Synthesis and Useful Reactions of Organosilicon Polymeric Precursors for Ceramics
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SYNTHESIS AND USEFUL REACTIONS OF ORGANOSILICON POLYMERIC PRECURSORS FOR CERAMICS
DIETMAR SEYFERTH*, CARSTEN STROHMANN, HENRY J. TRACY AND JENNIFER L. ROBISON Department of Chemistry, Massachusetts Institute of Technology Cambridge, Massachusetts 02139, U.S.A. Inorganic and organometallic polymers are macromolecular systems in which the polymer backbone contains elements other than the carbon, oxygen and nitrogen usually found in organic polymers [1]. To take as an example silicon-containing polymers, in the silicones the polymer backbone is composed of the Si-O repeat unit; in polysilazanes, of the Si-N unit; in polysilmethylenes, of the Si-C unit. In the polysilanes there are only silicon atoms in the polymer backbone. Many of the other metalloids and metals among the elements in the Periodic Table have been or, in principle, can be incorporated into polymeric systems, so it is clear that the field of inorganic and organometallic polymers is a very large one. Inorganic and organometallic polymers have been of interest to chemists for a long time. It was the commercial development of the silicones in the 1940's that gave this field of research its modem impetus [2]. Once it was appreciated how useful these versatile organosilicon polymers could be, chemists became interested in the possibility of developing other organometallic (and also inorganic) polymers, ones that might complement or even surpass the silicones as far as useful applications were concerned. Research on inorganic and organometallic polymers became very active in the 1950's and 1960's. Work in this area became an international effort, prompted by the need for new materials that would meet the exacting demands of the jet age that had effectively commenced around the end of World War II. Even greater demands, in terms of materials that would still be useful under extreme conditions, came with the space age. Inorganic and organometallic polymers were not unknown before the 1940's. Polymers of the type (R2 SiO)n had been prepared by Kipping and his students during the period 19101935, but their potential importance in terms of useful applications was not recognized. Some organometallic polymers went unrecognized as such for a long time: it must be remembered that macromolecular chemistry is a relatively new field. Thus the dialkyltin oxides were first prepared in 1854, but their polymeric nature was not recognized until nearly one hundred years later [3]. The research on inorganic and organometallic polymers carried out in the 1950's and 1960's covered a broad range: other organosilicon polymers such as the polysilazanes; polymetalloxanes; various boron-containing polymers including those derived from the very stable carboranes; polyphosphazenes; coordination polymers; metal-containing polyesters, polyamides and vinyl polymers. In all of these investigations it was the polymer per se that was of interest. The objective in most cases was a polymeric material whose properties at extremes of temperature would surpass those of the conventional organic po
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