerization of the phenyl glycidyl ether. The infrared spectrum of phenyl glycidyl ether is fairly complex. \Vith another epoxide such as 1,2-epoxydodecane, only the aliphatic C-C and C-H bonds Ivould be seen and the aromatic absorptions eliminated. Reaction of this epoxide with arsenic pentoxide save a material lvith a much simpler spectrum (Figure 4). The epoxy group \vas consumed, a very strong, broad peak appeared a t about 8.8 microns, and the hydroxyl absorption at about 3 microns \\.as Lveak. \Vhen the reaction solid \vas digested with dilute alkali to dissolve unchanged arsenic pentoxide, 30 mg. of a browm solid remained. Ignition on a spatula shelved good heat resistance, folloived by burning to leave a residue. VOL.
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Exposure Time, hours
Figure 3.
Tensile shear strength aging and testing at 260"
C. (500" F.)
Phosphate etch, 17-7 PH S.S. Formulation. Epoxy novolak, silicone-phenolic, arsenic pentoxide, aluminum powder
A.
1,P-Epoxydodecane
5.
1 ,P.Epoxydodecane after reaction with Asp03
The ultraviolet spectrum showed small peaks at 216 to 217 mp probably due to phenyl groups. The solid was unmelted a t 300' C. with some softening and was insoluble in toluene. methyl ethyl ketone, dimethylformamide, and dimethylsulfoxide. An infrared spectrum of a Nujol mull indicated a polyether \vith a very weak hydroxyl absorption. Reactions of Hydroxyl Groups. it'hen an excess of ethylene glycol \vas refluxed Ivith arsenic pentoxide, a 6070 yield of dioxane was obtained [b.p. 100' C., 1.4230; literature values b.p. 101.4' C . and r ~ $ 1.4221 ( 4 ) ] ; Xvith arsenic acid, yield was 757,. The reaction of an excess of 1-octanol with 0.352 mole of arsenic acid was carried out because this alcohol could not cyclize. A yield of 1.12 moles of water \vas obtained in the Dean-Stark trap ; this corresponded closely to the theoretical yield of 1.06 moles if esterification occurred. Fractional distillation ga\.e small amounts of l-octanol [b.p. 54-3" C.,'0.44 98
l&EC PRODUCT RESEARCH A N D DEVELOPMENT
mm., n: 1.4297; literature b.p. 184-85' C., ny,' 1.4304 ( 3 ) ] and di-1-octyl ether [b.p. 100-03' C. 0.4 mm., :n 1.4328. literature: b.p. 286.5' C.?:n 1.4305 ( S ) ] . These were confirmed by comparison of the infrared spectra with authentic samples. Redistillation of the major fraction (b.p. 194207' C.I'O.4 mm.) gave a material boiling at 198-204' C.I'O.44 mm., n? 1.4564 [literature for trioctyl arsenite, b.p. 21113' C. '2.5 mm., n$ 1.4569 ( 7 1 ) ] . This was shown to be the trioctyl ester of either arsenic or arsenious acid when hydrolysis of 2.1 mmoles of the distillate gave 6.24 mmoles of 1-octanol. The crude reaction mixture also gave low boiling fractions (b.p. 85-180' C.) which upon redistillation and drying of the water azeotrope gave a small amount of an olefinic material with an absorption at 6.05 microns. The reaction of 0.77 mole of 2-octanol with 0.176 mole of arsenic acid was carried out under reflux conditions. A total of 5.0 grams of water was collected in the Dean-Stark trap,
8
10
9
11
12
13
WAVE LENGTH (MICRONS)
Figure 5. A. B.
Infrared spectra
Phenylrnethyldiethoxysilane Phenylrnethyldiethoxysilane after reaction with As206
while the reaction temperature increased to 197.5 ' C. during 75 minutes. During the next 12 hours, the pot temperature decreased to 176' C., \vhile a n additional 3.0 grams of water was collected. Fractional distillation gave a n additional 5.4 grams of water and an 8370 yield of mixed octenes [b.p. 120-22' C., n? 1.4114. Literature: 1-octene b.p. 121.9122.1' C., ."," 1.4088 (2); cis-2-octene b.p. 124.1-124.7' C., n'," 1.4150 ( I ) ; and trans-2-octene n z 1.4132 (Z)] based on Zoctanol. T h e yield of water based on 2-octanol was 96.87,. Infrared examination of the olefin revealed it to be a mixture of 1-octene and cis- and trans-2-octenes. Interaction of lj3-diphenoxy-2-propano1 with either arsenic pentoxide or arsenic acid failed to show any signs of reaction upon infrared analysis. Of particular interest was the failure to detect olefinic absorptions. Reactions of EtO-Si- Linkage. Interaction of triphenylethoxysilane and arsenic acid resulted in complete solution a t 100' C . Continued heating to 200' C . gave a precipitate which was collected. washed with ether, and dried. This whitr solid was insoluble in a variety of solvents and had a melting point of 208-10 ' C. Infrared analysis showed a strong peak a t 10.80 microns. T h e Si-O-As+b linkage has been assigned a t 10.97 microns ( 6 ) . T h e absence of the broad, strong absorption between 9 and 10 microns indicated the lack of Si-0-Si linkages (Figure 5).
