A new vinyl aryl azide monomer, 4-azidophenyl methacrylate (APM), has been synthesized and characterized by 1H NMR and FT-IR spectroscopy. The thermal stability of APM has been investigated by temperature-dependent FT-IR spectroscopy and 1H NMR, and the monomer has been demonstrated to be quite stable at ambient temperature. Reversible addition–fragmentation chain transfer (RAFT) homopolymerization and copolymerizations of APM with methyl acrylate, methyl methacrylate, and styrene have been carried out at room temperature using a redox initiator, benzoyl peroxide (BPO)/N,N-dimethylaniline (DMA). The results show that the polymerizations bear all the characteristics of controlled/living free-radical polymerizations. Moreover, the cycloaddition of azido group to carbon–carbon double bond can be avoided in the polymerization process at room temperature.