Polydispersity effects in poly(isoprene-b-styrene-b-ethylene oxide) triblock terpolymers

Abstract

Four hydroxyl-terminated poly͑isoprene-b-styrene͒ diblock copolymers with comparable molecular weights and compositions ͑equivalent volume fractions of polyisoprene and polystyrene͒ but different polystyrene block polydispersity indices ͑M w / M n = 1.06, 1.16, 1.31, 1.44͒ were synthesized by anionic polymerization using either sec-butyllithium or the functional organolithium 3-triisopropylsilyloxy-1-propyllithium. Poly͑ethylene oxide͒ ͑PEO͒ blocks were grown from the end of each of these parent diblocks to yield four series of poly͑isoprene-b-styrene-b-ethylene oxide͒ ͑ISO͒ triblock terpolymers that were used to interrogate the effects of varying the polydispersity of the middle bridged polystyrene block. In addition to the neat triblock samples, 13 multicomponent blends were prepared at four different compositions from the ISO materials containing a polystyrene segment with M w / M n = 1.06; these blends were used to probe the effects of increasing the polydispersity of the terminal PEO block. The melt-phase behavior of all samples was characterized using small-angle X-ray scattering and dynamic mechanical spectroscopy. Numerous polydispersity-driven morphological transitions are reported, including transitions from lamellae to core-shell gyroid, from core-shell gyroid to hexagonally packed cylinders, and from network morphologies ͓either O 70 ͑the orthorhombic Fddd network͒ or core-shell gyroid͔ to lamellae. Domain periodicities and order-disorder transition temperatures also vary with block polydispersities. Self-consistent field theory calculations were performed to supplement the experimental investigations and help elucidate the molecular factors underlying the polydispersity effects. The consequences of varying the polydispersity of the terminal PEO block are comparable to the polydispersity effects previously reported in AB diblock copolymers. Namely, domain periodicities increase with increasing polydispersity and domain interfaces tend to curve toward polydisperse blocks. The changes in phase behavior that are associated with variations in the polydispersity of the middle bridged polystyrene block, however, are not analogous to those reported in AB diblock copolymers, as increases in this middle block polydispersity are not always accompanied by ͑i͒ increased domain periodicities and ͑ii͒ a tendency for domain interfaces to curve toward the polydisperse domain. These results highlight the utility of polydispersity as a tool to tune the phase behavior of ABC block terpolymers.

Manipulating the ABCs of self-assembly via low-χ block polymer design

“…2A and reinforce the microscopic origins of mixing deduced from TEM. (38,39) and α SIO ≈ 0.56 (40). Clearly, α LSO is strikingly different.…”

Design of high‐χ block copolymers for lithography

“…Table lists χ calculated by the aforementioned technique, based on a reference volume of 118 Å 3 . It should be noted that the choice of reference volume is completely arbitrary, but 118 Å 3 was chosen to conform to the conventions of most BCP and BCP‐lithography literature . It is necessary to use an identical reference volume when making comparisons between BCPs on the basis of χ , or to express χ in terms of an interaction energy density .…”

Ordered Three- and Five-ply Nanocomposites from ABC Block Terpolymer Microphase Separation with Niobia and Aluminosilicate Sols

“…Furthermore, the stability of ISO-oxide network phases may be rationalized in terms of the increased polydispersity of the combined O+oxide domain. Copolymers with blocks of different polydispersity are known to favor structures with surfaces curving towards the block of higher dispersity 44–47. Thus the stability of O+oxide minority network phases is expected to be higher than that of O+oxide majority network phases.…”