Synthesis of AB3-Type Miktoarm Star Polymers with Steroid Core via a Combination of "Click" Chemistry and Ring Opening Polymerization Techniques

Well-defined AB(3)-type miktoarm star-shaped polymers with cholic acid (CA) core were fabricated with a combination of click chemistry and ring opening polymerization (ROP) methods. Firstly, azide end-functional poly(ethylene glycol) (mPEG), poly(methyl methacrylate) (PMMA), polystyrene (PS), and poly(epsilon-caprolactone) (PCL) polymers were prepared via controlled polymerization and chemical modification methods. Then, CA moieties containing three OH groups were introduced to these polymers as the end groups via Cu(I)-catalyzed click reaction between azide end-functional groups of the polymers (mPEG-N-3, PMMA-N-3, PS-N-3, and PCL-N-3) and ethynyl-functional CA under ambient conditions, yielding CA end-functional polymers (mPEG-Cholic, PMMA-Cholic, PS-Cholic, and PCL-Cholic). Finally, the obtained CA end-capped polymers were employed as the macroinitiators in the ROP of epsilon-caprolactone (epsilon-CL) yielding AB(3)-type miktoarm star polymers (mPEG-Cholic-PCL3, PMMA-Cholic-PCL3, and PS-Cholic-PCL3) and asymmetric star polymer [Cholic-(PCL)(4)]. The chemical structures of the obtained intermediates and polymers were confirmed via Fourier transform infrared and H-1 nuclear magnetic resonance spectroscopic techniques. Thermal decomposition behaviors and phase transitions were studied in detail using thermogravimetric analysis and differential scanning calorimetry experiments. (c) 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014, 52, 3390-3399