Multicompartment micelle morphology evolution in degradable miktoarm star terpolymers

Multicompartment micelles with segmented wormlike structures consisting of alternating poly(ethylethylene) (PEE) and poly(γ-methyl-ω- caprolactone) (PMCL) layers were formed upon dispersing samples of μ-[PEE][poly(ethylene oxide)][PMCL] (μ-EOC) miktoarm star block terpolymers in neutral water. Subjecting these dispersions to a pH 12 aqueous buffer at 50 °C led to the hydrolytic degradation of the PMCL chains. After 4 weeks, the majority of the μ-EOC molecules were degraded into PEE-b-poly(ethylene oxide) (EO) diblocks and PMCL homopolymers. Although the resulting EO diblocks were expected to assemble into simple cylindrical micelles, the actual "daughter micelle" morphologies were much richer. The initial segmented wormlike micelles evolved into raspberry-like vesicle structures composed of spherical PMCL subdomains embedded in a PEE matrix. This dramatic change in the morphology of the multicompartment micelles is due to rearrangement of μ-EOC/EO/PMCL composite micelles to a structure that minimizes unfavorable interfacial interactions between the three mutually immiscible polymers. This type of micelle-to-micelle morphological evolution induced by block degradation in a miktoarm star terpolymer system holds promise for the development of "smart" delivery capabilities.