C. CLEMENT ANDERSON
ANNUAL REVIEW
Adhesives reported in the field of synthetic polymer adhesives with respect to recent publications and new products which have appeared in the marketplaces of industry
TABLE I .
No. 1
80
il'ame Alkylamine borane
n the past year, adhesive usage has continued to increase as chemists produced materials that would perform at more extreme environmental conditions, evidence better adhesion to a wider variety of substrates, cure faster at less rigorous conditions, and show longer pot lives and improved durability. Uses for the adhesives are as varied as the polymers which go into them as exemplified by a gelatin, resorcinol, formaldehyde formulation, methyl-2-cyanoacrylate, and a polyether, diisocyanate adhesive, all of which are used as surgical glues (75) ; polyvinyl chloride and polyethylene for use as fusible adhesives to supplant thread in many areas of garment manufacture (6) ; a polymethyl methacrylate resin mixed with its monomer for fast-setting tooth fillings (37); resorcinol, hexamethylenetetramine adhesive for bonding rubber to textile which eliminates the textile pretreaIment (5); and polybenzimidazoles and other heterocyclic polymers for bonding stainless steel, beq-llium, and titanium alloys. Other scientists have
I
Progress during the past year is
RECENTLY DEVELOPED EPOXY HARDENERS
Structure
R3NBH3
Actitity Latent 6 wk
Optional cohardener Anhydride
2
Imidazole
R.T. active
Amines, qhenols, dicyandiamide
3
Imidazole salts
Latent
Amines, phenols
4 5
Diaziridene Extracoordinate ammonium siliconate
R.T. reactive Latent
Diphenols Anhydride
6
Amine siloxanes
R.T. reactive
None
7
Aminoalkoxydioxaborinane
R.T. reactive
Amides, phenols
INDUSTRIAL A N D E N G I N E E R I N G CHEMISTRY
examined more closely the phenomena of adhesion and have made observations which may be utilized by the polymer chemist as he searches for polymers which will become the adhesives of tomorrow. Research is being conducted to determine the relationships of polymer morphology (33),compatibility of substrate and adhesive (76), and glass temperatures of high polymers (19) to adhesion and the production of a strong adhesive joint. This paper attempts to sumniarize briefly the progress made by chemists in the field of synthetic polymer adhesives during the past year with respect to recent publications and new products which have appeared at the market places of industry. Epoxy Adhesives
Continuing improvement has been evident in epoxy adhesives in the past few years as manufacturers attempt to produce hardener systems which will provide improved properties and may be included in the same package as the epoxy resin, and in epoxy resins which, when cured by conventional hardeners, produce adhesive joints showing peel strengths and shear strengths superior to past epoxy adhesives, both at ambient temperatures and at temperature extremes. Table I shows the various types of functionality used in several of the new epoxy hardeners. The epoxy hardeners in Table I all contain a nitrogenous moiety. The latent hardeners suitable for oriepackage formulations have the nitrogen complexecl or bonded in some manner and are not activated until sufficient heat is applied. The amine boranes (20) are stable for several weeks but can be cured at 250 O F in less than 1 hr. Although the system is latent to some degree, it is not what one can call suitable for a one-package formulation since six months should be the minimum period of time the formulation should remain stable. One of the main drawbacks of many of the latent hardeners is that they are not latent enough or that they do not cure the epoxy at low-cure temperatures such as 250 O F in less than 1 hr. The epoxy resins cured with amine boranes have desirable hardness and maintain this hardness at elevated temperatures. Another latent epoxy hardener is the salt of an imidazole (42). Imidazole, and in particular 2-ethy1,4-
