Synthesis of Bimodal Distributed Cyclic Olefin Copolymers with Improved Tensile Properties

Comprehensive Summary Ethylene/norbornene(NBE) copolymers are the most representative and widely‐used cyclic olefin copolymers (COCs). Higher NBE content in COCs leads to higher transparency, glass transition temperature and mechanical strength, but also makes the COC more brittle and therefore hampers its end uses. In this study, to improve the brittleness of COCs while maintaining their high strength, heat‐resistant and transparency, bimodal distributed COCs have been prepared via two selective catalysts reactive blending in one pot. The shape of the molecular weight distribution curves of the obtained COCs could be easily controlled by adjusting the proportion of the two catalysts. These COCs maintained high glass transition temperature, balanced tensile performance, high transparency. Roles of the molecular weight and NBE incorporation in physical properties of the COC blends were studied. As we proved, the bimodal distribution COCs, which were composed of COC with high NBE incorporation, high molecular weight and COC with low NBE incorporation, low molecular weight, showed evident improvement in tensile properties (elongation at break up to 9.6%, tensile strength beyond 50.5 MPa), which were more flexible than the neat ethylene/NBE copolymer, while their glass transition temperatures were almost equally high (beyond 130°C).