Polyether Based Thermoplastic Polyurethanes Effect of the Soft Segment Molecular Weight

A series of polyether-based thermoplastic polyure thanes, varying in soft segment molecular weight and hard seg ment content was prepared and studied. Poly(oxypropylene- oxyethylene) diols of M _n of 1000, 2000, 3000, and 4000 were the soft segment polyols. The hard segment, 4,4'-diphenyl methane diisocyanate (MDI) extended with 1,4-butanediol (BDO), and also the soft segment content were varied from 20 to 80 weight percent. Physical-mechanical, thermal (DSC) and dynamic-mechanical property data are used to elucidate the mechanical and morphological behavior of these polymers. Two distinct phases are detected in most of the polymers. The Tg of the amorphous soft phase decreases with increasing polyether molecular weight and is relatively unaffected by soft segment content except at very low levels (≤ 30%). Hard segments appar ently separate into ordered structures which melt between 150 and 220°C. The melting points and the heats of fusion generally increase with hard segment content and soft segment M _n . Soft segment molecular weight also has a significant influence on the mechanical properties of the polymers. In general, the ambient flexural moduli and the dynamic moduli (E') increase with in creasing soft segment M _n and the modulus/temperature curve is flattened.