<i>Fddd</i> Structure in Polystyrene-<i>block</i>-polyisoprene Diblock Copolymer/Polystyrene Homopolymer\nBlends

Abstract

We have induced <i>Fddd</i> structure in polystyrene-<i>block</i>-polyisoprene diblock\ncopolymer (SI) which does not\nhave <i>Fddd</i> phase by adding polystyrene (hPS) homopolymer.\nWe prepared the SI/hPS blend samples in the range of 0.627 < ϕ_PI < 0.646 and investigated the phase boundary of <i>Fddd</i> phase by using small-angle X-ray scattering (SAXS)\nand transmission electron microscopy (TEM), where ϕ_PI is volume fraction of polyisoprene (PI) in SI/hPS. We found the <i>Fddd</i> phase as an equilibrium phase in the range of 0.631\n≤ ϕ_PI ≤ 0.641 and 26.6 < χ<i>N</i> < 30.7, where χ and <i>N</i> are respectively\nthe Flory–Huggins interaction parameter between PS and PI and\npolymerization index of the SI. The <i>Fddd</i> phase boundary\nin the SI/hPS is similar to that in the neat SI block copolymer since\nthe effect of the addition of the hPS with the low molecular weight\non the phase diagram corresponds to that of the same change of PS\nvolume fraction in the neat block copolymer.