Alkyd Resins DEVELOPMENT OF AND CONTRIBUTIONS TO POLYMER THEORY R. R. Blienle American Cyunantid C o m p a n y , Bound Brook,
"rhe development of alkyd resins is that of the translation of the chemistry of polyesters to a wide variety of useful industrial products. This development has taken place largely during the last 25 years and has resulted in glew and improved coating compositions, adhesives, plastics, and textile fibers. Studies on the polyester reactions and the polymeric products obtained therefrom were among the first to reveal that polymers result from primary covalent reactions, that the physical properties of polymers are influenced by the constitution and structure of the interacting monomers, and that the type of polymer €ormed is determined by the functionality of the monomers used in polymer formation. Polyester polymer formation investigations also have provided the basis for the theoretical contributions that have been made to condensation polymer formation and particularly polymers of the cross-tie type,
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ins which would change from a fusible to a n infusible form U ~ U L the application of heat. These studies led t o the solid transparent glycerol phthalate resin first prepared by Watson Smith ( 3 6 ) . This product was reported as insoluble in water, but soluble in hot glycerol. By distilling the glycerol from the solution in vacuo, the fusibility of the product was varied. When all the free glycerol was removed, a transparent slaglike body containing glycerol and phthalic anhydride in the molecular ratio of approximately 2 t o 3 was obtained. On further heating this product puffed up into a brittle, vesicular mass which was uselese from a n industrial standpoint.
Glgcergl Phthalate Resins
Callahan (8),Friberg (It?), Arsem (Z), Dawson (IS), a ~ i d Howell ( d 3 ) of the General Electric laboratories carried out intensive investigations on the glycerol-phthalic anhydride reaction which resulted in new and useful resins of the heat convertible type. I n particular, they pointed out t h a t when part of the LKYD resins are indeed an appropriate subject for a symphthalic anhydride was substituted with monobasic acids, such posium in connection with the twenty-fifth anniversary of as butyric acid and oleic acid, more flexible resins resulted. A the Paint, Varnish, and Plastics Division of the AVERICAP; similar effect was obtained when a n aliphatic dibasic acid, such as CHEMICAL SOCIETY.Their growth and development has ocsuccinic acid, was employed. This work also showed that glyccurred along with t h a t of the Division. Particularly is this true eryl phthalate could be modified and flexibilized with castor of alkyd resins used as coating compositions as these resins have oil and t h a t high temperature baking varnishes could be prehad a large part in developing a general understanding of the pared, particularly from the oleic acid modified glyceryl phthalprinciples of polymer formation. Alkyd resins are polyestersa l e resin or from this same resin when castor oil had been incorthat is, polymers formed by the reaction of polyhydric alcohols porated. Because long periods at high temperatures of the and polybasic acids. Their formation is a typical example of order of 150' C. were required to convert thin films of these rescondensation polymerization. ins t o a n insoluble gel condition, they were of little use t o the The formation of polyesters with resinous characteristics has coating composition industry except for restricted electrical uses, long been known. Beraelius ( 4 ) reported a resin from tartaric one such use was a3 a protective film on brass lightning arrester acid and glycerol. Berthelot ( 3 ) prepared the glycerol ester of plates. Although baked films from solutions of these resins camphoric acid, and Von Bemmelen ( 3 7 ) prepared glyceryl sucpossessed excellent adhesion t o metals and fairly good flexibility, cinate and glyceryl citrate. Other early investigators who rethey lacked film building properties and were difficult t o pigment ported polyesters were Debus ( I $ ) , Lourenco (SS), Furaro and Furthermore, their cost was high largely because of the price nf Danesi (19). phthalic anhydride a t t h a t time. During World War I, the Gibbs-Conover process for the manuEarly I n c a s t i g a t i o n s facture of phthalic anhydride by the catalytic oxidation of naphthalene was introduced. This made low cost phthalic anhyThe initial stimulus toward detailed investigation of alkyd dride