SMALL-ANGLE X-RAY-ANALYSIS OF THE EFFECT OF TEMPERATURE ON THE SELF-ASSEMBLING COLUMNAR STRUCTURES FORMED BY A POLYMETHACRYLATE WITH HIGHLYTAPERED SIDE-GROUPS AND BY ONE OF ITS LOW MOLAR-MASS PRECURSORS

Small angle X-ray methods have been used to investigate the self-assem bling columnar structures formed by a polymethacrylate with large high ly tapered side groups, and by one of its low molar mass precursors. T he polymer is poly{2-{2-[2(2-methacryloyloxyethoxy)ethoxy] ethoxy}ethy l-3,4,5-tris(p-dodecyloxybenzyloxy)- benzoate} (H12-ABG-4EO-PMA); the precursor is 2-{2-[2-(2-hydroxpethoxy) ethoxy] }-ethyl-3,4,5-tris(p-do decyl-oxybenzyloxy)benzoate (H12-ABG-4EO-OH). Both the polymer and the precursor form three dimensionally ordered structures at room tempera ture, consisting of hexagonally packed cylinders with diameters in the region of 60 and 53 Angstrom, respectively, in which the interiors of the columns probably have helical arrays of the stacked tapered group s. At higher temperatures these are converted to columnar hexagonal (p hi h) liquid crystalline phases. At temperatures close to this transit ion for the precursor we detect two coexisting columnar structures, wi th the phi h structure having a diameter approximately 1 Angstrom high er than that in the solid state. For the polymer, the data are not so well resolved, and coexisting phases cannot be resolved. However, the changes in column dimensions are larger than for the precursor. Conver sion of the room temperature phase to the phi h phase at 40 degrees C results in an increase of 3 Angstrom in the diameter, which then decli nes by approximately the same amount as the temperature rises to 90 de grees C, close to the isotropization point. Cooling to room temperatur e does not immediately restore the room temperature structure. Rather, we obtain a quenched phi h structure, with a column diameter almost 1 0% higher. These dimensional changes correlate well with the changes i n diameter with temperature seen for the bulk fiber, and suggest a con tinuous rearrangement of the interiors of the columns in the phi h pha se, such as a partial unwinding of a disordered helical structure.