PERFORATED MONOLAYERS - FABRICATION OF CALIX[6]ARENE-BASED COMPOSITE MEMBRANES THAT FUNCTION AS MOLECULAR-SIEVES

This paper reports the synthesis, monolayer behavior, and polymerization characteristics of three new calix[6]arenes, and the fabrication and permeation selectivity (permselectivity) of a series of composite membranes derived from one such amphiphile. Monolayers of 5,11,17,23,29,35-hexakis(N-(2-(methyldithio)ethyl)carbamoyl)-37,38,39,40,41,42-hexakis(octyloxy)calix[6]arene (I) exhibit a collapse pressure of 53 dyn/cm; those prepared from 5,11,17,23,29,35-hexakis(mercaptomethyl)-37,38,39,40,41,42-hexakis(n-butyloxy)calix[6]arene (II), and 5,11,17,23,29,35-hexavinyl-37,38,39,40,41,42-hexakis(3,6-dioxa-1-heptyloxy)calix[6]arene (III) collapse at 16 and 26 dyn/cm, respectively. At the collapse point, the areas that are occupied by I-III are 165, 150, and 155 angstrom2/molecule, respectively. Polymerization of I via UV-induced disulfide disproportionation and II by air oxidation result in a modest reduction in surface pressure. In contrast, UV irradiation of III results in the complete loss of surface pressure and an apparent ''buckling'' of the film. Composite membranes that have been fabricated from Langmuir-Blodgett multilayers of I, plus polymeric supports having large permanent pores (i.e., Celgard and Nuclepore membranes), show a significant reduction in permeability toward He, N2 and SF6 but no enhancement in permeation selectivity (permselectivity). In striking contrast, analogous composites that have been constructed using poly[1-(trimethylsilyl)-1-propyne] (trimethylsilyl)-1-propyne] as support material, function as molecular sieves; i.e., He and N2 readily permeate the composites, but SF6 does not. On the basis of intrinsic permeability coefficients that have been calculated for He and N2 as a function of LB film thickness, it is concluded that this permselectivity is due to the selective transport across homogeneous multilayers of I.