The design, synthesis, and post-polymerization functionalization of linear poly(ethylene glycol) (PEG)-based polytriazole copolymers containing thiol-reactive maleimide functional groups as pendant side chains are described. A copper(I)-catalyzed Huisgen-type 1,3-dipolar cycloaddition reaction is utilized to prepare copolymers through a combination of diazide-and dialkyne-functionalized triethylene glycol derivatives, along with a dialkyne-functionalized furan-protected maleimide-containing monomer. After the polymerization, a microwave-assisted retro-Diels-Alder reaction is utilized to unmask the pendant maleimide groups by removal of the furan moieties. Post-polymerization modifications of these PEG-based copolymers containing the furan-protected maleimide group are accomplished using a photoinitiated radical thiol-ene reaction, whereas polymers containing the reactive maleimide group are functionalized using the Diels-Alder and nucleophilic thiol-ene reactions. The nucleophilic thiol-ene reaction is utilized to fabricate hydrogels by treatment of the maleimide-containing PEG polymers with dithiol-containing crosslinkers. Facile functionalization of thus-obtained hydrogels under mild conditions is demonstrated through the treatment of the residual maleimide groups within the hydrogel with a thiol-containing fluorescent dye.