| abstract |
The present invention relates to multilayer optical films and birefringent copolyester films. The birefringent copolyester optical layer or birefringent copolyester film comprises a major amount of naphthalate units, ethylene units, and a minor amount of branched or cyclic C4 to C10 alkyl units. Also described are certain copolyester polymeric materials further comprising subunits of a phthalate ionomer such as dimethyl sulfosodium isophthtalate ionomer. |