Crystallization-Driven Self-Assembly of Amphiphilic Triblock Terpolymers With Two Corona-Forming Blocks of Distinct Hydrophilicities

We report the synthesis and studies of self-assembly in solution of two related polyferrocenyldimethylsilane (PFS) ABC triblock terpolymers (TTPs), in which the BC blocks are amphiphilic comb diblock copolymers, PFS₂₇-b-POEGMA₁₈₀-b-PTDMA₁₇₈ and PFS₂₇-b-PTDMA₁₈₁-b-POEGMA₁₆₆. The subscripts refer to the mean degrees of polymerization. Crystallization-driven self-assembly of these TTPs was studied in four alcohol solvents of decreasing polarity. Poly­(tetradecyl methacrylate) (PTDMA) has limited solubility in 1-butanol below 45 °C, whereas POEGMA exhibits upper critical solution temperature (UCST) behavior in 1-hexanol (27 °C), 1-octanol (38 °C), and 1-decanol (42 °C). Consequently, the corona component below its UCST would be in a collapsed or microphase-separated state. PFS₂₇-b-POEGMA₁₈₀-b-PTDMA₁₇₈ dissolved in hot 1-hexanol, 1-octanol, and 1-decanol and formed long rodlike micelles upon cooling. Micelle fragments generated by sonication served as seeds for both seeded growth and self-seeding experiments, leading to rodlike micelles of uniform length. PFS₂₇-b-PTDMA₁₈₁-b-POEGMA₁₆₆ exhibited similar behavior in 1-butanol. The characteristic that these experiments have in common is that the outer block of the corona exhibits good solubility in the medium. PFS₂₇-b-PTDMA₁₈₁-b-POEGMA₁₆₆ in the more hydrophobic alcohols behaved differently. Seeded growth experiments led to raftlike objects made up of 5–10 rodlike micelles of similar length, lined up side-by-side. The length of the rods, and hence the length of the rafts, increased linearly with the unimer-to-seed ratio. Self-seeding experiments with these micelle fragments, particularly in 1-octanol and 1-decanol, also led to raftlike objects built up from uniform rodlike micelle building block. We propose a model for raft formation based on the idea that at T < UCST for the outer POEGMA block, there is an attractive interaction between the corona blocks of the micelles. This attraction is strong enough to promote association but not strong enough to lead to precipitation. Parallel alignment of the adjacent micelles of similar length maximizes the interaction between them.