commercially available. It also renewed interest in the resins came from the electrical industry. I n 1889, Arthur Smith phthalate alkyd resins, and, in the search for possible uses, it was called attention t o the adaptability of the reaction products of recalled t h a t the glyceryl phthalate resin had shown extraorphenols and aldehydes as electrical insulation materials, and for dinary adhesiveness t o smooth surfaces. At this same time t h e the next decade investigations were focused on these phenolsoaring price of shellac resulted in the commercial use of the earaldehyde resins. It was, however, Baekeland (2) who first relier glyceryl phthalate resins t o bond mica flakes and produce ported a systematic study of the phenol-formaldehyde reaction. mica sheets suitable for electrical commutators, lamp shades, His work led t o such modifications in the resins and to such imand similar products. . provements in the methods of hardening under heat and pressure Coincidental n i t h the renewed interest in the phthalate alkyd t h a t plastic articles could be made easily from the polymers of resins, investigations were in progress on the bodying and drying this reaction. The electrical industry immediately made use of of linseed and other drying oils, a field in which little scientific these results and by 1912 Bakelite became a standard insulating data had been published. It was found t h a t the observed material. changes could be explained from a colloidal veiwpoint. ,4thcor? Xaturally such laboratories as those of the General Electric was developed that drying (development of insolubility by reCompany undertook investigations, not only of the phen'ol-aldeaction with oxygen) was, basically a n intermolecular linking of hyde resins, but also of other synthetic resinous bodies, particumolecules a t the conjugated double bonds present in the fatt\ larly those that had heat convertibility properties-that is, res-
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acid radicals of the glyceride molecules by oxygen atoms. It was concluded that this intermolecular linking developed a definite three dimensional colloidal structure. These studies furthermore brought out the role of the glyceryl radical in developing complexity and molecular size as contrasted with that developed when the radicals of alcohols having fewer hydroxyl groups were substituted. They also emphasized the importance of the divalent character of the reacting element-that is, oxygen, in bringing about gelation in coating composition films when exposed to the air. This phenomenon was later termed element convertibility (29). Attention was called also to the difference in the structure between oxidized oils which are oxygen linked and heat treated oils which are intermolecularly linked through simple addition polymerization a t the double bonds. The concept helped materially to explain some of the physical and chemical differences observed between oxidized and heat treated oils. When the physical changes of glyceryl phthalate resin were compared with those of the heat treated drying oils, it was observed that there was considerable similarity. In addition, chemically, both were glycerides. However, when attempts were made t o incorporate the solvent-soluble solid form with drying oils, incompatibility resulted. I t was then conceived that if suitable unsaturated oxidizable acids, such as the mixed fatty acids of linseed oil, could be introduced a t the beginning of the condensation reaction and made an integral part of the complex glyceryl phthalate, a homogeneous resin might result which would possess both heat and oxygen converting properties. This concept was confirmed by experiments which were first performed in 1921. Furthermore, it was shown that the resulting homogeneous resin, when dissolved in fairly cheap, rapid evaporating solvents, produced adhesive, quick drying, durable films with good characteristics (28, 20). These films could be converted to an insoluble state by simple exposure to the oxygen of the air or to low temperature baking. These resins, with many subsequent modifications, form the basis of the present day alkyd resins of the coating composition field. About the same time that the first drying oil modified alkyd resins were made in the laboratory, revolutionary changes were taking place in the automobile finishing field, through the introduction of low viscosity nitrocellulose lacquers. Their use markedly reduced the finishing time with no sacrifice of durability compared to the natural