Metalio-organic polymers open new field New polymers exhibit heat resistance, semiconductivity, photoconductivity, or catalytic properties ORGANIC COATINGS—Polymers of metalio-organic compounds largely remain laboratory curiosities, mainly because chemists are just be ginning a systematic study of them. The laboratory work to date, how ever, has produced polymers whose properties suggest that metalio-or ganic polymers could be an important new field of polymer science. "Ruggedness," in the form of un usual resistance to heat, characterizes some of the new polymers reported to a symposium on metal-organic plastics systems at the 162nd ACS Na tional Meeting in Washington, D.C. Semiconducting and photoconducting properties are found for other poly mers. Still others appear to have po tential uses as catalysts, biological agents, or composites. Many of the polymers covered in the symposium—some disclosed for
the first time—contain metals different from metals in polymers already known. For example, Dr. Charles E. Carraher, Jr., of the University of South Dakota has made polyesters based on metal dicyclopentadiene dichlorides (CP2MC12), where the metals (M) are titanium, zirconium, and haf nium. The CP 2 MCl 2 's react with var ious dicarboxylic acid sodium salts to form polyesters that precipitate rapidly from solution. The polyesters that Dr. Carraher has made generally exhibit poor solu bility in most solvents, making so lution characterization difficult. They have weight-average molecular weights in the range of 104 to 106, as determined by light scattering. They remain solids to temperatures of 1200° C , although some color changes occur. Fibers. Although one particular in terest in these polyesters with a Group IV metal in their backbone comes from the possible cocatalytic value in Ziegler and other systems, some of these polyesters may find possible use as high-temperature fibers. The CP 2 TiCl 2 terephthalate fibers that Dr. Carraher has made retain their tex ture and matrix up to 1200° C. and remain somewhat flexible. These and
Copper coordination polymer is semiconductive I
I
Cu
Cu
I
I
J
Cu. Cu
\ CH" I CH
A/
\ .Chk
.N
V
_N
CH-
\
/
Cu * Ν
Cu'
I -Chk
CH"
Cu,
\
CH
I
Cu (Note: to simplify, substitueras on the nitrogen atoms have been omitted)
I
I
Cu
Cu
I
I
Arylethynyl polymers are photoconductive etc. I
R I C
R_C=C-CU-*-III
C I
R
Cu
I
t
ο
R — C =
C — Cu *+— HI
c etc. R = phenyl, p-methylphenyl, p-methoxyphenyl, p-nitrophenyl, α-pyridyl, £-pyridyl, ç-naphthyl, β-naphthyl, 9-anthracenyl, N-carbazolyl, and 2-pyrenyl-ethynyl
other polyesters containing titanium initially are a light yellow to orange as formed; in air at 300° to 400° C , they generally become dark grey or black, Dr. Carraher says. Further heating to 500° to 600° C. causes the polyesters to turn white. At 1000° C , all the Group IV metal polyesters are dark grey to white. The titanium polyesters made with terephthalate also will form fibers in an unusual way. If the polymers are made by interfacial condensation and allowed to dry on a glass petri dish, they have a flaky, granular texture without appearance of any threadlike composition, even under a 2000-fold magnification. If the polyester is scraped from the dish with a metal spatula, fibers 0.0002 mm. in diameter and up to 30 mm. in length form. The fibers pick up static electricity when scraped and retain some of the charge for as long as 30 minutes. Copolymerization of different metal-carbonyl derivatives leads to polymers with two metals in them, according to Dr. Charles U. Pittman of the University of Alabama. For example, styrene tricarbonyl chro mium will copolymerize with vinylcyclopentadienyl manganese tricar bonyl to give a polymer containing SEPT. 27, 1971 C&EN 37
Polyester polymers contain Group IVB metals
f^N
ci ^M
ο
+
9
0 II
0 0 II II • R - C -• 0 > —• -( M - 0 - C 1
0 - C - R - C -• 0 © -
é
M = titanium, zirconium, hafnium
