condensation copolymers such as polyesters are rendered photodegradable , by subjecting them to conditions under which they undergo ester interchange effectively causing polymer chain scission , in the presence of a keto carbonyl containing compound having chemical groups reactive with the condensation polymer products formed by the ester interchange . the compound reacts chemically with the polymer products to reform the high molecular weight condensation copolymer , but with the keto carbonyl groups chemically linked into the polymer chains to confer photodegradability thereon .