A series of ATRP-synthesized poly(IL) diblock copolymers exhibit morphological phase behavior with shifted phase boundaries and alkyl substituent dependent segregation.
Solvent-free,melt-state self-assembly of sphere-formingpolystyrene-b-poly(ethylene oxide) diblock copolymer/polystyrene-b-poly(ethylene oxide)-b-polystyrene triblock copolymer (SO/SOS) blends has been used to produce free-standing,roomtemperature ionic liquid (RTIL) composite membranes with excellent mechanical properties and CO 2 /N 2 separation performance. Membranes were prepared from vitrified SO/SOS diblock/triblock meltsby swellingwithgreater than 94 wt% 1-ethyl-3-methylimidazoliumbis(trifluoromethylsulfonyl)imide ([EMIM][TFSI]) ionic liquid. Thesefree-standingcomposite membranes were evaluated for their CO 2 /N 2 separation performance over a range of transmembrane pressures,with resultstraversingthe 2008 Robeson upper bound.Even with such high loadings of neat [EMIM][TFSI], these membranes exhibit the mechanical properties of solid elastomers, evident by the
Using
a unique one-pot convergent anionic polymerization strategy,
18 (polystyrene)star-b-(polyisoprene)linear-b-(polystyrene)star (S
n
IS
n
) pom-pom
triblock copolymers were synthesized varying a range of architectural
parameters including PS arm molecular weight (M
n,star), the number of arms contained in the star (n), and the PI midblock molecular weight (M
n,PI). A selected series of five of these 18, in which M
n,star was held approximately constant between
14.3 and 16.5 kDa, but with the numbers of arms in the star and PI
midblock molecular weight varied, were selected for detailed characterization
using rheology, AFM, and SAXS. The five selected all shared PS as
the minority component, with star volume fractions (f
PS) varying between 0.11 and 0.22. All samples showed
clear phase separation, with three of the five adopting a highly ordered
hexagonal packing of cylinders (HPC) confirmed through SAXS and AFM.
The remaining two systems were limited to liquid-like packing of cylindrical
domains (LLP). Longer midblock molecular weights and increased numbers
of arms in the star both showed a propensity to hinder formation of
a highly ordered hexagonal lattice. Increasing the number of arms
in the star also favored transitions to a disordered phase at lower
temperatures when overall S
n
IS
n
molecular weight was held constant. The behavioral
trends identified suggest interfacial packing frustration plays a
prominent role in determining the ability of the system to develop
highly ordered periodic structures. The chain crowding produced by
the PS star architecture intrinsically favors interfacial curvature
toward the majority PI component, contrary to that intrinsically favored
by the block composition alone. In the two systems in which the frustration
was architecturally most severe (largest n of 7.1,
highest M
n,PI of 191 kDa), evolution of
a hexagonal lattice could not be induced, even after significant thermal
annealing. The pom-pom architecture itself also appears to have a
significant impact on entanglement relaxation dynamics, with development
of HPC morphologies only possible at elevated temperatures.
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