Study of crosslinked polystyrene gels using proton and carbon-13 direct polarization - magic angle spinning NMR

The authors have recently demonstrated the particular aptness of ¹³C as well as ¹H Direct Polarization - Magic Angle Spinning (DP/MAS) NMR for the quantitative characterization of a chemically modified solvent-swollen polystyrene gel. The authors describe applications of DP/MAS NMR to the analysis of polystyrene gels, and focus on the crosslink junctions themselves. DP/MAS ¹³C and ¹H NMR is shown to give high resolution spectra of functionalized solvent-swollen polystyrene gels. This permits routine analysis of chemically modified crosslinked polystyrenes, taking advantage of the high sensitivity in ¹H, and of the fast, solution-like relaxation rates in ¹³C DP/MAS NMR. DP/MAS NMR would therefore be well suited to follow a reaction producing a gel-phase, for example measuring the kinetics of crosslinking polymerizations by NMR. Further, DP/MAS permits direct observation of the methyl groups in the crosslinker. This may allow access to the network dynamics of crosslinked polymer gels, by measuring the NMR relaxation rates of the crosslinks themselves.