OXIDATIVE COUPLING POLYMERIZATION IN A LANGMUIR MONOLAYER OF OCTADECYL 3,5-DIAMINOBENZOATE

In a Langmuir monolayer of the surface active monomer octadecyl 3,5-di aminobenzoate (ODDB), stabilized at a surface pressure of 10 mN/m and a temperature of 23.7 degrees C at the air-water interface, oxidative coupling polymerization occurs when copper(II) chloride was added or a lready was present in the subphase. Even in the absence of the catalys t this reaction takes place. Deposition of the polymerized monolayer o nto glass, zinc sulfide, or gold substrates, using the vertical dippin g method, gave transfer ratios between 0 and 0.4 on the downstroke and 1 on the upstroke. The multilayer films on zinc sulfide and gold subs trates were characterized by means of Fourier transform IR spectroscop y, and multilayer films on quartz were characterized by means of UV/vi s spectroscopy. Collected monolayers were characterized by means of si ze exclusion chromatography and again Fourier transform IR and UV/vis spectroscopy. During the stabilization of the monolayer without additi on of copper(II) chloride to the subphase, the area per molecule decre ased very slowly. Addition of copper(II) chloride enhanced this effect . The reduction of the area per molecule is probably caused by the pol ymerization itself accompanied by a reorientation of the molecules in the monolayer at the air-water interface. After stabilization the area per molecule was found to be about 27 Angstrom(2) and electron microg raphs showed the formation of a smooth monolayer. From this it has bee n concluded that a closely packed monolayer was formed. Fourier transf orm IR and UV/vis spectra of polymerized multilayer materials are anal ogous to the spectra of the azo polymer of ODDB prepared in bulk solut ion. Size exclusion chromatography revealed that the molecular weight and the molecular weight distribution of the coupling product with and without copper(II) chloride in the subphase were the same. The averag e molecular weight was somewhat lower than the high-molecular-weight p art of the corresponding material prepared in bulk solution.