| 摘要 |
PURPOSE:To provide an optical disk composed of a copolymer of methyl methacrylate, a styrene (derivative) and and alkyl methacrylate, and having a specific photoelastic coefficient, small birefringence, low hydroscopicity, and excellent transparency, mechanical strength, etc. CONSTITUTION:The objective optical disk is made of a copolymer prepared by copolymerizing (A) 30-70(wt)%, preferably 30-60% methyl methacrylate, (B) 20-60% alkyl methacrylate having 3-8C alkyl group, preferably 30-60% cyclohexyl methacrylate, and (C) 2-20% styrene (derivative), preferably 2-20% (p-methyl)styrene under a condition to attain a photoelastic coefficient of -5.0X10<-13>-+5.0X10<-13>cm<2>/dyne. |
