Chain Shuttling Polymerization for Cycloolefin Block Copolymers: From Engineering Plastics to Thermoplastic Elastomers

Abstract

Chain shuttling polymerization is a powerful approach for efficiently producing olefin block copolymers via simple one-pot polymerization. Herein, this method was used to synthesize ethylene-norbornene cycloolefin block copolymers (COBCs). Two bis(salicylaldiminato)titanium complexes with different monomer selectivities were used to generate alternating hard and soft blocks of high and low norbornene incorporation, respectively, in the presence of chain shuttling agents (diethyl zinc). The high glass transition temperature (T_g) of the hard blocks contributed to their high tensile strength, while the low T_g of the soft blocks led to their high ductility. By varying the concentration of norbornene during the copolymerization process, it is possible to tune the T_g values of the hard and soft blocks, thus achieving a transition in the mechanical properties of the COBCs from typical elastomers to plastics while maintaining high ductility and transparency. Compared with random cycloolefin copolymer plastics, the COBC in this study exhibited a 55-fold increase in elongation at break and maintained comparable tensile strength. This study highlights the development of a new class of chain shuttling catalytic systems to produce COBCs with widely tunable T_g values to modulate their mechanical properties.