Evolution of Reaction-Induced Phase Segregations in Bi-Soft Segment Urethane Oligomers

Oligomeric bi-soft segment isocyanate-terminated polyurethanes (ITPUs) are semi-finished goods crucial for the fabrication of various polyurethane (PU) products such as foams, thermoplastics, adhesives, dispersions, and elastomers. Incompatibilities and thus phase segregation phenomena play an essential role in tailoring the properties of the final products. In this work, the evolution of reaction-induced phase segregation (RIPS) in ITPUs is explored in terms of composition and morphology of the phase segregated products as well as competing second order kinetics of the reaction. The results suggest that mechanism and extent of the phase segregation are thermodynamically controlled following the ternary phase diagram of the reactants. A comprehensive description of the phase behavior during the reaction is provided demonstrating excellent control over the morphology of ITPUs by means of appropriate adjustment of the initial reactant composition. These results are fundamental for tailored morphology design as it is employed for instance in membrane synthesis.