Tuning phase separation morphology in blend thin films using well-defined linear (multi)block copolymers

Tuning phase separation morphology in polymer blend thin films is a promising strategy to improve their properties. In this study, a series of poly(n-butyl methacrylate)-b-polystyrene linear copolymers with the same overall degree of polymerization but different number of blocks are synthesized by macroRAFT-mediated emulsion polymerization, and used as compatibilizers in poly(n-butyl methacrylate)/polystyrene blend thin films with thickness of ca. 20 nm. It is verified that multiblock copolymer is more effective to diminish the size of phase separation domains compared to diblock copolymer. Self-consistent field simulation agrees with the experimental results, and demonstrates that the compatibilization behaviors of diblock and multiblock co-polymers are different. Diblock copolymer can compatibilize the blend well at a higher content, whereas mul-tiblock copolymers tend to give a smaller domain size but less homogeneous morphology. In addition, simulation results show that copolymers with a longer block length would produce a narrower interface, which may weaken the penetration of block copolymers into their corresponding phases. This study provides a pioneering attempt in clarifying the effect of block copolymers on blend phase separation morphology, and it will be of practical value in obtaining desirable mechanical properties of polymer thin films.