| 摘要 |
PROBLEM TO BE SOLVED: To obtain a substrate having good transfer property of signals, small warpage of the substrate and small difference in the refractive index in the perpendicular direction by specifying the viscosity average mol.wt., the alcohol which seals the molecular ends, and the glass transition temp. of a (co)polymer having carbonate coupling units of bisphenol-A polycarbonate and carbonate groups having bulky aromatic groups in the side chains. SOLUTION: The optical disk substrate is formed by using a polycarbonate having the following characteristics. The polycarbonate contains the coupling unit expressed by formula I (R is 1-3C alkyl or phenyl group) by 20 to 80 mol% and the coupling unit expressed by formula II in the whole polycarbonate coupling units, and it has 1×104 to 2.3×104 viscosity average mol.wt. and 100 to 400 deg.C glass transition temp. The molecular ends are sealed with alkylphenols having 10-20C alkyl groups. The polycarbonate is obtd. by the reaction of a specified dihydroxyaryl compd. and phosgene. As for a sealing agent for the end groups, dodecyl alcohol, palmityl alcohol or the like can be used. |
