A novel class of heterocyclic polymers and copolymers containing the 2-imidazolin-5-one ring structure is described. These polymers are prepared by reaction of bisazlactones and diamines, with or without suitable condensation monomers; the resultant polyamides are then thermally cyclodehydrated in the presence of a catalyst to produce the imidazolinone-containing polymers. Many of the poly(imidazolinones) are water soluble and therefore find utility in various aspects of water treatment, or in paper or fabric sizing.