The title polymers, in which both the stem and the graft are biodegradable, have been synthesized for the first time in a one-pot, lipase-catalyzed, graft-polymerization reaction (in bulk, at 70 degreesC) of beta-butyrolactone (beta-BL) and epsilon-caprolactone (epsilon-CL) onto chitin and chitosan. The reactivity order of the lactones was found to be epsilon-CL > beta-BL much greater than gamma-BL (no reaction). All the graft polymers prepared are insoluble in common organic solvents.