Amphiphilic ABCA tetrablock copolymers

The focus of this thesis is the morphology of amphiphilic ABCA tetrablock copolymers in the bulk state and in aqueous dispersion. Several model poly(ethylene oxide-b-styrene-b-butadiene-b-ethylene oxide) (OSBO) amphiphilic block copolymers were synthesized by addition of increasing PEO blocks to each end of a PS-PB diblock copolymer. The effects of molecular weight and composition on bulk morphology and aqueous aggregation behavior were investigated using a combination of transmission electron microscopy (TEM), small-angle x-ray scattering, and rheology.; A series of OSBO tetrablock copolymers with increasing amounts of PEO evenly distributed on each end of a symmetric PS-PB (f s ≅ fB) diblock formed morphologies with lamellar symmetry. Layered morphologies existed in the PS-PB diblock and in block copolymers with PEO weight fraction less than 0.52. TEM imaging of these morphologies illustrated subtle shifts in block arrangement as the PEO composition was varied.; Self-assembly of these amphiphilic block copolymers in water resulted in micellar aggregates that progressed in geometry from bilayers to cylinders to spheres as hydrophilic PEO block size was increased in relation to hydrophobic PS and PB blocks. Cryogenic TEM coupled with selective staining of PB domains revealed interesting micelle core structure that was a direct result of molecular architecture. Two varieties of vesicles were found; a thick-walled vesicle with concentric layering of PS and PB domains, and a thin-walled vesicle with azimuthal modulation between PS and PB. Wormlike micelles and spherical micelles with non-centrosymmetric arrangement of PS and PB in the core were observed. Models detailing the arrangement of core blocks were constructed. Segregation of core components facilitated the formation of vesicles and wormlike micelles at higher PEO compositions than in aggregates with mixed cores.; The viscoelastic behavior of each type of aggregate dispersion was summarized and compared. Branched wormlike micelles with continuous glassy PS and rubbery PB domains imparted elastic behavior to the solutions, which was enhanced by free radical crosslinking of PB domains.