\Yhen the reaction was repeated under forcing conditions with phenylmethyldiethoxysilane, the Si-O-As+S absorption was found at 11.O microns, having shifted closer to the assigned 10.97 microns (see Figure 4). The reaction of arsenic pentoxide with phenyl glycidyl ether primarily resulted in the homopolymerization of the oxirane compound to give a polyether, with some "normal" polymerization to the polymer containing secondary hydroxyl groups. The high melting solid had a n increased absorption at 8.9 microns, indicating formation of the C - 0 - C linkage, while only a very weak hydroxy peak was found. This was interpreted as evidence for terminal hydroxyl groups present in a polyether of the following structure:
r
i
8 The formation of the aliphatic polyether is considered one reason for improved thermal stability of the adhesive. The polyether should be more heat-stable than the normal polymer, because almost no secondary hydroxyl groups are present to undergo dehydration via beta elimination to form an olefin; VOL.
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Adhesive Ingredients
I
- - - -0- 7
OCHKHCH~
OCHK~CH~
iModel Compound 0 I\ OCH2CHCH2
O '' OCH~CHCH~
S
[ @:Fq&:Hz$-$ L---l
Epoxy Novolak
Phenyl glycidyl ether
r
1
I
h
nnr.
r
OH yHCH2O
0
1,3-diphenoxy-2-propanol
Epoxy Novolak Polymer
0-
EtO-Si 0
l
0-
0-I-
S i - 0 LI, TSi-OEtl 1
0
OEt Me
0
0
- C - Me
O-6-
OEt
0
I
XR-820bisphenol-A Condensate
the double bond would be easily oxidized at elevated temperature, leading to degradation of the polymer chain. One other advantage may result from the polyether structureimproved flexibility because of favorable bond angles. The reactions of the primary and secondary hydroxyl groups showed that both arsenic pentoxide and arsenic acid can function as efficient dehydrating agents. \Vith the primary alcohol, esterification to the arsenic ester was the preferred reaction, with ether formation as a side reaction. LYith the secondary alcohol, olefin formed in excellent yield. The course of the reaction with 2-octanol appeared to involve formation of the intermediate substituted arsenic acid as shown by an increase in pot temperature, followed by a drop in pot temperature as the lower boiling olefin was formed. Since the secondary alcohol gave the olefin as the major product, this was a matter of some concern. If this occurred in the adhesive: the high temperature properties would be adversely affected because the olefin would be oxidized. However, the reaction between 1,3-diphenoxy-2-propanol and arsenic acid failed to give evidence of olefin. I t thus appeared that olefin will not be formed in the adhesive system because is the secondary hydroxyl group in 1,3-diphenoxy-2-propanol much closer structurally to an epoxy polymer than the secondary hydroxyl group in 2-octanol. This, incidentally, points out the dangers inherent in the selection and use of model compounds. 100
l & E C P R O D U C T RESEARCH A N D DEVELOPMENT
Triphenylethoxysilane
The reaction between triphen)-lethoxysilane and phenylmethyldiethoxysilane with arsenic acid established the formation of the Si-O-Asf5 linkage. Since the Si-OEt moiety was present in the adhesive, it appeared reasonable to assume that the cured adhesive also contained these Si-O-.4s+s linkages and thus was converted to a serni-inorganic system. The presence of the Si-0-Et bond in the adhesive was based upon the synthesis to produce the bisphenol A-silicone polymer.
,\Ie.C.hIe
4
+
EtO-Si - 0 I OEt
-
Si
I
-0 -
OEt
SI
I OEt
-
OEt-Resin
+ EtOH
OH
In this condensation, gelation will occur readily if the reaction is carried too far. A gelled polymer resulted when 50% of the theoretical amount of alcohol was distilled. I n practice, the condensation is carried out until 45 to 4870 of the ethanol is obtained. Thus, the resin used in the adhesive contained Si-OEt groups which were available for reaction with the arsenic curing agents. The thermogravimetric analyses curve indicated good stability up to 371 O C. (700' F.) with fairly rapid weight loss at
1200 1
600 I
I
I
I
I
I
I
I
I
I
100
200
300
400
500
600
700
800
900
I
1000
Time, hours
Figure 6.
