Hybrid polymer networks (HPNs) based on unsaturated polyester resin (UPR) and epoxy resins were synthesized by
reactive blending. The epoxy resins used were epoxidised phenolic novolac (EPN), epoxidised cresol novolac (ECN) and
diglycidyl ether of bisphenol A (DGEBA). Epoxy novolacs were prepared by glycidylation of the novolacs using epichlorohydrin.
The physical, mechanical, and thermal properties of the cured blends were compared with those of the control resin.
Epoxy resins show good miscibility and compatibility with the UPR resin on blending and the co-cured resin showed substantial
improvement in the toughness and impact resistance. Considerable enhancement of tensile strength and toughness
are noticed at very low loading of EPN. Thermogravimetric analysis (TGA), dynamic mechanical analysis (DMA) and
diVerential scanning calorimetry (DSC) were employed to study the thermal properties of the toughened resin. The EPN/
UPR blends showed substantial improvement in thermal stability as evident from TGA and damping data. The fracture
behaviour was corroborated by scanning electron microscopy (SEM). The performance of EPN is found to be superior to
other epoxy resins