Mechanism of Drier Actio A Proposal and Panel Discussion presented before the Division of Paint, Plastics, and Printing Ink Chemistry a t tlie 124th Meeting of the ACS, Chicago, Ill., J o h n K . Wise, presiding
THIS
discussion departs from the usual presentation of cxperimental evidence, the results of original research, and subordinates experimental evidence to theory and perhaps to speeulation. The subject is a very controversial one in the field of paint and varnish chemistry-how do oil-soluble metal salts accelerate the oxidation and polymerization of unsat’urated triglycerides? I n the last 10 years, much good Twrk has been done on tlie chemical reactions involved in the drying of oils. Today, the geri-
era1 mechanism is fairly well accepted. The prinripal article in this discussion considers those chemical reactions iiivolwtl in the drying of oils and proposes a mechanism to explain ho~v oil-soluble metal compounds affect) these reactions. I2our ~ x perts in the field comment on and evaluate this proposal. Thi.: discussion is not expected to eliminate all cont,ro cerning drier action, but, it is designed t o spotlight arm.. of UTIcertainty a,nd to point the way for future research. JOHN K. WISE
E. R . 3IUELLER Organic Coatings Division, Battelle Memorial I n s t i t u t e , Columbus, Ohio
R1’
given by Elm ( 1 9 ; . This work was started almost a centu However, little real progress Tq-as made until after the first \Yorltl Il’ar. Most useful information has appeared since about 1930. Since then, a large number of investigators have added greatly to our knowledge of the thickening, gelling, and set,ting of oils, Colloid chemists made valuable contributions which helped t,o explain the process of film format’ion. It remained for the high polymer chemists, however, t o shed the most useful light on this highly intricat,e and complex subject during the last 15 to 20 years. P O I . Y l f E R I Z A T I O S BY HEAT. I n order t o understand more fully the oxidative polynierizat,ion process and the role of t,lie driers in it, the heat-induced polymerization of oils should be considered. Recently, there have appeared several excellent rcviem on this subject, (IO, 12, 67, 68). It has been rather clearly demonstrated by these and other investigators ( 1 5 ) that, threedimensional polymers must be formed before gelation can occur. Therefore, it must be assumed that this is what happens when films are baked or force dried. It has been shown by many Lvorkers that such a three-dimensional structure may be derived in several a-ays. hIost applicable in this discussion arc m t c r interchange of higher and lower molecular weight polymers arid cross linking a t the unsaturat,ed centers. Figure 1 depicts two hypothetical synthetic oil molecules which simply show the structure of several fatty acids attached to polyols. By cross linking of two fat’ty acids, one from each of tn-o such niolecules or similar molecules, one dimer fatty acid already forms a double-eized molecule. Ester interchange occurring in h o such or similar molecules would form a four-unit structure. By cross linking a t the unsaturated centers, it is generally believed that more or less cyclic polymers are formed, depending on the degree of unsaturation of the fatty acids involved.
NY investigators have studied the drying of oils and air-drying finishes. The effect, of factors--e.g., heat, oxygen, light, a.nd catalysts-on the conversion of an oil film to R “set” condition, has been ext,ensively investigated. Most of t,hk work has dealt with the effects of heating the oils or est,ersof fatty acids t o relatively high temperatures (260’ to 320’ C.) or osidizing them a t temperatures ranging from room tempcraturc or slightly above to 130’ C. Investigations concerning the efYect of catalysts, for the most part, have been almost entirely empirical. JVhile a lot of illformation is now available on the effect of these “accelerators,” mch as the common drier metals, on the air-drying process, the precise manner in Thich these materials function is still a subject of considerable controversy. I n the organic coatings industry, great strides have been made during the last 25 years in modifying the common vegetable oils to improve their over-all properties, including drying rate. Of particular interest are the quickdrying varnishes of various types made from these oils. Jl‘hile most, varnishes dry much faster than the oils, the process of air drying is generally considered to be affected very little, if a t all, by the resin component, regardless of the type of resin (4bj. For the sake of simplicity, this paper, therefore, nil1 deal only with the role of the drier metals in the oxidative-polymerization of oil films. I n order to better understand how catalysts or accelerators aid in the drying process, it is essential to consider first the processes of polymerization and drying in the absence of these accelerators. PROCESSES IIVVOLVED DURING DRYING
The physical and chemical processes operative in film formation have been extensively investigated by many workers, both in this country and abroad. A good historical review has been
562
March 1954
INDUSTRIAL AND ENGINEERING CHEMISTRY
-
Eleostearic, trans.CIS,trons
Olsic, cis 0
H
H H H
AAAAAliA Ltnolenlc,cis,cis, trans
Polnilic -
Penfoeryfhritai (tetrafunctional) ester of four types of neturol oclds
RcinOieiZ,cis Llneor
Figure 1.