resin-drying oil vehicles then in use. The advantages gained from these lacquer finishes more than offset the disadvantages of formulation, the many coats required t o attain proper film thickness, and the lack of solvent resistance. This latter characteristic, of course, was due to the fact that lacquers produced films simply by evaporation of the solvent and hence could be redissolved. Nevertheless, the economy resulting from the time saved in finishing with lacquers was so appealing that the development of nitrocellulose lacquers became a inajor undertaking of coating composition manufacturers and their suppliers. A large number of new organic solvents were introduced, particularly ketones and esters. Also, as a result of the varch for suitable plasticizers, other new chemicals came on the market. The demand of the coating composition industry for solvents, plasticizers, and lacquers coincided with the commercial introduction of glycols and their esters and ethers. This illustrates how the demands of a new development in one industry influence another; thus the availability of the glycols had a considerable influence on the development of alkyd resins. At first, the influence was chiefly theoretical in that it revealed to certain investigators (30)the fact that dihydric alcohols when reacted with dibasic acids always gave heat nonconvertible resins, while the reactions of higher polyhydric alcohols ,and dibasic acids gave heat convertible resins. However, commercial development of alkyd resins from glycols came much later, All this work on nitrocellulose lacquers had another influence on alkyd resin development. It was found that proper adhesion to metal surfaces required the use of compatible resins. Natural
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resins, such as dewaxed damar, were first used for this purpose. The rosin modified alkyds and nondrying oil alkyds were then found to be more compatible and more durable (16), and this led to their use in the lacquer field. During the period of 1921 to 1926, except for some exploration of the use of heat nonconvertible alkyd resins in lacquers, the development of alkyd resins was largely in the hands of the electrical industry laboratories. Alkyd resins went into commercial production as adhesives. Their use as plastics, however, seemed to be barred by the difficulty of obtaining the final insoluble and infusible state, that is the gel state, except by means of long heat treating cycles. Clear and pigmented articles were manufactured, but only by first curing in mass form and then machining to shape. At this period the use of alkyd resins as coating compositions was directed almost entirely toward obtaining a successful wire enamel which, with insulating varnishes, was currently of major interest to the electrical industry. Because of their outstanding adhesion, durability, hydrocarbon oil insolubility, and flexibility, unmodified, nondrying and drying oil modified alkyds were all actively explored. However, little work was carried out in using these products as decorative coating compositions because such compositions were of minor importance to these laboratories. If the major interest of the laboratories had been reversed, it is entirely probable that the coating composition industry would have had available much sooner the important drying oil modified alkyds.
Induetrial Applications The next step in the development of alkyd resins illustrates the value of exchange of experiences between investigators working in a common scientific field, but with different commercial interests. In 1926 two men, both of whom had worked on alkyd resins, discussed these polyester polymers. One was actively engaged in the manufacture of lacquer finishes. The other investigator called to his attention an advancement-namely, the attainment of a resin composition that could be applied like a lacquer and that possessed adhesion and flexibility with the added characteristic of being convertible to an insoluble and infusible state by either low temperature baking or simple exposure t o the oxygen of the air. Extensive activity in coating compositions containing alkyd resins as the sole vehicle then followed. At this time the electrical industry was entering the household appliance field. Durable, tough, flexible, white decorative finishes rapidly became a major requirement. Drying oil modified alkyd resins with their low temperature short time baking cycle and their comparatively good color retention offered a solution. Simultaneously a