Modified copolyesters and optical films including modified copolyesters

Abstract

Modified copolyesters having relatively low refractive indices and relatively high glass transition temperatures are disclosed. These modified copolyesters can be used in forming one or more layers in an optical film, such as a multilayer polymer film.

1 . A multilayered polymer film, comprising:
 a plurality of first optical layers comprising a birefringent first copolyester or polyester;   a plurality of second optical layers comprising a birefringent second copolyester; and   a skin layer disposed on the plurality of first optical layers or plurality of second optical layers, the skin layer having a thickness that is at least 10 times a thickness of an individual first or second optical layer.   
   
   
       2 . The multilayered polymer film of  claim 1 , wherein the plurality of first and second optical layers are arranged in alternating pairs. 
   
   
       3 . The multilayered polymer film of  claim 1  having about 25 to 2000 optical layers. 
   
   
       4 . The multilayered polymer film of  claim 1 , wherein the skin layer has a thickness of at least 12 micrometers. 
   
   
       5 . The multilayered polymer film of  claim 1 , wherein the skin layer is not birefringent. 
   
   
       6 . The multilayered polymer film of  claim 1 , wherein the skin layer has a higher index of refraction than the first and second optical layers.