I/EC
REPORTS AND INTERPRETS
N e w Reactions Needed
version, so that truly high molecular weight inorganic polymers will be obtained. The inorganic polymer symposium threw some light on present research efforts. Here are some examples :
Research for inorganic polymers has slowed down; new routes with "clean" reactions needed to step up the pace
f^. LOT of wheels are spinning trying to come up with inorganic polymers which will be useful surface coatings, elastomers, and other poly meric materials. But these wheels may be spinning in the mud now. Not much new or novel has come along in inorganic polymers in the past five years. It looks as though a cycle is complete and things have leveled off. Something radically new and different is needed—totally new mechanisms rather than research modeled after organic polymer mechanisms. This sums up the collecting opinions of Seymour Yolles of Du Pont and Morris L. Nielsen of Monsanto. The inorganic polymers in various research stages today are made mostly through condensation reactions to build up repeating units or back bones. The key building blocks are boron, nitrogen, oxygen, aluminum, silicon, phosphorus, and sulfur. By some definitions, an inorganic poly mer should not contain a carbon to carbon bond anywhere in the mole cule; to others, merely no carbon to carbon bonds in the backbone. Of late, researchers have com bined transition elements such as titanium, zinc, or chromium into backbones. Another route under study involves ferrocene-type struc tures (biscyclopentadienyl iron) or sandwich-type compounds. This is the newest type of bond and it might lead to interesting polymers in the future. Now, the emphasis is on research for novel bonds. In the future, there will be detailed studies of some of these reactions along with some re investigation of older work. Pos sibly, "clean" reactions will come up, with no side reactions, and high con 34 A
INDUSTRIAL AND ENGINEERING CHEMISTRY
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Scmiinorganic polymers based on an alternating aluminumoxygen chain (polyaluminoxanes). The chain is modi fied with an organic acid or al cohol attached to the alumi num atom. The aim is to make polymers which are sta ble at temperatures near 500° C. Compounds were made by transesterification reactions such as between aluminum isopropoxide and the correspond ing silyl acetate. (U. S. Borax)
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Monomer preparation such as the reaction of trimethylacetoxysilane with tetraisopropyl titanate. This leads to poly(trimethylsiloxy)mctalloxanc polymers with molecular weights around 42,300. Such compounds might have high temperature stability. (Hughes Aircraft)
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Condensation polymerizations to make polymers with alu minum-nitrogen backbones. A typical reaction; methylammonium chloride with triethylaluminum. (Cornell Uni versity)
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Polymers which have alternate, quadruply connected phospho rus atoms and an oxygen atom. There are three basic building blocks: an end group such as Ο Χ Ρ—Ο 1 /2, a middle group X Ο such as OV2—Ρ—Oy 2 , and a X branched group like OV2—Ο Ρ—Ο 1 /2. The polymers are OV2 made by heating one or more of these blocks—for example, a mixture of POX 3 and P 4 O 10 . X can be a number of radicals such as OLi, F, or Ν(ΟΓΙ 3 ) 2 . (Monsanto)
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Boron-phosphorus polymers which could be thermoplastic polymers useful in the coatings field. These are made by con densing monoalkyl phosphincs with diborane. (Du Pont) • Monomers with silicon-oxygenarsenic linkages such as tristriphenylsilyl arsenite. High molecular weight materials are made which might be elasto mers. (U. of Pennsylvania) • Polymers with zinc, chlorine, and ammonia made from diaminedichlorozinc by removing one mole of ammonia at 150° to 200° C. These materials can be drawn into monofila ments ; have elastomeric properties also. (Pennsalt) Certainly, the potential for inor ganic polymers is vast, as evidenced by the present areas of interest. To day there is much talk of using such polymers in high temperature air craft and missile projects, but there would be much more commercial value in elastomers and surface coat ings. For example, paints made from inorganic polymers would far outlast those from organic mediums. Plastic windows, coated with an in organic polymer, would be scratchproof for years. It would be possible to make materials with molecular weights around 3000 which would be stable fluids; might be lubricants. If wire were coated with an inorganic polymer, electric motors would run at temperatures up to 400° C. with much more efficiency; today, wires cannot be protected against such temperatures. In general, organic polymers are limited to around 250° C , but inorganic might extend the polymer range to 1000° C. or be yond. However, few inorganic polymers, in the defined sense, are on the mar ket today other than glasses, ce ramics, and similar refractory mate rials. Du Pont's Quilon, a steratochromic basic chloride which poly merizes on a surface to an inorganic polymer, is an example. So too is tripolyphosphate. In many ways, inorganic polymers of today are where organic polymers were 20 years ago. Organics emerged from that point on; will inorganic polymers do the same? (Continued on page 36 A)
