This observation could be attributed to the hydrophobicity of imidazole
ring at neutral pH [30] (exact analogy is N-alkylimidazole,
which has a similar N-substituted group as imidazole-terminal
PEG), which decreases the compatibility of I-PEG with water and
facilitates its phase separation into ATP. On the contrary, the phaseseparation
of C-PEG ATP is postponed due to the hydrophilic nature
of carboxylic acid terminals. The phase separation of [Bmim]Br ATP
is much difficult comparing with other polymer systems due to the
extreme hydrophilic nature of [Bmim]Br [20,26].