Showing papers by "Marc A. Hillmyer published in 1996"

Synthesis and Characterization of Model Polyalkane−Poly(ethylene oxide) Block Copolymers

Abstract: We describe the preparation of a new set of amphiphilic block copolymers with well-defined molecular weights and block volume fractions. The synthesis of a variety of polyalkane−poly(ethylene oxide) block copolymers was accomplished by a new polymerization−hydrogenation sequence. Initially, anionic polymerization of either butadiene or isoprene was performed followed by end capping with ethylene oxide. The resulting hydroxyl-terminated polydienes were catalytically hydrogenated to give the corresponding hydroxyl-terminated polyalkanes. These polymeric alcohols were then titrated with potassium naphthalenide to yield the analogous potassium alkoxides. This type of macroinitiator was employed in the polymerization of ethylene oxide. Seventeen polyalkane−poly(ethylene oxide) block copolymers were prepared in near quantitative yields with molecular weights ranging from (1.4 to 8.7) × 103 and poly(ethylene oxide) volume fractions ranging from 0.29 to 0.73. These polymers are model materials for block copolymer...

Complex Phase Behavior in Solvent-Free Nonionic Surfactants

Abstract: Unsolvated block copolymers and surfactant solutions are “soft materials” that share a common set of ordered microstructures. A set of polyethyleneoxide-polyethylethylene (PEO-PEE) block copolymers that are chemically similar to the well-known alkane-oxyethylene (CnEOm) nonionic surfactants was synthesized here. The general phase behavior in these materials resembles that of both higher molecular weight block copolymers and lower molecular weight nonionic surfactant solutions. Two of the block copolymers exhibited thermally induced order-order transitions and were studied in detail by small-angle scattering. The fundamental microstructural spacing was determined to be a crucial parameter in these transitions. Transitions from one ordered state to another occur only when the lattice spacing is nearly matched. These materials highlight the importance of epitaxy and molecular conformation in the phase transformations of soft material.