We report unusual thermoresponsive behaviors of one poly(N-isopropylacrylamide) (PNIPAm)-based diblock copolymer containing carboxylic azo moieties due to the introduction of one charged end-group. On heating, the ionized end-group prevented macroscopic phase separation of the block copolymer aqueous solution under basic conditions, leading to the absence of cloud point. The micelle solution showed a quick micelle-to-vesicle morphological transition via the end-group stabilized large micelles as a transition state when being stored at 50 degrees C for 2 h. Such a quick micelle-to-vesicle transition can be attributed to the joint effect of the charged end-group stabilization and the changed hydrophilic-hydrophobic balance of PNIPAm. When adding a tiny amount of Ca2+, macroscopic phase transition reoccurred by breaking the end-group protection layer. This study represents a unique separation of microscopic dehydration and macroscopic phase transition, providing a new way for design of stimuli-responsive polymers.