Liconic, cis,Irons.cis
(nondrying) QIYCOIester of two exceptional naturoi oclds
Exemplary Types of Natural Fatty acid Esters
Figure 2 is a diagram from Wheeler (58). It shows a dimer formed by the action of heat upon a normal linoleate and a thermally conjugated linoleate to form a substituted cyclohexene ring. It should be emphasized that the work of Bradley (13) and others has clearly demonstrated that, regardless of the degree of unsaturation of the fatty acids involved, the polybasic acids formed during heat polymerization are largely dimers, with very small amounts of trimer, and practically no tetramer. Thus, the molecular weights of the drying oil polymers are not at all large when compared t o high molecular weight polymers, such as polyethj-lene. Wheeler ( 5 7 ) has elegantly summarized the work of Bradley and Johnston (11) on the polymerized products of methyl esters of various fatty acids. I n this connection, these facts concerning the heat bodying of oils seem pertinent to this discussion: Isomerization to the conjugated form occurs in unconjugated oil> prior to polymerization. Side reactions occur and create esters of low molecular weight which may combine with monomers to form polymers of intermediate molecular weight. Functionality of the various fatty acids during heat polymerization will vary with the amount of more highly unsaturated fatty acid. present. Wheeler, Elm, and others have shown that the functionality of oleate will vary from about zero to something l e v than one in a 1: 1 mixture of oleate and linoleate.
OXYGEN-IYDUCED POLYMERIZ~TIOK. Several excellent reviews on the oxidative polymerization of drying oils have been recently published (19, 46, 82, 57). Khile the manner by which oils polymerize in the presence of oxygen a t room and slightly elevated temperatures is apparently considerably more complex than theii polymerization by heat, the two processes have many things in common. Many of the more important reactions involved in oxidative polymerization are now well established, although the exact mechanism of oxidative polymerization is still rather controversial. Bn abundance of literature on the subject dates back much further than the literature on heat polymerization. Much of it is speculative and often contradictory, making it difficult to obtain a clear-cut picture of the process. Still in all, good agreement has been reached in recent years by vaiious investigators on the subject, particularly with respect to the position and manner of the entry of oxygen into an unsaturated oil or hydrocarbon molecule in the initial stages of oxidation (6, 8, 9, 14, 16, 20, 21, 23-80, 34, 36, 3 7 , 4 1 , 49,64,66, 69). This is a very important consideration when attempting to explain the mechanism of diier action. In 1942 Farmer and his associates worked primarily with rubber hydrocarbons and methyl esters of unsaturated fatty acids. They theorized that oxygen enters the unsaturated hydrocarbon a t a carbon atom a t o the double bond in unconjugated systems. They observed that, in the initial stages of oxidation,
563
there was apparently no reduction in unsaturation. They demonstrated, also, that oxygen was taken up in molecular form to produce the monohydroperoxide. As oxidation continued, unsaturation decreased, viscosity increased, and peroxide values fell to a low level. Relatively high molecular weight oxygenated polymers, as well as intermediate molecular weight polymers, were formed. Moreover, compounds lower in molecular weight than the starting materials, as well AS considerable unchanged monomer, were detected in the distilled products. It thus appeared that Oxidation proceeds down an already oxidized molecule and that chain scission occurs. I n the case of conjugated hydrocarbons or fatty acids, oxygen is conceded by these authors to enter a t the double bond. A number of possible structures were postulated, all of which, together with their breakdown products, could affect the completely gelled or oxidized oil. Apparently, several types of reactions occur simultaneously and consecutively, depending on such factors as heat, light, and possibly catalysts. This seems t o be particularly true with respert to changes in temperature (35). Such factors as viscosity and surface exposed would seem to affect primarily the rate of the reactions occurring, although it has been shown (IS) that thick films gel a t a lower percentage of oxygen than do thinner ones. This does not necessarily indicate that the mechanisms of polymerization are significantly different, however. Ccl.
