From nongelating to gelating: synthesis and structural self-assembling property relationships of a homologous series of oligo(amide-triazole)s.

A homologous series of oligo(amide-triazole)s (OAT) [OAT-CO2H-2 n and OAT-COPrg-(2 n+1)] with an increasing number of primary amide (CONH) and triazole hydrogen-bonding functionalities was prepared by an iterative synthetic procedure. It was found that their self-assembly and thermoreversible gelation strength had a strong correlation to the number of hydrogen-bonding moieties in the oligomers. There also existed a threshold value of the number of CONH units, above which all the oligomers became organogelators. Hence, oligomers with ≤4 CONH units are devoid of intermolecular hydrogen bonding and also non-organogelating, whereas those that contain >4 CONH units show intermolecular association and organogelating properties. For the organogelators, the T(gel) value increases monotonically with increasing number of CONH units. On the basis of FTIR measurements, both the CONH and triazole C-H groups were involved in the hydrogen-bonding process. A mixed xerogel that consisted of a 1:1 weight ratio of two oligomers of different lengths (OAT-CO2H-6 and OAT-CO2H-12) was found to show microphase segregation according to differential scanning calorimetry, thus indicating that oligomers that bear a different number of hydrogen-bonding units exhibited self-sorting to maximize the extent of intermolecular hydrogen bonding in the xerogel state.