Nanoporous thermosetting membranes using reactive block polymer templates.

Abstract

Pressure driven membrane filtrations are a facile means of performing aqueous separations. The efficiency of these processes depends on the permeability and selectivity of a membrane, which is determined by its structure. This dissertation describes research investigating nanoporous thermosets templated by reactive block polymers as alternatives to current ultrafiltration membranes. The goal of the research was to develop materials with narrow pore size distributions and high void fractions for forming membranes with increased selectivity and permeability. The flux, filtration and fouling characteristics of membranes formed by selective removal of poly(lactide) from crosslinked films of dicyclopentadiene (DCPD) and the reactive block polymer poly(norbornenylethyl styrene-s-styrene)-b-poly(lactide) (PNS-PLA) were first explored. The results suggest that thin film composite membranes could achieve permeabilities and selectivities greater than current ultrafiltration membranes without excessive fouling characteristics. Additionally, hydrophilic and stimuli responsive membranes templated by reactive triblock terpolymers exhibited environmentally dependent fluxes demonstrating the ease of creating functionalized membranes using reactive triblock terpolymers. Further investigation into the compositional influences on the morphology of nanostructured PNS-PLA/PDCPD materials revealed that nanoporous bicontinuous structures form over a wide composition range and that different pore sizes are achievable by varying the PLA block size. Extension of reactive block polymer templating to vinyl crosslinking systems was demonstrated by crosslinking a poly(lactide)-b-poly(cyclooctene-s-norbornenylmethacrylate)-b-poly(lactide) reactive triblock copolymer with a variety of vinyl monomers. Although the soft nature of the poly(cyclooctene) prevented removal of polylactide due to collapse of the pores, nanoporous vinyl thermosets were realized by crosslinking a polylactide-b-poly(styrene-s-hydroxyethyl methacrylate-s-ethylene glycol dimetacrylate) reactive diblock copolymer with styrene and divinyl benzene.