Well-Controlled Block-Type Cyclic Olefin Copolymers with High Heat Resistance, Outstanding Strength and Low-Temperature Toughness

Abstract

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 EN₅₂-b-EN₁₉-b-EN₄₆ 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.