2-Methylene-5-phenyl tetrahydrofuran (2-M-5-PTF) was synthesized and its polymerization behavior under various conditions were investigated. With di-tert-butyl peroxide(DTBP) at 120℃ in benzene, 2-M-5-PTF polymerized to give polymers containing 70% of ring-opened ketone linkage, but with AIBN no polymerization occured. In the case of BPO-initiated polymerization, 2-M-5-PTF was isomerized to 5-methyl-2-phenyl-2,3-dihydrofuran. In the postulated mechanism of radical polymerization, a radical attacks at first on the methylene group of the ring to form dioxyauyl radical and this radical rearranges in turn to the energetically more stable benzyl radical, with ring opening. The benzyl or oxyalkyl radical will react then with another monomer to propagate. In the case of cationic polymerization with BF₃·ET₂O, the polymer obtained contained both 50% of ketone linkage formed by ring opening and 50% of cyclic structures. Also WCl₆-based catalyst system was found to be very effective for the polymerization of 2-M-5-PTF without ring opening. In copolymerization with MMA, AN, styrene, the copolymers contained 30%, 29%, 20% of 2-M-5-PTF.