The effects of acyl chain length on the micelle properties of poly(ethylene oxide)-block-poly(N-hexylL-aspartamide)-acyl conjugates

Abstract

Derivatives of poly(ethylene oxide)-block-poly(β-benzyl-aspartate), 12 :25 have been prepared via aminolysis of the benzyl protecting group with 6-amino-1-hexanol, followed by subsequent acylation with acetic anhydride, hexanoic acid, lauric acid, or stearic acid. A series of amphiphilic diblock copolymers based on poly(ethylene oxide)-block-poly(N-hexyl-aspartamide)-acyl conjugates with various acyl chain lengths have been prepared. The extent of esterification was determined by 1H-NMR. Aqueous micelle solutions were prepared by a dialysis method and the polymer series was characterized as a function of the acyl chain length. Transmission electron microscopy and dynamic light scattering revealed micelle-like structures of nanoscopic dimensions (< 100 nm). Environmentally sensitive fluorescent probes were loaded into the micelles in order to study the properties of the hydrophobic microdomain and to determine the critical micelle concentration (CMC). Steady-state fluorescence measurements indicated that the relative apparent core viscosity and polarity are modulated by the relative length of the attached acyl chains, as is the CMC. Increasing the acyl chain length results in a decreased CMC and a more viscous and less polar core region. Carefully chosen chemical moieties can be introduced in order to influence the properties of the poly(L-Asp) blocks of the micelles. As a result, the micellar properties can be altered via chemical modification in order to impact several key properties relevant to drug delivery.