ORDERED STRUCTURE IN MIXTURES OF A BLOCK COPOLYMER AND HOMOPOLYMERS .1. SOLUBILIZATION OF LOW-MOLECULAR-WEIGHT HOMOPOLYMERS

Microdomain structures of binary mixtures of poly(styrene-b-isoprene) diblock polymer (SI) and homopolystyrene (HS) and ternary mixtures of SI, HS, and homopolyisoprene (HI) were investigated as a function of volume fraction of SI (phi-b) in the mixtures for given molecular weights of HS (M(HS)), HI (M(HI)), and SI (M(b)) and volume fraction of polystyrene (PS) block chain (f) in the block polymer SI at a strong segregation limit. The systems studied here have characteristics of f = 0.45, M(HS)/M(b) = 0.068, and M(HI)/M(b) = 0.073. The results indicated that (i) the homopolymers HS and HI are solubilized essentially uniformly in the corresponding microdomains, causing changes of the microdomain morphology with the change of total volume fraction of the constituent polymer, e.g., PS and the size each microdomain, and that (ii) the long-range order of the microdomains is conserved down to a very low level of phi-b, with a phi-b as low as 0.10 being observed in this experiment.