A styrenic copolymer composition comprising 55% to 94% by weight of one or more styrenic monomers; 2% to 25% by weight of one or more maleate-type monomers; and 4% to 20% by weight of an elastomer composition comprising one or more partially hydrogenated elastomeric polymers comprising repeat units from one or more monomers according to the formula 63% 1,4 cis/trans butadiene, 1% 1,2 vinyl butadiene, 26% tetramethylene, and 10% butylene. The styrenic copolymer composition may also comprise one or more high molecular weight elastomeric polymers having a number average molecular weight of greater than 12,000 and optionally, polybutene. The styrenic copolymer composition is formed via polymerizing methods. A thermoplastic sheet is made by extruding the polymer melt composition to provide a thermoplastic sheet. The thermoplastic sheets can be thermoformed into containers suitable for use in microwave heating of food.