Metallocene Catalytic Insertion Polymerization of 1-Silene to Polycarbosilanes.

Yuelong Tian,Xiaoxu Lv,Min Ge,Shouquan Yu,Weigang Zhang

doi:10.1038/srep16274

Abstract

Metallocene of zirconium were used as a catalyst for an insertion polymerization of 1-methylsilene directly into pre-ceramic precursor polyzirconocenecarbosilane (PZCS) during dechlorination of dichlorodimethylesilane by sodium, which exhibits high catalytic effectiveness with the maximum conversion ratio of polycarbosilane up to 91%. The average molecular weights of polymers synthesized are less than 1400, all with very narrow polymolecularities. The mechanism of catalytic polymerization was assumed to be similar to a coordination insertion polymerization of 1-olefins by metallocenes. The obtained PZCS show high ceramic yields with formation of composite ceramics of ZrC-SiC, which are novel polymeric precursors of ultra-high temperature ceramic (UHTC) fiber and composite.

Highlights

Polycarbosilanes (PCS) are a family of polymers that contain both silicon and carbon atoms with or without an alternating order in their backbone
We performed a catalytic insertion polymerization of methylsilene using zirconocene in toluene to yield a wine red polyzirconocenecarbosilane (PZCS)
Polycarbosilane with a repeating (-CH2-SiHR-) unit can be distinguished by its infrared spectrum

Summary

Introduction

Polycarbosilanes (PCS) are a family of polymers that contain both silicon and carbon atoms with or without an alternating order in their backbone. PCS have been synthesized mainly as industrial polymeric precursors for silicon carbide ceramic fiber or monoliths[1,5]. It is usually produced via thermal rearrangement of polymethylsilanes[6,7] or by open ring polymerization of cyclic-carbosilane monomers[2,4]. A polycarbosilane with a repeated -CH2SiMeH- unit is clearly more thermodynamically stable than its isomer of polydimethylsilane (-SiMe2-) This was ignored after G Fritz’s systematic work that showed the thermal conversion of permethylsilanes into cyclic- and acyclic-carbosilanes[18]. We describe the inhibition of dimethylsilylene polymerization for 1-methylsilene polymerization into polycarbosilanes via a one-pot reaction This removes the requirements for an additional Kumada rearrangement via polydimethylsilanes (PDMS). The polycarbosilane is termed PZPCS for the purposes of this paper

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Conclusion