AbstractThe photodegradation of three polymer materials was studied, i.e., polyolefin, polyurethane, and a copolymer of styrene, butyl acrylate, and methyl methacrylate (P(St‐co‐BA‐co‐MMA) latex). These polymers are mostly used as film‐coating materials for producing controlled‐release fertilizers. The P(St‐co‐BA‐co‐MMA) latex film degraded at the highest rate and the film surface became porous under UV irradiation. The weak cross‐link chain in the latex film was broken and the connections between the microspheres were destroyed. A photo‐oxidative aging reaction weakened the tenacity of the latex film, which resulted in the easy release of microspheres from the film, leading to a reduction in film thickness and film tensile strength. Threfore, P(St‐co‐BA‐co‐MMA) latex is a promising coating material for controlled‐release fertilizers.