both chromium and manganese bonded to the polymer's backbone. Other copolymers of styrene tricarbonyl chromium with monomers such as styrene and methyl acrylate have been made by Dr. Pittman and his associates, Dr. Paul L. Grube and Dr. Orval E. Ayers. They also have added metals to polystyrene by reacting it with chromium, molybdenum, and tungsten tricarbonyl derivatives. No degradation of the polystyrene occurs during these polymerizations. Semiconductors. Polymers containing copper atoms have semiconducting properties and, in some cases, photoconducting properties. Dr. Seiichi Kanda of Tokushima University in Japan and coworkers have produced a series of coordination polymers by reacting dithiooxamide (rubeanic acid) or iV,Af'-disubstituted dithiooxamides with cupric sulfate in aqueous solution. He, Dr. Asahi Suzuki, and Dr. Kuwako Ohkawa find that the polymers have an atactic conformation. Their studies show that the specific conductivities and activation energies of the various polymers correlate with the formula weights of the substituents—such as methyl, cyclohexyl, and benzyl groups—on the nitrogen atoms. Cyclic hysteresis of conductivity under uniaxial pressure
indicates that the macromolecules orient and relax according to plastic flow that is reversible, Dr. Kanda says. Other chemists working with organocopper polymers, Dr. Yoskiyuki Okamoto at New York University and Dr. Aleksander Golubovic at the Air Force Cambridge Research Laboratories and their associates, have prepared various arylethynyl copper polymers. These polymers have substantial back coordination from metal d orbitals to antibonding orbitals of two acetylene groups bound to the coppers. As a result, the polymers exhibit both semiconductivity and photoconductivity. Conductivity is increased if the size of the aryl group is increased by replacing the phenyl group by an anthracenyl group, Dr. Okamoto says. Electron-donating groups such as —0CH3 on the aryl rings increase conductivity, whereas electron-withdrawing groups such as —N02 reduce conductivity. Photocurrent response and decay are slow, indicating that the photocarriers are deeply trapped in the polymer. If the aryl groups have a sterically hindered structure, the photoactivity is slower. This suggests that the more complex structure provides deeper traps for the carriers, Dr. Okamoto adds.
Polymers containing two different metals can be made
Λ^ y°:\ I
CO'
X
CO
C0
- U C H 2 - CH}
^ C H 2 - CH
/Μηχ CO' 1 XC0 CO Cr(CO).
(Note: the rings are different—one monomer is a styrene and the other a cyclopentadienyl)
38 C&EN SEPT. 27, 1971
Mn(C0)s
Insect hormone use requires caution J É ^ PESTICIDES—The great expecta^ J r tions that greeted the advent of the third generation of insecticides remain undiminished. However, enthusiasm for applications of insect juvenile hormone (JH) is being tempered with caution arising from a better grasp of the practical problems of use. Field testing has begun to yield some data on the efficiency of JH, and theoreticians are zeroing in on the mechanism that governs their operation. Part of the caution expressed by several contributors to the symposium on insect juvenile hormones is due to the amount of publicity that JH has been receiving. Dr. Julius J. Menn, of Stauffer Chemical Co., tells C&EN that one of the reasons for the JH symposium in Washington was to provide an opportunity for the display of hard data. The hope was that a more practical general appreciation of the potential for JH would result. One of the extensive field testing programs for JH mimics has been conducted by Hoffmann-La Roche, Inc. Entomologist R. W. Bagley of Hoffmann-La Roche described several studies of the effects of JH mimics on a variety of insects that infest alfalfa fields in Arizona and California. Unlike the broad-spectrum insecticides, JH mimics require a better planned and longer range program of application. Mr. Bagley cites several drawbacks to JH in particular. It isn't yet certain just how stable JH may be in the environment. In some cases the effects may not be prolonged for very great periods after application. A lack of persistence could require multiple applications or better formulations than are now being used. Probably the greatest problem is timing the application of JH in the field. Mr. Bagley suggests that a much closer observation of infestation than is now employed may be necessary. The JH mimics are active only in certain well-defined stages of an insect's development, and these stages are occasionally rather short in duration. In some cases mentioned by Mr. Bagley the response may be antiproductive. If an insect's larval stage is prolonged—the general effect of JH—then the result may be higher crop damage than without application of JH. It is in the larval stages that the insects usually do most of their damage. Because JH mimics are specific rather than broad-spectrum ma-
