Carbosilane polymer precursors to silicon carbide ceramics

• US 5,153,295 A
• Filed: 07/20/1990
• Issued: 10/06/1992
• Est. Priority Date: 07/20/1990
• Status: Expired due to Term

• Current Assignee: Starfire Systems, Inc. (Starfire Systems Holdings LLC)
• Original Assignee: Rensselaer Polytechnic Institute
• Inventors: Whitmarsh, Christopher K., Interrante, Leonard V.
• Primary Examiner(s): Marquis, Melvyn I.
• Application Number:
  US07/556,599
• Time in Patent Office: 809 Days
• Field of Search: 525/475, 528/10, 528/31, 528/32, 556/480
• US Class Current: 528/31
• CPC Class Codes: C04B 35/571 obtained from Si-containing polymer precursors or organosilicon monomers
• CPC Class Codes: C08G 77/60 in which all the silicon atoms are connected by linkages other than oxygen atoms

Abstract

Polycarbosilane compositions, which can serve as silicon carbide precursors, are formed by a Grignard coupling reaction of a halomethylcarbosilane followed by reduction using a metal hydride. The polycarbosilane compositions that result have a substantially 1:1 silicon to carbon stoichiometry, are substantially non-cyclic and branched, and comprise the repeat units SiH₃ CH₂ --, --SiH₃ CH₂ --, ═SiHCH₂ --, and .tbd.SiCH₂ --.

Claims

1. Polycarbosilane compositions of matter comprising the repeat units [SiR_x CH₂ ] and [SiR_x-1 (CH═

CH₂)CH₂ ], where R is hydrogen and x is from 0 to 3 and 1 to 3, respectively.

2. A process for forming polycarbosilane composition comprising the repeat unit [SiR_x CH₂ ], where R is hydrogen and x ranges from 0 to 3 which employs, as starting materials, a halomethylcarbosilane of the type [X₃ SiCH₂ X or] X_4-x Si(CH₂ X)_x, where X is halo and x is from 0 to 3, and which comprises a Grignard coupling reaction of the halomethylcarbosilane with magnesium to form a poly(halocarbosilane) followed by reduction of the poly(halocarbosilane).

3. A process as claimed in claim 2 wherein the halomethylcarbosilane is trichloro-chloromethylsilane.

4. A process as claimed in claim 2 wherein the Grignard coupling reaction is carried out using a mixture of magnesium metal and solvent.

5. A process as claimed in claim 4 wherein the magnesium metal is in the form of an amalgam with mercury or is produced in situ by reduction of a magnesium halide.

6. A process as claimed in claim 4 wherein the solvent is an ether.

7. A process as claimed in claim 4 wherein the solvent is diethylether.

8. A process as claimed in claim 4 wherein the solvent is a tertiary amine.

9. A process as claimed in claim 4 wherein the solvent is a hydrocarbon or a mixture of a hydrocarbon with an ether, polyether, or amine.

10. A process as claimed in claim 3 wherein the trichloro-chloromethylsilane is mixed with trichlorosilane or tetrachloro-silane.

11. A process as claimed in claim 3 wherein a mixture of halomethylsilanes of the general type X₃ Si--CH.sub.(3-n) X_n, where n is 2 or 3, or X_3-x R_x SiCH₂ X, where R can be either an organic or inorganic group and x can be 1 or 2, is employed in addition to the trichloro-chloromethylsilane.

12. A process as claimed in claim 3 wherein the trichloro-chloromethyl silane is mixed with compounds of the general formula X_3-x Si(CH₂ X)_x where X is 1 or 2.

13. A process as claimed in claim 2 wherein a metal cyanide is added during the Grignard coupling reaction.

15. Substantially non-cyclic, branched polycarbosilane precursors for silcon carbide having a substantially 1:

1 silicon to carbon stoichiometry which are comprised of the repeat units [SiH₃ CH₂ --], [--SiH₃ CH₂ --], [--SiH₂ CH₂ --]--, [═

SiHCH₂ --], [.tbd.SiCH₂ --].

14. A process as claimed in claim 16 wherein the metal cyanide is copper(I) cyanide.

16. Precursors to silicon carbide as claimed in claim 15 formed by the process of claim 2.

17. Precursors as claimed in claim 15 in which the average number of Si--H groups per unit is approximately equal to 2.

18. Precursors as claimed in claim 15 which contain terminal --SiH₃ groups.

19. Substantially non-cyclic, branched polycarbosilane precursors for silicon carbide which are comprised of the repeat units [SiR_x CH₂ ] and [SiH_x-1 (CH═

CH₂ CH₂ ], where R is hydrogen and x can range from 0 to 3 and 1 to 3, respectively.