Polybutadiene was treated with o-tolualdehyde under UV irradiation to produce random copolymers through Diels-Alder reactions on the backbone double bonds. The physical properties of the polymer products change as more of the aldehyde attaches to it. The copolymers were characterized by NMR spectroscopy. A bifunctional o-tolualdehyde was synthesized and used as a crosslinking agent.