Solid-state NMR relaxometry study of phenolic resins

1H wideline and 13C CP/MAS spin‐lattice (T1H) 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 T1H 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 T1H 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. Copyright © 2003 Society of Chemical Industry