DIHYDRONAPHTHALENE
POLYMERS N. D. SCOTT AND J. F. WALKER The R. & H. Chemicals Department, E. I. du Pont de Nemours & Company, Inc., Niagara Falls, New York
thalene dimer, melting a t 97.5" to 100" C. (IO), was also prepared by the destructive distillation of dihydronaphthoic acid.
A series of new hydrocarbon polymers has been produced by polymerization of the isomeric dihydronaphthaleneswith sodium naphthalene. From 1,4-dihydronaphthalene, light-colored thermoplastic resins are obtained. From 1,2-dihydronaphthalene are produced infusible polymers which, although completely insoluble in most solvents, form colloidal solutions in some halogenated aromatics. By the action of 80 per cent sulfuric acid on 1,2-dihydronaphthalene, it is converted to a mixture of dihydronaphthalene dimers. 1,4-Dihydronaphthalene is conveniently prepared as previously reported by the reduction of naphthalene with sodium and alcohol. It may also be produced by the hydrolysis of sodium naphthalene. This isomer is rearranged to 1,2-dihydronaphthalene by action of sodium ethylate.
Polymerization of 1,2-Dihydronaphthalene When sodium is allowed to react with naphthalene in dimethyl ether or the glycol diethers, sodium naphthalene (CloHsNas) is produced (8). When 1,2-dihydronaphthalene dissolved in one of the above-mentioned ethers is treated with a solution of this sodium compound, heat is evolved and a dihydronaphthalene polymer is precipitated (6). At low temperatures (-30" to -60" C.), 1,2-dihydronaphthalene is quantitatively polymerized by treatment with a relatively small amount of sodium naphthalene. Following the addition of a few drops of water to hydrolyze the sodium compound, the product may be isolated by filtration followed by washing with water to remove traces of sodium hydroxide produced by the hydrolytic reaction. The 1,2-dihydronaphthalene polymer obtained by the above procedure is a colorless powder possessing an unusual degree of thermal stability. It shows no sign of melting a t 250' C. and, when heated to higher temperatures, chars at a point only somewhat below red heat. Apparently it is completely insoluble in water and most organic solvents. Although its physical properties are such that its molecular weight cannot be determined by the usual procedures, i t is undoubtedly a polymer of extremely high molecular weight. When 1,2-dihydronaphthalene is polymerized in dimethyl glycol ether a t room temperature and above, the precipitated polymer, although qualitatively similar to polymer obtained in dimethyl ether a t lower temperatures, shows a fair degree of solubility in some materials. Apparently polymer prepared under these conditions has a lower molecular weight than the other product. In these cases the yield of precipitated polymer is generally not quantitative, but high yields in the neighborhood of 90 to 95 per cent are easily obtained. A polymer soluble in dimethyl glycol ether is produced as a by-product and may be isolated by distilling solvent from the filtered reaction mixture. A brittle resin melting at 165" C. and having an average molecular weight of 749 was obtained in one experiment. This resin is somewhat similar to the polymers of 1,4-dihydronaphthalene which will be discussed later. The infusible dihydronaphthalene poIymers produced a t 40" to 80" C. have the interesting property of forming colloidal solutions in high-boiling halogenated aromatics such as chloronaphthalene, bromonaphthalene, pentachloroethylbensene, chloroxylenes, and related compounds. When heated with these materials, the polymer swells and dissolves to form sirupy solutions which set to a gel or become extremely viscous on being cooled. The amorphous polymer of 1,2-&hydronaphthalene can also be obtained by treating the monomer with active sodium compounds other than sodium naphthalene. For example,
N CONNECTION with an investigation of the chemistry of naphthalene derivatives, attention was focused on the isomeric dihydronaphthalenes. Although dihydronaphthalenes are easily prepared from naphthalene in good yield, they have received comparatively little attention in recent years. A study of these compounds has resulted in the discovery of an interesting series of hydrocarbon polymers, the existence of which had not been previously reported in the chemical literature. There are two isomeric dihydronaphthalenes : 1,bdihydronaphthalene ( I ) prepared by the reaction of sodium with a solution of naphthalene in absolute alcohol, and 1,2-dihydronaphthalene (9) produced by the quantitative rearrangement of the 1,4-derivative on exposure to a hot solution of sodium ethylate. The former melts a t 24.5" to 25.0" C., the latter a t -8" to -7" C. Literature on the polymerization of these products is scanty. The similarity of the structure of 1,2dihydronaphthalene to that of styrene encouraged von Braun and Kirschbaum (2) to make a study of its polymerization. High polymers were not obtained in this work. Even after long exposure to heat and sunlight, 1,2-dihydronaphthalene was reported to remain substantially unchanged. Exposure to the action of concentrated sulfuric acid caused some polymerization, and the investigators obtained a crystalline dihydronaphthalene dimer melting a t 93" C. when a 10 per cent solution of monomer in benzene or petroleum ether was treated with an equal weight of this acid. A dihydronaph-
