Interpenetrating polymer networks (IPNs) of poly(ethy1ene oxide) (PEO) and poly(methy1 methacrylate) ( P M M A )
were prepared by simultaneous network formation. The PEO network was produced by acid-catalyzed selfcondensation of a,w-bis(triethoxysi1ane)-terminated PEO in the presence of small amounts of water. The P M M A network was formed by free radical polymerization of M M A in the presence of divinylbenzene as crosslinker. The reaction conditions were adjusted to obtain similar crosslinking kinetics for both reactions. A n attempt was made to construct a phase diagram of the IPNs by measuring the composition of the IPNs at the moment of the appearance of the phase separation, as indicated by the onset of turbidity. This composition could be determined because the siloxane crosslinks of the PEO network could be hydrolyzed in aqueous NaOH with the formation of linear, soluble PEO chains. The phase diagram was compared with phase diagrams of blends of linear polymers and of semi-IPNs (crosslinked P M M A and linear PEO), obtained under similar conditions, i.e. polymerization of M M A in the presence of varying amounts of PEO. It was observed that the form of the phase diagrams of the linear polymers is similar to that of the IPNs, but is quite different from that of the semi-IPNs. Thus, homogeneous transparent materials containing up to 60% of PEO could be prepared in the blends and the IPNs, but in the semi-IPNs, phase separation occurred with PEO contents as low as 10%.