In order to obtain novel temperature-responsive copolymers, poly(vinyl alcohol) (PVA) was chemically modified by introducing cyclic acetal functionalities in the polymer chain. The acetalization, reaction was carried out with acetaldehyde in water. The degree of acetalization was controlled in the range 10-25% by the initial aldehyde concentration. The copolymers obtained were characterized by ID (H-1, C-13, DEPT) and 2D (COSY) NMR techniques as well as by viscometry. The thermo-responsive properties were evaluated by measuring the cloud point temperature (T-cp) of the aqueous copolymer solutions.