Synthesis of hyperbranched polymers with controlled structure

Hyperbranched polymers (HBPs) are highly branched macromolecules with 3-dimensional globular structures, which have unique properties, such as low viscosity, high solubility, and a large number of terminal functional groups compared to linear analogues. They are easily prepared by the polymerization of an ABx monomer in which A and B represent two different functional groups. This facile one-pot synthesis is advantageous over the synthesis of a dendrimer which requires multi-step reactions. For the HBPs, the degree of branching (DB) is one of the most important intrinsic parameters as well as the molecular weight distribution, which has a significant influence on the physical and chemical properties of the polymeric materials. The DB is theoretically ∼50% for a polymer derived from an AB2 monomer; this value is assumed based on the equal reactivity of the two B functional groups of the AB2 monomer. Recently, several groups have successfully achieved a 100% DB, which is a characteristic property of dendrimers, by using several strategies. Moreover, HBPs with a controlled DB from 0 to 100% have been reported by changing the rate constants of the first reaction of B and the second one toward an A functional group. In addition, the molecular weight and molecular weight distribution of the HBPs can also be controlled. In this review, we focus on the recent progress in the synthesis of HBPs in order to control their structures, i.e., 100% DB, molecular weight and molecular weight distribution (≤1.1).