Patent ID: 8568893

Claim:
A birefringent film comprising an ester-based polymer having at least a repeating unit represented by the following formula (I): wherein A and B each independently represents a hydrogen atom, a halogen atom, an alkyl group having 1 to 6 carbon atoms, or a substituted or unsubstituted aryl group; a and b each independently represents any one of integers of 0 to 4; R 1 represents a hydrogen atom, a linear or branched alkyl group having 1 to 10 carbon atoms, or a substituted or unsubstituted aryl group; R 2 represents a linear or branched alkyl group having 2 to 10 carbon atoms; R 3 to R 6 each independently represents a hydrogen atom, a halogen atom, a linear or branched alkyl group having 1 to 6 carbon atoms, or a substituted or unsubstituted aryl group; and n represents an integer of 2 or more.