SAN-g-GO nanoparticles was prepared through solvent free reaction where the cyano group in SAN was converted to oxazoline groups during melt mixing in the presence of zinc acetate and ethanol amine. The oxazoline groups created through this reaction was confirmed by FTIR, TEM, NMR and XPS. The effect of SAN-g-GO nanoparticles on the demixing temperature and morphology evolution for different annealing times was carefully investigated in a classical LCST system PMMA/SAN using melt rheology and AFM respectively. The changes in viscoelastic behavior in the vicinity of demixing was investigated systematically for the control, and blends with GO and SAN-g-GO. Various models were used to gain insight into the spinodal decomposition temperatures of the blends. The demixing temperature (including the spinodal decomposition temperature) determined through rheological fingerprints increased significantly in the presence of polymer grafted nanoparticles in comparison to the control and blends with GO. The evolution of the morphology, interfacial driven coarsening as a function of temperature and the localization of nanoparticles were assessed using atomic force microscopy.