Crystalline Polymorphism of Alkyl Chains in Supramolecular Complexes of Polyethyleneimine with Octadecanoic Acid

The supramolecular complexes of branched polyethyleneimine and octadecanoic acid (PEI(OA) x ) were prepared vie interfacial reaction and homogeneous solution complexation. The binding mode and the crystalline polymorphism of alkyl chains in PEI(OA) x were investigated by FTIR spectroscopy and WAXS. There are three kinds of OA exist in the complexes, the first one is bound by primary amines through proton transferring, the second one associated with PEI through hydrogen-bonding, and the third one free OA. The crystal structure of alkyl chains in PEI(OA) x is different from that of complexes of linear poly(4-vinylpyridine) and pentadecylphenol reported by G. ten Brinke group. Hexagonal and orthorhombic and triclinic packing of alkyl chains may occur in PEI(OA) x with 0.32 ≤ x ≤ 4.16 and the hexagonal packing still occurs at high content of OA. The ordered packing of alkyl chains is determined by the binding mode of OA in PEI(OA) x as well as the specimen-preparing process.