leading manufacturer in the field of varnishes, paints, and lacquers explored and developed these alkyd resins from the viewpoint of the decorative coating industry as a whole. Alkyd resins as film forming materials were first described a t the fifth annual meeting of this Division of the AMERICANCHEMICAL SOCIETY (29). I t hardly seems necessary t o make more than passing mention of the importance of alkyd resins t o the modern coating composition industry. At first, color retention, after-tack, and high acid values were problems of concern. However, during the last 20 years, progress in manufacture, processing, formulation, end pigmentation have practically eliminated these minor defects. Initially, alkyd resins were prepared by the direct interaction of acids and polyhydric alcohols. Today the monoglyceride, ester interchange, and solvent processes also are employed. The search for improved alkyd resins has played a major role in the commercial availability of many new chemicals. The importance of color has introduced new raw materials, such as specially distilled and fractionated drying oil acids. Alkyd resins have been largely responsible for the commercial availability of such polybasic acids as fumaric, tricarballylio, aconitic, sebacic, adipic, terephthalic and itaconic, and maleic and chlorophthalic
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INDUSTRIAL AND ENGINEERING CHEMISTRY
anhydrides. Moreover, commercial exploration of the Dielshlder reaction has been activated to furnish the adducts of maleic anhydride with certain terpenes, rosin, and cyclopentadiene. The commercial availability of pentaerythritol, dipentaerythritol, triniethylol propane, sorbitol, mannitol, and the glycols has been enhanced. Acute shortage of unsaturated fatty acids and drying oils in World War 11, coupled with the large military demand for alkyd -resins, was largely responsible for the development and wide use ,of dehydrated castor oil and isomerized linseed oil. Alkyd resin research also played a major role in furnishing the initiative to prepare and separate from the monomers, dimer drying oil acids. With successful use of alkyd resins as decorative finishes, the ,entire coating composition industry became synthetic resin minded. In turn, examination of all kinds of synthetic resins for h i s h e s expanded the use of alkyd resins. Thus, the low water resistance of many alkyd resin films was corrected by a phenolic alkyd resin combination. Color, mar resistance, hardness, and baking cycles were improved by combining alkyd resins with organo-soluble urea formaldehyde and melamine formaldehyde resins. This not only accelerated the commercialization of these resins, but also produced entirely new and improved finishes. Recently silicone resins have been cocondensed with alkyds leading to new high temperature stable finishes. It is expected that as other polymers become available, further new and improved coatings will be forthcoming. Alkyd resins, that is polyester polymers, have not been confined entirely to the coating industry. The plastic industry today is using large amounts of contact or low pressure laminating resins, largely based o n polyester polymers. These resins employ linear polymer type alkyd resins which have a number of C=C linkages per polymer molecule. One way of obtaining such alkyds is to incorporate either maleic or fumaric acid in the polyester; the esterification is carried out so that during the process of ester formation the C=C react,ivity is inhibited. The polyester then is dissolved in a liquid vinyl monomer such as styrene or diallyl phthalate-to yield a liquid resin that can be applied to fabrics by regular impregnating equipment. N o inert organic solvent is used. The result is a fabric containing a resin which, in the presence of proper catalysts, readily converts to the insoluble and infusible gel state by addition polymerization. This is accomplished by cross tying the polyester chains through addition polymerization with the vinyl group of the monomer, in which the linear polyester is dissolved. The path to solventless coating compositions is indicated. Alkyd resins which are highly elastomeric in character have been prepared. Thus, mrhen dihydric alcohols and dibasic aliphatic acids are incorporated in sufficient amounts into trihydric alcohol-dibasic acid alkyds, internal flexibilization results and a rubbery gel is obtained. These products, charact,erized by excellent oil resistance, can be reinforced with fillers and handled similar to rubber. Another