No abstract

SynopsisThe effect of water vapor on a polyimide has been investigated in the temperature region of -190 to 325OC using an automated torsion pendulum. A damping peak, T H~O developes at -122°C (1 Hz) in the thermomechanical spectra of the polymer which is due to water-polymer interactions.The peak intensifies as the humidity of the conditioning atmosphere, a t both 30" and at 325OC, increases and attains a limiting value a t about 3000 ppm, H20. The process is reversible. It is concluded that the number of sites in the polymer for interaction with water is low and limited (<0.3 molecule HzO per polymer repeat unit) and, assuming direct proportionality between the intensity of the loss peak and the amount of water adsorbed, that the adsorption of water vapor follows the Langmuir isotherm.

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SynopsisPoly(acry1ic acids), poly(styrenesu1fonic acid), and their block and random copolymers were tested for their ability to form dynamic membrznes on partially cured asymmetric cellulose acetate. Chemically modified porous polypropylene (Celgard) was also used as a support for poly(acry1ic acid). Salt rejections, water fluxes, and streaming potentials of membranes were tested under hyperfiltration conditions. Sorption of the polyelectrolytes by the cellulose acetate supports was studied using spectrophotometric, 22Na tracer, and electron microscopy techniques. The dynamic membrane formation was noted only for poly(acry1ic acid) and for its 1:4:1 block copolymer with poly(styrenesulfonic acid). The uneffectiveness of other polyelectrolytes was discussed in terms of a negative zeta potential of cellulose acetate. The increase in salt rejection (R) due to the polyelectrolyte is strongly dependent on the initial R, of the support. Sharp maxima in the AR -versus-R, curves have been noted for R, in the range of 40-55%. The most significant improvement in the hyperfiltration characteristics of cellulose acetate was attained with the 1:4:1 block co$olymer. Flux of 17 gfd a t 350 psi and R = 93% was obtained in short-term tests for a 0.1N feed solution. Long-term tests did not reveal any flux or salt rejection decline for membranes in which poly(acry1ic acid) was complexed with phosphoramidic groups grafted onto Celgard.

The equilibrium constant of complexation of bromine with hexamethylphosphoric triamide (H M PA) has been determined by l H n.m.r. spectroscopy by using a ' competitive complexation ' method. Solid adducts of bromine with poly-HM PA, a polymer analogue of HMPA, have been isolated from chloroform solutions.HEXAMETHYLPHOSPHORIC TRIAMIDE (HMPA) has a strong tendency to form molecular complexes with electron acceptors? Its donor properties have been attributed to the pronounced basicity of the oxygen of its PO group.2 Though formation of charge transfer complexes between bromine and electron donors has been extensively i n v e ~t i g a t e d , ~. ~ no information is available about its complexation with HMPA. Polymeric analogues of hexamethylphosphoric triamide (Poly-HMPA) were recently synthesi~ed,~ and it was observed that solid adducts precipitate upon addition of bromine to their chloroform solutions.6 We decided, therefore, to investigate the interaction of bromine with HMPA and with poly-HMPA.