Mechanical and Thermal Properties of Poly(urethane urea) Nanocomposites Prepared with Diamine-Modified Laponite

Nanocomposites based on segmented poly(urethane urea) were prepared by reacting a poly(diisocyanate) with diamine-modified Laponite-RD nanoparticles that served as a chain extender. The nanocomposites were prepared at a constant NH2 to NCO mole ratio of 0.95, while varying the fraction of diamine-modified Laponite relative to the free diamine chain extender. Compared to neat poly(urethane urea), all nanocomposites showed increased tensile strength and elongation at break. As Laponite loading increased, tensile properties passed through a maximum at a particle concentration of 1 mass%, at which a 300% increase in tensile strength and 40% increase in elongation at break were observed. A maximum in urea and urethane hard-domain melting endotherms was also observed at this Laponite loading. Optimal mechanical and thermal properties coincided with a minimum in the size of the inorganic Laponite phase. Nanocomposites containing diamine-modified Laponite had higher tensile strengths than those with nonreactive monoamine-modified Laponite or diamine-modified Cloisite