As it turned out, the reaction temperature served to distinguish the formaldehyde reactions between aniline and phenol. Through appropriate cooling, we kept the reaction between cardanol aminohydrin and formaldehyde at room temperature. The resulting reaction mixture visibly increased in viscosity indicating the presence of resin formation. The
13C NMR spectrum corresponding to the room temperature reaction of formaldehyde with cardanol-epoxy-aniline adduct (sample F1) is shown in Fig. 2(d). The
13C shifts of the phenol carbons stay the same (labelled as P
1–P
6), but the peaks for aniline carbons have all moved because many different structures have been produced. Thus, the phenol moiety stays unreacted, but the aniline moiety has reacted with formaldehyde at room temperature (A confirmation experiment was also done where formaldehyde was added to cardanol at room temperature, and no change in
13C NMR spectrum was observed). Because of the excess formaldehyde used and the low temperature, there are several peaks in Fig. 2(d) corresponding to the formaldehyde oligomers at 87‒94 ppm and related methoxy peaks at around 55 ppm. The methoxy peaks are derived from methanol, present in formaldehyde as a stabilizer. These peaks from formaldehyde self-reactions have been previously reported [
25,
26]. When the same cardanol aminohydrin/formaldehyde reaction mixture was heated to 65 °C, the phenol started to react and an insoluble, crosslinked material was obtained. However, it seems that if we generate the cardanol aminohydrin/formaldehyde adduct at room temperature, it can serve as a prepolymer, which can then be subjected to further polymerization at a higher temperature with the phenol on cardanol (self-condensation) or with a second component to produce a copolymer.