Phase Behavior and Structure of Supramolecules Formed by Poly(4-vinylpyridine) and Fanlike Benzoic Acid Derivative with Long Hydrophobic Tails

We investigated the self-assembly behaviors of supramolecules formed by poly(4-vinylpyridine) (P4VP) and a fanlike small molecule, 3,4,5-tris(hexadecyloxy)benzoic acid (THBA), via hydrogen bonding interactions. Different from other commonly studied small molecules, THBA bears three particularly long hydrophobic tails and tends to form stable crystals by itself, which gives rise to unusual phase behaviors and structures. We used FTIR to investigate the degree of complexation and find that it is not monotonically increased to a plateau with increasing THBA but reaches a maximum and then decreased. This is attributed to the crystallization of excess THBA that induces a debonding of the originally associated THBA. The crystallization-induced dissociation and macrophase separation are further evidenced by DSC and X-ray scattering analyses. Below the orderdisorder transition temperature, a coexistence of lamellae and hexagonally packed cylinders is found in melted P4VP(THBA) supramolecules. After the associated THBA crystallizes, the complexes exclusively form hexagonally packed cylinders due to the bulky tails of THBA, in the absence of the lamellar structure generally seen in other polymer-based supramolecules.