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Symmetric Poly(ethylene oxide-b-styrene-b-isoprene) Triblock Copolymers: Synthesis, Characterization, and Self-Assembly in Bulk and Thin Film
journal contribution
posted on 2014-09-23, 00:00 authored by Yali Qiao, Rachel Ferebee, Bongjoon Lee, Indranil Mitra, Nathaniel
A. Lynd, Jeffery Hayat, Gila E. Stein, Michael R. Bockstaller, Chuanbing TangThe synthesis, characterization,
and self-assembly of a series
of linear poly(ethylene-b-styrene-b-isoprene) (PEO−PS−PI) triblock copolymers containing
nearly equal volume fractions of PEO and PI (fPEO ≈ fPI) and various fractions
of the middle PS block (70.8 vol % ≤ fPS ≤ 75.6 vol %) is reported. A range of azide-functionalized
poly(ethylene oxide-b-styrene) diblock copolymers
were prepared by atom transfer radical polymerization (ATRP) of styrene
using the same batch of PEO-macroinitiator, followed by azide-functionalization.
Monohydroxyl-terminated poly(cis-1,4-isoprene) was
first alkyne-functionalized and then sequentially attached to azide-functionalized
PEO−PS via copper(I)-catalyzed azide−alkyne cycloaddition
reaction, producing PEO−PS−PI triblock copolymers with
low dispersity. Bulk samples of each linear triblock copolymer reveal
the formation of a binary microdomain structure in which a PS and
PI domains mix to form a uniform matrix for spherical PEO microdomains,
and the PEO microdomains are arranged in a BCC lattice. Additionally,
the thin film ordering of these triblock copolymers was investigated
using a high-humidity solvent annealing process, both with and without
low concentrations of a lithium salt. The morphology was analyzed
by atomic force microscopy and GISAXS, revealing layers of spherical
PEO domains arranged with in-plane hexagonal symmetry. The inclusion
of salt increased both the size and periodicity of PEO domains.