Alternating degradable copolymers consisting of a vinyl ether (VE) unit with an ionic liquid-type moiety and a conjugated aldehyde were synthesized by living cationic copolymerization and subsequent modification. The alternating copolymers exhibited upper critical solution temperature (UCST)-type phase separation behavior in water like the corresponding ionic liquid-type VE homopolymers. In addition, the copolymers exhibited lower critical solution temperature (LCST)-type phase separation behavior in acetone. Both the UCST- and LCST-type thermosensitive behaviors were most likely induced by the interpolymer electrostatic interactions among the pendant ionic liquid-type groups. The alternating copolymers were completely degraded by acid hydrolysis because of the cleavage of the acetal linkages, generated through the crossover reaction from VE to aldehyde, in the main chain.