methyl imidazole discussed later, is an excellent epoxy hardener. By reacting the imidazole with an acid, such as acetic, phosphoric, or lactic, a latent hardener may be formed which, when mixed with an epoxy resin and heated to the proper temperature, provides a cure nearly as satisfactory as imidazole itself. A novel class of latent epoxy curing agents is the extracoordinate siliconate salts (40). These salts are prepared by merely warming the appropriate reactants in a suitable solvent. The reactants are composed of an amine, catechol, and trimethoxy phenyl silane. When this mixture is warmed in methanol for 15 min, the crystalline product, an extracoordinate siliconate, is formed and may be recovered by filtration. These salts may be used in conjunction with anhydrides to produce fast curing, latent epoxy formulations. An example of this is benzyldimethylammonium phenyl siliconate which cures in 8.5 sec at 200 "C and has a shelf life of five months when present in an epoxy at 2 phr along with 14 phr of trimellitic anhydride. The epoxy formulations can be cured by the siliconate salts alone and adhesive lap shear strengths of 3000 psi recorded with 25 phr ethylenediamine siliconate, (HzNCHZCHZNH3)$i(CgH402)3, and a cure temperature of 175 "C. The work on epoxy hardeners has not only been concentrated on latent systems. Several new systems have been developed which afford faster and more complete cures. The foremost of those is 2-ethyl,4-methyl imidazole (35). This hardener imparts excellent properties, such as chemical resistance, oxidation resistance, high heat-distortion temperature, and superior electrical properties (73). Due to these favorable characteristics, the mechanism of cure has been investigated (77). I t was determined by these investigators that the rate of reaction of the 2-ethyl,4-methyl imidazole with the epoxy group was faster than the rate of polymerization which indicated that the imidazole becomes permanently attached to the polymer chain. They also determined that the adduct of one mole of imidazole and one mole of oxirane was an excellent hardener and that the second mole of epoxy reacts with the ring nitrogen rather than the hydroxyl of the mono adduct; therefore, the imidazole molecule becomes an effective cross-linking agent. This can be seen in Figure 1. I t is this cross-linking, VOL. 6 0
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81
Figure 7.
The imidazole molecule becomes an ejecective cross-linking agent in this reaction
TABLE I I . PEEL STRENGTHS OBTAINED USING DIOXABORINANE, DlCYANDlAMlDE HARDENER
Dicyandiamide, Phr
Dioxaborinane, Phr 3
0
3 10
0
5 10
10
Peel strength, lb./in. 30-35 40-50 90-100 100-120
~~
TABLE I I I. PROPERTIES O F PENTAERYTHRITOLBASED EPOXY 110-120 1000-1 500 CPS Most organic solvents and water Curing Pot life, room temp.(') agent Time TETA 5-10 min NMA 7 3 wks MDA 5 hr(*) Heat distortion temp.(D) 200'F Hardness (Shord D)(*j 88 Tensile strength, psi(D) 11,000 Tensile elongation, yo(h) 3 1 Pot life of 10-50-g masses. a Methylene dianiline used as hardener.
Epoxide eq. wt. Viscosity, 25'C Solubility
(1
~~~
TABLE IV.
PROPERTIES OF URETHANEMODIFIED EPOXY 10,500 psi
Tensile strength
a
82
Heat distortion temp.
180 OF
Tensile shear -67
3600 psi
OF(*)
Tensile shear 77 ' F
5200 psi
Tensile shear 180 OF
4200 psi
Peel strength 77 "F(.j
82 lbs
Cured with 8 phr dicyandiamide.
