| 摘要 |
PURPOSE:To obtain an optical element substrate which is excellent in heart resistance and clarity, consisting chiefly of a specified copolymer made of a methyl methacrylate unit, an arom. vinyl compd. unit, an unsaturated aliphatic acid unit and a 6-membered ring anhydride unit. CONSTITUTION:A copolymer having a molecular structure in which four different recurring units, i.e. a methyl methacrylate unit A, an arom. vinyl compd. unit B, an unsaturated aliphatic acid unit C and a 6-membered ring anhydride D of formula I (where R1 and R2 are H, methyl) are arranged at random is prepared, wherein the numerical requirements of formulas II, III, IV, V and VI must be satisfied when the contents of units A, B, C and D are a, b, c and d wt.%, respectively, and the viscosity of the copolymer in a concn. of 10wt.% in its methyl ethyl ketone solution at 25 deg.C is 2-10 cP. An optical element substrate is composed of this copolymer as a principal ingredient.
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