End group effect on surface and interfacial segregation in PS-PMMA blend thin films

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 bi-continuous 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.