Mesomorphous Structure Change Induced by Binding Site Difference in Ionic Complexes of Linear Polymers and Dendritic Amphiphiles

Abstract

Ionic complexes of linear poly(ethylenimine) (lPEI) and poly(allylamine hydrochloride) (PAH) with 3,4,5-tris(n-alkan-1-yloxy)benzoic acid [(3,4,5)nG1-COOH, n = 8, 10, 12, where n is the number of carbon atoms in the alkyl tail) or 3,4,5-tris[(p-(n-dodecan-1-yloxy)benzyloxy]benzoic acid [(4-3,4,5)12G1-COOH] dendrons [or the corresponding potassium salts (3,4,5)nG1-COOK and (4-3,4,5)12G1-COOK] were prepared. The complexes were characterized with XRD, FTIR, TG, DSC, and polarized optical microscopy (POM). The complexes of lPEI-(3,4,5)nG1 were found to be in the lamellar smectic A or C (SmA and SmC) phase, while the PAH-(3,4,5)nG1 complexes were in the hexagonal columnar (Φh) phase. All of these complexes were in the ionic thermotropic liquid crystal state at room temperature because their melting temperature, if had, was much lower. Interestingly, the complexes lPEI-(4-3,4,5)12G1 and PAH-(4–3,4,5)12G1 were also in the same SmA or SmC phase and Φh phase, respectively, regardless of whether there was an additional mesogen unit benzenyloxy moiety (−C6H4CH2O−) in the dendron, increasing the long period and adjustability of the alkyl tails. This study demonstrates that the binding site plays an important role in determining the mesomorphous structure of the polymer−dendritic amphiphile complexes. Furthermore, the PAH complexes exhibited a higher clear point than the corresponding lPEI complexes due to the different binding sites in these two polymers. The alkyl chain length (n ≤ 12) of the dendron and the difference in dendron chemical structure had little effect on the mesomorphous structure and clear point of the polymer−dendritic amphiphile complexes. The present results provide a profound insight into the role of polymer topological structure in controlling the supermolecular structure for the polymer−dendritic amphiphile complexes.