approach to rubberlike products is to prepare linear alkyds with unreacted C=C groups and then to vulcanize with peroxide, sulfur, etc. Again, reinforcing fillers can be incorporated and the result,ing product niechanically worked like rubber. Alkyd resins are being used in the textile field. The first flbers made from polyesters, called superpolyesters, were prepared by Carothers and Hill ( 1 1 ) . Recently a polyester fiber, based primarily on terephthalic acid and glycol, known as Terylene, has been introduced in England by Imperial Chemical Industries ( 7 ) . This appears t'o have real promise as a textile fiber. The excellent adhesion of alkyd resins to cellulose makes thcin an important component, in pigmented emulsions for the dyeing and printing of cellulosic fabrics with lightfast pigments. Application on the fabric followed by simple curing is all that is necessary to attain the so-called resin pigment dyeing and printing of textiles now in wide commercial use. Pigmented aqueous emulsions of alkyd resins also have found
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commercial application as coating compositions, particularly for interior wall decoration. The ease with which solutions of alkyd resins can be emulsified together with their property of forming insoluble durable films through oxygen convertibility makes this development an important one. The wide variety of polyester polymers that can be obtained and the relative simplicity of the chemical reaction involved havc helped considerably in clarifying the mechanism of polymer formation. Balsams, waxes, hard brittle fusible transparent resins, flexible hard infusible resins, fibers, heat-setting adhexives, rubberlike compositions, baking varnishes, air converting varnishes, low pressure setting plastic compositions, and others are illustrative of the many physical forms of polyesters that have been prepared. Detailed studies governing the formation of these products have been an important guide to the a t t b h n e n t of these forms with polymers in general. It has already been described how the drying oil modified alkyd resins followed as a result of earlier scientific investigations of polymerization of drying oils. In turn, the functionality concepts which grew out of the study of the polyester reaction assisted later in throwing light on the chemistry of drying oils (6). In the early twenties, as a result of extensive research on polyoxymethylene and polystyrene polymers, Slaudingcr and coworkers indicated that' these products were threadlike molecules formed exclusively by primary valence union of monomers. Their papers drew a parallelism between these polymers arid many of the natural polymers, such as celluloae, starch, and rubber. Their work constitutes the first explanation of high molecular weight organic molecules-that is, macromolecules, as being the result of no more than ordinary chemical union.
Polweutter Polgmer FormmdfaPn. Herzog ( 2 0 ) introduced the theory that resin formation was the result of the presence of certain radicals in the interacting molecules which he called resinophores. The attainment of polyester resins through the interaction of polyhydric alcohols and polybasic acids confirmed the primary valency concepts of Staudinger and co-workers and developed the idea that, polyreactivity in interacting monomers was the important factor in polymer formation. The radicals to which Herzog drew attent,ion actually induced polymer formation not because of some particular atomic grouping, but because they were polyfunctional. An hypothesis of polymer formation was postulat,ed by Kienle in 1924 which differed from previous concepts in that polyfunctional reactivity and the resulting spatial arrangement of the interacting moleculcs were used to explain such widely divergent polymerization processes as the heat treatment of drying oils, the oxygen convertibility of drying oils, t'he phenol-formaldehyde reaction, the alkyd resin reaction, the vulcanization of rubber, and the formation of certain inorganic glasses. Experimental proof was needed t o show that, the hypothesis definitely held for polymer format,ion in general, hence publication was delayed until 1930 ( 2 5 ) . In tho interim, Kienle and Hovey experimentally tested the hypothesis by preparing a, wide variety of polyester reactions. They also carried out some of the first kinetic studies of resin formation ( 2 2 , 80). In particular, these investigations brought out the fact that dihydric alcohols reacting with dibasic