Thermal conditions of the process of manufacturing large-block, optically pure products based on polystyrene and polymethyl methacrylate (scintillators, light concentrators, bulletproof glass, etc.) have been experimentally and theoretically studied. The flow sheet of the process includes two sequentially connected reaction apparatuses, i.e., a tubular reactor for frontal polymerization and a semi-continuous molding reactor. Prepolymer is formed in the tubular reactor and is fed to the molding reactor. As this reactor is being filled, polymerization continues under autothermal heating conditions. After filling, the molding reactor is replaced by a similar one, while the filled reactor is kept in a temperature-controlled oven for final polymerization followed by cooling and removal of the product.