Thermoassociative graft copolymers: NMR investigation and comparison with rheological behaviour

The thermoassociative properties of semidilute solutions of graft copolymer s containing poly(N-isopropylacrylamide) (PNIPA) side chains are studied by H-1 NMR. Upon heating, the PNIPA grafts self-aggregate into hydrophobic mi crodomains and their H-1 NMR signal is no longer detectable. This phenomeno n is attributed to the glassy structure of the aggregates' core and allows a direct detection of the aggregation process. On this basis it becomes pos sible to detect the formation of the microdomains by salting-out (with pota ssium carbonate) or their dissociation by adding an anionic surfactant (sod ium dodecyl sulfate). The H-1 NMR observations are compared to the rheologi cal data previously obtained and to small-angle neutron scattering measurem ents performed in similar conditions. A good correlation is evidenced betwe en the macroscopic and microscopic transitions probed by the different tech niques.