Effects of Catalyst Complex on In Situ Polymerization and Formation Processes of Reactive Polyurethane Coatings

Reactive polyurethane (RPU) coatings are prepared via simultaneous polymerization and formation without any solvent. Therefore, it not only lowers the total organic carbon (TOC) emissions but also reduces energy consumption. However, its polymerization rate is relatively low at room temperature, and the whole process takes longer than 120 min. Although heating can enhance the rate, it also makes controlling the reaction more difficult. In addition, the present single catalyst is very sensitive to humidity. At high humidity, polyaddition of RPU cannot be efficiently achieved, significantly limiting mechanical properties. To overcome these drawbacks, the effects of selected catalysts on the microstructure evolution during the in situ polymerization and formation process of RPU coatings are investigated. Although the whole process still contains three stages as chain extension, gelation, and microphase separation, the polymerization rate of RPU coatings can be controlled by optimizing the mass ratio of the catalyst complex containing dibutyltin dilaurate (DBTDL) and 1,4-diazabicyclo[2.2.2]octane (DABCO). When the mass ratio of DBTDL to DABCO is 1:1, the polymerization rate is 44% faster than with the single catalyst DBTDL. Simultaneously, the breaking strength (14.56 MPa) and breaking elongation (813%) of the RPU coatings prepared by the catalyst complex are almost unchanged. The acceleration is mainly caused by the steric hindrance effect of the catalyst complex, which improves the catalytic selectivity and the interaction between -NCO and -OH groups in polyol. Moreover, the preparation process is less sensitive to humidity when the catalyst complex is applied. Even at 60% humidity, the final gel content can reach 92.1 ± 1.3%, 9.5% higher than that with the single catalyst DBTDL (84.1 ± 1.0%). Thus, the present catalyst complex can significantly shorten processing time and reduce humidity-related effects during preparation, thereby benefiting the PU industry.