Formation of Disk- and Stacked-Disk-like Self-Assembled Morphologies from Cholesterol-Functionalized Amphiphilic Polycarbonate Diblock Copolymers

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 mPEG(113)-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 mPEG(113)-b-P(MTC-Chol)(4) and mPEG(113)-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.