Synthesis, Molecular Characterization, and Phase Behavior of Miktoarm Star Copolymers of the AB_<i>n</i> and A_<i>n</i>B (<i>n</i> = 2 or 3) Sequences, Where A Is Polystyrene and B Is Poly(dimethylsiloxane)

Abstract

Novel miktoarm star copolymers of polystyrene[poly(dimethylsiloxane)n] or PS(PDMS)n (n = 2 or 3) type as well as of the inversed sequence, namely, (polystyrene)n[poly(dimethylsiloxane)] or (PS)nPDMS (n = 2 or 3), were synthesized by combining living anionic polymerization with chlorosilane chemistry. The miktoarm star copolymers were extensively characterized through size exclusion chromatography, vapor pressure/membrane osmometry, proton nuclear magnetic resonance, and differential scanning calorimetry, in order to verify the successful synthesis. All samples with varying volume fractions and narrow dispersity indices (D̵ < 1.1) were morphologically characterized by transmission electron microscopy and small-angle X-ray scattering, in order to study their self-assembly behavior as well as to examine the effect of the complex architecture on the final adopted morphologies. For specific PS(PDMS)n (n = 2 or 3), morphologies different from those expected from theoretical predictions (self-consistent field theory or Gaussian statistics) were obtained, while for the inversed sequences, namely, (PS)nPDMS (n = 2 or 3), no discrepancies were evident. This fact further confirmed the impact of the number of arms as well as the flexibility of the segments (PS being stiffer than PDMS) on the structure/property relationship.