Mixed morphology in low molar mass fluorinated block copolymers

New low molar mass (M-n similar to 20 kg mol(-1)) polystyrene-b-poly(methyl methacrylate-co-perfluorohexylethyl acrylate) (PS-b-P(MMA-co-FA)) block copolymers were synthesized all consisting of similar to 70 mol% PS block and similar to 30 mol % P(MMA-co-FA) block. The amount of FA counits in the latter block was increased (0.5, 1, 3 and 4 mol%) in order to enhance the incompatibility between the two blocks and to form different self-assembled nanostructures. The block copolymers were thermally annealed by Rapid Thermal Processing (RTP) over wide ranges of temperatures and times. Complementary SEM and AFM analyses evidenced that the introduction of FA counits above a critical content (similar to 2 mol%) drove a self-assembly process through mixed morphologies. These were formed at a distance from the polymer-air interface and consisted of perpendicular cylinders of P(MMA-co-FA) in a PS matrix laying at the substrate- polymer interface, and surmounted PS stripes and PS dots. Modification by low amounts of FA produced block copolymer samples that self-assembled in new, mixed nanostructures, even though they possessed much lower molar masses than those of analogous well established PS-b-PMMA block copolymers.