polymers made up of chains , which contain and / or are cross - linked by carbamoyl hydroxamate groups , are prepared by the interaction of hydroxamic acid and isocyanate groups contained in monomeric or polymeric molecules . the resulting polymers are thermally degradable and have utility for the preparation of foamed polymers such as polyurethanes or polyureas . upon heating , the carbamoyl hydroxamate links evolve co 2 and cleave to produce amine and isocyanate groups . the isocyanate groups may be allowed to react with the amine groups , to form n , n &# 39 ; -- disubstituted urea groups , or caused to react with other active hydrogen functions , such as hydroxyls , to form a variety of products , such as polyurethanes .