NMR of tracer molecules in networks

Liquid NMR techniques were used to elucidate the molecular organization and dynamics of poly[tetra(ethylene glycol)dimethacrylate] and poly[tetra(ethylene glycol)diacrylate] as a function of cure. The change in line width of the monomer was used to determine the extent of cure and indicate the mobility in the polymer matrix. Line widths of different parts of the monomer peaks broadened at different extents of cure. Non-reacting tracer molecules (dimethylsulphoxide, methyl acetate, decalin, cyclohexane and dodecane) were also introduced into the curing system at low concentrations and their line widths observed. It was found that they broadened at differing rates and persisted well into the later stages of the cure when the monomer peaks had broadened into the baseline. In typical cures the monomer peaks broadened simply but, in atypical cases, the line shapes showed that there were two monomer domains one constrained and the other unconstrained. All tracers became constrained with increasing cure, except dodecane. The line shape of pure monomer was also followed as a function of temperature and found to broaden in similar fashion to the monomer during a typical cure.