SELF-ASSEMBLY AND PATTERNS IN BINARY-MIXTURES OF SI BLOCK COPOLYMER AND PPO

Self-assembled patterns were investigated for solvent-cast films of the binary mixtures of poly(2,6-dimethylphenylene oxide) (PPO) and poly(styrene-b-isoprene) diblock copolymers (SI) using transmission electron microscopy. The pattern formation was found to generally depend on both the microphase transition for the block copolymer and the liquid-liquid phase transition for the mixtures of the two polymers PPO and SI (the macrophase transition). The patterns with uniformly distributed micro-domains in space were obtained when the microphase transition occurred prior to the macrophase transition. In this case, PPO and polystyrene (PS) block chains in SI are mixed with each other and segregated from the domains composed of polyisoprene (PI) block chains. On the other hand, when the macrophase transition occurred prior to the microphase transition, periodic concentration fluctuations of SI and PPO with a characteristic spacing of LAMBDA-macro on the order of micrometers first developed probably due to spinodal decomposition. This pattern formation and growth were followed by the microphase transition, generating the microdomains of a characteristic spacing LAMBDA-micro on the order of 100 nm. The pattern growth was eventually pinned down by vitrification to result in formation of a nonequilibrium structure with spatially varying microdomain morphology, a superlattice with the two spacings, LAMBDA-macro and LAMBDA-micro. An interesting relation between the pattern and the thermal behavior as observed by DSC was also found.