A Novel Blocked Waterborne Polyisocyanate Crosslinker With High Branch Structure and Its Application

ABSTRACT The polyester polyols intermediate, synthesized from the polymerization of pyromellitic dianhydride (PMDA) and trimethylolpropane (TMP), was reacted with isophorone diisocyanate (IPDI) to obtain branched polyester‐type polyisocyanate. Then, the unreacted isocyanate groups (‐NCO) were blocked by methyl ethyl ketone oxime (MEKO). Subsequently, a linear polyether‐type polyisocyanate was concurrently incorporated into the branched system through the polymerization of hexamethylene diisocyanate (HDI) and polyethylene glycol 600 (PEG‐600). Finally, the remaining ‐NCO was also blocked and the free carboxyl groups were neutralized. By adjusting the isocyanate index (R 1 value) in the branched structure and changing the mass percentage of the linear structure, a series of blocked waterborne polyisocyanate crosslinkers with high branch structure (SWPI) were successfully obtained. Structural verification was achieved through FT‐IR and 1 H‐NMR analysis. Systematic investigations were conducted on the thermal behavior and water dispersion of these crosslinkers, along with a preliminary evaluation of the cured materials. The results suggest that the adhesion of SWPI‐cured materials can achieve 1.43 MPa, and the maximum decomposition temperature of the cured material is about 12°C higher than that of pure resin.