Synthesis Mechanism and Performance Evaluation of the Viscosity Adjustable Hexamethylene Diisocyanate Trimer

This work proposes a new preparation method for polyisocyanate with adjustable viscosity using hexamethylene diisocyanate (HDI) as a raw material. The innovation of this method lies in the continuous recovery or supplementation of HDI during the reaction process, resulting in a mass percentage of HDI in the reaction system of 30–80%. The reaction system is then heated and further reacted. The viscosity range of polyisocyanate products can be adjusted and expanded by controlling the mass percentage of HDI, the holding time, and the temperature during the reaction process. At the same time, it ensures that the polyisocyanate products have sufficient cross-linking density, low production cost, and low equipment requirements. Various characterization methods were used to analyze the low-viscosity HDI trimer. The results showed that the composition, structure, molecular weight, and element content of the prepared NT31000 HDI trimer with a viscosity of 390 mPa·s were highly consistent with those of the commercially available TLA-100 HDI trimer with a viscosity of 500 mPa·s. NT31000 and TLA-100 HDI trimers were added to the resin as curing agents to prepare the NT31000 and TLA-100 coatings. The results show that the NT31000 low viscosity HDI trimer can form a network with the resin, resulting in coatings with good mechanical properties, including gloss, adhesion, flexibility, impact resistance, and the same quality as comparable to TLA-100 HDI trimer products on the market.