INDUSTRIAL A N D E N G I N E E R I N G CHEMISTRY
in which the cross-linking agent is an unsaturated fivemembered ring, which probably imparts the outstanding properties obtained using this material. Amine functional siloxanes (24) that are the reaction products of alkoxy functional siloxanes and hydroxy functional amines have been investigated as epoxy hardeners. These materials are readily soluble in epoxy resins and are reactive at ambient temperatures. The cured epoxy resins were transparent, amber, hard tough solids which have heat distortion temperatures ranging from 87 to 170 " C . The cured resins did, however, have excellent weathering properties and remained essentially unchanged after 56 days of water immersion. Another silicon-containing epoxy hardener that has recently been investigated is a tris(alky1amino)silane ( 2 ) . The investigators were primarily interested in the potential use of the silazane-cured epoxy as a potting compound. Their evaluation indicated that these resins had very good physical and dielectric properties. The typical polyamide, polyepoxide adhesive, has been improved by the use of an aminoalkoxydioxaborinane (78). This additive, especially when used with dicyandiamide, produces bonds which have exceptionally high peel strengths. Table I1 indicates the peel strengths obtained when an 80/20 by weight mixture of polyamide resin/"Epon 812" is cured with dicyandiamide and 2-((3-dimethylaminoethoxy)-4-methyl1,3,2-dioxaborinane, Table I1 indicates the synergistic effect of the dicyandiamide on the dioxaborinane. These formulations have been stable in a 50% solution of methanol and trichloroethylene. These mixtures can be cured in less than a minute at temperatures over 350 O F . Fast cures may also be obtained when equal molar ratios of a diepoxide, a diphenolic compound, and a diaziridine compound are mixed (38). The cured resins were unaffected by water, acetone, ethylene dichloride, or toluene. Not only has research been expended on the discovery and development of novel hardener systems for epoxy resins, but new resins have been developed. This past
year has resulted in the appearance of several new epoxy resins with each having one or several specific properties that are improvements over conventional epoxy resins. One such novel thermosetting epoxy resin is derived from pentaerythritol and epichlorohydrin (77) as shown in Figure 2. The resin has a functionality of approximately 2.2 (26) and cures two to eight times faster than a conventional diglycidyl ether of bixphenol A. The resin is water-soluble and may be cured by amines and anhydrides. T h e manufacturers have suggested that the material may be used alone or as a reactive diluent. Table I11 lists some of the data which has been recorded to date. The resin is an active diluent which not only increases the rate of cure but reduces the viscosity to less than half when present at 20% concentration with the common epoxy resin. A unique feature of the epoxy is that it will adhere to wet surfaces and exhibit excellent adhesion in the cured state. I t is expected that the resin will find greatest use when blended with other resins since it is somewhat brittle when used alone. Another developmental epoxy resin now available is one which has been developed so that the adhesive will not only have the excellent tensile shear strength typical of epoxy resins but also have the often elusive peel strength. The latter property, depending on the method of testing and the members being peeled, may vary from very small values to quite impressive values for a given system and may often be obtained at the expense of high temperature strength. A resin which claims to exhibit good peel strength and good high temperature performance is a urethane-modified epoxy (7). The investigators report that the urethane-modified epoxy produces drastically improved peel values while not sacrificing high-temperature tensile shear strength as can be seen in Table IV. I t ha5 been indicated that a general requirement for the development of a high peel strength is a high temperature; however peel values greater than 40 lb/in. were obtained at cure temperatures less than 300 O F . Much of the published data has been obtained with dicyandiamide as the curing agent (9). Epoxy resins are used industrially over a wide spectrum of applications and are often blended with other
Figure 3. Resin based on phenylene oxide
