¹³C-NMR study on cure-accelerated phenol-formaldehyde resins with carbonates

Both liquid- and solid-state carbon-13-nuclear magnetic resonance (¹³C-NMR) spectroscopies were used to investigate the cure acceleration effects of three carbonates (propylene carbonate, sodium carbonate, and potassium carbonate) on liquid and cured phenol-formaldehyde (PF) resins. The liquid-phase ¹³C-NMR spectra showed that the cure acceleration mechanism in the propylene carbonate-added PF resin seemed to be involved in increasing reactivity of the phenol rings, whereas the addition of both sodium carbonate and potassium carbonate into PF resin apparently resulted in the presence of ortho-ortho methylene linkages. Proton spin-lattice rotating frame relaxation time (T_1ρH) measured by solid-state ¹³C cross polarization/magic-angle spinning NMR spectroscopy was smaller for the cure-accelerated PF resins than that of the control PF resin. The result indicated that the cure-accelerated PF resins are less rigid than the control PF resin.