(CH$7 COOCH3
10,12, CONJUGATED, LINOLEATE
+
-
COOCH3
9, 12, NORMAL, LINOLEATE
DIMER
Figure 2. Heat Dimerization of Ethyl Linoleate Wheeler (58)
It is possible that the mechanism of polymerization may vary somewhat, depending on the type of coating being studied. It has been shown that the same drier metals may induce crystallization in some types of coatings and apparently retard it in others
(4). TYPESOF POLYMERS. While the exact compositions of all polymers formed under varying conditions of oxidation of unsaturated oils have not been positively identified, many compounds have been isolated, and they shed considerable light on the course of the reactions. The various fatty acids show the same relative degree of functionality in oxidation polymerieation that they do in heat polymerization. However, their functionality in the former will usually be slightly greater. -4s in heat polymerization, the induced conjugation of unconjugated groups usually precedes polymerization (2, 47, 57). Again, the functionality of the oleate is considerably enhanced by small amounts of more highly unsaturated fatty acid esters, such as linoleate (36, 88). It is postulated that the autoxidation of oleate is catalyzed by the hydroperoxide resulting from the union of oxygen with the linoleate. Significantly, it has been demonstrated that the alcohol attached t o the fatty acid chains has no apparent effect upon the oxidation mechanism of the fatty acids (15,51). OXYGENATED COMPOUNDS AND DERIVATIVES.Numerous investigators have shown that a large number of oxygenated compounds or derivatives are formed during autoxidation. These products will vary both with respect to the starting substances and the conditions prevailing. Some of these products of the
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
564
~ STRCCTURCS TABLE I. ORGANICO X Y G E%TED 0
'I
Aldehydes
R-C-H 0 I/
Organic acids
~-6-0~ 0-0
Cyclic peroxides
I
R-C-C-R or
'd /I 0 R-C-CH:,
Esters
K-C-0-R
best discussed together. IVhen comparing ox\.~en-indiic~:.rl polymerization n-ith heat polymerizat,ion, reference was matlr the fact that most workers are novi in agreement with the theoi,. that molecular oxygen first adds t o the oil a t the douhle bond iii conjugated systems to form products, such as cyclic perosidc..
I 1 ! I
--C-C--.
I t is now generally agreed that oxygen first adds at
:I
0-0
1
R-C-C-R
Epoxides
Vol. 46, No. 3
'4
I1
0
0
double bond in uiiconjugated systems as ell as in conjugateil ones. However, after the oxygen adds a t a double bond, thc double bond shifts to produce an a-methylenic hydroperoxide,, as shown in Figure 4. Gunstone and Hilditch (M),while ~vorkiiig with emall amounts of methyl linoleate in methyl olmte, were perhaps the first t,o propose this mechanism of oxygeij addition iri unconjugated systems. In the same year, Farmer ( 2 2 ) a i v accepted this vien., which is contrary to his earlier views (20: t'hat perosidation begins a t an e-methylenic carbon in UII-. conjugated systems. Gibson (34) also presents evidence thxt t,he nen- concept of oxygen initially adding a t the double bond is valid. He substantiates this with a good theoretical discussion that hydroperoxides are formed by a combined mechanism between the -C=Cdouble bonds and e-methglenic gi'oiips (-CH$-) to initiate a chain reaction.
'I
R-C-R
Ketones
0
II
R-C-0-OH
Peracids
OH Hydroxyls
R-C-R
Hydroperoxides
R&=C--F:
OOH
oxjdative process are shown in Table I. Certain of these products, part,icularly t,he aldehydes formed during the autoxidation of cottonseed oil, have been identified and t,heir source established (55). 811 of these structural products are capable of entering into further reactions. The course of these subsequent reactions, may depend, in a large measure, on t,he reaction conditions and mat,erials present-e.g., wat,er and driers.
