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Click‐Dendronized Poly(amide–triazole)s—Effect of Dendron Size and Polymer Backbone Symmetry on Self‐Assembling and Gelation Properties
Author(s) -
Chow HakFun,
Lau KwunNgai,
Chan ManChor
Publication year - 2011
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201101045
Subject(s) - dendrimer , steric effects , copolymer , monomer , hydrogen bond , polymer chemistry , amide , polymerization , chemistry , polymer , degree of polymerization , intermolecular force , molecule , crystallography , stereochemistry , organic chemistry
Nine dendronized poly(amide–triazole)s 2‐G m G n ( m =1–3, n =1–3), were prepared by the 1:1 copolymerization between AA‐type dendritic diazides 4‐G m ( m =1–3) and BB‐type dendritic diacetylenes 5‐G n ( 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‐G m and 5‐G n 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‐G m G n 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‐G m G n and the previously reported series 1‐G n suggested that the polymer backbone symmetry played a subtle role in controlling their self‐assembling and gelating properties.