Abstract: A novel optical element substrate which comprises a random copolymer comprising, in specific weight proportions, a methyl methacrylate unit, an aromatic vinyl compound unit, an unsaturated aliphatic acid unit and a hexagonal acid anhydride unit of the formula ##STR1## The substrate has excellent heat resistance, thermal stability, transparency, resistance to scratching and metal layer corrosion preventive properties and exhibits advantageously low double refraction and warpage. The novel substrate can be advantageously employed as a substrate for an optical element such as an optical disc, e.g. a digital audio disc, a video disc and a disc capable of being directly read after recording, a mirror, a lens and the like.

Abstract: A resin composition comprising (A) a copolymer comprising hexagonal units selected from hexagonal acid anhydride units, hexagonal imide units and mixtures thereof, methyl methacrylate units, (meth)acrylic acid units and optionally aromatic vinyl compound units, (B) a graft copolymer rubber, and (C) at least one polymer selected from a polyamide and a polycarbonate, wherein the weight proportions of components (A), (B) and (C) relative to the total weight of components (A), (B) and (C) are in the ranges of from 5 to 50%, from 5 to 50% and from 45 to 80%, respectively. The resin composition has surprisingly improved impact strength not possessed by any of the individual component polymers of the resin composition, while maintaining advantageous properties, such as moldability, other mechanical strengths, rigidity, heat resistance, moisture resistance, chemical resistance and dimensional stability, attributed to the individual component polymers.

Abstract: A novel random copolymer containing, in specific ratios, methyl methacrylate units, aromatic vinyl compound units, methacrylic acid units, hexagonal anhydride units and hexagonal imide units of the formula ##STR1## has been found to have excellent optical properties, mechanical strength, heat distortion resistance, heat decomposition resistance and oil resistance, and have low water absorption. The copolymer can advantageously be employed as a material for parts of light electric apparatus, engineering plastics, lenses, optical fiber cables, and is especially useful as a material for a substrate of optical discs.