OXYGEN IN O I L
TIME-
Figure 3.
Stages of Oxidative Polymerization Powers (52)
OXIWATIOK PROCESS
PoTvers ( 5 2 ) arbitrarily divides the &ages in the oxidation of drying ails into four main steps-viz., inhibition, peroxide forination, peroxide decomposition, and polymerization. Figure 3, taken from this article, while admittedly purely arbitrary and varying with conditions of materials employed, forms the basis for the following discussion, including the role of the driers. IKHIBITION. During the induction period, no significant, amount of oxygen is absorbed by the oil. Coincident with the first detectable absorption of oxygen, peroxides begin t80f o r m Inhibition is generally at,tributed to the presence of antioxidants, such as the tocopherols in natural oils, although this is often hard to verify (43). Moreover, other factors, not too well understood, may also be responsible. The general observations on reconstituted oils shoTy no induction period. Evidence exists, however, that highly purified, unsaturated fatty acids may have a relatively long induction period at temperat,ures somewhat above room temperature, while both rosin and purified a b i d e acid have a comparatively short induction period. Catalysts, such as the drier metals, particularly cobalt, greatly shorten this induction period and often eliminate it entirely. PEROXIDE FORMATION AND DECOXPOSITION. The peroxide format,ion and decomposition stages in the oxidative process are
Farmer's earlier view (20) (hydroperoxidat'ion) a t an 01-' niethylenic carbon, while once fairly well substantiated b y the kinetic studies of Bolland and Gee ( 9 ) ,seems t o have been fairly well disproved. Hotvever, very recently, Allen and Xummerow (3)show evidence t'hat this original mechanism may be valid in some cases. It seems entirely possible that bot'h mechanisms may operate, depending on conditions of oxidation and the starting materials, including driers. The rate of peroxide development is generally much faster \ ~ i t h catalysts present. Hov-ever, m-ithout catalysts, much higher peroxide levels occur. With oils that have an induction period, the peroxide level usually builds up faster initially with driers. Undoubtedly, this happens because driers shorten the induction period, and peroxides are about the first products of oxidat'ion. However, in oils or fatty acids having no perceptible induction period, the peroxide levels are initially about the same with or without driers, and then the peroxide level of the samples with drier falls off sharply apparently as polymerization sets in far in advance of final total oxygen uptake. Jackson and Rummeroiv ( 4 0 ) studied che effect of zinc, manganese, and cobalt driers on t,he autoxidation of unconjugated linoleic acid a t 35", 6 j o , and 90" C. They measured the peroxide values obtained as a func-
INDUSTRIAL AND ENGINEERING CHEMISTRY
March 1954
tiori of time, as well as the specific ultraviolet absorption coefficient. Figure 5, taken from this work of Jackson and Kummerow shows the peroxide levels obtained in both conjugated and unconjugated linoleic acids with and without cobalt drier a t 65" C. At this temperature, the peroxide values rise a t about the same rate initially with or without drier This was even more pronounced at 90" c.
-
H I
R-CH.CH-C-CH*CH-R'
+ 02
I
W I
R-CH-CH-C-CHsCH-R' I
*
oo%--
n
-
R-CH-CHaCH-CH-CH-R'
{ H
..
R-CH-CH-CH-CHsCH-R'
I
I
DOH
OOH
In Figure 6,. the corresponding data are given for these same materials oxidized a t 30" C.--about room temperature. Here the peroxide values rise much more slowly without drier, but much more rapidly attain a higher level both in the conjugated and unconjugated acids with drier. I n the case of the conjugated acids, the curves cross after about 70 hours and level off after about 120 hours. It would be interesting to know what the "set" time of such oil films would be.