polymeric materials, such as nylon, NBR, and various vinyl resins to impart peel strength. When they are cured with a suitable hardener such as pyromellitic dianhydride or benzophenone tetracarboxylic dianhydride, the cured resins can withstand temperatures of 200 to 250 "C for several hours without extensive degradation; however, at higher temperatures epoxy resins are unsuitable. T o improve the thermal stability of epoxy resins, resins have been developed which are based on phenylene oxide (27) as shown in Figure 3. The resins were cured by Lewis' acid catalysts and were used primarily as coatings; however they did show thermal and oxidative stability that was an improvement of at least 100 O C over the conventional epoxy resins cured in a similar manner. The investigators indicated that the cured resins exhibited excellent adhesion to titanium, aluminum, and various grades of steel. Encapsulation
For the past few years, the concept of the encapsulation of one component of an adhesive, whether to harden an epoxy resin, or provide a transient tack for a pressure sensitive adhesive, has been accepted as one which has great potential but very difficult to adapt for adhesive usage, particularly where reactive species are concerned. Several patents and papers have appeared that indicate the various methods of preparation and a variety of suggested applications. A number of applications for capsular adhesives are found in the aerospace industry (74). Some of the uses that are still being developed are: a sealant used in air frame construction that contains an anticorrosive pigment, and a fast-curing resin
Figure 2. A thermosetting resin from pentaerythritol and epichlorohydrin VOL. 6 0
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AUGUST 1960
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Figure 4. Model compounds of low molecular weight species that may be present in heat reactive butylphenolic resins
that will permit astronauts to attach themselves to the ship while they are outside of the vehicle. A latent epoxy curing agent has been prepared in which an amine hardener is encapsulated by the reaction of an acid chloride on the surface of the amine particles (27). I n the preferred example, 2,4,5,6-tetrachloro-m-xylene a+’-diamine is divided into a fine powder and dispersed in a nonsolvent which contains a diacid chloride such as sebacyl chloride. After treatment, the particles may be dispersed in an epoxy resin and the formulation will be usable after three months on the shelf. This same adhesive formulation, when heated to 250 O F will rapidly cure an epoxy resin with a resultant lap shear strength in excess of 3000 psi. Another application of capsules in adhesive formulations is where pressure sensitivity is acquired by a resin only after hollow capsules are crushed, thereby permitting the pressure-sensitive adhesive to come into contact with the substrate (8). I n this case, the capsules do not contain a reactive component, but only act as a barrier between adhesive and substrate. Neoprene
Figure 5. Free methylol group in the ortho position hydrogen bond with chlorine atoms
3200 .
0
6OOoc
A
700°F
1600 -
Y
5 +
6C3 430
l
l
20
40
1
l
60 80
i
l
1
1
1
1
1C3 120 14C I60 180 20C
HOURS AT TEST TEMPERATURE
Figure 6. Tjpical values of tensile shear strength after long-time aging at 600 and 700 OF f o r a pohbenzimidazole adhesive formulation for 7 ?ear at 600 OF and 200psi,and then cooled under pressure 84
Last year it was reported (72) that the phasing of neoprene-phenolic resin cements was due to low molecular weight species of phenolic resin and that phasing was retarded or halted completely when these low molecular weight materials were removed from the system. Since commercial heat reactive phenolic resins contain significant amounts of mononuclear and dinuclear species, an investigation was carried out to determine the effect of these species on neoprene cement phasing. The investigators fractionated commercial phenolic resins and reported that only the lowest molecular weight fraction and the unfractionated material separated into two phases (39). This was in agreement with past work. These scientists prepared model compounds of low-molecular-weight species that may be present in heat-reactive butyl phenolic resins, some of which are shown in Figure 4. Experiments with the model compounds indicated that the 4-tert-butyl-2,6-di(hydroxymethyl)phenol was unique in that it was the only compound which caused phasing and viscosity increase in neoprene cements. I t was observed that the amount of sedimentation which accumulated increased as the 4-tert-butyl 2,6-di(hydroxymethyl)phenol increased. This was also true when any 2,6-dialcohol derivative of phenol was added to a cement formulation. I t was of particular interest that the 2,4-dialcohol of phenol has essentially
INDUSTRIAL A N D E N G I N E E R I N G CHEMISTRY
C. Clement Anderson is Research Associate i n the Coatings and Resins Division of PPG Industries, Research and Development Center, Springdale, P a . T h i s is D r . Anderson’s second year to compile the adhesives review.
