In this investigation, epoxidized phenolic novolac
resin has been used as a modifier for UPR. To our
knowledge this is the first study of this type involving
EPN. The blends are highly compatible and have a
shelf life of at least 6 months. The hydroxyl and carboxyl
end groups of UPR or unreacted anhydrides can
open the epoxy rings of the EPN at the peak exothermic
temperature attained during the cure of polyester
resin. This can lead to the formation of hybrid networks
of EPN and UPR with idealized structures
shown in Figure 1.