A limitation in the use of hydrophilic polymers as implantable devices is their inherently poor mechanical strength. Using interpenetrating polymer networks (IPNs) consisting of both hydrophilic and hydrophobic networks is an effective method of strengthening these polymers. In this work, a series of poly(dimethyl siloxane) (PDMS)/poly(acrylic acid) (PAAc) sequential IPNs were synthesized and their properties, including swelling, morphology, and mechanical strength, were investigated. A reinforcing effect of the addition of PAAc to PDMS was observed at a concentration of 20 wt%, where this component had a bimodal size distribution. All of the IPNs exhibited rubbery behavior in the swollen state. Phase inversion in the IPNs occurred at about 60 wt% of PAAc. However, the swelling data showed that the phase inversion in the swollen state occurred at PAAc contents lower than those for dry IPNs. The improved cell behavior, reported in previous works for PDMS/PAAc IPNs with about 20 wt% PAAc, can, in addition to the increased surface wettability, be attributed to the bimodality of PAAc particles size distribution in the IPN.