The polymerization of a mixture of cis (ca. 30%) and trans (ca. 70%) isomers of 7-tetradecene oxide (7-TDO) with methyl trifluoromethansulfonate (methyl triflate) as initiator has been investigated. The main reaction products afforded during the polymerization were a linear polyether, a cyclic dimer [2,3,5,6 tetra(n-hexyl)dioxane], and 7-tetradecanone. The ketone is formed both via pinacol rearrangement of the monomer and a transfer reaction when all the monomer is consumed, and is favoured by an increase of temperature. Kinetic studies on the ring opening polymerization of this system were performed by means of H-1 and F-19 NMR spectroscopies. Approximate rate constants of initiation (ki) for the cis and the trans isomers were determined at 298, 314 and 329 K in bulk, and at 298 K in C6D6 The reaction time of the cia isomer is faster than that of the trans isomer, with an initial molar reactivity ratio of about 11:1 at 298 K, and of about 7:1 at 329 K tin bulk). The activation energies of the initiation reaction for the cis and the trans isomers were calculated to be 59 and 73 kJ/mol, respectively. By means of H-1-, F-19- and C-13-NMR the structure of the propagating species is reasonably well identified as an oxonium macroion rather than a linear triflic macroester.