A macromonomer (M1) of 2-cyclopropyl-2-oxazoline (Cicloxa) was prepared by the ring-opening cationic polymerization of 2-cyclopropyl-2-oxazoline initiated by chloromethylstyrene and in the presence of sodium iodide as catalyst. The reaction was carried out at 77 ° C in acetonitrile. The cyclopropyloxazoline macromonomer with a vinyl group at the end of the polymer chain, had a degree of polymerization of 25 monomer units and a molecular weight of 2,912. The macromonomer had sensitivity to temperature having a conformational change (LCST) at 18°C, when dissolved in water. The macromonomer will allow, through its polymerization with other monomers, the production of new temperature-sensitive polymers as graft copolymers or hydrogels.