Highly thermostable and low birefringent norbornene-styrene copolymers with advanced optical properties: A potential plastic substrate for flexible displays

This article reports the synthesis and characterization of an extremely high thermostable cyclic olefin copolymer with advanced optical properties resulting from the vinyl addition copolymerization of norbornene with styrene catalyzed by a substituted fluorenylamidodimethyltitanium catalyst [Me 2 Si(3,6-tBu 2 Flu)(tBuN)]TiMe 2 activated with a [Ph 3 C] [B(C 6 F 5 ) 4 ]/Al(iBu) 3 cocatalyst using o-dichlorobenzene as solvent. The prepared copolymer possesses a glass transition temperature as high as polyimide (Tg > 300 °C) and a high transmittance which is comparable with that of the conventional optical resins ([T] > 90%). The incorporation of polystyrene, which exhibits a negative birefringence into the vinyl-added polynorbornene that possesses an intrinsic positive birefringence, effectively reduced the birefringent magnitude of the norbornene-styrene copolymer due to a mutual compensation between these opposite-sign birefringences. The absence of any functional and aromatic heterocyclic groups and the presence of highly hydrophobic saturated bicyclic rings in the copolymer main chains effectively prevented the diffusion of water/oxygen and thus enhanced the dimensional and optical stabilities of the material. Preliminary results on the characterization of the thermal stability, mechanical, and optical properties of the vinyl-added norbornene-styrene copolymers indicate that they satisfy all the rigorous requirements for a polymer to be applied as a flexible substrate for the manufacturing of the flexible displays.