Two block copolymers with poly(silylene acetylenearyleneacetylene) (PSA) as block A and polydimethylsiloxane (PDMS) as block B have been synthesized by Grignard reagent. The structure and properties of the copolymers have been studied. The chopped T700 carbon fibers have been used to reinforce the copolymers to obtain the composites. The ablation and change of composition on the surface of composites have been further investigated. The results show that there are two block structures of ethynyl-endcapped copolymers. The copolymer with ABA structure (PPSOA-1) is solid at room temperature, and the other with BAB structure (PPSOA-2) is viscous. The thermal stability of the cured PPSOA-1 is higher than that of the cured PPSOA-2. The chopped T700 carbon fibers reinforced copolymer composites keep shape well after 300 s at 600 C in a muffle furnace and maintain above 91% weight retention. Under the heat flow of 1 MW m À2 , there are white inorganic layers on the surface of the composites after ablation in 120 s at 1200 C. The white layer on the T700CF reinforced PPSOA-1 composite is hollow and composed of amorphous carbon-containing silica. The block copolymer of PDMS-co-PSA with excellent thermal stability is promising for utilization in thermal protection systems.
Carbon-fiber-reinforced carbon-silicon carbide (C/C-SiC) composites were prepared by impregnating carbon fibers with ethynylphenyl-terminated poly(silylene-acetylene) (EPTSA) as a single-source precursor with subsequent hot pressing and pyrolysis. The structural evolution, crystallization behavior, and graphitization of bulk C-SiC ceramics, as well as their mechanical properties and ablation behavior, were investigated. The EPTSA precursor starts to transform into inorganic SiC ceramic materials at 800 • C, which is characterized by an amorphous structure with weight loss, shrinkage, and densification between 800 and 1000 • C. The formation of SiC crystals inhibited the growth of the graphitic structure between 1000 and 1200 • C. As the temperature was raised, both graphite and SiC crystals continued to grow, and the crystalline forms became more complete. The carbon-fiber cloth (T300CF)-reinforced C-SiC composite (T300CF/C-SiC) prepared using polymer infiltration and pyrolysis (PIP) exhibited excellent mechanical properties. After five PIP cycles, the flexural strength, flexural modulus, and interlaminar shear strength of the T300CF/C-SiC composite reached 169 MPa, 32.5 GPa, and 9.38 MPa, respectively. In addition, the chopped-carbon-fiber-reinforced C-SiC composite fabricated using the PIP process demonstrated good oxyacetylene-torch ablation properties.
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