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Differential Gelation and Self‐Sorting Properties of Two Isomeric Polyamides Due to the Parallel vs Anti‐Parallel Alignment of Backbone Dipoles

Two isomeric bottlebrush polyamides P‐1 and A‐1 having the same repeating monomer dipole units aligned along the polymer backbone in pseudo‐parallel and pseudo‐anti‐parallel, respectively, were synthesized and characterized. Both polymers can form thermoreversible gels with aromatic solvents but P‐1 was found to show inferior gelation strength as compared to that of A‐1. Furthermore, despite their close structural resemblance, a 1:1 mixture of the P‐1 and A‐1 polymers was shown to exhibit self‐sorting in the gel state. Gel formation was found to be a kinetically trapped process via H‐bonding, π−π stacking interactions and side chain interdigitation. The differential gelation and self‐sorting properties can be explained by the local dipole‐dipole interactions originated from the different modes of backbone dipole alignment. In single gel systems, the antiparallel‐aligned dipoles in A‐1 facilitated a more compact molecular packing due to the enthalpically more favorable polymer chain association. On the other hand, the parallel‐aligned dipoles in P‐1 gave rise to a less stable head‐to‐head packing, which had difficulties to convert to the more stable head‐to‐tail packing in a kinetically trapped environment. In the mixed gel system, it is the unfavorable hetero‐polymer mismatch dipole‐dipole interaction that inhibited the mixing of the A‐1 and P‐1 polymers and led to self‐sorting.

Authors:   Chui-Fan Leung, Hak-Fun Chow
Journal:   Chemistry - A European Journal
Year:   2017
Pages:   n/a
DOI:   10.1002/chem.201605819
Publication date:   14-Feb-2017
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