Extending the Scope of "Living" Crystallization-Driven Self-Assembly: Well-Defined 1D Micelles and Block Comicelles...

Fiber-like block copolymer (BCP) micelles offer considerable potential for a variety of applications; however, uniform samples of controlled length and with spatially tailored chemistry have not been accessible. Recently, a seeded growth method, termed "living" crystallization-driven self-assembly (CDSA), has been developed to allow the formation of 1D micelles and block comicelles of precisely controlled dimensions from BCPs with a crystallizable segment. An expansion of the range of core-forming blocks that participate in living CDSA is necessary for this technique to be compatible with a broad range of applications. Few examples currently exist of well-defined, water-dispersible BCP micelles prepared using this approach, especially from biocompatible and biodegradable polymers. Herein, we demonstrate that BCPs containing a crystallizable polycarbonate, poly(spiro[fluorene-9,5'-[1,3]-dioxan]-2'-one) (PFTMC), can readily undergo living CDSA processes. PFTMC- b-poly(ethylene glycol) (PEG) BCPs with PFTMC:PEG block ratios of 1:11 and 1:25 were shown to undergo living CDSA to form near monodisperse fiber-like micelles of precisely controlled lengths of up to ∼1.6 microm. Detailed structural characterization of these micelles by TEM, AFM, SAXS, and WAXS revealed that they comprise a crystalline, chain-folded PFTMC core with a rectangular cross-section that is surrounded by a solvent swollen PEG corona. PFTMC- b-PEG fiber-like micelles were shown to be dispersible in water to give colloidally stable solutions. This allowed an assessment of the toxicity of these structures toward WI-38 and HeLa cells. From these experiments, we observed no discernible cytotoxicity from a sample of 119 nm fiber-like micelles to either healthy (WI-38) or cancerous (HeLa) cell types. The living CDSA process was extended to PFTMC- b-poly(2-vinylpyridine) (P2VP), and addition of this BCP to PFTMC- b-PEG seed micelles led to the formation of well-defined segmented fibers with spatially localized coronal chemistries.