| abstract |
The invention relates to a transparent substrate with low birefringence. The transparent substrate comprises polyimide having a repeat unit of formula (I) and has a birefringence below 0.005: n n n n n n n n n n n n , wherein each A of the repeat unit, being the same or different, represents an aromatic or aliphatic group, and at least one A is an aromatic or aliphatic group containing sulfonyl functionality; each B of the repeated unit, being the same or different, represents an aromatic or cycloaliphatic group; and n is an integer greater than one. |