Sequential and single-step, one-pot strategies for the transformation of hydrolytically degradable polyesters into multifunctional systems

Because of the significant interest in synthetic polymer systems with increasing degrees of complexity, we have focused attention upon the development of chemistries for the conversion of polyester backbones into functional materials. Facile conjugation strategies involving the reactions of both aminooxy and sulfonyl hydrazide nucleophiles with poly(epsilon-caprolactone-co-2-oxepane-1,5-dione) (P(CL-co-OPD)) are studied as general methodologies employing a sequential vs a single-step approach. Agreement between product and feed stoichiometries was achieved with both of the model hydroxylamines, O-dodecylhydroxylamine or O-benzylhydroxylamine. However, when sequential reactions were performed with either hydroxylamine together with dansyl hydrazide, considerable deviations in the product composition, relative to the reaction feed stoichiometries, were noted. For a sequential series of reactions, the successful use of aminooxy and sulfonyl hydrazide molecules required ketoxime ether formation prior to sulfonyl hydrazone formation to ensure the maximum retention of the ligand linkages throughout the process. Multigraft polymers, produced by the single-step method using exclusively aminooxy compounds with an excess of backbone ketone units, were efficient and had observed incorporation ratios in agreement with reaction stoichiometry. The incorporation of dansyl hydrazone linkages in this one-pot, single-step method suffered from low coupling efficiency, as was observed also in the sequential reactions.