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%.