565
same correlation is noted with the conjugated acids. However. the total peroxide value attained with the conjugated acids is only about half as large (350). Presumably, in all cases where lower peroxide peaks were realized, peroxide decay and subsequent polymerization had set in much earlier. It is unfortunate that several other pertinent measurements were not made-e.g., viscosity increase and gelation time-so that advancement of polymerization could be better correlated with peroxide development and decay. An examination of these authors' ultraviolet data a t 65" C. (Figure 7 ) shows that the highest degree of conjugation attained in the unconjugated acids corresponded very closely to the highest level of peroxide at approximately the same time, whether or not driers were used. Thus, it would appear that a t a high level of peroxides, the peroxides must be in the form of hydroperoxides and predominantly conjugated. This is in agreement with the findings of Lundberg and Chipault ( 4 7 ) that in the early stages of autoxidation of methyl linoleate, diene conjugation occurs, and these dienes are predominantly in the form of hydroperoxides.
W
e
g
800
L 400
0
20 800 I
I
I
I
I
I
I
I
40
60
80
100
120
TIME OF OXIDATION IN H O U R S
Figure 6. Effect of Cobalt Naphthenate Drier on Peroxide Value of Unconjugated and Conjugated Linoleic Acids Oxidized at 30" C. 1. Linoleic acid 2. Linoleic acid with drier 3. Conjugated linoleic acid 4. Conjugated linoleic acid with drier
TIME OF OXIDATION IN H O U R S
Figure 5 . Effect of Cobalt Naphthenate Drier on Peroxide Value of Unconjugated and Conjugated Linoleic Acids Oxidized at 65' C. 1. 2. 3. 4.
Unconjugated linoleic acid Unconjugated linoleic acid with cobalt drier 10,12-Linoleic acid 10,12-Linoleic acid with cobalt drier
I n the case of the unconjugated acids, the peroxide level remains much higher after 120 hours for the sample without drier. Interestingly enough, the sample with drier breaks off sharply in peroxide value a t about 80 hours and falls below that of the conjugated acid samples. P1esumab1yJ such a film also would set much before the peroxide level finally drops off. It would appear significant that, with t h e unconjugated acids, maximum peroxide values obtained are about the same (800) with drier a t 30" C. and without drier at 65" C. Thus, the drier at room temperature does about the same as heat a t force-dry temperature. The peroxide values obtained are just about half nf those obtained with no drier a t 30" C. Almost exactly the
At 30' C., Figure 8, the same general observations hold, escept that the degree of conjugation has dropped somewhat prior to the attainment of maximum peroxide. This would indicate peroxide formation a t a faster rate than peroxide decomposition and piobably the beginning of polymerization ( l 7 , 1 8 ) In another experiment carried out a t 90" C., using only unconjugated linoleic acid in conjunction with 0.1% each of either cobalt, manganese, or zinc metals in the form of naphthenates or no drier over a period of 20 hours, the peroxide values rose to their highest levels in approximately the same period of time, 2l/2 to 3 l / 2 hours. The highest level attained with cobalt was about 500, while with zinc it was about 800, and with manganese it was almost as high as with zinc a t almost exactly the same time. The peroxide level attained without drier was very low even a t the end of the experiment. Thus, efficiency of a drier metal-e.g., zinc-commonly thought to be of little value by itself in the air drying of oil films is demonstrated a t 90' C. I t would have been interesting to have observed the efficiency of zinc alone a t 30' C. or with varying minute amount8 of cobalt. When the ultraviolet data are observed, it is clear that, even without drier, the highest level of conjugation obtained is quite high and increases in the following order: no drier crestingto carry out a detailed study o l the lilin formation of several typical fatty acid est,ers,singly and in admixture, and parallel such studies with controlled hulk oxidation procedures under a selectrd number of pract,ical conditions. 10 driere and drier metals, singly or in admixture with other. c
INDUSTRIAL AND ENGINEERING CHEMISTRY
March 1954
metals or catalysts, such as organic peroxides, should be used a t room and elevated temperatures. Suitable experiments to elucidate the chemical changes taking place during observed changes in physical properties should be carried out. The following information is believed to be most needed: 1. Information about the amount of oxygen that enters the sample, and the form in which it exists a t critical point3 in the drying process. Progress along this line could be made by combining data from weight gain, ultimate analysis (including direct oxygen) determinations, chemical determination of peroxide and acid, and infrared measurement of total OH and C=O. There is a good possibility t h a t several other infrared absorption maxima observed in drying oils could be interpreted in terms of functional groups responsible for the absorption. 2. Determinations of rates of development and decay of different oxygen groups so that postulated theories about consecutive and simultaneous reactions could be evaluated. 3. Extensive double bond analyses, including chemical, ultraviolet, and infrared data, to provide a double check on methods and minimize analyt’ical errors which result from use of only one method. 4. Investigation of the role of chain scission by a combination of infrared measurement of terminal chain decrease, methyl group change, plus simultaneous analysis of volatile compounds formed. 5. Structural examination of products for interpolymers.
