Method for cast molding plastic substrate

A method for obtaining a molded transparent plastic substrate by radical polymerizing a polymerizable monomeric liquid composed of at least one polyfunctional (meth)acrylate compound alone or admixed with at most 10% of other radical polymerizable monomers, the polymerization reactions consisting essentially of radical polymerization reactions, any catalyst present being a radical initiator, by a cast molding method, wherein in a first step the final shape of the plastic substrate is obtained by radical polymerizing the polyfunctional (meth)acrylate compound under cast molding conditions in a mold until the glass transition temperature of the polymerizing composition reaches 10.degree. to 100.degree. , in a second step the shaped substrate as obtained in the first step is removed from the mold, and in a third step the substrate is post-cured at a temperature below 150.degree. C. free of the restraints of a mold to obtain a substrate having a glass transition temperature of 110.degree. C. or more, and this substrate is then further post-cured at a temperature of 150.degree. C. or more, the shape of the final product being that imparted by the first step.