Phase behaviors of ABAC tetrablock terpolymers
2012-11
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Phase behaviors of ABAC tetrablock terpolymers
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2012-11
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Abstract
The thesis focuses on the composition and the asymmetric effect on the phase
behaviour of the tetrablock terpolymers using poly(styrene-b-isoprene-b-styrene-bethylene
oxide) (SISO) as the model system, synthesized via a living anionic
polymerization method and characterized with NMR, GPC, TEM, SAXS, DSC and DMS.
In the compositional study, two series of the isoprene-rich and the styrene-rich
symmetric SISO samples (the S blocks are divided equally) are studied in addition to the
series with equal volume fractions of the S and I blocks. In the isoprene-rich series, the
hexagonally ordered core-shell spherical and cylindrical morphologies (P6/mmm and
P6/mm space group symmetries) have been identified with increasing O contents. The
temperature dependence is examined using one specimen in the isoprene-rich series near
the order-disorder boundary. A dodecagonal quasicrystalline (QC) phase has been
identified to occur as an intermediate state between the simple hexagonal order (P6/mmm)
and the Frank-Kasper σ-phase ( P /mnm 42 ) before the sample disorders, with THEX < TQC
< Tσ < TODT. The TEM results reveal a QC morphology with a 12-fold rotational
symmetry and the existence of the local dodecagonal quasicrystalline approximants that
lack of any long-range translational order.
The sequence of phases in the styrene-rich SISO series is the disordered state,
spheres with a BCC lattice, liquid-like packed (LLP) spheres and the hexagonally (HEX)
ordered cylinders. For SISO with fO = 11%, LLP, 12-fold QC after shorter annealing time
of 30 minutes and Pm3n phase after longer annealing time of one day, σ-phase and the
disordered states are formed with increasing temperatures; and for another SISO with fO
v
= 15%, the LLP spheres and HEX cylinders are formed. Changing the molecular
architecture from the ISO triblocks to the SISO tetrablocks drives the preference from the
hyperbolic interfaces inherent in the network morphologies to the higher, and zero Gauss,
curvature surfaces present in the core-shell spheres and cylinders.
In the asymmetric study, the asymmetric parameter τ = NS/(NS+NS’) = 0.21 – 0.70 is
the only variable. The core-shell spheres on a hexagonal lattice and LLP have been
observed at lower temperatures; the 12-fold QC phase with shorter annealing time of 30
minutes and the Pm3n phase after longer annealing time of one day have been observed
at intermediate temperatures before the Frank-Kasper σ-phase is formed at the higher
temperatures before the samples disorder. The phase behaviors of the symmetric SISO and the asymmetric SIS’O tetrablock terpolymers are nearly identical.
Overall, six, and possibly more, sphere-forming phases have been identified in the
SISO tetrablock terpolymers: BCC ( Im3m ), LLP, P6/mmm, QC, Pm3n and P /mnm 42
(σ-phase). These phases indicate the great design flexibility and opportunities for the
novel phase formation with the ABA’C tetrablock molecular architecture at various
molecular weights and compositions
Description
University of Minnesota Ph.D. dissertation. November 2012. Major: Chemical Engineering. Advisor: Frank S. Bates. 1 computer file (PDF); x, 225 pages.
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Zhang, Jingwen. (2012). Phase behaviors of ABAC tetrablock terpolymers. Retrieved from the University Digital Conservancy, https://hdl.handle.net/11299/144124.
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