Solid-state NMR relaxometry study of phenolic resins

Abstract

H-1 wideline and C-13 CP/MAS spin-lattice (T-1H) relaxation solid-state NMR experiments have been performed in order to investigate the cure state of phenolic novolac resins. Due to the process of spin diffusion, a single averaged T-1H decay time was found which was sensitive to the cure state of the network structure. Measurements as a function of temperature revealed that mobile end-groups and branches determine the most efficient pathway of T-1H relaxation. Combined with FTIR measurements, it is shown that rearrangements of the hydrogen bond structure take place upon heating-cooling. There are strong indications that the process of disruption-reformation of the hydrogen bonds is not completely reversible. (C) 2003 Society of Chemical Industry.