New thermoassociative polymers were developed on the basis of the self-aggregation behaviour induced by heating of the ＇poly(N-isopropylacrylamide) (PNIPA)/water＇ binary system. The preparation of the graft copolymers involves a 2-step method with (1) the synthesis of amino end functionalised oligo-NIPA by radical polymerisation initiated with a convenient redox system based on thiol and (2) a ＇grafting onto＇ reaction of the PNIPA chains on a poly(acrylic acid) backbone. In semi-dilute aqueous solution, the resulting graft copolymers exhibit a large viscosity enhancement upon heating as soon as the temperature exceeds the lower critical solution temperature (LCST) of the PNIPA side chains. The influence of various physicochemical parameters (copolymer concentration, shear rate) and structural characteristics (side chains length) an the thermothickening behaviour are examined and interpreted using the concept of thermally induced physical network.