Controlled individual and partial polyethylene nanofibers with high Tm2 prepared by PPM-supported Cp2TiCl2 catalysts

Abstract

Controlled individual and partial nanofibrous polyethylenes with high second melting point (T_m2) were obtained through ethylene-confined polymerization. Cp₂TiCl₂ catalysts were loaded into porous polymer microspheres (PPMs) with different average nanopore diameters through a chemical reaction. Subsequently, controlled confined polymerization occurred inside the PPM-supported Cp₂TiCl₂ catalysts by changing the pore structure of the PPMs. SEM, FTIR, XPS, XRD, ¹³C NMR, and SAXS were performed to confirm the loading of Cp₂TiCl₂ catalysts inside PPM supports and the structure of polyethylene. PPM-supported Cp₂TiCl₂ catalysts with the smallest average pore diameter exhibited the highest polymerization activity. Different original polyethylene morphologies, such as individual and partial nanofibers, were obtained. PPMs with small pore diameters increased the possibility of obtaining individual polyethylene nanofibers. Moreover, after removing residues through physical treatment, the polyethylene obtained by using the PPM-supported Cp₂TiCl₂ catalysts revealed a high T_m2 (up to 142.9 °C), whereas the polyethylene obtained by using homogeneous Cp₂TiCl₂ catalysts showed a T_m2 of 137.9 °C. SAXS analysis indicated that the high T_m2 was due to the entanglement of polyethylene chains in amorphous layers caused by the unique cross-linked multimodal pore structure of the PPM supports. In addition, the high T_m2 showed good stability even after storage for 1 year or dissolution in good solvents for 80 h at 150 °C.