Polymers containing maleimide groups on their side chains have been synthesized by utilization of a novel styrenic monomer containing a masked-maleimide unit. AIBN initiated free radical polymerization and reverse additionfragmentation chain transfer (RAFT) polymerization was utilized for synthesis of copolymers containing masked maleimide groups as side chains. The maleimide groups were unmasked via the retro DielsAlder reaction. Orthogonally functionalizable copolymers were obtained by copolymerization of the maleimide-based monomer with other reactive monomers to yield copolymers that are reactive towards thiol- and amine-containing molecules, or two different thiol-containing molecules sequentially via the nucleophilic thiol-ene and the free-radical thiol-ene click reactions.