The thermal decomposition process of the flame retardant BPPDN is shown in
Fig. 1(a). BPPDN first decomposed at
Tmax1 = 286.2 °C until
T5%=413.9 °C, which corresponded to the crosslinking of the phenolphthalein structure to generate CO
2, in agreement with the weight loss percentage obtained from the theoretical calculations. This was also in line with our initial design idea that the phenolphthalein structure crosslinked quickly to dilute flammable gas and burst flammable radicals, which was well evidenced in the subsequent vertical burning test results. In addition, thermal behavior of two intermediates and BPPDN were tested by DSC (
Fig. 1(b)). The intermediates 3-APN and BPP-D showed sharp melting peaks, indicating their purity. At higher temperature, the exothermic peak for 3-APN indicated that the bisphthalonitrile groups started to crosslink at 222 °C and reached the peak at 245 °C. The DSC curve of BPPDN started to show an obvious exothermic peak at 250 °C, which was also attributed to the crosslinking. Therefore, BPPDN was isothermally treated in a muffle furnace at the temperatures of 230 °C, 250 °C and 300 °C for 5 min each, and then subjected to infrared spectrometry respectively. For comparison, the FT-IR spectrum of the original BPPDN was also recorded (
Fig. 1(c)). At 230 °C, the characteristic absorption peak of N-H in the triazine ring and the absorption peak of –OH overlapped; while the new peak at 2890 cm
−1 appeared, which was attributed to the generation of the triazine and phthalocyanine rings. Moreover, the peak ascribed to cyano rings at 2232 cm
−1 gradually weakened after thermal treatment, further disappeared completely at 300 °C. The two newly observed peaks at 1638 cm
−1 and 1618 cm
−1 belonged to the C
C and C
N of the phthalocyanine ring, which were difficult to distinguish due to the conjugation of the two bonds and the similarity of their wavenumbers; as the temperature increased, the redshift of the peak at 300 °C was 3593 cm
−1, revealing that the cyclization reaction occurred. The above results showed that heat treatment at 230 °C and higher temperature of bisphthalonitrile groups generated triazine rings or phthalocyanine rings.
阻燃剂 BPPDN 的热分解过程如图 1(a) 所示。BPPDN 首先在 Tmax1 = 286.2 °C 分解,直到 T5%=413.9 °C,这对应于酚酞结构的交联生成 CO2,与理论计算获得的失重百分比一致。这也符合我们最初的设计思路,即酚酞结构快速交联,稀释易燃气体,爆裂易燃自由基,这在随后的垂直燃烧测试结果中得到了很好的证明。此外,通过 DSC 测试了两种中间体和 BPPDN 的热行为 [图 1(b)]。中间体 3-APN 和 BPP-D 显示出尖锐的熔解峰,表明其纯度。在较高温度下,3-APN 的放热峰表明双苯二腈基团在 222 °C 开始交联,并在 245 °C 达到峰值。 BPPDN 的 DSC 曲线在 250 °C 时开始显示明显的放热峰,这也归因于交联。因此,BPPDN 在 230 °C、250 °C 和 300 °C 的马弗炉中分别等温处理 5 min,然后分别进行红外光谱测定。为了进行比较,还记录了原始 BPPDN 的 FT-IR 光谱 [图 1(c)]。在 230 °C 时,三嗪环中 N-H 的特征吸收峰与 –OH 的吸收峰重叠;而在 2890 cm-1 处出现新峰,这归因于三嗪和酞菁环的产生。 此外,2232 cm−1 处归因于氰基环的峰在热处理后逐渐减弱,在 300 °C 时进一步完全消失。 在 1638 cm-1 和 1618 cm-1 处新观察到的两个峰属于酞菁环的 C C 和 C N,由于两个键的共轭和波数的相似性,很难区分;随着温度的升高,300 °C 时峰的红移为 3593 cm-1,表明发生了环化反应。以上结果表明,在 230 °C 和较高温度下对双苯二腈基团进行热处理,生成三嗪环或酞菁环。