Substituted aromatic compounds incorporated-cardanol-formaldehyde novolac resins were synthesized by acid base catalyzed reactions. A number of improved high temperature stable interpenetrating polymer networks (semi-IPNs) were prepared by condensing novolac resins and polyurethanes prepared from castor oil and diisocyanates of varying NCO/OH ratio. The structure of these semi-IPNs were studied using various characterization techniques such as IR, nuclear magnetic resonance (NMR) spectra. The scanning electron microscopy of some of the semi-IPNs have been studied and the morphology has been examined. The samples were subjected to wide angle X-ray diffraction analysis. The degree of crystallinity (X-cr) was computed on the basis of the crystal defect concept, developed by Ruland and Vonk.