We designed and used a cyclohexenyl-functionalized amphiphilic macromolecular reversible addition fragmentation chain transfer (macro-RAFT) agent as surfactant and polymerization mediator for (mini) emulsion polymerization of styrene (St), aiming at synthesizing nanoparticles with vinyl-enriched surface and well-defined polymer chains. Unexpectedly, the pendent cyclohexenyl units in the macro-RAFT agent were found to undergo significant copolymerization with St exclusively during the nucleation period in the ab initio emulsion polymerization, leading to the consumption of cyclohexenyl groups, positive deviation of molecular weights, and broad molecular weight distributions. By contrast, in miniemulsion polymerization, the radical polymerization exhibited superb selectivity toward St monomers relative to the pendent cyclohexene vinyl units just as in the solution polymerization. The obtained polymer chains retained designed molecular weights, low polydispersity indexes, and quantitative cyclohexenyl functionalities confined to the particle surface. Thus, PSt particles with vinyl-enriched surface were obtained via miniemulsion polymerization.