an optical data storage comprising a thermoplastic copolycarbonate is disclosed . the copolycarbonate contains at least one unit derived from dihydroxydiphenyl ether and at least one unit derived from at least one member selected from the group consisting of 4 , 4 ′ dihydroxybiphenyl and 1 , 1 - bis -- 3 , 3 , 5 - trimethylcyclohexane .