Structure and curing mechanism of high-ortho and random novolac resins as studied by NMR

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• 作者：Masahiro Nomoto ; Yukio Fujikawa ; Tadashi Komoto ; Takeshi Yamanobe
• 关键词：Phenolic resin ; Curing mechanism ; High-ortho ; Pulse NMR ; Cross-link
• 刊名：Journal of Molecular Structure
• 出版年：2010
• 出版时间：15 July 2010
• 年：2010
• 卷：976
• 期：1-3
• 页码：419-426
• 全文大小：958 K

文摘

¹H pulse NMR and ¹³C CPMAS NMR measurements are carried out for novolac resins in order to investigate the structure and curing mechanism. Thermal behavior of molecular mobility obtained from spin–spin relaxation time, T₂, indicates that the hydrogen bond network formed in novolacs is predominant factor of glass transition for novolacs without cross-link agents. In presence of cross-link agent, hexamethylenetetramine (HMTA), the appearance of adducts between novolacs and HMTA is recognized. At curing temperature, the rigid fraction increased as a final step of curing. Different thermal behavior of mobility is observed for random and high-ortho novolacs/HMTA. Formation of adducts occurred at lower temperature for high-ortho novolac. ¹³C NMR chemical shift and quantum chemical calculation suggest that high acidity of phenolic OH of o-novolac caused by intramolecular hydrogen bonding is responsible for the formation of adducts at lower temperature.