acids always resulted in heat nonconvertible resins, while a trihydric alcohol with the dibasic acid or anhydride, such as phthalic anhydride, gave a heat convertible resin. Thisexperimental work laid the foundation of an understanding of the causes of the difference between linear and three dimensional polymer formation. Work on alkyd resins in the 1911 to 1914 period already had shown that, if saturat,ed aliphatic monobasic acids were employed in part, in the polyester reaction, flexibility could be improved. Further experiments revealed that, incorporation of monohydric alcohols resulted in similar improvements in the resins. These experiments showed that the size and shape of the monomers and
April 1949
INDUSTRIAL AND ENGINEERING CHEMISTRY
position of the reactive groups used in preparing a polyiner influence the physical properties of the final polymer. These factors in polymer formation appear t o have been first observed and proved in polyester research. The broad classification of synthetic resins into heat nonconvertible, heat convertible, and element convertible types was proposed by Kienle in 1928 (%$,37). At this time in discussing the mechanism of resin formation ( S 7 ) it was shown also that the magnitude of the polyreactivity of the interacting monomer molecules was the factor responsible for a final polymer falling into one of these three classes. A general theory of polymer formation, largely dependent for proof on data obtained from polyester studies, was actually worked out by Kienle in 1928 ( 2 6 ) . The postulates made then have since been modified t o a degree ( 2 6 ) , but in general have proved valid by any number of polymer forming reactions. Meanwhile, Carothers and co-workers began their investigations on a wide variety of bi-bifunctional reactions (9). They first investigated a number of polyester reactions, later extending their studies to polyanhydride, polyamide, and other similar condensation systems. This work furnished experimental evidence of the similarity in principle of both addition and condensation reactions. Carothers termed the first A polymers and the latter C polymers. Carothers’ investigations further gave ample support to the fact that when bifunctional monomers were reacted linear polymers resulted, except in the few cases where the total number of atoms of the reacting molecules after condensation, totaled 5, 6, or 7. I n these special cases, single chemical rompounds of a cyclic nature resulted. Later Carothers and eo-workers extended their polyester studies so that extremely high molecular weight polymers, called superpolymers, were formed. This work showed that these superpolymers could be extruded from melts t o give single filament fibers which subsequently in the case of polyamides, led to the development of nylon. The initial detailed studies (50) on the polyester reaction were extended by investigations of Honel ( S I ) , Bozza ( 5 ) , and Savard and Diner (34). I n later more complete investigations carried out by Kienle, Petke, and van der Meulen ( S I , 32), it was shown that esterification of the LY- and p-hydroxyl groups of glycerol occurred at different rates and t h a t some intraesterification and anhydride formation also was important in the polyester reaction, The work on polyesters, particularly those of the heat convertible type, has been a major factor in leading to the present understanding of the phenomenon of gelation. This also is referred to as the insoluble and infusible state or the state of arrested motion. Kienle and Hovey (28, 30) in their original work considered the attainment of this state in higher functional systems as a consequence of complex three dimensional structures attained through the chance reaction of hydroxyl and carboxyl groups. Carothers ( 1 0 )introduced the concept that gelation was due to the formation of infinitely large molecules. Flory (f7) and later Stockmeyer ( 3 6 ) both carried out excellent theoretical analyses of gelation based principally on polyester data and arrived at the conclusion that gelation was the result of the formation of infinite networks. When Flory (17‘) applied his theory t o the polyester systems studied by Kienle et al., he found some disagreement between his theoretical calculations on these systems and the actual experimental data reported. Flory suggested that this was due to intraesterification and anhydride reactions which had been shown t o occur in addition t o the normal interesterification reon the other hand, suggested that gelation action. Kienle (M), in polyester and similar condensation polymer systems was the result of the attainment of a sufficient concentration of complex intertwining three dimensional molecules of a moderately low degree of polymerization t o induce a sort of log jam and thus effect a state of arrested motion in the polymer as a whole. Further detailed studies of polyester systems are warranted and undoubtedly will contribute considerably t o a still further clarification of this
