AbstractSequential interpenetrating networks (IPN's) were obtained from a tetrafunctionally end‐linked network [prepared from hydroxyl‐terminated poly(dimethylsiloxane) (PDMS) chains having a number‐average molecular weight of 21.3 × 103 g mol−1] by swelling it with very short vinyl‐terminated PDMS chains (∼450 g mol−1), which were then themselves tetrafunctionally end linked, Simultaneous IPN's were prepared from a mixture of the same two types of PDMS chains, with different end‐linking agents and catalysts for the two separate reactions. In elongation studies, both types of IPN's showed upturns in modulus which were similar to those shown by the usual bimodal networks, which are prepared from mixtures of chains having identical end groups, and are thus entirely interconnected. The sequential IPN's have values of the high deformation modulus close to those of the interconnected networks, possibly because their lack of connectivity is compensated for by the stretching of the long chains by the short‐chains used to form the second network, Values of the ultimate strength are smaller for the IPN's, thus demonstrating the advantage of direct bonding between the long and short network chains. The simultaneous IPN's, however, have unusually large extensibilities, which makes their energies for rupture comparable to those of the corresponding interconnected bimodal networks.