Recent Progress on Hyperbranched Polymers Synthesized via Radical-Based Self-Condensing Vinyl Polymerization

Abstract

This short review article summarizes recent reports on using controlled radical polymerization (CRP) of inimers (compounds containing initiating group and vinyl group in one molecule) or transmers (compounds containing chain transfer group and vinyl group in one molecule) for the synthesis of hyperbranched polymers. These inimers and transmers that carry numerous functional groups could be homopolymerized, i.e., self-condensing vinyl polymerization, or copolymerized with monovinyl monomers, i.e., self-condensing vinyl copolymerization, using atom transfer radical polymerization (ATRP), nitroxide-mediated polymerization (NMP) or reversible addition fragmentation chain transfer (RAFT) polymerization techniques, producing hyperbranched polymers and hyperstar polymers with tunable molecular weights, compositions and degree of branching. Recent reports that attempted different strategies to regulate polymer–polymer reactions were introduced, demonstrating possible syntheses of hyperbranched polymers with better defined structures and relatively low molecular weight dispersity. Finally, several CRP-produced hyperbranched polymers were discussed on their applications for encapsulation of guest molecules, nanomedicine, diagnostic imaging and catalysis.

Long‐Chain Hyperbranched Polymers: Synthesis, Properties, and Applications

“…Since the discovery of SCVP by Fréchet et al. in 1995, it has undergone very fruitful achievement and serves as one of the most popular techniques in preparing HBPs despite its characteristic of broad polydispersity and ill‐defined structures . In this method, an inimer that is a vinyl monomer possessing a second functional group capable of initiating the polymerization of other vinyl groups is used, and has been expanded for use with various “living” techniques to control the molecular weight distribution of the materials and prevent gelation.…”

“…Wang and coworkers successfully prepared various functional HBPs via the so‐called deactivation ATRP of multi‐vinyl monomers with a high conversion . Gao's group developed a new synthetic method by using confined micellar space in microemulsion to access HBPs with high molecular weight and uniform structure . However, the SCVP process may only lead to the formation of conventional HBPs with short subchains, which was comprehensively reviewed recently by Rimmer and Gao .…”

Ligand effect in the synthesis of hyperbranched polymers via copper‐catalyzed azide‐alkyne cycloaddition polymerization (CuAACP)

“…These results provide an easy method to vary the structure of hyperbranched polytriazole polymers with tunable molecular weights and DB values. We envisage that this method can be easily applied to many other functional monomers, which could enable access of polymers with more sophisticated yet precise structures …”

Detailed Structural Analysis of the Hyperbranched Polymers Formed in Self‐Condensing Vinyl Polymerization

“…The cyclization reaction between the unreacted vinyl group on the focal point unit and A* or B* group within the same HB polymer molecule was not considered. For a CSTR, all connection reactions were assumed irreversible, and for instance, in the case of inimer based on the reversible addition–fragmentation chain transfer (RAFT) polymerization, the vinyl group must be on the R‐group, not the Z‐group . For the controlled radical polymerizations or the reversible‐deactivation radical polymerizations, the irreversible bimolecular termination reactions were not considered in the present reaction model.…”

“…The SCVP employs a special type of monomer (AB*), called inimer, in which the A group represents a vinyl group and the B* group refers to the initiating site. SCVP can be achieved by a wide variety of living/pseudo‐living polymerization techniques, such as living ionic polymerization and reversible‐deactivation radical polymerization …”