A new vinyl aryl azide monomer, 4-azidophenyl methacrylate (APM), has been synthesized and characterized by H-1 NMR and FT-IR spectroscopy. The thermal stability of APM has been investigated by temperature-dependent FT-IR spectroscopy and H-1 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.