Abstract

Trans-1,4-polybutadiene (TPBD) is a semicrystalline polymer whose properties are strongly governed by its trans content. Its highly linear backbone and the absence of pendant groups provide the material with excellent dynamic performance and a relatively high melting temperature, making it attractive for advanced polymer applications. When the trans content exceeds 90%, TPBD exhibits thermoplastic semicrystalline behavior with unique polymorphism, characterized by a reversible monoclinic-to-hexagonal phase transition. However, the presence of unsaturated bonds along the main chain creates challenges during conventional melt processing, including thermal crosslinking and entropy-driven relaxation of oriented chains, which limit its applications and hinder the development of high-performance tapes.

The thesis addresses these limitations by controlling the polymerization and crystallization of TPBD directly during synthesis. First, polymerization conditions were fine-tuned using a bis(benzimidazolyl)amine chromium single-site catalyst and an optimized solvent system. Faster crystallization was promoted during polymerization, leading to the formation of nascent reactor powders composed of platelet-like single crystals with approximately 99% trans content and a molecular weight of around 500 kg·mol⁻¹. Electron diffraction, DSC, SEM, and solid-state ¹³C NMR confirmed the formation of chain-folded lamellar crystals with a controlled entanglement state. These crystals exhibited a reversible monoclinic-to-hexagonal phase transition, while annealing in the high-entropy hexagonal phase promoted lamellar thickening through enhanced chain mobility and reduced surface energy.

Second, the influence of polymerization medium was systematically investigated. Compared with toluene, pure n-heptane promoted rapid crystallization of the growing chains during polymerization, synthesizing nascent reactor powders with a platelet-like morphology, >99% trans content, a higher melting temperature, and improved thermal stability. By reducing the catalyst concentration and extending the reaction time in n-heptane, UHMWTPBD with a molecular weight exceeding 2 × 10⁶ g·mol⁻¹ was achieved for the first time. Its low-entangled nascent structure enabled solid-state sintering and uniaxial drawing, reaching a draw ratio of 9. The oriented tapes exhibited a melting temperature of approximately 151 °C, a Young’s modulus of about 11 GPa, a tensile strength of 374 MPa, and an engineering toughness of 9731 kJ·m⁻³.

Finally, oriented UHMWTPBD tapes were established as precursors for electrically conducting carbon tapes. The oriented tapes were stabilized through crosslinking and sulfonation prior to carbonization, allowing them to retain their shape at temperatures between 1000 and 1500 °C while yielding approximately 37% carbon residue and a carbon content of about 96%. WAXD, Raman spectroscopy, XPS, and AFM confirmed the formation of a graphite-like structure, enhanced electrical conductivity, and an increase in Young’s modulus from approximately 10 to 80 GPa.