QUANTITATIVE SOLID-STATE C-13 NMR-STUDIES OF HIGHLY CROSS-LINKED POLY(DIVINYLBENZENE) RESINS

Three highly cross-linked poly(divinylbenzene) resins have been prepar ed from p-divinylbenzene and two grades of ''divinylbenzene'' from com mercial sources using suspension polymerization methodology and employ ing toluene as a porogen. These materials along with XAD-2 and XAD-4 f rom the Rohm and Haas Co. have been examined by solid state C-13 nucle ar magnetic resonance (NMR) techniques. In particular, quantitative si ngle pulse excitation (SPE) experiments have been carried out to analy ze the molecular structure of each resin in terms of quantifying the v arious types of carbon atom present. This has allowed the level of res idual unreacted vinyl groups to be determined and hence the effective cross-link ratio of each resin. Whereas the monomer feed composition i s known reasonably accurately for the in-house resins, no such informa tion is available for XAD-2 and XAD-4. However, the SPE NMR spectra al so allow the levels of ethylstyrene and divinylbenzene residues to be assessed as well, and so a full analysis of residual double bond conte nt and cross-link ratio is also possible for the commercially sourced resins. In general real cross-link ratios are significantly lower than the feed ratio of divinylbenzene isomers. Thus similar to 100% diviny lbenzene yields similar to 55% cross-linking, similar to 80% divinylbe nzene yields similar to 40-45% cross-linking, and 50% divinylbenzene y ields similar to 30-35% cross-linking. There is therefore some uniform ity in the percentage efficiency in the consumption of divinylbenzene in cross-links, with perhaps a marginal lowering of efficiency at very high absolute levels.