Phase separation and surface properties of poly(propyl methacrylate-b-methyl methacrylate) diblock copolymers

The phase separation and surface characteristics of poly(propyl methacrylate-b-methyl methacrylate) (PPrMA-b-PMMA) diblock copolymers were studied and compared to strongly phase-separated poly(pentyl methacrylate-b-methyl methacrylate) (PPMA-b-PMMA) block copolymers (BCPs). PPrMA-b-PMMA with varied compositions and molar masses was synthesized by living anionic polymerization. The phase separation was studied by DSC, SAXS, TEM and AFM. The experimental data were compared to the calculated phase diagram. PPrMA-b-PMMA BCPs were weakly phase-separated, and indications for the existence of a relative broad interface between the blocks were observed. Nevertheless, two ordered morphologies—hexagonally packed cylinders and lamellae—depending on the molar composition were distinguished. The phase separation in thin films was studied by AFM in comparison with PPMA-b-PMMA. The wetting behavior of the thin films was examined by contact angle measurements. The water contact angles on PPrMA-b-PMMA were clearly influenced by both blocks. XPS confirmed the presence of both blocks in the top surface layer, which was different to PPMA-b-PMMA diblock copolymers where the top layer consisted only of PPMA blocks. Thus, only the weakly phase-separated PPrMA-b-PMMA BCP system allowed the generation of phase-separated films with tunable wetting characteristics.