Fluorophobic effect in the self-assembly of polymers and model compounds containing tapered groups into supramolecular columns

The synthesis and characterization of the tapered building blocks 3,4,5-tris-(1H,1H,2H,2H,3H,3H,4H,4H,5H,5H,6H,6H,7H,7H,8H,8H-perfluorododecan-1- yloxy)benzoic acid (11-8/ 4), 3,4,5-tris(1H,1H,2H,2H,3H,3H,4H,4H,5H,5H,6H,6H-perfluorododecan-1-yloxy)benzoic acid (11-6/6), 3,4,5-tris(1H,1H,2H,2H,3H,3H,4H,4H-perfluorododecan-1-yloxy)benzoic acid (11-4/8), 2-{2-[2-(2-hydroxyethoxy)ethoxy]ethoxy}ethyl 3,4,5-tris(1H,1H,2H,2H,3H,3H,4H,4H,5H,5H,6H,6H,7H,7H,8H,8H-perfluorododecan-1- yloxy)benzoate (19-8/4), 2-{2-[2-(2-hydroxyethoxy)ethoxy]ethoxy}ethyl 3,4,5-tris-(1H,1H,2H,2H,3H,3H,4H,4H,5H,5H,6H,6H-perfluorododecan-1-yloxy) benzoate (19-6/6), and 2-{2-[2-(2-hydroxyethoxy)ethoxy]ethoxy}ethyl 3,4,5-tris(1H,1H,2H,2H,3H,3H,4H,4H-perfluorododecan-1-yloxy)benzoate (19-4/8) and of the methacrylates and polymethacrylates of 19-8/4, 19-6/6, and 19-4/8 (i.e, 20-8/4, 20-6/6, 20-4/8 and respectively 21-8/4, 21-6/6, and 21-4/8) are described. All tapered building blocks 11-m/n, 19-m/n, and the polymers 21-m/n (where m + n = 12 and m = number of hydrogenated, n = number of perfluorinated methylenic groups of their alkyl tails) self-assemble into tubular supramolecular architectures which display an enantiotropic hexagonal columnar (Φ_h) mesophase. The self-assembling ability of model compounds and polymers was compared to that of their perhydrogenated analogues. From the perhydrogenated compounds, only the polymer 21-12/0 forms a Φ_h phase. Semifluorination of all model compounds and polymers first decreases the melting temperature of the supramolecular assembly and uncovers and/or enhances the thermal stability of the Φ_h phase (n = 4). A further increase of n from 4 to 6 and respectively 8 increases both the isotropization temperature of the Φ_h phase and the melting temperature. A parallel increase of the diameter of the supramolecular columns with the increase of n is observed. A mechanism for this dramatic increase in the self-assembly process via microsegregation of the perfluorinated and perhydrogenated parts of the tapered groups due to the fluorophobic effect was proposed.