Tensile shear a t
260" C. (550"F.) in air
Phosphate etch, 17-7 PH S.S. Formulation. Epoxy novolak, silicone-phenolic, arsenic trioxide, arsenic trisulfide, aluminum powder
538' C. (1000" F.) ; thermal stability of the arsenic-containing that hydrolytic stability was dependent on film crystallinity system was decidedly inferior to a poly(aluminosi1oxane) and and wettability or solubility in water in addition to the rate of somewhat poorer than a good phenolic resin filled with alumihydrolytic attack. Factors favoring the hydrolytic stability of num. Hoivever. the oxidation stability of the Si-O-As+S the adhesive are its highly cross-linked structure and high polymer was decidedly better for long periods of time at 31 6 O C. molecular weight, which reduced solubility. (600 F.) than the more heat-stable phenolic system. T h e hydrolytic stability of the Si-O-As+S cured adhesive is Summary decidedly superior to most Si-0-metal bonds, as shown by salt Insight into the part played by arsenic compounds in curing spray exposure and water immersion tests. Kary and Frisch the epoxy novolak-silicone-phenolic polymer led to a new con( 70) studied the hydrolysis of C1-Si(R),-O-A4s(0)-O-Si(R)~Cl cept of synthesizing semi-inorganic adhesives. Much effort and observed that the hydrolysis gave polymers containing has gone into the synthesis of semi-inorganic polymers by polyarsenic and silicon. although some cleavage of the Si-0-As merization of semi-inorganic monomers. -4lthough a wealth bonds occurred. Chamberland and MacDiarmid (7) found of new chemistry has resulted, a polymer with sufficient mothat the hydrolytic stability of Si-0-As linkages varied from lecular weight to have structural integrity has yet to be obremarkable stability to very rapid attack. They believed tained, primarily because of premature precipitation of the growing chain. Our current research is concentrating upon the reaction of heat-stable organic polymers Tvith reactive inorganic reagents, to obtain polymers with molecular Iveights sufficient l8O0 to be useful for structural applications. A new adhesive and sealant system was developed. The organic resins used were the same; the major difference was the replacement of arsenic pentoxide by arsenic trisulfide as the curing agent. Preliminary data on these materials are shown in Figures 6 and 7 .
1
literature Cited
(1) Beilstein's Handbuch der Organischen Chemie, 1-200, 2nd suDDlementarv volume. (2) Bkilstein's Handbuch der Organischen Chemie, 1-221. (3) Zbid., 1-418. (4) Ibid., XIX-3. (5) Black, J. M., Blomquist, R. F., Adhesives Age 5 , 30 (1962). (6) Chamberland, B. L., MacDiarmid, 4.G., J . Am. Chem. SOC. 8 2 . 4542 (1960). (7) Zbid., 83, 549' (1961). (8) Devaney, L. \V., Panian, G. Li'., Ibid., 75, 4836 (1953). (9) Janis, E. C., Boram, W. R.: Riel, F. J., Susman, S. E., LVright Air Develop. Center, WADC Tech. Rept. 59-11 (February 1959). (10) Kary, R. M., Frisch, K. C., J . Am. Chem. Soc. 79, 2140 (1959). (11) Kuz'min, K . I., KamaY, G., Sbornik Stater Obshcher Khim., Akad. AVaukS.S.S.R.1 , 223-8 (1953).
- Unsealed - - - -- Sealed with Sealant
200
RECEIVED for review November 2, 1961 ACCEPTEDMarch 29, 1962
3-inch butt joint overlaps, silicone-phenolic laminates, '/a inch thick, epoxyphenolic adhesive Sealant formulation. Epoxy novolak, arsenic trisulfide, glass flakes
Division of Organic Coatings and Plastics Chemistry, 140th Meeting, ACS, Chicago, Ill., September 1961. Investigation of reactions of arsenic compounds with the components of the adhesive was carried out for the U. S. Navy, Bureau of Weapons, under Contract No. NOrd-19075. Porter W. Erickson of the Naval Ordnance Laboratory acted as the technical monitor.
1/4
1 Time. hours at 266'C (55O'F)
Figure 7.
Tensile shear strength at 288" C.
(550"F.)
VOL. 1
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