The synthesis of novel hybrid hydrogels by stepwise copolymn. of multi-arm vinyl sulfone-terminated poly(ethylene glycol) macromers and a-w cysteine oligopeptides via Michael-type addns. is described. Crosslinking kinetics, studied by in situ rheometry, can be controlled by pH and the presence of charged amino acid residues in close proximity to the Cys, which modulates the pKa of the thiol group. These end-linked networks were characterized by their equil. swelling in water, by their viscoelastic properties in the swollen state, and by their sol. fraction. Structure and properties are sensitive to the prepn. state including stoichiometry and precursor concn. and less sensitive to the pH during crosslinking. For each network the concn. of elastically active chains (n) was calcd. from exptl. detd. sol fractions using Miller-Macosko theory and compared to values obtained from swelling and rheometry studies and by calcn. from Flory's classical network models. Hydrogels were also prepd. with varying macromer structures, and their properties were shown to respond to both macromer functionality and mol. wt. [on SciFinder (R)]