Comparison of Loading Efficiency between Hyperbranched Polymers and Cross-Linked Nanogels at Various Branching Densities.

The effect of branching point structures and densities is studied between azido-containing hyperbranched polymers and cross-linked nanogels on their loading efficiency of alkynyl-containing dendron molecules. Hyperbranched polymers that contained "T"-shaped branching linkage from which three chains radiated out and cross-linked nanogels that contained "X"-shaped branching linkage with four radiating chains are synthesized in microemulsion using either atom transfer radical polymerization (ATRP) or conventional radical polymerization (RP) technique. Both polymers have similar density of azido groups in the structure and exhibit similar hydrodynamic diameter in latexes before purification. Subsequent copper-catalyzed azide-alkyne cycloaddition reactions between these polymers and alkynyl-containing dendrons in various sizes (G1-G3) demonstrate an order of dendron loading efficiencies (i.e., final conversion of alkynyl-containing dendron) as hyperbranched polymers > nanogels synthesized by ATRP > nanogels synthesized by RP. Decreasing the branching density or using smaller dendron molecules increases the click efficiency of both polymers. When G2 dendrons with a molecular weight of 627 Da are used to click with the hyperbranched polymers composed of 100% inimer, a maximum loading efficiency of G2 in the loaded hyperbranched polymer is 58% of G2 by weight. These results represent the first comparison between hyperbranched polymers and cross-linked nanogels to explore the effect of branching structures on their loading efficiencies.

Chain-growth click polymerization of AB2 monomers for the formation of hyperbranched polymers with low polydispersities in a one-pot process.

Hyperbranched polymers are important soft nanomaterials but robust synthetic methods with which the polymer structures can be easily controlled have rarely been reported. For the first time, we present a one-pot one-batch synthesis of polytriazole-based hyperbranched polymers with both low polydispersity and a high degree of branching (DB) using a copper-catalyzed azide-alkyne cycloaddition (CuAAC) polymerization. The use of a trifunctional AB2 monomer that contains one alkyne and two azide groups ensures that all Cu catalysts are bound to polytriazole polymers at low monomer conversion. Subsequent CuAAC polymerization displayed the features of a "living" chain-growth mechanism with a linear increase in molecular weight with conversion and clean chain extension for repeated monomer additions. Furthermore, the triazole group in a linear (L) monomer unit complexed Cu(I) , which catalyzed a faster reaction of the second azide group to quickly convert the L unit into a dendritic unit, producing hyperbranched polymers with DB=0.83.