<p>Polyisocyanates represent a principal class of monomers utilized in the synthesis of polyurethanes. The polyisocyanates that are currently in commercial use have their origin in the petrochemical industry. It should be noted, however, that there are also green polyisocyanates available, which are obtained from bio-based monomers. The chemical structure and functionality of isocyanates have a significant impact on the feasibility of their utilization in polyurethane synthesis. The objective of this study was to investigate the modification of a bio-based triisocyanate in order to create a difunctional isocyanate. The products resulting from the modification process, conducted with the use of ethanol and various catalysts, were characterized through the application of spectroscopic techniques, including Fourier transform infrared spectroscopy FTIR and proton nuclear magnetic resonance ¹H NMR. Furthermore, the rheological behavior of the products resulting from the modification of triisocyanates was also evaluated. The thermal behavior and stability were characterized using differential scanning calorimetry DSC and thermogravimetric analysis TGA. The results demonstrated that the type of catalyst employed has a significant impact on the thermal behavior of triisocyanate modification products. Products based on metal–organic catalysts, exhibited lower thermal stability compared to blocked triisocyanates modified with tertiary amine catalysts or without catalysts.</p>