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

Both liquid- and solid-state ¹³C-NMR spectroscopies were employed to investigate the cure-acceleration effects of three carbonates [propylene carbonate (PC), sodium carbonate (NC), and potassium carbonate (KC)] on liquid and cured phenol-formaldehyde (PF) resins. The liquid-phase ¹³C-NMR spectra showed that the cure-acceleration mechanism in the PC-added PF resin seemed to be involved in increasing reactivity of the phenol rings, while the addition of both NC and KC 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-CP/MAS-NMR spectroscopy was smaller for the cure-accelerated PF resins than for that of the control PF resin. The result indicated that cure-accelerated PF resins are less rigid than the control PF resin.