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When a solution of sodium naphthalene in dimethyl glycol ether is added to a solution of 1,4-dihydronaphthalene in the same solvent a t room temperature, the green color of the sodium compound gradually disappears and the solution becomes dark red in color. Hea,t is gradually evolved and external cooling is required to keep the reaction mixture below 50" C . The active reaction is complete in about 20 to 30 minutes, biit polymerization continues a t a slow rate and a p prosimat'ely 3 hours are required if a good yield of polymer is to be obtained. At the end of this time the sodium compounds are hydrolyzed by addition of a few cubic centimeters of water, and a colorlesssolution containingsuspended sodium hydroxide results. Since the polymer tends t o become colored if this mixture is worked up directly, the precipitated alkali is carbonated with gaseous carbon dioxide. The carbonate is then filtered off, a,nd the solvent is distilled from the filtrate under reduced pressure. The dihydronaphthalene in the reaction mixture is almost quantitatively polymerieed by this procedure, and 9.nearly colorless resin melting in the neighborhood of 100' C. and having an average molecular weight of 400 to 450 is obtained. If the polymerization is carried out a t 0" C., the reaction proceeds a t a slower rate and the polymer has a higher molecular weight figure. If the reaction is allowed to proceed a t this temperature for shout 50 hours, a resin melting a t 165" to 160' C. is produced. On vacuum diatillation of the lower melting 1,4-dihydronaphthalene resins, sizable fractiom of a liquid dimer may be obtained. A t a pressure of 1 mm. this liquid distills in the range 195" to 205' C . A t higher temperatures fractions having t h e average molecular weight of a trimer may also be obtained. Dimer obtained in this way differs from 1,2-dihydronaphthalene dimers in that it is converted to higher poIymer o n t r e a t m e n t with sodium naphthalene in dimethyl glycol ether. Resins obtained from 1,4-dihydronaphthalene by the procedure outlined above are brittle glassliike solids with a density of 1.14 and a refractive index of 1.6. They are insoluble in water a n d alcohols, moderately soluble in gasoline, and extremely soluble in n a p h t h a , terpentine, benzene, toluene, chloroform, and trichloroethylene. They are highly compatible with naphthalene, rosin, beeswax, vegetable oils, (Above) DIHYDRONAPHTE~ALENE RESIK (Below) DIMER OF ~ , ~ - D ~ H Y D R o N AhPI ~ N ~n ~POTSUED ~ ~ L E N ~ a n d m a n y o t h e r maKP ROOMTEMPERATURE terials. Although they
sodium anthracene and sodium benzophenone are equally effective. Treatment with other polymerizing agents gives soluble polymers of low molecular weight. Aluminum chloride gives a red brittle resin having a moleciilar weight of 388 plus a viscous oil, apparently a dihydronaphthrtlcne dimer. A study of the dimerization of 1,2-dihydronaphthalene with sulfuric acid resulted in the development of a new and p r m tical procedure for preparing a product of this type (f1 ) . This w&s accomplished by treating 1,2-dihydronaphthaIene with sulfuric acid having a concentration of approximately 80 per cent. A smooth exothermic reaction took place and a praotically quantitative yield of a light yellow viscous liquid w&s obtained. This product distilled a t 235' to 350" C. at 15 mm. pressure and had the correct molecular weight for dihydronaphthalene dimer. On standing, it partially crystallized and then proved separable into two fractions. A p proximately half of the crude material wag isolated as rr colorless crystalline compound melting at 51" to 62' C . even after repeated crystallization from petroleum ether and from ethyl aoetate. The remaining product was a liquid dimer. Neither of these products ansmrs to the description of the dihydronaphthalene dimers previously reported. Treatment of the crude dimer with sodium n a p h t h a l e n e does not cause further polymerization.
