there is disclosed a process for preparing chemically modified styrene polymers and copolymers which comprises treating a polystyrene or a styrene copolymer with an acyl halide in the presence of a lewis acid so as to introduce ketone groups into the treated polymer or copolymer in an amount sufficient to promote environmental photodegradation of the treated polymer or copolymer . the resulting modified polymers may be used as degradable packaging materials , or as additives to promote the environmental degradation of polystyrene and related materials .