Thin films of polystyrene (PS)/poly (methyl methacrylate) (PMMA) blends with different end groups were investigated using TOF-SIMS and AFM. PS with -OH and -NH2 end groups were blended in toluene solvent with pure PMMA homopolymer, and PMMA having anhydride end group. The ToF-SIMS spectra of PS-OH/PMMA resembled that of pure PS-PMMA blends showing an increase of PMMA intensity after annealing. On the contrary, the PS-NH2 blended with PMMA showed an increase in PS intensity on the surface after annealing. The ToF-SIMS spectra were similar to that of a pure PS-PMMA di-block copolymer. These results indicate copolymer formation at the surface. The PS-NH2 with PMMA-anhydride blend spectra showed very slight changes in spectra before and after annealing and the AFM images revealed spinodal bicontinuous structures on the surface before and after annealing. The copolymer formation is found to occur in the as-cast film itself and not after thermal treatment. (c) 2006 Elsevier B.V. All rights reserved.