Evidence of Liquid-Liquid Demixing During Bi-Soft Segment Polyurethane Prepolymerization

Bi-soft segment isocyanate-terminated polyurethanes (ITPUs) currently play a major role in the industrial production of high performance polyurethanes (adhesives, coating, foams, thermoplastics, nanoparticles, dispersion). The present contribution reports on the investigation of liquid-liquid demixing phenomena during the synthesis of bi-soft segment ITPUs. For this purpose, a dedicated experimental setup based on coupled in-line reaction monitoring via UV/Vis and FTIR technique was developed. It was used to monitor phase separation and reaction progress in the course of a prepolymerization using 1,6-hexamethylene diisocyanate and a polyether polyol mixture. Such phenomena may have a great impact on reaction kinetics and product quality. Furthermore, in-line FTIR analysis appeared to be sensitive to phase separation processes in the way that it predominantly detects the continuous phase rather than the dispersed droplets.