C-13 AND N-15 CP/MAS NMR CHARACTERIZATION OF MDI-POLYISOCYANURATE RESIN SYSTEMS

A series of MDI-polyisocyanurate resins were prepared under a variety of reaction conditions from 4,4′-methylenebis(phenylisocyanate) (MDI) and from15N-enriched MDI, using stannous octoate as catalyst. The formation of cross-links via isocyanurate ring formation and the fate of the unreacted isocyanate were monitored by both13C and15N CP/MAS NMR methods, and an optimal cure temperature of ca. 120 °C was determined for this particular system. Urea linkages and other less predominant structures such as amine, biuret, and uretidione were clearly identified by15N CP/MAS. The ability of15N CP/MAS to yield quantitative results on the extent of cross-linking is demonstrated.15N CP/MAS proves to be a powerful technique for structure elucidation in these complex macromolecular systems. © 1990, American Chemical Society. All rights reserved.