title: Different Gelation and Self-Sorting Properties of Two Isomeric Polyamides Owing to the Parallel versus Anti-Parallel Alignment of Backbone Dipoles.
abstract: Two isomeric bottlebrush polyamides P-1 and A-1, with the same repeating monomer dipole units aligned along the polymer backbone in pseudo-parallel and pseudo-antiparallel fashion, respectively, were synthesized and characterized. Both polymers can form thermoreversible gels with aromatic solvents but P-1 was found to show inferior gelation strength compared with 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 through hydrogen bonding, π-π stacking interactions, and side chain interdigitation. The different gelation and self-sorting properties can be explained by the local dipole-dipole interactions originating 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 owing 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.affiliation: Department of Chemistry and Center of Novel Functional Molecules, The Chinese University of Hong Kong, Shatin, NT, Hong Kong SAR, P.R. China.
authors.forename: Chui-Fan
authors.initials: CF
authors.lastname: Leung
authors.affiliation: Department of Chemistry and Center of Novel Functional Molecules, The Chinese University of Hong Kong, Shatin, NT, Hong Kong SAR, P.R. China.
authors.forename: Hak-Fun
authors.identifier: http://orcid.org/0000-0002-7621-0851
authors.initials: HF
authors.lastname: Chow
mesh_terms: D000577:Amides / Q000737:chemistry; D002152:Calorimetry, Differential Scanning; D005782:Gels / Q000737:chemistry*; D006860:Hydrogen Bonding; D007536:Isomerism; D009682:Magnetic Resonance Spectroscopy; D008968:Molecular Conformation; D008970:Molecular Weight; D011108:Polymers / Q000737:chemistry*; D012212:Rheology; D053838:Scattering, Small Angle; D012997:Solvents / Q000737:chemistry; D017550:Spectroscopy, Fourier Transform Infrared; D014961:X-Ray Diffraction
chemical_list: D000577:Amides; D005782:Gels; D011108:Polymers; D012997:Solvents
keywords: dipole-dipole interactions; physical gels; polyamides; self-sorting; supramolecular chemistry