Crystallization-Driven Solution Self-Assembly of μ-ABC Miktoarm Star Terpolymers with Core-Forming Polyferrocenylsilane Blocks

A comparative study of the solution self-assembly behavior of two polystyrene-arm-polyisoprene-arm-polyferrocenylsilane (mu-SIF) miktoarm star terpolymers of similar composition has been conducted: one with a short, atactic, noncrystallizable poly(ferrocenylethylmethylsilane) (PFEMS) block (mu-SIFa) and one with a short, crystallizable poly(ferrocenyldimethylsilane) (PFDMS) block (mu-SIFc). Both solvent composition and the amorphous/crystallizable nature of the polyferrocenylsilane (PFS) block exhibited a profound influence on the morphologies of the micelles obtained. In hexane, the formation of uniform spherical micelles with an amorphous, phase-mixed PS/PFS core was observed for both mu-SIFa and mu-SIFc. The introduction of cyclohexane (a theta-solvent for PS at 34.5 degrees C) to give a 1:1 cyclohexane/hexane (v/v) solvent composition resulted in the formation of distorted spherical micelles with a core composed of phase-separated PS and PFS, for both mu-SIFa and mu-SIFc. Interestingly, the distorted spherical micelles formed from crystallizable mu-SIFc evolved with time into elongated fiber-like structures with a phase-separated PS and PFDMS core, while the noncrystallizable counterpart, mu-SIFa, remained as distorted spheres. It was found that in ethyl acetate, a good solvent for PI and PS, mu-SIFa remained unimeric in solution, whereas mu-SIFc formed cylindrical micelles composed of a crystalline PFDMS core and a phase-separated, patchy, PS and PI corona. Finally, seeded growth of mu-SIFc from short, cylindrical PFDMS-b-PDMS seeds (PDMS = polydimethylsiloxane) was demonstrated, yielding BAB block comicelles where outer segments derived from mu-SIFc blocks bore a strong resemblance to that ultimately formed under conditions of homogeneous nucleation.