RESEARCH
Ethylene, Internal Olefins Copolymerize Anionic catalyst systems give copolymers with alternating monomeric units, high crystallinity Alternating copolymers of ethylene and internal olefins have been synthe sized by Dr. Giulio Natta and his co workers at Istituto di Chimica Industriale del Politecnico, Milan, Italy. The copolymers are made from inter nal olefins that can't be homopolymerized with Ziegler-type organometallic catalysts (C&EN, Aug. 7, page 39). The same catalysts, though, are active in alpha olefin polymerizations. The internal olefins, however, can be copolymerized with ethylene or other reactive monomers. But reac tion rates are slower than during the polymerization of ethylene itself. In ternal olefins that have been copoly merized with ethylene include cis- and trans- butene-2, pentene-2, cyclobutene, cyclopentene, and cyclohexene. The copolymerization rates and composition of the copolymers pro duced depend on the type of catalyst used. Alternating copolymers having a high content of monomeric units derived from the internal olefin are obtained by using high concentrations of the olefin, low concentrations of ethylene. High ethylene concentra tion gives polyethylene almost ex clusively, according to Dr. Natta in a paper read by Prof. P. Corradini (for merly with the institute, now at Universita' di Cagliari, Sardinia) at the International Symposium on Macromolecular Chemistry, held in Montreal, Que.
The new copolymers are a result of continuing studies of stereospecific polymerizations being made at Milan. Alternating copolymers of dimethylketene and symmetrical ketones were made last year by Dr. Natta's group (C&EN, Oct. 31, 1960, page 4 1 ) . These linear, crystalline polymers have a polyester structure. Anionic catalyst systems such as vanadium tetrachloride/aluminum trihexyl are used in the internal olefin copolymerizations. But none of the anionic catalysts homopolymerizes in ternal olefins. Nor are two internal olefin monomers bound directly to each other, as shown by detailed studies of the ethylene and butene-2 copolymerizations at —30° C. (JACS, Aug. 5, 1961). Structure. The alternating struc ture of the ethylene-butene-2 product is confirmed by these results: • When ethylene concentration is held as low as possible in the liquid phase during the copolymerization, neither the copolymers produced nor their fractions contain more than 50 mole (/c of butene-2. • Infrared spectra of the copolymers show intense absorption at 13.2 microns due to sequences of two methylene groups; absorption bands at 13.6 and 13.9 microns (from longer sequences) are absent. • Catalytic systems, such as vana
dium tetrachloride and aluminum trialkyl produce ethylene-do'-butene-2 alternating copolymers having a speci fic gravity of 0.90, an identity period along the chain axis of about 9.15 Α., and a melting range (by x-ray deter mination) from 130° to 135° C. Further evidence for the alternat ing structure is the high crystallinity of some of the ethylene-^butene-2 copolymers. The same evidence also shows high steric regularity, the Milan chemists say. In fact, they predict that the copolymers have stereoregular diisotactic (all methyl group pairs on one side of the chain) or disindiotactic (methyl group pairs alternately above or below) structures, since each monomeric unit of butene-2 has two tertiary carbons. Exact configurations of the copolymers are being deter mined. Catalytic Systems. Many catalytic systems, under the right conditions, can be used to make ethylene-cisbutene-2 copolymers that are rich in crystalline fractions. Some systems that have limited stereospecificity in the polymerization of alpha olefins are effective for the copolymerizations. Catalysts that aren't stereospecific in alpha olefin polymerization—a sys tem like vanadium triacetylacetonate/ aluminum diethylmonochloride, for in stance, gives completely atactic pro pylene polymers—also aren't stereo specific in the copolymerization of ethylene with cis-butene-2. Such cat alysts promote the formation of co polymers that are either completely amorphous (specific gravity of 0.87) or have only low crystallinity. All of the alternating ethylene-iransbutene-2 copolymers made so far with any of the catalysts are noncrystalline at room temperature. Steric factors may influence the rate of copolymeri zation as -well as the polymer's steric structure.
Ethylene Copolymerizes with Butene-2 to Give Alternating Copolym ers In these runs, ethylene pressure was constant.