AUTHOR
Figure 7. A cross-linked network is formed by the reaction of the carboxyl group and the acetamido groups
Figure 8. A n example of an oxadiazole-imide polymer
no effect on the rate of phasing. This led the investigators to suggest the following mechanism: the p-tertbutylphenoldialcohol is adsorbed onto the metal oxide particles through chelate bonding. They believe that the free methylol group in the ortho position hydrogen bonded with chlorine atoms as shown in Figure 5. As yet, the ability of the 2,6-dialcohol to cause phasing and viscosity increase and the inability of the 2,4-dialcohols to do the same have not been clarified. High-Temperature Polymers
Polymers, suitable for high-temperature adhesive applications, particularly in the aerospace industry, have been steadily developed and improved. Several papers have appeared which discuss the performance and bonding procedures of polybenzimidazole adhesives where this type of adhesive is used for bonding titanium,
beryllium, and stainless steel (22, 23, 43). Figure 6 shows typical values of tensile shear strength after longtime aging at 600 and 700 "F for a polybenzimidazole adhesive formulation cured for one hour at 600 "F and 200 psi, and then cooled under pressure. The polyimide adhesives which have more long-term stability at elevated temperatures are still in the development stage. A more recently developed polyimide adhesive will maintain a tensile shear strength at 550 O F of 1000 psi for 4000 hr (4). Linear polyimides which are prepared from m-phenylene diamine and 3,4,3',4'-benzophenone tetracarboxylic dianhydride have been modified so that they may thermoset (3). This has been accomplished by replacing a portion of the m-phenylene diamine with 2,4-diaminoacetanilide and 3,5-diaminobenzoic acid. The polyimide is then cured and a cross-linked network is formed by the reaction of the carboxyl group and the acetamido groups thus forming an amide cross-link. This can be seen in Figure 7 . Polymers of this type exhibited greater flexural strength than the linear polymers; however, the strength decreased more rapidly, and after 1000 hr at 315 "C, both modified and linear polymers had the same flexural strength. Several new polymers recently have been synthesized that are stable at elevated temperatures (30). These polymers contain two different heterocycles which alternate regularly along the polymer chain. The combinations prepared include oxadiazolebenzimidazole, oxadiazole-pyromellitimide, and thiazole-pyromellitimide. All of the polymers prepared exhibited excellent high-temperature stability and none melted or decomposed below 500 "C in an inert atmosphere. All of the polymers could be formed into films. By the careful selection of the two heterocycles and the aromatic hydrocarbon units, polymers were produced having the desired balance of thermal stability, tractability, crystallinity, modulus, glass transition temperature, and drawability. An example of an oxadiazole-imide polymer is shown in Figure 8. All of the polymers were thermally stable as indicated by TGA analyses. Films of polyoxadiazole-imide were superior to polypyromellitimide in heat age studies in air at 300 and 350 O C . No information is given as to adhesive applications; however, combinations may produce resins which do not require the rigorous cure schedules of the present hightemperature adhesives and produce more dense glue lines. Carboxylated Resins
I t is well-known in the adhesive field that small amounts of carboxyl functionality greatly improve the adhesion of a resin to metal (7, 28). Table V shows the increase in peel strength with increasing carboxyl content of ethylene, acrylic acid copolymers (36). Carboxylated polyolefins have also formed strong bonds to high and low density polyethylene, to surface treated Teflon and Tedlar and to cellulosic mateVOL. 6 0
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AUGUST
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05
TABLE
V.
.PEEL --- STRENGTH - . ..-. . - . .. VS. .- . CARBOXYL
__ ENT . OF AN ETHYLENE-ACRYLTC ACID COPOLYMER
Wt.
yo acrylic acid
0
11
14
19
1
56
81
100
Peel strength on aluminum lb/in. at 2 in./min 20-mil thick specimen
TABLE
V I . 20% ACRYLIC ACID-ETHYLENE COPOLYMER PEEL STRENGTH VS. NEUTRALIZATION
r0 Neutralization
I
Peel strength, lb/in.
