The use of 1,3-dipolar cycloaddition reactions between azides and alkynes (click chemistry) has been extremely successful as a versatile synthetic tool to construct novel polymeric systems.[1] Whereas the main thrust has been focused on building up highly elaborate polymeric architectures, such as block copolymers, star polymers, dendrimers, and hyperbranched polymers, it is also noted that the physical properties of such poly(triazole)-based materials are little studied.[1c]Additionally, although there are many examples of the synthesis of dendrimers using click chemistry, only a few concern the preparation of dendronized polymers.[2] These are polymers incorporating multiple dendron segments stemming from a linear polymer backbone and are commonly prepared by graft-to, graft-from, or macromonomer polymerization approaches.[3] The major challenges for these approaches are the difficulty in ensuring complete dendron coverage in the graft-to and graft-from strategies, and the sometimes poor polymerization efficiency in the macromonomer strategy. To improve the synthetic efficacy, it is necessary to make use of reactions that offer perfect conversion efficiency (such as click chemistry). Herein we wish to report a) the successful click synthesis of two different series of dendronized polymers (DPs), AmDP1-AmDP3 and EsDP1-EsDP3, from heterobifunctional amide-linked macromonomers (AmM1-AmM3) and ester-linked macromonomers (EsM1--EsM3), respectively, b) the novel and unique organogelation property of one such poly(triazole)-based dendronized polymer AmDP2, c) the remarkable functionalgroup synergistic effect on polymer interchain H-bonding, owing to the placing of many amide functionalities in close proximity along the polymer chain, and most importantly d) that the macromolecular interactions among the dendronized polymer chains are strongly influenced by the size of dendritic appendages and the nature of the linker functionality. To our knowledge, synthesis of dendronized polymers by AB-type macromonomer polymerization has not been reported before. Moreover, although physical organogels based on dendrimers [4] and linear polymers [5] are known, those based on click poly(triazole) polymers [6] and dendronized polymers [7] are extremely rare.The click macromonomer polymerization is basically a step-growth polymerization. Therefore, to achieve a higher degree of polymerization (DP), it must be ensured that the AB-hetero-bifunctional monomers AmM1-AmM3 are of perfect purity and structural homogeneity. For this purpose, we made use of the symmetrical aliphatic hydrocarbon-based Meldrums acids 1-3[8] as our starting materials. Simple functional-group transformations then led to the target amide-linked macromonomers AmM1-AmM3 in good yields and high purities (see Supporting Information). The macromonomers AmM1-AmM3 were then polymerized in the presence of sodium ascorbate and CuSO 4 in a 1:1:1 solvent mixture of THF, DMF, and water at 25 8C for 4 days. To counteract the poor solubility of the products, DMF was added to m...

This Feature Article gives a summary on the conformational and supramolecular properties of a special type of click molecules, namely, main chain and cyclic oligo- and polytriazoles. The triazole ring is an interesting structural motif since it is a hydrogen bond donor and acceptor, a large molecular dipole and also a metal ligand. It can interact with a wide variety of functionalities, e.g. hydrogen bonding partners (e.g. amides or anions), molecular dipoles, and metal ions to generate many fascinating conformational features such as pseudo rod-like, U-turn, helical, double helical structures, beta-strands and beta-sheets. Oligo- and polytriazoles can also exhibit interesting supramolecular attributes such as host-guest complexation, self assembly, chemosensing and gelating properties. It is believed that many new and unique conformational and supramolecular properties can be created by incorporating the correct type of functional group partners into the oligo- and polytriazole backbone. This type of research can also advance our understanding on functional properties of such triazole-rich compounds.

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Nine dendronized poly(amide-triazole)s 2-Gm Gn (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 (1)H 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-Gm Gn was found to decrease with increasing size of the dendron (i.e., 2-G1 G1>2-G1 G2>2-G2 G1≈2-G2 G2>2-G1 G3≈2-G3 G1>2-G2 G3≈2-G3 G2>2-G3 G3). Among the nine polymers, only 2-G1 G2 and 2-G2 G1 were good organogelators for aromatic solvents, while the 2-G2 G2 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-Gm Gn 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.