Methods for the synthesis of polysilanes

Details Methods for the synthesis of polysilanes Methods for the synthesis of polysilanes

1988-10-14

1991-01-22

Marquis, Melvyn I.

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

From silicon reactant having at least one...

556430, 528 33, C08G 7700

Patent

active

049872028

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION

This invention relates to improved methods and techniques for preparing polysilanes in increased yields, higher molecular weights and/or lower polydispersities, and for controlling the polymerization of silanes to form polysilanes.
Interest in polysilanes, a "new" class of polymers with a backbone of silicon atoms bonded to various organic substituents, (Scheme 1), is growing rapidly as a result of an increasing number of emerging technological applications for the materials. These include uses as: precursors to SiC fibers, S. Yajima, Am. Ceram. Soc. Bull., 62, 893 (1983) and references therein; ceramic reinforcements, K. Mazdyasni, et al., J. Am. Ceram. Soc., 61, 504 (1978); vinyl polymerization catalysts, A. R. Wolff, R. West, and D. C. Peterson, 17th Organosilicon Symposium, Fargo, ND (1983); conductive polymers for batteries, mid-UV solvent-developed photoresists, D. C. Hofer, R. D. Miller and C. G. Willson, SPIE Adv. Resist Tech., 469, 16 (1984); imageable etch barriers in bilayer microlithography, H. Hiraoka, et al., U.S. Pat. No. 4,464,480 (1984); contrast enhancement layers, D. C. Hofer, R. D. Miller, C. G. Willson, A. Neureuther, SPIE Adv. Resist Tech., 469, 108 (1984); self-developing deep UV photoresists and imageable etch barriers, etc., J. M. Zeigler, L. A. Harrah, and A. W. Johnson, SPIE Adv. Resist Tech., 539, 166 (1985). Several of these are covered in U.S. Ser. Nos. 597,005 and 616,148, both now allowed, and both of which disclosures are entirely incorporated by reference herein. ##STR1##
Despite the technological potential of these materials, well-controlled and reproducible methods for making them in high yield, high molecular weight, and with narrow molecular weight distributions have not been reported. Since these qualities are of major importance for many applications, particularly those in the microelectronics processing area, a need exists for improved synthetic methods and routes to polysilanes.
Polysilanes are prepared by the reductive Wurtz-type coupling of the corresponding dichlorosilanes with an alkali metal, typically sodium (Scheme 1). Copolymers can be synthesized by using a mixture of two (or more) dichlorosilane monomers. This method generally gives a mixture of linear polymer and cyclic low molecular weight oligomers. For most of the aforementioned applications, the cyclics fraction is of little or no value. It is desirable to shift the course of the reaction to production of as much linear polymer as possible at the expense of the cyclics. In methods known to the prior art, this reaction normally produces a molecular weight distribution in the linear polymer fraction which is highly polydisperse (Mw/Mn>25) and has at least two (and often more) molecular weight modes. This extremely high polydispersity is particularly detrimental to the proposed application of polysilanes as photoresists or imageable oxygen reactive ion etch barriers, since it can lead to low apparent photospeed, degradation of physical properties, or both. Thus, it would be highly desirable to have an improved route to polysilanes which give higher yields of linear polymer having decreased breadth (polydispersity) of the molecular weight distribution. Polysilanes have been prepared by the reaction in Scheme 1 since the first preparation of the intractable (Ph.sub.2 Si).sub.n by Kipping, J. Chem. Soc., 125, 2291 (1924); ibid., 119, 830 (1921). Burkhard, (U.S. Pat. No. 2,554,976 (1951); C. A. Burkhard), J. Am. Chem. Soc., 71, 963 (1949), teaches the preparation of insoluble, infusible (Me.sub.2 Si).sub.n (where Me=CH.sub.3) of MW about 3200 by the above reaction carried out in aromatic or aliphatic hydrocarbons in an autoclave at a temperature above the melting point of the sodium metal reductant. No differentiation is provided regarding order of reactant addition and no specific studies of the effect of varying the reaction solvent are reported. Clark (U.S. Pat. No. 2,606,879 (1952)) describes the preparation of various silane homopolymers as greasy or wax-like mixtures by

REFERENCES:
patent: 2606879 (1952-08-01), Clark
patent: 4588801 (1986-05-01), Harrah et al.
Plochocka et al., "Solvent Effect in Radical Copolymerization and Sequence . . . ," Polym. Prep., 19, 240 (1978).
Park et al., "Characterization of Styrene-Acrylamide Copolymers by Intrasequence Cyclization Reactions," Polym. Prep. 27 (2)81 ('86).

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