Novolac resin/poly(n-butyl methacrylate), P(n-BMA), sequential interpenetrating polymer networks (both semi and full types) were prepared and characterization of the various compositions (up to 40% by weight of PF incorporation) was performed in terms of mechanicals, namely, ultimate tensile strength (UTS), percentage elongation at break (% E.B.), modulus, and toughness. Thermal properties were studied by differential scanning calorimetry and thermogravimetric analysis (TGA). Crosslink densities of the IPNs were calculated using Flory-Rehner equation. The morphological features were studied through scanning electron microscope. There was a gradual decrease of modulus and UTS with consequent increases in % E. B. and toughness with increasing proportions of P(n-BMA). An inward shifting and lowering of the glass transition temperatures of the IPNs (compared with that of pure phenolic resin) with increasing proportions of P(n-BMA) were observed. The TGA thermograms exhibit two-step degradation patterns. A typical cocontinuous bi-phasic morphology is evident in the micrographs. © 2006 Wiley Periodicals, Inc.