Research Department, Chemistry Division, U.S. Navy, NAWCWD, China Lake, CA 93555, USA.
Biomacromolecules. 2013 Mar 11;14(3):771-80. doi: 10.1021/bm3018438. Epub 2013 Feb 1.
A series of renewable bis(cyanate) esters have been prepared from bisphenols synthesized by condensation of 2-methoxy-4-methylphenol (creosol) with formaldehyde, acetaldehyde, and propionaldehyde. The cyanate esters have been fully characterized by infrared spectroscopy, (1)H and (13)C NMR spectroscopy, and single crystal X-ray diffraction. These compounds melt from 88 to 143 °C, while cured resins have glass transition temperatures from 219 to 248 °C, water uptake (96 h, 85 °C immersion) in the range of 2.05-3.21%, and wet glass transition temperatures from 174 to 193 °C. These properties suggest that creosol-derived cyanate esters may be useful for a wide variety of military and commercial applications. The cure chemistry of the cyanate esters has been studied with FTIR spectroscopy and differential scanning calorimetry. The results show that cyanate esters with more sterically demanding bridging groups cure more slowly, but also more completely than those with a bridging methylene group. In addition to the structural differences, the purity of the cyanate esters has a significant effect on both the cure chemistry and final Tg of the materials. In some cases, post-cure of the resins at 350 °C resulted in significant decomposition and off-gassing, but cure protocols that terminated at 250-300 °C generated void-free resin pucks without degradation. Thermogravimetric analysis revealed that cured resins were stable up to 400 °C and then rapidly degraded. TGA/FTIR and mass spectrometry results showed that the resins decomposed to phenols, isocyanic acid, and secondary decomposition products, including CO2. Char yields of cured resins under N2 ranged from 27 to 35%, while char yields in air ranged from 8 to 11%. These data suggest that resins of this type may potentially be recycled to parent phenols, creosol, and other alkylated creosols by pyrolysis in the presence of excess water vapor. The ability to synthesize these high temperature resins from a phenol (creosol) that can be derived from lignin, coupled with the potential to recycle the composites, provides a possible route to the production of sustainable, high-performance, thermosetting resins with reduced environmental impact.
已经通过缩合 2-甲氧基-4-甲基苯酚（愈创木酚）与甲醛、乙醛和丙醛合成的双酚制备了一系列可再生的双（氰酸酯）酯。通过红外光谱、（1）H 和（13）C NMR 光谱以及单晶 X 射线衍射对氰酸酯进行了充分的表征。这些化合物的熔点范围为 88 至 143°C，而固化树脂的玻璃化转变温度范围为 219 至 248°C，吸水率（96 小时，85°C 浸泡）为 2.05-3.21%，湿玻璃化转变温度为 174 至 193°C。这些性质表明，愈创木酚衍生的氰酸酯可能在各种军事和商业应用中具有用途。通过傅里叶变换红外光谱和差示扫描量热法研究了氰酸酯的固化化学。结果表明，具有更多空间位阻桥接基团的氰酸酯比具有亚甲基桥接基团的氰酸酯固化速度更慢，但也更完全。除了结构差异之外，氰酸酯的纯度对材料的固化化学和最终玻璃化转变温度都有显著影响。在某些情况下，将树脂在 350°C 后固化会导致明显的分解和放气，但在 250-300°C 终止的固化方案会生成无空隙的树脂小块，而不会降解。热重分析表明，固化后的树脂在 400°C 以下稳定，然后迅速降解。TGA/FTIR 和质谱结果表明，树脂分解为酚、异氰酸和包括 CO2 在内的二次分解产物。在氮气下固化树脂的产炭率为 27-35%，而在空气中的产炭率为 8-11%。这些数据表明，通过在过量水蒸气存在下进行热解，这类树脂可能有潜力从木质素衍生的酚（愈创木酚）回收至母体酚、愈创木酚和其他烷基化的愈创木酚。从可以从木质素衍生的酚（愈创木酚）合成这些高温树脂，再加上复合材料的回收潜力，为生产具有降低环境影响的可持续、高性能、热固性树脂提供了一种可能的途径。