The study outlined, carried out on a carefully controlled sample series, would require considerable cooperation among several specialized drying-oil chemists and analysts. When simultaneous data are obtained on identically treated samples, it may be possible to predict with some degree of certainty the mechanism of drier action under the conditions prevailing. Where autoxidation processes are employed, this information could be utilized to produce better products. ACKNOWLEDGMENT
The author wishes~to thank Clara D. Smith, who did the spectrographic work, and his associates, who assisted in carrying out the experimental program. ~~
LITERATURE CITED
Adams, K., Auxier, R. Tlr., and Wilson, C. E., Ofic.Dig. Federation P a i n t & Varnish Production Clubs, No. 322, 669-81 (1951). dllen, R. R., Jackson, $., and Kummerow, F. A,, J . Am. Oil Chemists’ Soc., 26, 395-9 (1949). Allen, R. R., and Kummerow, F. A., Ibid., 28, 101-5 (1951). Austin, A. E., Brand, B. G., A’fueller, E. R., and Schwarta, C. RI., presented before the Division of Paint, Varnish, and Plastics Chemistry at the 118th Meeting, AM, CHEM.Soc., Chicago, Ill,, 1950. Balfe, A I . P., and Chatfield, H. W., J . Sac. Cheni. I n d . (London), 59, 31-4 (1940). Bawi, C. E. H., J . Oil & Colour Chemists’ Assoc., 36, 443-79 (1953). Bennett, E. F., “Driers and Drying,” London, Chemical Publishing Co., 1941. Bloomfield, G. F., J . Chenz. Soc., 1943, 356-60. Bolland, J. L., and Gee, G., Rubber Chem. and Technol., 20, 60917 (1947). Bardley, T. F., in hIattiello, J. J., “Protective and Decorative Coatings,” Vol. 3 , Chap. 4, pp. 87-113, Kew York, John Wiley & Sons, Inc., 1943. Bradley, T. F., and Johnston, W, B., IND.EXG.CHI:M., 32, 802-9 (1940). Bardley, T. F., and Tess, R. W., Ibid., 41, 310-19 (1949). Carrick, L. L., and Snoddon, W.J., Ofic.Dig. Federation Paint & Varnish Production Clubs, No. 322, 682-91 (1951). Carriere, &I., Ann. f a c . s e i . Marseille, 19, 11-154 (1947). Chipault, J. R., Nickell, E. C., and Lundberg, W. 0.. Ofic. Dig. Federation P a i n t & Varnish Production Clubs. No. 322, 74050 (1951).
