Evolution of molecular composition of polycarbosilane and its effect on spinnability

The molecular composition of polycarbosilane (PCS) and its evolution in the synthesis process, as well as the contribution of each component to the spinnability of PCS, were explored by combining distillation separation with gel permeation chromatogram peak-splitting. The results show that PCS is composed of four kinds of molecules with different structures, namely M(L), M(M), M(H), and M(SH) (number-average molecular weights of 531, 1207, 2731, and 10 977, respectively). In the synthesis process, PCS changed from containing two components to three components, and finally to four components. The PCS can be spun when it is composed of M(L), M(M), and M(H), but is not suitable for spinning when it is composed of one, two, or four components. For a PCS having three components, increasing the amount of M(H) and restricting M(L) to within a certain range can enhance the spinnability of PCS. The underlying mechanism is controlled by the linear structure of M(H) and its low melting point by there being an appropriate M(L) content, which ensures melting, de-foaming, and stability in spinning. The final optimum ratio is found to be an M(H) content of 30–45%, an M(M) content of 30–51%, and an M(L) content of 18–25%.