A novel hydrophobic monomer was synthesized from the acetoacetic ester and dodecylamine by condensation reaction in mild conditions. The modification by the dodecyl groups monomer was involved in the Michael addition reaction with acrylic (or methacrylic) acid followed by radical polymerization. Both linear and crosslinked novel betaine-type polyampholytes bearing hydrophobic "tail" and hydrophilic "head" were obtained. The linear polymer was characterized by viscometry, FTIR, and Raman spectroscopy. Swelling-shrinking behavior of linear and crosslinked samples was studied in water-DMF and water-DMSO mixtures. The applicability of hydrophobically modified polybetaines as pour point depressants (fluidity improvers) was also demonstrated. (C) 2004 Wiley Periodicals, Inc.