Alkoxysilane functionalized isocyanurates were prepared from hexamethylene diisocyanate (HDI) isocyanurate and 3-aminopropyltriethoxysilane. The reactants and functionalized isocyanurate were characterized by H-1, C-13 and Si-29 NMR, IR and electrospray ionization-mass spectrometry. Two-dimensional NMR was necessary to accurately assign the proton and carbon spectra for both the reactants and functionalized products. The composition of the HDI isocyanurate was a mixture of oligomers ranging from two to three HDI monomers. The functionalization reaction was performed neat, and as a function of dilution. As expected, substitution on the isocyanurate becomes more uniform with increasing solvent content.