569
(16) Criegee. R., Pilz, H., and Flygale, H., Ber., 72, 1799-1804 (1939). (17) Elliott, S. B., presented as part of the Joint Symposium on Drying Oils of the University of Minnesota and Minnesota Section, AM. CHEM.Soc., Minneapolis, Minn., March 27-29, 1947. (18) Elm, A. C., IXD. ENG,CHEM.,26, 386-8 (1934). (19) [bid., 41, 319-24 (1949). (20) Farmer, E. H., Trans. Faraday Soc., 33, 340-8 (1942). (21) Ibid., pp. 356-61. (22) Ibid., 42, 228-36 (1946). (23) Farmer, E. H., Bloomfield, G. F., Sundralingam, A,, and Sutton, D. A., Ibid., 38, 348-56 (1942). (24) Farmer, E. H., Koch, H. P., and Sutton, D. A., J . Chma. Soc., 1943, 541-7. (25) Farmer, E. H., and Michael, S.E., Ibid., 1942, 513-19. (26) Farmer, E. H., and Sundralingam, A., Ibid., pp. 121-30. ( 2 7 ) Ibid., 1943, 125-33. (28) Farmer, E. H., and Sutton, D. A , , Ibid., 1942, 139-48. (29) Ibid., 1943, 119-22. (30) Ibid., pp. 122-5. (31) Fiscella, C. T., and Zacharakis, L. G., Am. Paint J., 37, 60-5 (1953). ( 3 2 ) Gamble, D. L., Barnett, C. E., IND.ENG. CHEX, 32, 375-8 (1940). (33) Gardner, C., Am. Paint J . , 37, 18 (1953). (34) Gibson, G. P., J . C k e m . SOC.,1948, 2275-90. (35) Gunstone, F. D., and Hilditch, T. P., Ibid., 1945, 836-41. (36) Ibid., 1946, 1022-5. (37) Hargreaves, K. R., and XIcGookin, A . , J . Soc. Chem. I d . (London), 69, 186-91 (1950). (88) Hess, P. S.,and O’Ilare, G. A, ISD. ENG.CHEX, 44, 2424-8 (1952). (39) Honn, F. J., Beaman, I. I., and Daubert, B. F., J . Am. Ciiem. SOC.,71, 812-16 (1949). (-20) Jackson, A. H., Kummerow, F. A , J . Am. Oil Chemists’ Sue., 26, 460-5 (1949), (41) Jordan, L. A., J . Oil & Colour Chemists’ Assoc., 35, 577-95 (1952). ( 42) Klebsattel, C. A . , in Mattiello, J. J., “Protective and Decorative Coatings,” Vol. 1, Chap. 22, pp. 499-534, New Tork, John Wiley & Sons, 1941. (43) Klebsattel, C. A., presented before the Division of Paint, Varnish, and Plastics Chemistry a t the 1lGth RIeeting, -%sf. CHEM.SOC., Atlantic City, N. J., 1949. (44) Konen, J. C., Hanseh, L. I., and Formo, M. W., presented before the Division of Paint, Varnish, and Plastics Chemistry a t the 116th Meeting, L4M.CHEM.SOC., Atlantic City, S . .J., 1949. (45) Krumbhaar, W.H., Foreword to Bennett, E. F., “Driers and Drying,” London, Chemical Publishing Co., 1941. (46) Lundberg, W. O., presented before the Division of Paint, TTarnish, and Plastics Chemistry a t the 116th Meeting, -AM CHEM.Soc., Atlantic City, N. J., 1949. (47) Lundberg, W. O., and Chipault, J. R., J . Am. Chem. Soc., 69, 833-6 (1947). (4.8)Mills, hl. R., “Introduction to Drying Oil Technology,” London, Pergamon Press, 1982. (49) RIorrell, R. S., Rolam, T. R., Davis, W. R., Marks, S.,Phillips, E. O., and Sim, W.E.,Trans. Faraday Soc., 38,362-72 (1942). (50) Mueller, E. R., and XIcSweeney, E. E., Am. Paint J . , 34, 26, 28, 66-8 (1949). (51) Overholt, J. L., and Elm, A. c., IND. ENG.CHEM., 32, 378 8 3 (1940). (52) Powers, P. 0.;Ibid., 41, 304-9 (1949). (53) Powers, P. O., Overholt, J. L., and Elm, A. C., Ibid., 33, 125763 (1941). (54) Sutton, D. A , , J . Chem. Soc., 1944, 242-3. (55) Swift, C. E., O’Conner, R. T., Brown, L. E., and Dollear, F. G., J . Am. Oil Chemists’ Soc., 26,297-300 (1949). (56) Waters, W.A , , J . Chem. Soc., 1946, 409-15. (57) Wheeler, D. H., IND.EYG.CHmr., 41, 252-8 (1949). (58) Wheeler, D. H., Ofic. Dig. Federation P a i n t & Varnish Production Clubs, NO. 322, 661-3 (1951). (59) Wibaut, J. P., and Strang, A,, Koninkl. Ned. Alcad. Wetenschap., Proc., 54B, 102-9, 229-35 (1951). RECEIYED for review December IR, 1953.
ACCEPTED January 2.5, 19.54.
