Linear and crosslinked betaine-type poly-ampholytes based on ethyl 3-aminocrotonate and unsaturated carboxylic acids have been synthesized by very fast polymerization in bulk and solution. Bulk polymerization occurred exothermically even at room temperature and without adding an initiator. the polyampholytes showed stimuli-responsive properties with respect to pH, ionic strength, water/organic solvent mixtures, and metal ion complexation.