Network formation in ABC triblock copolymers.

摘要

This thesis reports formation of network morphologies in ABC triblock copolymer materials resulting from controlled changes in molecular architecture and chemical composition. Two classes of linear ABC molecules were prepared (via anionic polymerization) in this research—those containing polystyrene (PS), polyisoprene (PI), and polydimethylsiloxane (PDMS), and those containing polystyrene, polyisoprene, and poly(ethylene oxide) (PEO). Morphological characterization included SAXS, TEM, dynamic mechanical spectroscopy, and optical activity measurements.; In the first system, compositionally symmetric (i.e. f _PS ≈ f_PI ≈ f _PDMS), but sequentially distinct PS-PI-PDMS and PI-PS-PDMS molecules were probed for differences in phase behavior near the order-disorder transition (ODT). As a consequence of segment interactions forced by a change in connectivity, ordered-state symmetry and ODT temperatures were different for PS-PI-PDMS and PI-PS-PDMS. Blends of PS-PI-PDMS and PI-PS-PDMS molecules, each with M _w near 104 g/mol, formed gyroid morphologies over a wide range of blend compositions. As unfavorable PS-PDMS segment interactions drove mixing of PS and PI, blend self-assembly resembled that in AB diblock samples.; In the second system, a streamlined synthetic approach enabled efficient production of PI-PS-PEO triblock copolymers having various segment compositions. Within the range 0.10 f_PEO 0.25, three unique network morphologies were identified. Depending on the ratio f_PI/f_PS, core-shell gyroid, orthorhombic network, and alternating gyroid morphologies persist in this range of f_PEO. These results vividly illustrate the superior access to network microstructures in ABC triblock versus AB diblock copolymers.