Well‐Controlled Block‐Type Cyclic Olefin Copolymers with High Heat Resistance, Outstanding Strength and Low‐Temperature Toughness
Dong Huang, Li Jin, Xu Lu, Kunyu Zhang, Fei Wang, Di Wu, Yafei Wang, Li Pan, Yang Li, Yue‐Sheng Li
Abstract
Comprehensive Summary As an important class of transparent polyolefins, cyclic olefin copolymers (COCs) exhibit a wide range of properties, from soft (low cyclic unit content in a random copolymer) to hard (high cyclic unit content in a random copolymer) thermoplastics. A higher cyclic unit content in a random copolymer results in increased rigidity and heat resistance, but at the expense of material toughness, especially under low temperature. To achieve a trade‐off, block‐type COCs composed of well‐defined hard‐soft and hard‐soft‐hard segments with high molecular weights ( M n > 200 kDa) and relatively narrow molecular weight distributions ( M w / M n < 1.42) were prepared via quasi‐living copolymerization. Compared to random copolymers, di‐block COCs retained satisfactory heat resistance and optical transparency and exhibited superior tensile properties (tensile strength: 56.2 MPa, elongation at break: 254.4%), while tri‐block COCs with the same hard‐soft segments and an additional hard segment exhibited even better tensile properties, achieving a tensile strength of 67.3 MPa, elongation at break of 286.9%, all while maintaining high optical transmittance (> 90%). Even at temperatures below 0 °C, the tri‐block copolymers EN 52 ‐ b ‐EN 19 ‐ b ‐EN 46 demonstrated a satisfactory tensile strength (> 64.0 MPa) and elongation at break (> 65.6%), highlighting the advantages of the alternating hard‐soft segment structural design in COCs.