Understanding of ZnO-Catalyzed Polyurethane Synthesis from Bisurea for Further Exploration of One-Pot Synthesis and Property Evaluation Thereof

ZnO is considered to be a good catalyst for the synthesis of polyurethanes (PUs) by alcoholysis of bisureas (BUs). ZnO tends to form Zn(NCO) 2 (NH 3 ) 2 in the presence of urea at high temperature, so does it in the alcoholysis of BUs. Here, attempt is made to understand the role Zn(NCO) 2 (NH 3 ) 2 plays in the alcoholysis of BUs. A loading of Zn(NCO) 2 (NH 3 ) 2 at 5 mol% is found to be sufficient to catalyze the polymerization and the reaction time is greatly cut from 40 h (catalyzed by ZnO) to 26 h, with similar chemical structures and properties. The tensile strength, elongation at break, and toughness for PU–Zn-5 can reach 43.8 MPa, 330%, and 94.0 J cm −3 , respectively. One-pot synthetic strategy is then further introduced to improve the efficiency of the polymerization. Zn(NCO) 2 (NH 3 ) 2 , BU, and PU can be synthesized in one-pot, by adding ZnO, urea, diamine, LiBr, and diol sequentially. The feasibility of this one-pot method is verified, indicated by the similar reaction time, chemical structures, molecular weight, thermal and mechanical properties. This one-pot synthetic strategy offers an efficient way to synthesize PUs directly and simply from urea, diamines, and diols, which is beneficial for improving the molecular diversity of PUs.