Preparation of novel composite membranes: Reactive coating on microporous poly(ether imide) support membranes

Abstract

Poly(ether imide) asymmetric membranes can be covalently functionalized with aminic modifiers. When poly(ethylene imine), i.e., a polyvalent high molecular weight modifier, is used, the functionalization is connected with the support membrane pore-filling in a very thin layer. The poly(ethylene imine) layer is, however, not stables at increased temperatures and does not fill completely large pores. The layer can be stabilized by crosslinking with oligomeric poly(ethylene glycol) diglycidyl ether (PEGDGE), but this does not improve the coverage of large pores. The poly(ethylene imine) functionalized membrane can be stabilized, however, by reactive coating with copolymers of methacrolein with 1-vinylpyrrolidone instead stabilization with PEGDGE with a coverage of the large pores. The copolymers having various ratios of both polymeric units were prepared by free radical polymerization. The methacrolein units of copolymers, which comprised predominantly 1-vinyl-2-pyrrolidone units, had aldehyde groups in a free reactive form. These aldehyde groups react readily with the amine groups of the poly(ethylene imine) layer, while 1-vinylpyrrolidone units render the coating hydrophilic. The membranes coated under optimal conditions had nanofiltration separation properties at high water fluxes. Good adhesion between the coating layer and the support membrane, which results from the covalent binding, should allow separations under harsh conditions.