Ionically Self-Assembled Thermotropic Liquid Crystalline Complexes of Linear Polysiloxane and Dendritic Amphiphiles

A series of polyelectrolyte-dendritic amphiphilic complexes with high degrees of substitution were prepared by ionic self-assembly of the polyelectrolyte poly (3-aminopropyl) methylsilane hydrochloride (PSI) with dendritic 3,4,5-tris(n-alkan-1-yloxy)-benzoic acid potassium salt [(3,4,5)nG1-COOK, n = 8, 10, 12, 14, and 16, where n was the number of carbon atoms in the alkyl tail]. These complexes PSI-(3,4,5)nG1 were characterized with wide-angle X-ray diffraction (WAXD), small-angle X-ray scattering (SAXS), Fourier transform infrared (FT-IR), thermogravimetry (TG), differential scanning calorimetry (DSC), and polarized optical microscopy (POM). WAXD profiles indicated a transition from liquid crystalline (n = 8, 10) to crystalline phase (n = 12, 14, and 16) in the PSI-(3,4,5)nG1 resulted from the dendritic amphiphiles at room temperature. PSI-(3,4,5)nG1 (n = 8, 10) were found to be in the hexagonal columnar (Phi(h)) liquid crystalline phase, with the lattice parameter a = 3.05, 3.35 nm for n = 8, 10, respectively. On the other hand, PSI-(3,4,5)nG1 (n = 12, 14, and 16) formed end-to-end bilayer lamellar crystalline structures with the long periods d = 4.56, 5.04, and 5.68 nm for n = 12, 14, 16, respectively, at room temperature. An ionic thermotropic liquid crystalline state was obtained from PSI-(3,4,5) nG1 at temperatures: (a) below the clearing point T-i (n = 8, 10), and (b) between the melting point T-m and T-i (n = 12, 14, and 16). This research provides an easy way to obtain complexes with high degrees of substitution through the self-assembly of the linear polysiloxane and dendron amphiphiles, and demonstrates that the alkyl tail lengths of the bound dendritic amphiphiles play an important role in determining the mesomorphous structure for the polyelectrolyte-dendritic amphiphile complexes.