Hydrolytically and Reductively Degradable High‐Molecular‐Weight Poly(ethylene glycol)s

Reductively degradable multiblock polymers for gene and drug delivery were synthesised by oxidative polycondensation of poly(ethylene glycol)‐cysteine derivatives containing ester or urethane bonds. Hydrolysis of the polymers at pH = 5.5, 7.4 and 8.0 and reductive degradation with glutathione and dithiothreitol were studied. The hydrolysis rate of polymer esters increased with increase in pH; the hydrolysis of polymer urethanes was negligible. Chemical substitution of the pendant COOH or NH2 groups significantly affected the rate of the polymer degradation. Surface modification of poly(L‐lysine)‐DNA complexes with PEG‐cystine multiblocks led to the formation of reductively degradable nanoparticles. magnified image