Nanoporous thermosets via Reactive Encapsulation of a Chemically Inert Solvent versus Free Radically Polymerized and Pha
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Nanoporous thermosets via Reactive Encapsulation of a Chemically Inert Solvent versus Free Radically Polymerized and Phase Separating Systems Vijay I. Raman and Giuseppe R. Palmese Department of Chemical Engineering, Drexel University, Philadelphia, PA-19104. ABSTRACT Nanoporous thermosets are used as polyelectrolytes in fuel cells, separation membranes, and sensors and actuators, etc. Design of nanoporous thermosets for such applications entails controlling permeability by tailoring the pore size and pore chemistry. Usually free radically polymerizing and simultaneously phase separating systems are used to synthesize porous thermosets. A novel method of synthesizing nanoporous polymeric materials is employed in this work. This technique involves the synthesis of nanoporous thermosets by reactive encapsulation of an inert solvent using step-growth crosslinking polymerization reaction carried out until completion without phase separation into macroscopic phases. Key structural features of the porous materials synthesized by the reactive encapsulation technique were investigated by Scanning Electron Microscopy (SEM) after extraction and supercritical drying using carbon dioxide. Micrographs of the materials synthesized using the reactive encapsulation technique showed that the porous materials of pore size less than 100nm are obtained. Micrographs also showed that the reactive encapsulation technique can be employed to synthesize nanoporous polymeric materials of desired porosity and pore size by changing the solvent content. In addition, porous thermosets were also synthesized using free radical chemistry and phase separating system. The differences in the porous morphology of both these systems were enunciated using SEM micrographs. INTRODUCTION Nanoporous polymeric materials are used as polymer electrolytes in fuel cells, [1-2] separation membranes, [3-4] sensors, [5] and templates for nanoparticle synthesis, [6-7] .Diffusion of a permeant or mixture of permeants through the porous material and adsorption onto the surface of the pores are key phenomena that form the basis for applications of nanoporous material. Permeability of the porous materials is defined as the product of effective diffusivity (D) and solubility (S). The effective diffusivity is a function of the size and shape of the porous material for a given permeant. Solubility depends on the interaction between the permeant molecules and the polymer network. Therefore, design of nanoporous polymeric materials for these applications entail controlling the permeability through the porous materials by tailoring the pore size and pore thermodynamic activity. A novel method of designing nanoporous thermosets via reactive encapsulation technique in which pore size can be tailored is discussed in this communication. Mostly, porous thermosets are synthesized using free radically polymerizing and phase separating systems, [8]. In these systems, the final pore size and structural distribution of the material depends upon the thermodynamic path that the s
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