Polymerization of 1,4-Dihydronaphthatene
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Since 1,4-dihydronaphthalene does not contain conjugated unsaturation of the type exhibited by styrene, it would not a t first be expected to polymerize on treatment with sodium naphthalene. However, polymerization does take place when this compound is treated with sodium naphthalene in dimethyl glycol ether a t ordinary temperatures (7). Practically colorless brittle hydrocarbon resins are thus obtained. T h e s e resins a r e apparently a mixture of d i hydronaphthalene polymers for which the degree of polymerization varies from 2 dihydronaphthalene units per molecule t o approximately 5 or somewhat h i g h e r. Depending upon t h e c o n d i t i o n s under which the polymerization is carried out, products -6th melting points ranging from a p proximately 90" to 160" C. may be obtained in good yield.
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color somewhat on exposure to air when heated, they have a good degree of thermal stability and cracking does not take place until temperatures in the neighborhood of 370" to 450" C. have been attained. On hydrogenation in the presence of Raney nickel or other active hydrogenation catalysts, dihydronaphthalene resins absorb up to about 6 moles of hydrogen per dihydronaphIn
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and only 10 to 20 seconds should elapse before the iodide is added. The 1,4-dihydronaphthalene prepared from sodium naphthalene is easily identified by the formation of the charactenstic mercuric acetate addition product (melting point 122" C.) which is produced when it is agitated with an aqueous solution of this salt (4). It reacts with bromine to give an approximately quantitative yield of 1,Cdihydronaphthalene dibromide melting a t 71" to 72" C. Its behavior on treatment with sodium naphthalene serves as an additional confirmation of its strucu z N C ,\nn mately ture. On 10 heating per cent this solution product of sodium with an ethylate approxifor
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3 to 4 hours a t 150" C., it is completely converted to the 1,Zisomer.
dCh STYRENE
1,2-DlHYbRONAPHTHALENE
COMPARISON OF STRUCTURAL FORMULAS
Polymerization Theory Although the polymerization of 1,2-dihydronaphthaIene by sodium naphthalene is a definite catalytic process, the polymerization of 1,4dihydronaphthalene appears to have a more complicated mechanism. An appreciable concentration of sodium naphthalene is required, and the polymerization proceeds a t a comparatively slow rate which may be accelerated by increasing the temperature or the catalyst concentration. Sodium benzophenone does not act as a catalyst for this polymerization as in the case of the 1,2-dihydronaphthalene. The polymerization is also influenced by the solvent employed. When dimethyl ether or methyl ethyl ether is used as the solvent, only low yields of the lowest polymers are obtained. It is possible that the 1,4dihydronaphthalene is partially rearranged before polymerization and that the rate of polymerization is controlled by the rate a t which rearrangement takes place. The final polymer may thus be an interpolymer of 1,2- and 1,4dihydronaphthalene. It is not improbable that sodium naphthalene could bring
thalene unit (3). The melting point of the resultant resin is raised 30" to 40" C. by this procedure and the color stability is improved. Hydrogenated resin possesses solubilities and compatabilities more like those of saturated hydrocarbons. For example, the unhydrogenated resin will dissolve only 3 to 4 per cent paraffin without loss of transparency whereas hydrogenated material will take up approximately 10 per cent.
Preparation of Dihydronaphthalenes
As previously stated, 1,4dihydronaphthalene may be prepared by the reduction of naphthalene by means of sodium and ethyl alcohol. It may also be obtained by reaction of sodium naphthalene with water (6). If this procedure is carried out at temperatures below -30" C. or by addition of water to sodium naphthalene as formed, the product is not polymerized and good yields of 1,4-dihsdronaphthalene are obtained. If the process 'Is carried 'out a t room temperature in dimethyl glycol ether and the sodium naphthalene is allowed to build up in the solution, the dihydronaphthalene polymerizes as formed and the naphthalene is quantitatively converted to resin. I n the preparation of 1,4dihydronaphthalene by either of the processes described above, it is difficult to obtain a complete conversion of the naphthalene involved, and the crude distilled product usually contains 75 to 85 per cent dihydronaphthalene. The remainder of this material is largely naphthalene. Tetrahydronaphthalene is also present when an excess of sodium is employed. Crude distilled dihydronaphthalene is a satisfactory product for resin preparation and was so employed in our 1,4- DlHYORONAPHTWLRNl I,Z-OIHYORONAPHTHP~NE work, The dihydronaphthalene content of this material is easily determined since it reacts quantitatively and practically inSODIUM NAPYTUALLNL DIMCTHYL GLYCOL EWER) stantaneously with bromine. Bromination of impurities is avoided if the product sample is treated with a measured excess of bromine in carbon tetrachloride and then shaken with an excess of 5 per cent potassium iodide acidified with a little hydrochloric acid. The iodine liberated can .. .. then be determined by volumetric titration DIHYDROWTHALLNE RESINS DIMER OF INFUSIBLE POLYMCR OF and the bromine consumption calculated. (MCLTIM W 901160*C) 1,2- DlWORONAPHTHALeNE 1,2- DIHYDRONARITHALLNL The reaction with bromine should be carINTERRELATION OF DIHYDRONAPHTHALENE PRODUCTS ried out in the absence of direct sunlight,
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about this rearrangement of 1,4-dihydronaphthalene at low temperatures just as sodium ethylate does a t higher temperatures. The fact that mixtures of 1,4 and 1,Bdihydronaphthalene containing up to 70 per cent of the latter are polymerized to clear soluble resins containing none of the insoluble 1.2-uolvmer lends credence to this theow. Although this
thalene in a satisfactory manner.
