¹H NMR Spectroscopic Investigations on the Micellization and Gelation of PEO−PPO−PEO Block Copolymers in Aqueous Solutions

Abstract

The effects of temperature, polymer composition, and concentration on the micellization and gelation properties of poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (PEO-PPO-PEO) block copolymers in aqueous solutions were investigated by 1H NMR spectroscopy. It was found that the temperature-dependent behavior of PPO blocks, observed as changes in chemical shift, half-height width, and integral value, could be attributed as an intrinsic tool to characterize the transition states during unimer to micelle formation. The 1H NMR spectral analysis revealed that the hydrophobic part, PPO, of the Pluronic polymers plays a more significant role in the temperature-induced micellization, whereas the transitional behavior of Pluronic polymer, i.e., from micellization to liquid crystals formation, resulted in the drastic broadening of the spectral signals for the PEO, indicating that the PEO segments play a more significant role in the crystallization process. It was also observed that the temperature-dependent changes in the half-height width of the PEO -CH2- signal are sensitive to the liquid crystalline phase formation, which could be attributed to the close packing of spherical micelles at high polymer concentrations or temperatures.

Solubilization of Aromatic Hydrocarbons in Ethylene Oxide‐Propylene Oxide Triblock Micelles: Location of Solubilizate and its Effect on Micelle Size from 2D NMR and Scattering Techniques

“…The block copolymers TBCP30, TBCP40 and TBCP50 (1%) had CMTs of 20.7, 21.6 and 24.5°C, respectively ( Fig. 1) which are in agreement with previous literature values obtained from other methods [40,41]. The CMT values were low for copolymers with low %PEO which is quite expected.…”

Mechanism of PEO–PPO–PEO micellization in aqueous solutions studied by two-dimensional correlation FTIR spectroscopy

“…The conformational changes of EO segments of PEO-PPO-PEO block copolymers during micellization were validated by FTIR, FT-Raman and NMR studies [14,[32][33][34]. The 2D spectra of Pluronics give further information about the sequence of the two types of conformations: nonpolar conformation changed before polar conformation of EO segments during the heating process.…”

A concise analysis of the effect of temperature and propanediol-1, 2 on Pluronic F127 micellization using isothermal titration microcalorimetry

“…The CMC of Pluronics is a widely studied phenomenon: it has been determined using various techniques such as surface tension measurements [3], Fourier transformed infrared spectroscopy [4,5], 1 H NMR relaxation studies [6,7], dynamic light scattering, fluorescence spectroscopy [8], and differential scanning microcalorimetry which allows determination of the enthalpy change related to the micellization process from integration of the heat capacity versus the temperature [9,10]. These experiments also provide the onset temperature for micellization, i.e., the CMT.…”