Provided are methods for linking polypeptides (including peptides and proteins) to other moieties using radical imitated thiol-ene chemistries, for example, modifying a polypeptide by introducing reactive thiol groups and reacting the thiol groups with olefin-containing reagents or alkyne-containing reagents under conditions that support radical thiol-ene or thiol-yne reactions. The reactive thiol groups have greater activity for radical thiol-ene reactions that a cysteine thiol group, including thiol groups that are separated from the peptide backbone by at least two carbon atoms, for example, the thiol group of a homocysteine residue. Also provided are compositions and biomaterials containing the linked polypeptides, for example, peptide and protein conjugates, and thiol-ene based biocompatible hydrogel polymers, and their uses in the medical field.