Abstract
The effect of 1-alcohols on aqueous solution behavior of polyethylene oxide–polypropylene oxide–polyethylene oxide (PEO–PPO–PEO) triblock copolymers was investigated from cloud point (CP), viscosity, dynamic light scattering (DLS) and 1H NMR. Three triblock copolymers Pluronics® P103, P104 and P105, each having same size middle PPO block but varying PEO end blocks, were used. Short chain alcohols (methanol, ethanol and 1-propanol) increased CP and critical micellization temperature (CMT) while medium chain alcohols (1-butanol, 1-pentanol and 1-hexanol) showed a decrease. The results are explained on the basis of structure and hydrophobicity of alcohols. Short chain alcohols affect by enhancing the hydrogen bonding and hydrophobic hydration while medium chain alcohols replace water molecules from PPO core and induce micelle growth at temperatures close to CP. Nuclear Overhouser Effect Spectroscopy (NOESY) experiments reveal that the P104 chains have significant motional freedom inside the micelles, leading to a folding of the PPO chains towards methyl protons of hydrocarbon chain of C 4–C 6 alcohols molecules in the micelles. The added alcohols can be used to tune the micellization and micellar characteristics of these amphiphilic copolymers.
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