Abstract
In this study, the supramolecular complex of 3,5-bis(hexadecyloxyl)benzoic acid (BHBA) and Poly(4-vinylpyridine) (P4VP) via hydrogen bonding is investigated. FTIR was utilized for observing the hydrogen bonding between P4VP and BHBA or in free BHBA dimers. SAXS and WAXS was applied for studying the morphology of supramolecular complex and excess BHBA molecules, and the thermal property and morphology evolution with temperature is studied by DSC and in situ SAXS and WAXS. Due to its two-tailed molecular structure, pristine BHBA forms unique crystalline structure after annealed and lamellar structure after quenched, which both found in P4VP(BHBA)x complexes. Surprisingly, though with formation of supramolecular complex, no ordered structure is found in SAXS profile. The reason is considered as that the steric hindrance of tails of BHBA is too large for lamellar structure, and too weak for hexagonally-packing cylindrical structure. With addition of BHBA, detachment of side chains due to crystallizing competition is observed by FTIR after a saturating plateau and coiling of P4VP due to detachment is also confirmed by SAXS. For P4VP(BHBA)x, where x is the molar ratio of BHBA to 4VP repeating unit, it is found the x = 0.8 is unique point where BHBA is shown excess but does not form carboxylic acid dimer, and the alignment of supramolecular complex is especially less ordered. This is possibly because the amount of excess BHBA is too little for self-aggregating and they insert in BHBA domain in supramolecular complex, thus interfering with the interdigitating between BHBA domains. This is the distinct characteristic of supramolecular complex with two-tailed side chain molecule different from the complexes with single or three-tailed ones.
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