Synthesis and Ceramic Conversion Reactions of 9-BBN-Modified Allylhydridopolycarbosilane: A New Single-Source Precursor to Boron-Modified Silicon Carbide
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- 作者：Alexis R. Puerta ; Edward E. Remsen ; Mark G. Bradley ; Walter Sherwood ; and Larry G. Sneddon
- 刊名：Chemistry of Materials
- 出版年：2003
- 出版时间：January 28, 2003
- 年：2003
- 卷：15
- 期：2
- 页码：478 - 485
- 全文大小：143K
- 年卷期：v.15,no.2(January 28, 2003)
- ISSN：1520-5002
文摘
The design, synthesis, and properties of a new type of poly(borocarbosilane) polymer,9-borabicyclo[3.3.1]nonane-modified allylhydridopolycarbosilane (AHPCS-9-BBN), that hasproven to be an excellent processible single-source precursor to dense silicon carbide ceramicsis reported. The polymers were synthesized in high yields by the reaction of allylhydridopolycarbosilane (AHPCS) with 9-borabicyclo[3.3.1]nonane (9-BBN). The spectroscopic datafor the AHPCS-9-BBN polymers, along with results of the hydroboration reaction of 9-BBNwith the model compound allyldimethylsilane, are consistent with predominantly anti-Markovnikov hydroboration of the polymer allyl groups. The degree of polymer hydroborationwas controlled by varying the reactant ratios with the compositions of the modified polymersranging from (SiH2CH2)0.95(Si(allyl)2CH2)0.044(Si(allyl)(CH2CH2CH2-9-BBN)CH2)0.006 to (SiH2CH2)0.95(Si(allyl)2CH2)0.012(Si(allyl)(CH2CH2CH2-9-BBN)CH2)0.038. The AHPCS-9-BBN polymers are soluble and stable in hydrocarbons and aromatics. Solution properties analysisindicated molecular weight growth and intrinsic viscosity decrease with increasing boronincorporation. Thermal gravimetric analyses showed that the AHPCS-9-BBN polymers havethermal stabilities similar to that of the parent AHPCS polymer and thus maintain theprocessibility needed for their use as precursors to matrix materials. Bulk pyrolyses at 1600
C of the AHPCS-9-BBN polymers produced SiCB ceramic chars with boron contents rangingfrom 0.1 to 0.8% depending upon the degree of polymer modification. XRD studies showedthat the 1800 and 2000 C AHPCS-9-BBN ceramic chars had larger grain sizes thanceramics derived from the parent AHPCS polymer. Most significantly, in agreement withprevious studies that have shown that the presence of small amounts of boron (<1%) canenhance SiC sintering, it was found that with increasing temperature the AHPCS-9-BBN-derived ceramics exhibited dramatic increases in their densities compared to those derivedfrom the parent AHPCS.
C of the AHPCS-9-BBN polymers produced SiCB ceramic chars with boron contents rangingfrom 0.1 to 0.8% depending upon the degree of polymer modification. XRD studies showedthat the 1800 and 2000 C AHPCS-9-BBN ceramic chars had larger grain sizes thanceramics derived from the parent AHPCS polymer. Most significantly, in agreement withprevious studies that have shown that the presence of small amounts of boron (<1%) canenhance SiC sintering, it was found that with increasing temperature the AHPCS-9-BBN-derived ceramics exhibited dramatic increases in their densities compared to those derivedfrom the parent AHPCS.