American Chemical Society
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Effect of Monomer Structure on the CuAAC Polymerization To Produce Hyperbranched Polymers

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journal contribution
posted on 2016-07-27, 17:49 authored by Xiaosong Cao, Yi Shi, Weiping Gan, Hannah Naguib, Xiaofeng Wang, Robert W. Graff, Haifeng Gao
A series of AB2-R monomers that were composed of one alkynyl group (A), two azido groups (B2), and a dangling group (R) were applied in the copper-catalyzed azide–alkyne cycloaddition (CuAAC) polymerization for synthesis of hyperbranched polymers. Several structural variables, including the linker between the alkynyl group and the diazido unit (S1), the linker between the two azido groups (S2), and the composition of R group, were systematically changed to study their effects on the polymerization kinetics, the molecular weights, and the degree of branching (DB) of the hyperbranched polymers. Within the investigation, all polymerizations eventually showed chain-growth features although their starting moments when exhibiting linear increase of molecular weights based on conversions were delayed by the increased length of S1 linker, but little influenced by S2 and R groups. The AB2-R monomer with longer S1 linker, due to slower hopping of Cu catalysts between neighboring structural units, resulted in more leftover oligomers and decreased overall molecular weights. High DB > 0.75 was achieved in all hyperbranched polymers with various S1 lengths and R groups and slightly influenced by the steric hindrance and the rate of catalyst hopping. Instead, the increase of S2 linker from C2 to C4 lowered the reactivity of the second azido group in linear units and resulted in an evident decrease of the DB from DB = 0.73 to 0.55, respectively.