Low Length Dispersity Fiber-Like Micelles from an A-B-A Triblock Copolymer with Terminal Crystallizable Poly(ferrocenyldimethylsilane) Segments via Living Crystallization-Driven Self-Assembly

Solution self-assembly of a linear ABA triblock copolymer with two terminal crystallizable poly(ferrocenyldimethylsilane) (PFS) core-forming "A" blocks and a central poly(dimethylsiloxane) (PDMS) corona-forming "B" block has been investigated. The low dispersity (D = 1.05) copolymer, PFS₂₆-b-PDMS₅₈₄-b-PFS₂₆ (block ratio 1.0:22.5:1.0), was prepared through a combination of living anionic polymerization and end-to-end coupling. The block ratio and dispersity were established by a combination of MALDI-TOF mass spectrometry, ¹H NMR, and GPC. Individual 1D fiber-like micelles with looped PDMS coronas were formed in mixed solvents of hexane and decane. Low length-dispersity fiber-like micelles of controlled length were prepared from short seed micelles of PFS₂₆-b-PDMS₅₈₄-b-PFS₂₆ derived from sonication using the seeded growth method termed living crystallization-driven self-assembly. In addition, seeded growth of blends of both PFS₂₆-b-PDMS₅₈₄-b-PFS₂₆ and PFS₂₆ homopolymer and of PFS₂₆-b-PDMS₅₈₄-b-PFS₂₆ and the analogous diblock copolymer PFS₂₆-b-PDMS₂₉₂ were also explored. Large aggregates with fiber-like protrusions were formed by spontaneous nucleation of the blends of PFS₂₆-b-PDMS₅₈₄-b-PFS₂₆ and PFS₂₆. High-aspect ratio ribbon-like micelles were formed by adding the blends of PFS₂₆-b-PDMS₅₈₄-b-PFS₂₆ and PFS₂₆ to the cylindrical PFS₂₆-b-PDMS₅₈₄-b-PFS₂₆ seeds. In contrast, surprisingly, seeded growth of blends of PFS₂₆-b-PDMS₅₈₄-b-PFS₂₆ and PFS₂₆-b-PDMS₂₉₂ or the individual components using seeds of either PFS₂₆-b-PDMS₅₈₄-b-PFS₂₆ or PFS₂₆-b-PDMS₂₉₂ showed that growth was only detected in the case of matching of the seed and multiblock copolymer chemistries.