Simultaneous grafted interpenetrating polymer networks (IPNs) based on [castor oil-poly(ethylene glycol) (PEG)] polyurethane and poly(alkyl methacrylate) were synthesized by simultaneously coupling castor oil and PEG with 2,4-toluene diisocyanate and by radical polymerization of alkyl methacrylate with castor oil. The gel content of the IPNs is similar to96% in most cases. The IPNs were characterized by infrared spectroscopy. The effects of compositional variation of the IPNs on phase transfer catalytic efficiency and mechanical properties, and conductivity of the IPNs complexed with LiClO4 were also studied. The results show that the IPNs have good phase transfer catalytic ability in the Williamson reaction and exhibit a maximum conversion of potassium phenolate at 55% polyoxyethylene (PEO). The phase transfer catalytic ability of the IPN increases with molecular weight of PEG used in the IPN synthesis and with the length of alkyl groups of the grafts, but decreases with increasing crosslinking degree. The complex of the IPNs with LiClO4 exhibits good ionic conductivity at room temperature in the range 10(-5)-3 x 10(-4) S/cm. This ionic conductivity decreases with increasing either the crosslinking degree or the molecular weight of PEG used, but increases with increasing PEO content. The more compatible are the grafts with PEO, the lower is the conductivity. Either butyl methacrylate or ethyl methacrylate is a good choice for the monomer in the synthesis of the IPNs for use as phase transfer catalysts and ion conducting materials. The IPNs showed high tensile strength in the range 10-20 MPa. The good mechanical properties of the IPNs favor their applications as a strong solid polymer electrolyte film and an easily recoverable phase transfer catalyst. (C) 2003 Wiley Periodicals, Inc.