Synthesis of functional polymers with controlled architecture by CRP of monomers in the presence of cross-linkers: From stars to gels

Recent developments in the synthesis of functional polymers with controlled architecture and site-specific functionality via applying controlled radical polymerization (CRP) techniques are reviewed. Particular emphasis is placed on the strategy of employing divinyl cross-linkers to introduce branching points into polymer chains during the copolymerization procedures. By rational selection of initiator, monomer and divinyl cross-linker and their polymerization sequence, star-like polymers with a cross-linked core but various arm compositions and site-specific functionalities are formed. In contrast, concurrent copolymerization of both monomer and cross-linker generates “randomly” branched polymers or gels. As compared to the conventional radical copolymerization procedures, the copolymerization of cross-linker in CRP processes shows retarded gelation behavior and produced branched polymers and/or gels with more homogeneous structure and preserved chain-end functionality. This is because of the fast initiation and quick reversible deactivation reactions in CRPs. Progress related to other synthetic strategies to introduce branching points in polymer chains is also discussed, including the use of a multifunctional initiator, the use of a multifunctional coupling agent (MCA) by click reactions, and the use of an AB* inimer.