0
10
4 5 2 0
20
30
8
4
40 2
50 0
TABLE V I I . ADHESION OF ACID-MODIFIED ETHYLENE-VINYL ACETATE/WAX BLENDS TO VA R IOUS SUBSTRATES Vinyl acetate Acid number Melt index Heat seal bond strength, lb/in. Aluminum foil “Mylar” polyester film Polypropylene film PVC film, plasticized
20y0Polymer in para& wax 28 28 0 6 6 6
I
rials such as paper, cloth, and wood. However, acrylic acid copolymers are less stable in an oxidative environment when compared to noncarboxylated polyethylene and ethylene-alkyl acrylate copolymers (47). When the carboxyl groups are neutralized, the bonding efficiency is reduced and the peel values drop correspondingly as seen in Table VI. Not only is polyethylene made more useful for adhesive applications, but the ethylene-vinyl acetate copolymers, widely used in hot melt applications, are also improved and their utility is increased over a wider area. The manufacturer of the acid-modified ethylenevinyl acetate resins claim the following advantages over the noncarboxylated resins; better oil and grease resistance, greater hot tack, and improved adhesion to nonporous substrates (70) Due to the presence of the carboxyl groups, compatibility with waxes is somewhat diminished ; however, the improvement of adhesion is outstanding, as shown in Table V I I . The presence of the carboxyl groups also makes it possible to have greater hot tack with the formulation at the same viscosity as the standard ethylene-vinyl acetate adhesives. I t is quite possible that other commercial resin producers will be developing resins that contain carboxyl functionality in order to improve the performance of their products. I
Surface Treat ments
Various surface treatments have been used to improve the adhesion of different materials to polyethylene, Among these treatments are : chromic acid, chlorine 200 plus light, concentrated sulfuric acid, ozone or nitrous 410 oxide plus uv light, flames, uv or y-radiation, and Bonds were made fo. 1 sec at 200 “ F and 20 psi. Peel strength was run at 5 in./min. various other electronic treatments. These treatments remove weak boundary layers and usually change the critical surface tension of the polyethylene so that the adhesive used can wet the surface more effectively. A recent paper (32) has compared the various treatments TABLE V I I I . ADHESION PROMOTERS WHICH with respect to the strength of the bonds which were HAVE BEEN INVESTIGATED OR ARE NOW UNDER I NVESTl GAT ION formed. The investigators found that a linear relationNo. Comfiound ship between critical surface tensions and corresponding bond strengths existed. This was true until there was 1 j - C l CsH4(CHz)iiCOOH cohesive failure of the polyethylene. Preliminary prim2 fi-Cl CsHd(CHz)iaCOOH 3 p-C1 C~H~(CHZ)~~CH(COOH)CH~COOH ers gave the smallest increase in bond strength whereas oxidations, heat, and radiation all led to maximum bond 4 j-ClCaH4(CH~)~zCH(COOH)CHzCHzCOOH strengths, as indicated by the cohesive failure of 5 fi-C1 CeH4(CHz)i7COOH the polyethylene. The scientists recommended chromic P-Cl CsH4(CHz)i,COOH 6 acid and all forms of radiation, electron, ion bombard7 p-C1 CsH4CO(CHz)iaCOOH ment, uv, and y-radiation. The highest shear strength 8 fi-C1 CeH4CO(CHz)ieC O O H was recorded by using the “casing” technique. Fluorinated plastic materials can also be treated to enhance the strength of the incipient bond. The treatment consisted of treating the fluorinated plastic with a photopolymerizable coating such as the polyvinyl ester 86
200 70 40 170
450 160
