Non-Isocyanate Polyurethanes by Alcoholysis of Alkyl Bisurea with Li Salt-Assisted Melting: Synthesis and Properties

Alcoholysis of bisureas (BUs) would be of great potential among the non-isocyanate routes for preparing polyurethanes, if the issue of the high melting temperature and the poor solubility for BUs can be solved. In this study, it is proposed to introduce Li salt to assist the melting of BUs via a eutectic system. It is found that the melting point of BUs indeed can be reduced to 170 degrees C or even lower by adding 40 mol% of LiCl or LiBr. In the polymerizations of BUs with diols, it is found that ZnO nanoparticles (30 +/- 10 nm) are the most efficient catalyst in the catalyst screening study. Four polyurethanes are successfully synthesized and the glass transition temperature of them is detected to be 34-45 degrees C. PU1010 is tougher than other polymers so that it is able to be molded. The Young's modulus of PU1010 is 195.1 MPa, while the strength and the elongation at break are 36.4 MPa and 280%, respectively. The toughness calculated is 67.3 J cm(-3). This Li salt-assisted melting strategy not only realizes the synthesis of polyurethanes through alcoholysis of BUs, but can also be extended to the synthesis of other high performance polymers.