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Literature Cited (1) Bamberger and Lodter, Ber., 20, 3705 (1887). (2) Braun, van, and Kirsohbaum, Ibid., 54,604-10 (1921).
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(5) Scott, u. s. Patent 2,146,447(1939). ( 6 ) Scott and Walker, Ibid., 2,055,708(1936).
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ill) Walker,'U. S: Patent 2,168,011(1939).
VINYL RESINS Influence of Chemical Composition upon Properties and Uses S. D. DOUGLAS Carbide and Carbon Chemicals Corporation, South Charleston, W. Va.
In common with other synthetic resins, the characteristics and usefulness of the vinyl resins may be varied by suitable changes in manufacturing conditions. As an example of resins of this type, the vinyl chloride-vinyl acetate copolymers may be modified by controlling degree of poly0 ONE familiar with the complexities of synthetic resins i t is apparent that wide variations in physical and mechanical properties may be attained by appropriate modifications of the manufacturing process. I n studying the particular class of resins formed by the conjoint or simultaneous polymerization of two typical vinyl compounds, vinyl chloride and vinyl acetate, an excellent opportunity has been offered to consider the effect of variation in chemical composition upon the characteristics and practical usefulness of the resin. In order to discuss these vinyl chloride-vinyl acetate resins adequately, it will be desirable first to describe briefly the synthesis, structure, and characteristics of the vinyl resins in general and of polyvinyl chloride and polyvinyl acetate in particular.
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Synthesis and Structure of Vinyl Resins Vinyl resins in general are prepared by polymerization rather than by a condensation reaction typified by the phenolic, urea, and alkyd resins. The resin molecule consists of a linear chain in which the monomers have reacted with one another a t the double bond to form high molecular weight polymers. The reaction may be brought about by irradiation with ultraviolet light or by addition of a small amount of a peroxide, ozone, or tetraethyllead (3). Vinyl compound polymerization is a chain reaction in which a large number of molecules react in rapid sequence to form one macromolecule. Polymerization is influenced by several factors. For example, traces of certain impurities act as inhibitors and either retard the rate of polymerization or lower the molecular weight of the resin formed, or both.
merization and vinyl chloride-vinyl acetate composition. The properties of the resulting resinshandtheir industrial applications are described in detail. A brief discussion of polyvinyl chloride and polyvinyl acetate, and their relation to the vinyl chloridevinyl acetate copolymers is included. Rate of polymerization varies directly as the square root of the catalyst concentration and doubles with every 8" C. rise in temperature. It is also directly proportional to the concentration of the vinyl compounds present. I n other words, solvent lowers the rate of polymerization, and the amount of reduction is specific for each solvent. Average molecular weight, or degree of polymerization of the resin produced, is directly proportional to the solvent concentration in the charge. Compounds that are solvents for the monomer but not for the polymer affect the molecular weight in the same way as do solvents for the polymer. Each solvent has a specific effect upon the average molecular weight. The latter decreases with increase in temperature and in catalyst concentration. The properties of the resulting resin are closely associated with its molecular weight and with the relative quantities of the various polymer bands of which the resin is composed. Certain characteristics vary with the average molecular weight, others are independent of it. Thus tensile and impact strengths, abrasion resistance, and viscosity in solution increase, while water absorption, refractive index, hardness, and electrical properties remain practically constant. Solubility in organic solvents rises with decrease in molecular weight.
Polyvinyl Chloride and Acetate Turning now to a consideration of specific vinyl resins, some of the properties and applications of polyvinyl chloride will be mentioned. This material is unusually strong and water- and chemical-resistant, but i t softens so slowly with rise in tem-
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