Polycarbonsilane (PCS) is an important precursor of silicon carbide (SiC) fibers and ceramics. The ceramic yield of PCS is relatively low, about 60 %, which may bring some deficiencies in its applications. In this work, a novel precursor cyano-polycarbosilane (PCSCN) is synthesized by hydrosilylation reaction between PCS and acrylonitrile using a rhodium-containing catalyst, although acrylonitrile is generally not easy for hydrosilylation. After introducing tiny amounts of cyano (-C≡N) groups into the PCS molecules, the ceramic yield of PCSCN can increase largely to over 80 %. The ceramization mechanism of PCSCN is investigated by FTIR, TG, XPS, ESR, NMR, Raman and XRD analyses. It is found that some crosslinking structures in PCSCN are formed between SiH bonds and CN groups from about 200 ℃, which can be responsible for the high ceramic yield. The existence of a little more N, O and free C elements in the pyrolysis products may inhibit the growth of crystalline β-SiC. Moreover, the PCSCN precursor can also be melt-spun into continuous fibers by tailoring its molecular weight and softening point. The oxidized PCSCN fiber with relatively low oxygen content can be pyrolyzed without melting, and the final SiC fiber with an oxygen content as low as 8.5 % is obtained.

聚碳酸酯（PCS）是碳化硅（SiC）纤维和陶瓷的重要前体。PCS的陶瓷产率相对较低，约为60％，这可能会在其应用中带来一些不足。在这项工作中，尽管丙烯腈通常不容易进行氢化硅烷化，但是通过使用含铑催化剂的PCS与丙烯腈之间的氢化硅烷化反应合成了一种新型的前体氰基-聚碳硅烷（PCSCN）。将少量氰基（-C tinyN）引入PCS分子后，PCSCN的陶瓷收率可大幅提高至80％以上。通过FTIR，TG，XPS，ESR，NMR，拉曼和XRD分析研究了PCSCN的陶瓷化机理。发现在PCSCN中一些交联结构在Si H键和C之间形成N基团从200℃左右开始，这可能是高陶瓷产率的原因。热解产物中更多的N，O和游离C元素的存在可能会抑制晶体β-SiC的生长。此外，还可以通过调整PCSCN前体的分子量和软化点将其熔纺为连续纤维。可以将氧含量相对较低的氧化PCSCN纤维热解而不熔化，从而获得氧含量低至8.5％的最终SiC纤维。