Length Control and Block-Type Architectures in Worm-like Micelles with Polyethylene Cores

Abstract

We present evidence for "living"-like behavior in the crystallization-driven self-assembly of triblock copolymers with crystallizable polyethylene middle blocks into worm-like crystalline-core micelles (CCMs). A new method of seed production is introduced utilizing the selective self-assembly of the triblock copolymers into spherical CCMs in appropriate solvents. Seeded growth of triblock copolymer unimers from these spherical CCMs results in worm-like CCMs with narrow length distributions and mean lengths that depend linearly on the applied unimer-to-seed ratio. Depending on the applied triblock copolymer, polystyrene-block-polyethylene-block-polystyrene (SES) or polystyrene-block-polyethylene-block-poly(methyl methacrylate) (SEM), well-defined worm-like CCMs with a homogeneous or patch-like corona, respectively, can be produced. In a subsequent step, these worm-like CCMs can be used as seeds for the epitaxial growth of a different polyethylene containing triblock copolymer. In this manner, ABA-type triblock co-micelles containing blocks with a homogeneous polystyrene corona and those with a patch-like polystyrene/poly(methyl methacrylate) corona were prepared. While the epitaxial growth of SEM unimers from worm-like SES CCMs with a homogeneous corona yields triblock co-micelles almost quantitatively, the addition of SES unimers to patchy SEM wCCMs results in a mixture of ABA- and AB-type block co-micelles together with residual patchy wCCMs. Following reports on self-assembled block-type architectures from polymers containing core-forming polyferrocenylsilane blocks, these structures represent the first extension of the concept to block co-micelles from purely organic block copolymers.