| 摘要 |
<p>An optical-disk substrate which is satisfactory in transferability and releasability during molding, is reduced in warpage, and has high strength. The optical-disk substrate is made of a hydrogenated styrene polymer in which the content of nucleus-hydrogenated styrene units is 80 wt. % or higher and which has a reduced viscosity (in toluene, 0.5 dl/g, 30°C) of 0.3 to 0.6 dl/g, the radius-direction shrinkage of the disk as measured at the glass transition temperature of the hydrogenated styrene polymer being 4.5% or lower. Also provided is a hydrogenated styrene polymer which is suitable for producing the optical-disk substrate. In this polymer, the content of nucleus-hydrogenated styrene units is 80 wt. % or higher. The polymer has a glass transition temperature of 130°C or higher and has a relaxation spectrum at 200°C satisfying the following relationship (1) log(H(τ)• τ) ≤ 6.5(10-2 ≤ τ ≤ 104) [wherein log is common logarithm; τ is relaxation time (sec); and Hτ(Pa) is the relaxation spectrum at 200°C].</p> |
