Morphological behavior of linear ABC and ABAC Block terpolymers.

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.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