Synthesis and properties of liquid polycarbosilanes with hyperbranched structures

Abstract

Liquid polycarbosilanes substituted by unsaturated groups were prepared by a one-pot synthesis with Cl 2 Si(CH 3 )CH 2 Cl, Cl 3 SiCH 2 Cl, and CH 2 ¼ ¼CHCH 2 Cl (or HCBCMgBr) as the starting materials. The as-received polycarbosilanes were characterized by gel permeation chromatography, Fourier transform infrared spectroscopy, and nuclear magnetic resonance and were confirmed to have hyperbranched structures. The polymer yield, SiAH content, side reaction, unsaturated group content, and polymer structure are affected by the amount of the starting materials in feed. The thermal properties of the polycarbosilanes were investigated by thermogarvimetric analysis. The ceramic yield of allyhydridopolycarbosilane is about 60% and that of ethynylhydridopolycarbosilane is over 75%, indicating that the liquid polycarbosilanes have great potential to be promising precursors to SiC. Moreover, the compositions of the polycarbosilanes and the final ceramics can be tailored by controlling the amount of the starting materials.

Synthesis and characterization of a propargyl‐substituted polycarbosilane with high ceramic yield

“…3 In a previous study, we investigated the side reactions of THF solvent and SiACl bonds in chlorosilanes in detail. 12 It is supposed that oxygen-containing units, such as SiAO(CH 2 ) 4 ASi and SiAO(CH 2 ) 4 ACl, are introduced into AHPCS and EHPCS because of the side reaction. Therefore, in this study, Cl 3 SiCH 2 Cl was partially methoxylated to reduce the amount of active SiACl bonds; this was expected to inhibit the side reaction.…”

“…Therefore, in this study, Cl 3 SiCH 2 Cl was partially methoxylated to reduce the amount of active SiACl bonds; this was expected to inhibit the side reaction. According to some articles, 3,12,16 we supposed that the initial step in the polymerization was the formation of the intermediate R 3 (1)…”

“…[13][14][15] To obtain a stoichiometric SiC, we synthesized another hyperbranched ethynylhydridopolycarbosilane (EHPCS) and investigated its pyrolytic conversion to SiC, including the pyrolysis behavior, structural evolution, and crystallization behavior. 16 Among the synthesis process of AHPCS and EHPCS, 11,12,16 chlorosilanes underwent a side reaction with tetrahydrofuran (THF) used as a conventional solvent for the Grignard reaction; this resulted in the incorporation of oxygen derived from THF into the polymer chain. However, oxygen-containing polymeric precursors led to the generation of SiAOAC and SiAOASi units in the final SiC ceramics.…”

“…[3][4][5][6][7][8][9][10] In a previous study, we successfully synthesized a hyperbranched allyhydridopolycarbosilane (AHPCS) by a one-pot synthesis with chloromethyltrichlorosilane (Cl 3 SiCH 2 Cl), chloromethylmethyldichlorosilane [Cl 2 Si(CH 3 )CH 2 Cl], and allyl chloride as the starting materials, and we could control the composition of this AHPCS by controlling the amounts of the starting materials. 11,12 Subsequently, the polymer-toceramic conversion of this AHPCS for SiC-based ceramics was further studied. [13][14][15] To obtain a stoichiometric SiC, we synthesized another hyperbranched ethynylhydridopolycarbosilane (EHPCS) and investigated its pyrolytic conversion to SiC, including the pyrolysis behavior, structural evolution, and crystallization behavior.…”

“…17,18 To obtain silicon-based nonoxide ceramics, it is necessary to prepare polymeric precursors containing no oxygen or low oxygen contents. On the basis of previous studies, [11][12][13][14][15][16] a liquid hyperbranched hydrodipolycarbosilane (HPCS) with a low oxygen content was prepared by a modified synthesis route, which involved Grignard coupling of partially methoxylated Cl 3 On the other hand, propargyl groups were introduced into the HPCS backbone to increase the ceramic yields of the polymeric precursor. The resultant PHPCSs were characterized by means of gel permeation chromatography (GPC), Fourier transform infrared (FTIR) spectroscopy, NMR, and thermogravimetric analysis (TGA).…”