Kumada Rearrangement of Polydimethylsilane Using a Catalytic Process

Abstract

Polycarbosilane was synthesized from polydimethylsilane in the presence of ZSM-5 (Si/Al=30) as a catalyst at 350oC-400oC. Characterization of synthesized polycarbosilane was performed with 29Si Solid NMR, FT-IR, and GPC analysis. Number average of molecular weight (Mn) of the polycarbosilane was ranged from 350 to 2340.

Thermal Oxidation Curing of Polycarbosilane for SiOC Fiber Process

“…It is closely related to molecular structure of PCS. Model of the molecular structure of PCS which was reported by Hasegawa et al 2 and Kim et al 14 indicates that molecular PCS composes SiC 4 bond structure in the backbone and methyl and hydrogen bond in the pendent which act as a cross-linking site with oxygen during thermal oxidation curing 3,14 . Low M w PCS (PCS_1) has high SiC 3 H bond whereas high M w PCS (PCS_2) has high SiC 4 bond portion.…”

Control of structure formation of polycarbosilane synthesized from polydimethylsilane by Kumada rearrangement

“…The peaks between −50 and −30 ppm are attributed to Si–Si units of linear polysilane backbone (–SiMe 2 –SiMe 2 –, –SiMe 2 –HSiMe–, etc.) according to the literature 48, 60, 64. The broad peaks at −5 ∼ 5 ppm and −20 ∼ −5 ppm are assigned to SiC 4 and HSiC 3 groups, respectively.…”

“…The reaction mechanism of PCS synthesized from PDMS by thermal decomposition is referred to as the well-known Kumada rearrangement. 11,48,58 According to this mechanism, silicon free radical is formed first when Si-Si bond is cleaved by heating, followed by rearrangement involving insertion of methylene group in Si-Si chain to give Si-CH 2 -Si and Si-H groups (Scheme 1). 11,59 Therefore, it is very important to control the dissociation of Si-Si chain in the first step.…”

“…according to the literature. 48,60,64 The broad peaks at 25 5 ppm and 220 25 ppm are assigned to SiC 4 and HSiC 3 groups, respectively. The ratios of SiC 4 /HSiC 3 and HSiC 3 /Si-Si in the PCS-I are 0.17/1 and 1/0.59, respectively, suggesting that the dissociated Si-Si bonds in PDMS mainly convert into HSiC 3 groups in PCS-I through Kumada rearrangement under this reaction condition.…”

“…22,[38][39][40] Although many precursors are available, the most successful ones for commercial polycrystalline SiCbased fibers 41 are PCS and PMCS (M 5 Ti, Zr, Al). Most ongoing research on SiC-based fibers in Japan, 42 France, 43,44 Russia, 45 Korea, [46][47][48] and China 49 utilizes PCS as the precursor, because of its low cost and high ceramic yield.…”