I N D U S T R I A L A N D E N G I N E E R I N G CHEMISTRY
TABLE I X . COMPARISON OF LAP SHEAR STRENGTHS OF VARIOUS STRUCTURAL ADHESIVES W I T H AND W I T H O U T COUPLING AGENTS
Lap
shear Adhesion promoter % psi(,) 1450 None y-aminopropyl1 2350 triethoxysilane y-mercaptopropyl1 3120 Nitrile/phenolic trimethoxysilane 2380 Polyvinyl butyral/ None y-aminopropyl1 2700 phenolic triethoxysilane y-mercaptopropyl1 2960 trimethox ysilane None 1410 y-aminopropyl1 1675 triethoxysilane y-mercaptopropyl1 1580 trimethoxysilane a 2024T3 aluminum, 0.063 in. thickness, ‘(2 in. overlap. Tests run at 73 O F . Appropriate cure schedule IS used in each case. Adhesive t y j e Nitrile/phenolic Nitrile/phenolic
of cinnamic acid (25). T h e coating was then exposed to uv light at the appropriate conditions and then bonded. Bonds made with the treated material were significantly higher in strength than those with the untreated fluorinated plastic. Adhesion Promoters Adhesion promoters or coupling agents are usually small molecules that can interact by some mechanism with the solid substrate and the polymeric adhesive. Whatever the mechanism, the coupling agent must be strongly adsorbed on the surface of the adherent, ideally as a monomolecular layer. The portion of the molecule which is not adsorbed presents a surface which can be more easily wetted by the adhesive. Other specifications for a satisfactory coupling agent are that it should be sufficiently inert chemically, should have a low surface energy, and should form a hydrophobic barrier film to avoid the accumulation of water which could prevent efficient wetting by a n organic liquid adhesive (34). Molecules which should give optimum results are reported to have a p-chlorophenyl group and a carboxyl group; the two portions being connected by an aliphatic chain. The investigators indicated that such chlorinecontaining surfaces are hydrophobic and resistant to chlorine hydrolysis and have critical surface tensions of wetting of 40 dynes/cm. or more, and that the carboxylic acid groups are effective in promoting adsorption and adhesion to many substrates such as metals, glasses, and ceramics. Therefore, p-chlorophenyl alkyl-substituted mono- and polycarboxylic acids have recently been investigated. Table VI11 shows compounds which have been and are now being studied (29,34). Results of this research have indicated that this type of coupling agent is strongly adsorbed on a surface in a specific orientation and is useful in the improvement of adhesion. Similar types of molecules that contain sili-
icon are commercially available as coupling agents. Typical adhesion promoters are gamma-aminopropyltriethyoxysilane, gamma-mercaptopropyltrimethoxysilane, and N-beta- (aminoethyl) -gamma-aminopropyltrimethoxysilane. These materials are designed for use at concentrations of less than 1% based on the adhesive solids and they improve the bond strength by improving the bond between polymer and substrate, and polymer and reinforcing filler (31). Table IX shows the improvement of bond strengths when such agents are used in the adhesive formulation. REFERENCES (1) Baum, B. O., and Imhof, L. J., U. S. Patent 3,211,804 (1765). (2) Bilow, N., and Murphy, R . F., J. AppI. PolymerSci., 11, 2107-20 (1967). (3) Bower, G. M., Freeman, J. H., Traynor, E. J., Frost, L. W., Burgman, H . A., and Ruffing,C. R., Ibtd., 6,Part A-1, 877-87 (1968). (4) Burgman, H . A., Freeman, J. H., Frost, L. W., Bower, G. M., Traynor, E. J., and Ruffing, C. R . , Ibid., 12, 805-29 (1968). (5) Chem. Eng. News, 40-1 (4/22/68). (6) Chem. Week, 57-8 (4/6/68). (7) Clarke, J. A., and Hawkins, J. M., ACSPreprint,“Organic Coatings and Plastics Chemistry,” 28 ( l ) , 468-75 (1768). (8) Danielson, A. J., and Berg, H . A. (to Minnesota Mining and Mfg. Co.), U. S. Patent 3,331,729 (1967). (7) Dow Epoxy Resins, Tech. Rept. No. 45, “Experimental Epoxy Resin QX-3579.” (10) D u Pont Co., Tech. Inform. Bull., A-6848 (Nov 1767). (11) Farkas, A,, and Strohm, P . F., J . Appl. PolymerSci., 12,159-68 (1768). (12) Garrett R . R . and Lawrence, R . D., Adhesive and Sealant Council, Inc., P~Gc., 1966’Spring’Seminar (March 1966). (1 3) Houdry Process and Chemical Co., a Division of Air Products and Chemicals, Inc., 1965,” EMI-24 Curing Agent for Epoxy Resin Systems.” (14) Huber, H. F., and Stroble, H. G . , Adhesives Age, 10, 28-32 (1767). (15) Ind. Res., pp. 37-8 (April 1968). (16) Iyengar, Y., and Erickson, D. E., J.Appl. PolymerSci., 11, 2311-24 (1767). (17) Jordan, J. M . , Michelotti, F. W., Pearce, E. M . , and Zeif, M., ACS Preprint, “Organic Coating and Plastics Chemistry? 28 (11, 335-41 (1768). (18) Kennedy, R . J. (to E. I. D u Pont & Co.), U. S. Patent 3,336,415 (Aug 15, 1967). (19) Lee, H . L. (to Callery Chemical Co.), U. S. Patent 3,347,827 (Oct. 17, 1967). (20) Lee, L . H . , J.Appl. PolymerSci., 12, 717-30 (1968). (21) Levine M . and Neme, M . J. (to General Motors Gorp.), U. S. Patent 3,375,299 (i9685. (22) Litvak, S., Adhesives Age, 11 ( l ) , 17-24 (1768). (23) Ibid., ( Z ) , 24-8 (1968). (24) Markovitz, M . and Kohn L S ACS Preprint, “Organic Coatings and Plastics Chemistry,” i8 (l), 372-407’(1;68). (25) Matlock, V. R . (to North American Aviation), U. S. Patent 3,343,776 (1767). (26) Mitchell, T. E., “Raw Materials,” T h e Adhesive and Sealant Council, Spring (1968). (27) Neville, R . G., Mahoney, J. W., and MacDowall, K. R., J , Appl. Polymer Sci., 12, 607-18 (1768). (28) O’Donnell, D. V., and Suen, T. J., U. S. Patent 3,214,488 (1965). (29) O’Rear, J. G Smegoski, P. J. and James F. L., ACS Preprint, “Organic Coatings and Plaitics Chemistry,” i7 ( Z ) , 4-10 (i767). (30) Polniaszek, M. C., and Schaufelberger, R . H., “Adhesives and Sealant Council, (‘Raw Materials,” 1968. (31) Preston, J., andBlack, W. B., J.PoIymerSci.,5 , 2429-39 (1767). (32) Rauhut, H . W., ACS Reprint, “Organic Coatings and Plastics Chemistry,” 28 (l), 545-59 (1968). (33) Schonhorn, H., and Ryan, F . W., J. Polymer Sci.,6 , Part A-2, 231-40 (1968). (34) Shafrin, E. G., and Zisman W. A ACS Preprint, “Organic Coatings and Plastics Chemistry,” 27 (21, 11-56 (176y). (35) Shell International Research, Brit. Patent 1,050,679 (Dec 7, 1966). (36)-Smarock, W. H., and Bonotto, S., SOC.of Plastics Engineers, Inc., Ann. Tech. Conf. XIII, 119-131, May 1767. (37) Sn der W H Wilson, C. E., Newman, G. V., and Semen, J., J . Appl. Sei., 11, iYoe-i7 (i967). (38) Strother, Jr., G. W. (to Dow Chemical Co.) U . S. Patent 3,346,533 (Oct 16, 1967). (39) Tanno, T., Shibuya, I., “Adhesives and Sealant Council, R a w Materials,” 1968. (40) Vincent, H . L.,,Opp;,iger, P. E., Frye, C. L., ACS Preprint, “Organic Coatings and Plastics Chemistry, 28 (l), 504-11 (1968). (41) Wargotz, B., ACS Preprint, “Organic Coatings and Resins,” 28 ( l ) , 560-5 (1968). (42) Warren, D . (to Shell Oil), U.S. Patent 3,356,645 (Dec. 5, 1767). (43) Yoshino, S. Y., Nadler, M. A., and Richter, D. H., Adhesiues Age, 10, 26-34 (1967).
VOL.
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