Reaction‐induced phase separation in hexamethylene diisocyanate‐based poly(propylene oxide)/poly(ethylene oxide) bi‐soft segment oligomers

• Published in: Polymer international 2018-04, Vol.67 (4), p.481-489
• Main Authors: Wenning, Christian, Schmidt, Annette M, Leimenstoll, Marc C
• Format: Article
• Language: English
• Subjects: Differential scanning calorimetry; Elastomers; Ethylene oxide; Foams; Hexamethylene diisocyanate; Incompatibility; Metals; Oligomers; phase behaviour; Phase diagrams; Phase separation; Plastic foam; Polyethylene oxide; Polyurethane foam; Polyurethane resins; polyurethanes; Propylene; Propylene oxide; reaction‐induced phase separation; Segments; soft segment; Spectroscopy; Ternary systems; Titration
• ISSN: 0959-8103; 1097-0126
• DOI: 10.1002/pi.5539

Oligomeric bi‐soft segment isocyanate‐terminated polyurethanes (ITPUs) are semi‐finished materials crucial for the synthesis of various PU products like foams, thermoplastic parts, dispersions or elastomers. Incompatibilities and thus phase separation phenomena play an essential role in tailoring the properties of the final products. Therefore, a detailed knowledge of these phenomena is mandatory in order to design products with properties meeting the requirements of a given application. In this study the reaction‐induced phase separation during the formation of ITPUs by application of two partially miscible soft segments is presented. The physicochemical basics of this process as well as the extent of the resulting phase separation are discussed on the basis of the initial phase diagram of the reactants. Reaction monitoring by NCO content titration and UV–visible spectroscopy reveals a dependency between the onset of phase separation and conversion. It is found that an increase of the initial content of hexamethylene diisocyanate delays the onset of phase separation. Differential scanning calorimetry reveals further that the phase separation is a direct consequence of the incompatibility of the soft segments. Overall, the findings support the hypothesis that the mechanism and the extent of phase separation are closely related to the ternary phase diagram of the reactants. © 2018 Society of Chemical Industry The physicochemical nature of reaction‐induced phase separation during the formation of isocyanate‐terminated oligomers based on two partially miscible soft segments is presented and discussed.