Effect of Interaction between Transition Metal Oxides and Nitrogen Atoms on Thermal Stability of Polybenzoxazine

Abstract

To investigate the interaction of transition metal oxides with polybenzoxazine and their influence on the thermal degradation mechanism of polybenzoxazine, transition metal oxides Y 2 O 3 , La 2 O 3 , Pr 6 O 11 , and Gd 2 O 3 were added to benzoxazine monomer based on p-cresol and aniline to prepare polybenzoxazine composites. The chemical structures and final polymerization extent of polybenzoxazine and its composites were characterized by Fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), and differential scanning colorimetry (DSC). The molecular weights of these cured samples were determined by gel permeation chromatography (GPC). The influence of transition metal oxides on the thermal properties of polybenzoxazine matrix was investigated using dynamic mechanical analysis (DMA), thermogravimetric analysis (TGA), thermogravimetric analyzer interfaced with Fourier transform infrared spectroscopy (TG-IR), and (pyrolysis-gas chromatography-mass spectrometry)Py-GC-MS. The results show that transition metal oxides can form coordination interactions with the nitrogen atoms of polybenzoxazine. The coordination interaction can anchor the aniline and make the molecular weights of polybenzoxazine matrix increase, which delays evaporation of aniline during thermal degradation, improves the char yield at 800 • C, and increases the glass transition temperatures (T g ) of polybenzoxazine composites.

Effect of La2O3 on the thermal stability of polybenzoxazine based on 4,4′-diaminodiphenyl methane

“…3, indicating that the addition of La 2 O 3 did not change the fundamental chemical structures of BB polybenzoxazine, which was similar to the influence of transition metal oxides on the chemical structures of polybenzoxazine based on p-cresol and aniline (PC-a) [7].…”

“…Furthermore, the char yield at 800°C of BB also lessened with the incorporation of La 2 O 3 when normalized for the La 2 O 3 content. All these were different from that TiO 2 and La 2 O 3 could improve the thermal stability and the char yield at 800°C of PBa and PC-a polybenzoxazines [6,7].…”

“…The cleavage of C-N and C-C bonds produced aniline and its derivatives during the thermal degradation process of PC-a, and the initial weight loss was mainly from the volatilization of the amine compounds. When the transition metal oxides were incorporated into PC-a, the N atoms of PC-a formed the coordination interaction with metal ion, which anchored aniline and its derivatives and thus restrained their evaporation during the thermal degradation process, resulting in the increase of char yield at 800°C of PC-a [7]. As to BB polybenzoxazine, the amine structure existed in the chemical crosslinking network, as displayed in Scheme 3b, therefore, the amine compounds were very difficult to evaporate during the thermal degradation process of BB even if the C-N and C-C bonds in the Mannich bridge broke, resulting in that the appearance of the amine gases (about 420°C) was obviously later than that of the phenolic gases in BB.…”

“…Accordingly, the major degradation gases of BB polybenzoxazine included benzene, phenol, amine and their derivatives between 300 and 550°C, and the alkene was detected with the increase of temperature, which was similar to the kinds of the thermal degradation gases of PC-a and other polybenzoxazines based on aniline or aliphatic amine. However, the appearance of the phenolic gases was earlier than that of the amine gases during the thermal degradation process of BB, just the reverse from those polybenzoxazine, in which the volatilization of the amine compounds was earlier [7,[10][11][12][13][14]. Figure 7 is the FTIR spectra of thermal degradation gases of the BB/La0.5 %.…”

“…The previous research indicated that the transition metal oxides could improve the thermal stability and char yield at 800°C of polybenzoxazines based on aniline and bisphenol-A or p-cresol (abbreviated as PBa or PC-a) [6,7], moreover, our study showed that the increase of char yield was assigned to the formation of coordination interaction between transition metal oxides and the nitrogen atoms of PC-a polybenzoxazine, which anchored the pendent aniline structure and retarded the evaporation of aniline and its derivatives during the thermal degradation process [7]. However, the primary amine as the starting materials of benzoxazine is various and the amine structure in polybenzoxazines can also be different, which can influence the formation of coordination interaction between metal oxides and nitrogen atoms and alter the retardation of the coordination interaction on the volatilization of the amine degradation gases, resulting the changing of the effect of La 2 O 3 on the thermal stability and char yield of polybenzoxazine.…”