Click-Dendronized Poly(amide-triazole)s-Effect of Dendron Size and Polymer Backbone Symmetry on Self-Assembling and Gelation Properties

Nine dendronized poly(amide-triazole)s 2-GmGn (m = 1-3, n = 1-3), were prepared by the 1: 1 copolymerization between AA-type dendritic diazides 4-Gm (m = 1-3) and BB-type dendritic diacetylenes 5-Gn (n = 1-3) under the copper(I)-mediated click coupling conditions. The degree of polymerization value of the polymers was found to range from 15-50, and decreased with increasing size of the dendron, suggesting steric hindrance had a retardation role on the copolymerization efficiency. Based on FT-IR and H-1 NMR studies, it was found that significantly strong, interchain hydrogen bonding between the amide units was present in the solution state after copolymerization, whereas the monomers 4-Gm and 5-Gn were devoid of any intermolecular hydrogen-bonding interaction. Hence a positive allosteric hydrogen-bonding effect was observed after polymerization, and could be rationalized by the zip effect. The strength of the interchain association in polymers 2-GmGn was found to decrease with increasing size of the dendron (i.e., 2-G1G1>2-G1G2>2-G2G1 approximate to 2-G2G2>2-G1G3 approximate to 2-G3G1>2-G2G3 approximate to 2-G3G2>2-G3G3). Among the nine polymers, only 2-G1G2 and 2-G2G1 were good organogelators for aromatic solvents, while the 2-G2G2 polymer, bearing the closest structural resemblance to the previously reported organogelator 1-G2 prepared from the polymerization of AB-type monomers, was devoid of gelating power. Careful analysis of structures of the present polymer series 2-GmGn and the previously reported series 1-Gn suggested that the polymer backbone symmetry played a subtle role in controlling their self-assembling and gelating properties.