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interesting phenomenon, so important in the industrial use of many polymers. Cornish ( I S ) recently outlined a proposal for a detailed study of the pentaerythritol-dibasic acid reaction. This investigation should prove scientifically valuable in that all of the hydroxyl and carboxyl groups present have equal reactivity; hence it complies with the assumption made in the simplest theoretical treatment. Research in the field of polyesters also has contributed to an understanding of the relation between the viscosity of a molten polymer and the molecular weight. Flory ( 1 6 ) ,on the basis of linear polyesters, developed a n exact relation between viscosity and chain length. This is another illustration of the contribution which polyester investigations have made t o our understanding of polymers. Finally, polyester investigations have contributed t o polymer theory by distinguishing between active and potential functionality. Only the active functional groups of the monomeric reactants lead t o polymer formation. Potential functional groups also must be considered but only when activated. Alkyd resins used as decorative coatings are illustrative of polymers formed through reacton of the active functional hydroxyl and carboxyl groups, while the potentially functional C=C groups are largely inactive. When these resins are exposed as thin films to oxygen, this group becomes active and gel formation results. 4 s new raw materials become available and further detailed investigations of the polyester reaction and its products are completed, further advances can be anticipated,
Eiteruture Cited Arsem, W. C., U. S. Patents 1,098,776-7 (June 2, 1914). Baekeland, L., IND. ENG.CHEM.,1, 149 (1909); 4, 737 (1912). Berthelot, M. M., Compt. rend., 37, 398 (1853). Berrelius, J., Rapport ann., 26 (1847). Bozza, G., Giorn. chim. ind. applieata, 14, 294,400 (1932). Bradley, T. R., IND. ENG.CHEM., 29,579 (1937); 30,689 (1938). Brewster, F.R., Teztile WorEd, 97, No. 6. 123 (1947). Callahan, M. J., U. 9. Patents 1,108,329-30 (1914); 1,108,332 (1914); 1,091,627-8 and 1,091,732 (1914). Carothers, W. H., “Collected Papers on Polymerization, High Polymers” Vol. I, New York, Interscience Pub. Co., 1940. Carothers, W. H., T r a n s . Faraday Soc., 3 2 , 4 4 (1936). Carothers, W. H., and Hill, J. W., J. Am. Chem. Soe., 54, 1559 (1932).
Cornish, G. R., Chemistry 6% Industry, 1948, No. 3, p. 42. Dawson, E. S., U. S. Patent 1,141,944 (June 8,1915). Debus, H., Phil. May., 16,438 (1858). Ellis, C., “Chemistry of Synthetic Resins,” Vol. 11, p. 906, New York, Reinhold Pub. Corp., 1935. Flory, P. J., J . Am. Chern. Sac., 62, 1057 (1940). Flory, P. J., Ibid., 63, 3083, 3091, 3096 (1941); Chem. Rev., 39, 137 (1946).
Fiiberg, L. H., U. S. Patent 1,119,592 (Dec. 1, 1914). Furaro, A,, and Danesi, L., Jahrb. Fort. Chem., 799 (1880). Herrog, 2. angew. Chem., 35, 465,641 (1922). Honel, Paint, Oil 6% Chem. Rew., 91, 19 (1931). Hovey, A. G., dissertation, Union College, Schenectady, N. Y . (1927).
Howell, K. B., U. 5 . Patent 1,098,728 (June 2, 1914). Kienle, R. H., American Institute of Chemists, Northwestern University, unpublished (1928). Kienle, R. H., IND. ENG.CHEM., 2 2 , 5 9 0 (1930). Kienle, R. H., J.Soe. Chem. I n d . , 55, 229 (1936). Kienle, R. H., Massachusetts Institute of Technology, unpublished (1928). Kienle, R. H., U. S. Patent 1,893,873 (Jan. 10, 1933). Kienle, R. H., and Fersuson. C. S.. IND.ENG.CHEM..21, 349 (1929).
Kienle, R. H., and Hovey, A . G., J. Am. Chem. Soc., 51, 509 (1929); 52, 3636 (1930).
Kienle, R. H., and Petke, F. E., Ibid., 61, 2268 (1939); 62, 1053 (1940): 63. 491 (1941).
Kienle, R. H:, van der Meulen, P. A., and Petke, F. E., Ibid., 61,2258 (1939). (33) (34) (35) (36) (37)
Lourenco, A. V., Ann. chim. etphys., [3] 67, 313 (1863). Savard, J., and Diner, S.,Bull. soc. chim., 51, 597 (1932). Smith, W., J.Soc. Chem. Ind., 20, 1073 (1901). Stockmeyer, W. H., J. Chem. Phys., 1 1 , 4 5 (1943). Von Bemmelen, J., J. prakt. Chem., 69, 8 4 , 9 3 (1856).
RECLIVED April 28, 1948.
