Solubilization and location of phenol and benzene in a nonlinear amphiphilic EO–PO block copolymer micelles: 1H NMR and SANS studies

Abstract

The aqueous solution behavior of a poly(ethylene oxide)–poly(propylene oxide), PEO–PPO, star block copolymer Tetronic® T904 with solubilized phenol and benzene was examined by cloud point (CP), viscosity measurements, 1D and 2D NMR experiments, dynamic light scattering(DLS), and small angle neutron scattering (SANS) techniques. Both the solubilizates decreased the CP and the critical micelle temperature (CMT) of T904. This behavior is explained in terms of the free energy of hydration of the phenol/benzene and the replacement of water molecules from the PPO and PEO blocks by the formation of hydrogen bonds which induced micellization and phase separation at lower temperature. The effect of solubilizates on micellar growth was investigated by viscosity and DLS. Benzene molecules solubilized in T904 micelles are found in intimate contact with the PEO chain while we find that the phenol molecules are located within micelle palisade layer as well as at the micelle–water interface. The SANS data indicate that these solubilizates significantly influence the solution behavior of the copolymer; the structure of micelles stays essentially constant as a function of solubilizate concentration. On the other hand, the shell thickness changes rapidly with phenol concentration. The results showed that phenol decreased CP/CMT and had a more pronounced effect on micellar growth as compared to benzene.