This study is designed to synthesize novel degradable polymers by radical addition–fragmentation ring‐opening copolymerization of bio‐based thiocarbonyl compounds with various vinyl monomers. Thiocarbonyl l‐lactide is capable of radical copolymerization with acrylates and styrene via radical addition to the carbon–sulfur double bonds followed by ring‐opening as well as controlled copolymerization in conjunction with the reversible addition–fragmentation chain transfer (RAFT) process. The obtained polymers possess ring‐opened thioester and ring‐retained thioacetal functionalities in the backbone, both of which could be cleaved under appropriate conditions with different chemical stimuli.