Determination of Block Copolymer Micelle Core T_g Using ¹H NMR Transverse (T₂) Relaxation Measurements of Micelle Coronas

The dynamic properties of poly(ethylene glycol) (PEG) corona chains in block copolymer (BCP) micelles were investigated with H-1 nuclear magnetic resonance (NMR) spectroscopy. The H-1 NMR spectra of BCP micelles show the PEG peak is significantly broadened, which suggests a difference in mobility in PEG segments near to the core and far from the core. H-1 NMR transverse (T-2) relaxation measurements suggest that the overall mobility of the PEG chains in BCP micelles is about 5-10 times slower than that of the fully hydrated PEG segments and is significantly influenced by the glass transition of the micelle core domain. The micelle core glass transition causes an increase in the Arrhenius activation energy, suggesting that the rigid nature of the core domain below T-g increases the energy barrier of rotation of the PEG near to the core domain. Therefore, this study establishes that corona T-2 measurements can be used to determine the micelle core T-g.