EFFECTS OF THE POLYAMIDE MOLECULAR-STRUCTURE ON THE PERFORMANCE OF REVERSE-OSMOSIS MEMBRANES

Thin-film composite reverse osmosis membranes of polyamides were prepa red by interfacial polymerization. Various benzenediamines and poly( a minostyrene) were interfacially reacted with various acyl chlorides to prepare a skin layer of composite membranes. Among the membranes prep ared from the structural isomeric monomers of benzenediamines and acyl chlorides, i.e., the same chemical composition but different in the p osition of functional groups on the aromatic ring, the membrane with t he best salt rejection was obtained when the reacting groups forming a mide are located at the same position on the aromatic ring. Membranes prepared by interfacially reacting various diamines with trimesoyl chl oride revealed that the salt rejection depends on the linear chain str ucture of polyamides and network formed by crosslinking. Membranes obt ained by interfacial polymerization of poly(aminostyrene) with trimeso yl chloride showed higher water flux but lower salt rejection than tho se obtained by interfacial polymerization of various benzenediamines w ith trimesoyl chloride. Membranes obtained here showed the typical tra de-off behavior between salt rejection and water flux. However, membra nes prepared by interfacially reacting trimesoyl chloride with a mixtu re of poly(aminostyrene) and m-phenylenediamine or a mixture of poly(a minostyrene), m-phenylenediamine, and diaminobenzoic acid showed a per formance advantage over usual membranes, i.e,, a large positive deviat ion from the usual trade-off trend. (C) 1998 John Wiley & Sons, Inc.