In the performance data of various polyamide and related membranes published to date there should be valuable information for molecular design of more excellent barrier materials. But at present a means for their evaluation and optimization is still not clear. One of the reasons may at least come from the competitive flood of proposals for the detailed mechanisms of reverse osmosis, e.g. the solution-diffusion model, the sieve model, the preferential sorption model and so on.109)

Polyamides as barrier materials

The permeability of various ionic salts through poly(γ-methyl L-glutamate) (PMLG) membrane, which consists of noncharged α-helical molecules, was studied. Based on the results, the mechanism of ion transport and the degree of hydration of ions in the membrane and their relation to salt rejection is discussed. The permeability coefficient of salt, PS, is almost independent of salt concentration over a wide range of concentration in aqueous solution, which contrasts with the case of charged membranes. The activation energy for PS is about 15 kcal/mole, which is almost half of that for cellulose acetate membranes. The ionic diffusion coefficient Di. decreases with increase of ionic radius, but it does not obey Stokes' law. The behavior is analyzed by the free volume theory, and it is found that the degree of ion hydration in PMLG membranes is depressed especially in the case of strongly hydrated ions in aqueous solution. This fact also explains the good permeability of salt through the rather hydrop...

Permeability of ionic salts through poly(γ-methyl L-glutamate) membrane

A new block copolymer composed of polyamide as outer segments and polyoxyethylene as an inner segment was prepared by the anionic polymerization of a bicyclic oxalactam, 8-oxa-6-azabicyclo[3.2.1]octan-7-one. A polyoxyethylene having terminal isocyanate groups was used as an activator obtained from polyoxyethylene glycol and an excess of tolylene-2,4-diisocyanate. A hydrophilic membrane was easily obtained by casting from a chloroform–methanol (10: 1) solution of the resulting block copolymer. The interaction of the copolymer membrane with water molecules was discussed in relation to the adsorption and permeation of water.

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Preparation of a Novel Block Copolymer by the Anionic Polymerization of a Bicyclic Oxalactam Activated with Isocyanate-Terminated Polyoxyethylene and Characterization of Its Hydrophilic Membrane

This study pertains to the development of poly (alpha-amino acid) membranes which have potential as biomaterials. Copoly (L-alanine, L-methionine) membranes have been subjected to oxidation which produced a hydrophilic structure allowing the improvement of oxygen permeability. L-Methionine residues in the copolymers were converted to methionine sulfoxide and/or sulfone groups by action of hydrogen peroxide in various reaction compositions. Water absorption, permeability to oxygen dissolved in water, and tensile strength of the modified membranes were changed with the extent of oxidation. The water absorption was found to increase with oxidation time from 10 to 300%. The oxidation time dependency on the oxygen permeability coincided with the increase in the water absorption. The permeability coefficients of oxidized membranes were of the order of 10(-9) cm3 (STP) cm/cm2 s cm Hg, while those of unoxidized membranes were approximately 10(-11). As expected, the tensile strengths of oxidized membranes were smaller than those of unoxidized ones. In addition, the effect of L-alanine and L-methionine residue composition on the membrane properties is discussed.

The effect of oxidation of copoly(L‐alanine, L‐methionine) membranes on oxygen permeability and tensile properties

Sorption and permeation of poly(n-hexyl l-glutamate) — organic solvent systems

To elucidate the mechanism of water permeation, permeation of water and water vapor through a series of poly(n-alkyl L-glutamates). polymers of methyl, propyl, and butyl glutamate were studied. It was confirmed that water and water vapor permeability were almost one order higher than in cellulose acetate membrane and increased with increasing length of the side chain. The activation energies of the hydraulic permeability of water and the diffusion coefficient of water vapor are almost three times those for pure viscous flow of water. The behavior is analyzed by the free-volume concept for mass transport, and the result shows that the mechanism of water permeation involves the molecular transport of clusters of several water molecules, though the size of the cluster is extremely small compared with that in bulk viscous flow. Separation of water-soluble solute through the homogeneous polypeptide membrane was examined. Though the rejection of NaCl is not as good as in cellulose acetate membranes, th...

T. Nakagawa

Papers

Water and water vapor permeation and solute separation through poly(n-alkyl L-glutamate) membranes