酚醛树脂热降解过程中的结构变化

采用综合热分析对比研究了自制酚醛树脂和商业酚醛树脂的热降解过程,利用固体核磁共振和红外光谱技术研究了热降解过程中树脂结构的变化规律以期指导成炭率高、热稳定性高的新型酚醛树脂的合成。结果表明:酚醛树脂的热降解过程可分为3个阶段:首先是醚键以及未反应的羟甲基等端基的热降解;其次是亚甲基热解断裂为甲基;然后是酚羟基发生脱水环化成炭。其中亚甲基的热解对酚醛树脂的热稳定性及高温下的成炭性能有着至关重要的作用。固体核磁共振比红外光谱更直接,更清晰地反应出酚醛树脂在热降解过程中的结构变化。

The structural changes of phenolic resin during thermal degradation

The self-made and commercial phenol-formaldehyde type resins(PFR) were studied by thermo gravimetric analysis(TGA).Their structural changes during thermal degradation were investigated by fourier-transform infrared(FTIR) and solid-state 13C nuclear magnetic resonance(13C-NMR) spectroscopy to guide the synthesis of novel phenolic resin with high char yield and thermal stability.The results showed that the degradation process of PFR could be divided into three stages.Ether bonds and unreacted terminal hydroxymethyl groups of the cured resin degradated in the first stage.In the second stage,methylene bridges decomposed into methyl groups then yielded both phenol and cresol homolog.Cyclodehydration and forming char of phenolic hydroxyl occurred in the third stage.The thermal stability and char yield of PFR were depended on the degradation process of methylene bridges.The structural changes of phenolic resin during thermal degradation could be observed more directly and clearly by 13C-NMR than FTIR.