Synthesis and Characterization of Trichlorophenol-blocked Polyaryl Polyisocyanate

Typical blocked isocyanate systems are used to obtain the performance of two-component polyurethane system in a one-component mixture. In this study a blocked adduct was synthesized by 2,4,6-trichlorophenol (TCP) as blocking agent for polyaryl polyisocyanate (PAPI). This blocking reaction was in the presence or absence of the catalyst (dibutyltin dilaurate, DBTDL). Elimination of the isocyanate groups and the formation of urethane bonds were studied by FTIR spectroscopy and titration methods. FTIR Spectrum indicates that the NCO groups of the isocyanate molecule are blocked with TCP and the added catalyst should make the reaction faster than that of un-added catalyst. The blocked adduct was characterized by 1H NMR, 13C NMR, DSC and TG/DTA. The 1H NMR and 13C NMR spectra of blocked adduct demonstrated that the structure of the carbamate was observed. Thermal dissociation of blocked diisocyanates was analyzed by DSC and TG/DTA techniques. Deblocking temperature obtained by DSC and TG/DTA techniques was compared. Based on DSC data, it was found that deblocking of blocked PAPI started at 75°C. In general, TG/DTA results showed the same trend as DSC. Deblocking temperature value obtained by TG/DTA technique was lower than DSC value. Differential thermal analysis showed the blocked PAPI began to deblock at 70°C.