LOW BIREFRINGENT COPOLYMER

摘要

A low birefringent material which may comprise an acrylic copolymer having a lactone ring structure that can provide a positive phase difference and a structure unit that can provide a negative phase difference, the material satisfying the following requirements: (A) the material has a glass transition temperature (Tg) of 100°C or higher; (B) a film comprising the material shows a total light transmission of 85% or higher; and (C) in a film comprising the material, the phase difference is 10 mm or less per 100 µm of thickness of the film in the plane-wise direction, and the difference between the phase difference per 100 µm of thickness of the film in the plane-wise direction after the film is stretched by 1.5 times and that before the film is stretched is 20 nm or less. The low birefringent material has excellent transparency and heat resistance, also has other desired properties including mechanical strength and molding processability, has a low staining property when no nitrogen atom is contained, and particularly has a high optical isotropy.