Morphological behavior of linear ABC and ABAC Block terpolymers.
2010-05
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Morphological behavior of linear ABC and ABAC Block terpolymers.
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2010-05
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Abstract
An array of fascinating morphologies has been documented in ABC triblock
terpolymers, including four distinct, triply periodic network phases. This thesis
investigates the phase behavior of three terpolymer systems: poly(ethylene-bcyclohexylethylene-
b-dimethylsiloxane) (ECD) triblocks, CECD tetrablocks, and
poly(styrene-b-isoprene-b-styrene-b-ethylene oxide) (SISO) tetrablocks. CECD and SISO
are examples of a previously unexamined block polymer chain architecture: the ABAC
tetrablock. The ABAC architecture provides an additional synthesis strategy for
producing new ordered phases, or expanding the range of stability for a given
microstructure.
A series of ECD triblocks with varying D block length and equal E and C content was
prepared by sequential anionic polymerization and catalytic hydrogenation. Two samples
exhibited order-order transitions from hexagonally arranged spheres of D in C/E lamellae
to O70 (orthorhombic network structure with Fddd space group symmetry) with
increasing temperature. The observation of O70 in the ECD system provides further
evidence of the “universality” of this orthorhombic network structure in triblock
terpolymers. However, the smaller window of stability for O70 in ECD as compared to the previously-studied ISO system suggests that differences in block statistical segment
lengths can greatly affect the equilibrium morphology.
Characterization of CECD and SISO tetrablocks revealed the remarkable effects that
molecular architecture can have on phase behavior. An orthorhombic network structure
with Pnna symmetry (O52) was identified on the basis of small-angle X-ray scattering and
v
transmission electron microscopy between hexagonally packed cylinder and core-shell
cylinder morphologies in a series of CECD terpolymers. Microphase separation of the D
blocks created spherical domains at the junctions of the trivalent connectors that make up
the O52 network topology, while this intriguing morphology was stabilized by the
terminal C chains in the CECD chain architecture. Formation of D spheres could also be
confined within a C/E LAM2 microstructure to create a structure-in-structure morphology
by tuning the CECD composition. In the SISO system, inverted (minority I chains
constituted the matrix) core-shell spheres and cylinders were identified. ISO triblocks
with similar compositions formed LAM2, O70, and three-domain lamellae. These results
again suggested that the ABAC molecular architecture was responsible for a striking
morphological change.
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University of Minnesota Ph.D. dissertation. May 2010. Major: Chemical Engineering. Advisors: Frank S. Bates and Timothy P. Lodge. 1 computer file (PDF); xviii, 283 pages, appendices A-C.
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Bluemle, Michael James. (2010). Morphological behavior of linear ABC and ABAC Block terpolymers.. Retrieved from the University Digital Conservancy, https://hdl.handle.net/11299/91879.
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