Ultra-high-molecular weight cyclic olefin copolymers with excellent all-round performance prepared via highly effective quasi-living copolymerization

Cyclic olefin copolymers (COCs) are a type of engineering thermoplastics that have excellent transparency, high heat deflection temperature, high tensile modulus, and rigidity, but low elongation (usually below 5 %). Achieving COCs with better mechanical performance, particularly toughness, while maintaining their other properties, is a critical goal that remains a significant challenge. Herein, COCs with an ultra-high-molecular weight (UHMW)—an average molecular weight of up to 2046 kDa—and a relatively narrow molecular weight distribution (Mw/Mn < 1.66), were prepared via a highly efficient, quasi-living catalytic system under mild polymerization conditions. The dependence of the tensile properties, impact properties, wear rate, mean friction coefficient, water vapor transmission rate, and oxygen permeability of the newly obtained COCs on their molecular weight was studied in-depth and compared with those of a commercial COC (Topas 6013, with a molecular weight of 144 kDa). As clearly shown, the obtained UHMW-COCs not only provided satisfactory heat resistance and excellent optical transparency but also demonstrated excellent mechanical performance, tribology behaviors, and barrier properties. Compared with the COCs with lower molecular weight but similar norbornene (NBE) incorporation and optical transmittance, these UHMW-COC samples possessed a higher glass transition temperature, higher tensile strength (up to 73.5 MPa), better elongation at break (6.8 %), better impact strength (4.0 kJ/m2), and a lower wear rate (2 × 10−5 mm3/mN), as well as a lower mean friction coefficient (0.48), lower water vapor transmission rate (0.68 g·mm·m−2·day−1), and lower oxygen permeability (1.60 Barrer). These all-round properties, together with their original advantages, make the UHMW-COCs promising for a broad range of high-end applications.