SYNOPSIS Polydimethylsiloxane (PDMS)/polystyrene (PSt) interpenetrating polymer network (IPN) membranes were prepared by the bulk copolymerization of styrene and divinylbenzene in the PDMS networks. The interpenetration of PDMS and PSt resulted in the improvement of mechanical properties of PDMS. Transmission electron microscope (TEM) observation demonstrated that the PDMS/PSt IPN membranes have microphase-separated structures consisting of a continuous PDMS phase and a discontinuous PSt phase. When an aqueous ethanol solution was permeated through the PDMS/PSt IPN membranes by pervaporation, the PDMS/PSt IPN membranes exhibited ethanol permselectivity, regardless of the PDMS content. The effects of their microphase-separated structures on the permeability and selectivity for aqueous ethanol solutions are discussed experimentally and theoretically. 0 1996 John Wiley & Sons, Inc.

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INTRODUCTIONMany studies on developments of polymer membranes have been undertaken for the separation and concentration of aqueous ethanol solutions by pervaporation.' In pervaporation, the permeability and selectivity of membranes depend on both the solubility and diffusivity of the permeants in them. The solubility of the permeants into the membranes is governed mainly by the affinity of the membranes for the permeants, which results from their chemical structures. The diffusivity of the permeants in the membranes is influenced mainly by the physical structures of the membranes. Therefore, the physical and chemical structures must be precisely designed for the development of high-performance membranes.As ethanol-permselective membranes for the concentration of aqueous ethanol solutions, the polydimethylsiloxane (PDMS) membrane, the ~ * To whom correspondence should be addressed.Journal of Applied Polymer Science, Vol 61, 1315Vol 61, -1324Vol 61, (1996 0 1996 John Wiley & Sons, Inc.CCC 002 1 -8995/96/0813 poly[ 1-(trimethylsily1)-1-propyne] (PTMSP) membrane, and their derivatives are well The ethanol permselectivities of their membranes are attributed to their stronger affinity for ethanol and to the relatively high diffusivity of the ethanol in the membranes. Therefore, the ethanol permselectivity of the membranes can be enhanced by improving their affinity for ethanol and the diffusivity of ethanol in the membranes on the basis of the design of their physical and chemical structures.There are some studies on the permeation and separation of aqueous ethanol solutions through the PDMS membrane by pervaporation. The PDMS membrane is ethanol permselective, since it has a stronger affinity for ethanol than for water. The high diffusivity of ethanol in the PDMS membrane, which results from free rotation of Si-0 bonds, also causes excellent ethanol permselectivity. Although the PDMS membrane has many advantages such as low surface free energy, high gas permeability, and good biocompatibility,'8-22 its mechanical properties are rather poor. Therefore, the PDMS membrane is often reinforced by using an inorganic filler like silica and introducing a rigid polymer.23T o remove the disadvantages of the PDMS membrane, a variety of graft and block copolymers containing dimethylsiloxane were also synthesized as membrane materials.Polymer blending is a promising technique for the improvement of physical and chemical properties of material^.'^ However, blending of general polymers is difficult because there are few combinations of miscible polymers. Since phase separation generally takes place in the blending of immiscible polymers, improvement of physical and chemical properties of materials is rarely achieved.One of the methods to blend various polymers is the formation of an interpenetrating polymer network (IPN), which is defined as a combination of two polymers in network form.2"3* IPN attracts our attention, since improvement of the material properties is expected. Therefore, IPNs containing PDMS as a component were s...