pH-Responsive homopolymers and copolymers with naphthoic acid side groups were synthesized via base-assisting living cationic polymerization. To this end, the feasibility of the living cationic polymerization of ethyl 6-[2-(vinyloxy)ethoxy]-2-naphthoate (EVEN) was first examined using a base-assisting initiating system. Et1.5AlCl1.5 as a Lewis acid catalyst induced the living cationic polymerization of EVEN in the presence of ethyl acetate or 1,4-dioxane in CH2Cl2 at 0 degrees C. In contrast, the use of naphthoxyethyl vinyl ether (NpOVE), which is a nonsubstituted counterpart, resulted in a poorly controlled polymerization under these conditions. The presence of the carboxy ester was most likely critical in preventing side reactions. A subsequent alkaline hydrolysis of the side-chain esters quantitatively yielded a carboxy-containing polymer. Aqueous solutions of this polymer underwent pH-driven phase separation at pH 7.0. Well-defined random and block copolymers were also prepared with various functional segments, and their stimuli-responsive behaviors were investigated in terms of solution transmittance and aggregate size. Block copolymers containing two different pH-responsive segments formed micelle-like structures between the two phase-separated pH values, and dual stimuli-responsive copolymers containing a pH-responsive polyacid segment and a thermosensitive segment self-assembled in the water in response to both the pH and temperature. (c) 2013 Wiley Periodicals, Inc.