Hyperbranched polymers represent an intriguing class of shape-persistent soft nanomaterials that could be easily produced in one-pot reaction to obtain highly branched arborescent structures. Although traditional synthesis of hyperbranched polymers suffers from the poorly defined structures and broad molecular weight distribution, recent progress on synthesis methods allows the production of structurally defined polymers in tunable molecular weights, composition and degree of branching. This review summarizes the recent advance on synthesis of hyperbranched polymers and their applications as biomaterials in tissue engineering scaffolds, diagnostic probe carriers and drug delivery fields.

Atom transfer radical polymerization (ATRP), as one of the most successful controlled radical polymerization techniques, has been broadly used by polymer chemists and nonspecialists for synthesis of various functional materials, although the use of copper as traditional catalyst often results in undesired color or properties. The first homopolymerization of an initiable monomer, that is, inimer, is reported via metal‐free ATRP using 10‐phenylphenothiazine (Ph‐PTH) as photocatalyst in both solution and microemulsion media. Although polymerizations of inimers in both media can be carried out, only the microemulsion polymerization of methacrylate‐based inimer 1 effectively confines the random bimolecular reaction within each segregated latex and produces hyperbranched polymers with high molecular weight and low polydispersity. Several experimental parameters in the microemulsion polymerization of inimer 1 are subsequently studied, including the Ph‐PTH amount, the solids content of microemulsion, and the light source of irradiation. The results not only provide an effective method to tune the structure and molecular weights of hyperbranched polymers in confined‐space polymerization, but also expand the toolbox of using metal‐free ATRP method for synthesizing highly branched polymers in controlled manner.

Friedel–Crafts (FC) polycondensation of 1,4-dimethoxybenzene with 4-substituted benzaldehyde species was used to prepare telechelic oligomers and high-molar-mass multisegmented block copolymers.

NMP) [20][21][22][23][24] and reversible addition-fragmentation chain transfer (RAFT) polymerization have been intensively applied in the (co)polymerization of inimers and transmers, primarily in solution, for synthesis of branched polymers with various compositions. For instance, those synthesized by ATRP possess high density of chain-end initiating groups and are easy to extend with vinyl monomers using the same technique. [4,48] However, all the solution (co)polymerizations have been shown to result in broad molecular weight distributions due to the random bimolecular (monomer-monomer, monomer-polymer, and polymer-polymer) reactions. [48] Meanwhile, biphasic dispersed systems, such as microemulsion [49][50][51] emulsion, and miniemulsion, [52] have long been employed in conventional radical polymerization and were recently applied in RDRP techniques, [50,51,53] exhibiting intriguing compartmentalization effects on regulating polymerization kinetics and polymer structures. Previous work by our group established a one-pot method for SCVP of inimer in microemulsion through Activators Generated by Electron Transfer [54] (AGET) ATRP. The key feature in this method was that micelles functioned as confined space to segregate the polymerization of inimers into each discrete nanoparticle, which effectively regulated the polymer-polymer reaction and defined the dispersity of the hyperbranched polymers based on the uniformity of the latexes. [4] Further investigation verified the versatility of the method by using a variety of inimer species carrying different reactive and degradable groups. [5] The utility of these hyperbranched polymers was expanded to the synthesis of seeded two-step one-pot polymerization and produce core-shell structured branched polymers. [6] Herein, we present the first, to the best of our knowledge, one-pot copolymerization of inimer and monomer in confined space, that is, microemulsion, providing a simple framework for producing branched polymers with varied compositions and branching densities, while retaining the same extent of polymer molecular weight. To explore the suitability of copolymerization of monomers with inimers in AGET ATRP microemulsion, a model system was developed, consisting of a monomer and inimer with similar structures and vinyl reactivity. The ratio of monomer to inimer was varied to alter the structural composition while holding constant all other formulation parameters, Branched PolymersAtom transfer radical copolymerization of monomer and inimer (containing initiating and monomer fragments in one molecule) is carried out in a micro emulsion to produce branched copolymers with similar molecular weights but varied branching densities. The monomer 2-(isobutyryloxy) ethyl methacrlyate (IEM) shares a similar structure as the selected inimer 2-(2-bromoisobutylryloxy) ethyl methacrylate (BIEM) and provides microemulsification with little change of micelle size upon varying the molar ratio of monomer to inimer (γ ) from 2 to 50. The copolymerization of IEM and BIEM in the disc...