A novel polymer bearing coumarin pendants of 4-allyloxy-2H-chromen-2-one (ACO) was synthesized by atom transfer radical polymerization (ATRP) in toluene at 110°C using 2-Bromoisobutyryl bromide (BIBB), Cu (I) Br, and 2,2′-bipyridyl (bpy) as initiator, catalyst, and ligand, respectively. The most appropriate molar concentration ratio of [ACO] : [BIBB] : [Cu (I) Br] : [bpy] was found to be 40 : 1 : 1 : 2 for controlled polymerization. Successful chain extension polymerization of poly (4-allyloxy-2H-chromen-2-one) (PACO) confirms the livingness of the process. The activation energy (Ea) (76.26 kJ mol−1) and enthalpy of activation (ΔH‡) (73.07 kJ mol−1) were in good agreement to each other proving the feasibility of the reaction and negative value of entropy of activation (ΔS‡) (−320 J mol−1 K−1) supported the highly restricted movement of reacting species in transition state during polymerization. Initial polymer decomposition temperature of PACO was found to be 130°C. SEM analysis revealed that polymer surface is not smooth with pointed rod like shapes. The polymer/Ag nanocomposite was synthesized and examined in view of antibacterial effect against Enterococcus faecalis, Staphylococcus aureus, Escherichia coli, Proteus mirabilis, and Klebsiella pneumonae. PACO and its Ag nanocomposite (PACON) have been found to be active selectively against bacterial pathogen E. fecalis with minimum inhibitory concentration of 50 and 32 μg mL−1, respectively. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012