We report vinyl—methacrylate, acrylate, and styrene—protection by unique sulfoxide chemistry applying to atom transfer radical polymerization (ATRP). Three sulfoxide-protected (SP) vinyl-functionalized ATRP inimers were synthesized. Latent vinyl-functionalized polymers were synthesized via ATRP using the SP inimers. Alpha end vinyl-functionalized polymers were prepared by deprotection through simple heating of the synthesized SP polymers. In kinetics study, the (meth)acrylate type was confirmed to faster for the deprotection reaction than styrene type. The methacrylate-functionalized product was exhibited a high vinyl functionality greater than 98%. This concept provides an efficient way to introduce vinyl functionality into well-defined polymers as the latent monomer moiety and thus has vast potential for macromolecular engineering applications.