Formation of disk- and stacked-disk-like self-assembled morphologies from cholesterol-functionalized amphiphilic polycarbonate diblock copolymers

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A cholesterol-functionalized aliphatic cyclic carbonate monomer, 2-(5-methyl-2-oxo-1,3-dioxane-5-carboxyloyloxy)ethyl carbamate (MTC-Chol), was synthesized. The organocatalytic ring-opening polymerization of MTC-Chol was accomplished by using N-(3,5-trifluoromethyl)phenyl-N′-cyclohexylthiourea (TU) in combinations with bases such as 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) and (-)-sparteine, and kinetics of polymerization was monitored. By using mPEG-OH as the macroinitiator, well-defined amphiphilic diblock copolymers mPEG113-b-P(MTC-Chol)n (n = 4 and 11) were synthesized. Under aqueous conditions, these block copolymers self-assembled to form unique nanostructures. Disk-like micelles and stacked-disk morphology were observed for mPEG113-b-P(MTC-Chol)4 and mPEG113-b-P(MTC- Chol)11, respectively, by transmission electron microscopy (TEM). Small-angle neutron scattering supports the disk-like morphology and estimates the block copolymer micelle aggregation number in the dispersed solution. The hydrophobic nature of the cholesterol-containing block provides a versatile self-assembly handle to form complex nanostructures using biodegradable and biocompatible polymers for applications in drug delivery. © 2013 American Chemical Society.