Herein, we present a method to control the dual cross-linking of radical and urethane reactions for the enhanced polymer coatings by protecting and deprotecting vinyl functionalities using sulfoxide chemistry. We exploited this chemistry to produce highly cross-linked polymers suitable for use as protective coatings. Briefly, dually cross-linkable polymers with sulfoxide-protected vinyl and hydroxyl functionalities were synthesized. Subsequently, thermal curing resulted in the reaction of the hydroxyl functionalities with isocyanate cross-linkers to form urethane cross-links. At the same time, the sulfoxide-protected vinyl functionalities were deprotected and participated in vinyl cross-linking via radical addition reactions. The real-time monitoring of the dual-cross-linking behavior and mechanical properties of the cross-linked films revealed enhanced cross-linking when the reaction rate of the vinyl functionalities was retarded during thermal curing. Thus, this work provides insights into methods of enhancing dual-cross-linking reaction efficiency, and the developed system has applications for the low-temperature preparation of automotive clearcoats.