Butene-2 isomer
Catalyst system
CIS
VCI4/AI(hexyl)3 VCI4/AI(hexyl)3 V(acetylacetonate)3/ AI(C2H5)2CI V(acetylacetonate)3/ AI(C2H5)2CI δ.ΤίΟΙ3/ΑΙ(02Ηδ)3
trans cis trans cis 52
C & E N AUG. 14, 1961
C.for• 500 minutes except where noted Molar ratio butene-2/ Transition transi metal/ tion aluminum metal Solvent (moles)
All runs at -30°
Mole % butène in product
1/2.5 1/2.5 1/5
50 50 64
n-Heptane n-Heptane Toluene
1/5
64
Toluene
6
1/1
29
Toluene (0°C, 1200 min.)
4
38 16 20
magnetic stirrer Sodium in liquid ammonia
Dehydrobufotenine
Structure previously thought correct Bufotenine
^ 9235-C,
NMR Shows Dehydrobufotenine Is Tricyclic Uncertainties in the structure of dehydrobufotenine have been cleared up using its nuclear magnetic resonance spectrum, according to Dr. B. Witkop, Dr. F. Marki, and Dr. A. V. Robertson of the National Institute of Arthritis and Metabolic Diseases, National Institutes of Health, Bethesda, Md. Several years ago Dr. Witkop noted that the structure then believed to be correct was inconsistent with the ultraviolet spectrum observed for dehydrobufotenine. The UV spectrum resembles serotonin's (whose structure is the same as bufotenine except that it lacks the two N-methyl groups). Final confirmation of dehydrobufotenine's structure [JACS, 83, 3341 (1961)] came from study of the NMR spectrum taken in perdeuteromethanol. Tetramethylsilane was used as the internal standard. The spectrum reveals three aromatic protons; one is typical of a proton at C-2 of a 3-substituted indole (r = 3.10), the other two fit the requirements for protons at C-6 (r = 3.24, 3.38) and C-7 (r = 2.77, 2.92). This shows that C-4 is substituted. The expected bands were found for the six methyl hydrogens and the four methylene hydrogens. Others have reported that dehydrobufotenine undergoes a fission with sodium in liquid ammonia, typical of quaternary anilinium bases. The structure given by the NIH scientists accounts for all the spectral and chemical facts known for dehydrobufotenine.
Absolute Configuration of Isocitric Acid Shown The absolute configuration of natural isocitric acid and the molecular structure of an azidopurine have been found by scientists at The Institute for Cancer Research, Philadelphia, Pa. Using Bijvoet's method for determining the absolute configuration of an asymmetric molecule, Dr. Carroll K. Johnson, Dr. A. L. Patterson, Dr. D. van der Helm, and Jean A. Minkin confirmed the configuration of natural isocitric acid selected by Dr. T. Kaneko
and co-workers of Osaka University, Osaka, Japan, last year. The Philadelphia group used molybdenum radiation on the rubidium salt of isocitric lactone and both copper and chromium radiation on the potassium salt. The Bijvoet method depends on the difference in observed intensities when x-rays are diffracted by opposite sides of the same set of planes in an asymmetric crystal. X-ray studies of an azidopurine show that the azide group cyclizes to form a five-membered ring with four nitrogens. The analysis by Dr. Jenny P. Glusker, Dr. van der Helm, and Dr. Warner E. Love also showed water of crystallization. This tetrazole is produced from 6-hydrazinopurine with sodium nitrite.
EXCLUSIVE FEATURE... s w i v e l c l a m p with swinging arm A compact, quiet-running apparatus which utilizes a rotating field of magnetic force to induce variable speed stirring action. Dynamically balanced to prevent vibration and "walking." Stirring is accomplished by means of a small magnetized bar, which is placed in the liquid to be stirred and which is rotated by magnetic force consisting of a permanent bar magnet attached to the shaft of an electric motor and mounted in an aluminum housing with flat top 4 % inches diameter and 43^ inches high, on cast metal base. Can be used either on the table or on a support rod, attached by means of the clamp with swivel joint and swinging arm, an exclusive feature of the Thomas Stirrer. Center of stirrer top is adjustable between 3 and 4 ]/2 inches from support rod. Stirrer can be easily raised or lowered on the rod, and swings in or out of position in a horizontal plane. Particularly convenient in both the mounting and use of closed system assemblies. 9235-C. Stirring Apparatus, Magnetic, Thomas, with enclosed rheostat. With
rheostat in stirrer housing. With swingout clamp, two stirring bars, and connecting cord; for 115 volts, 60 cycles, a.c 37.20 Copy of Bulletin 778 sent upon request
ARTHUR H. THOMAS CO. Laboratory Apparatus and Reagents VINE ST. AT 3RD · PHILADELPHIA 5, PA. AUG.
14,
1961
C&EN
53
