Relationship between structure and dynamic mechanical properties of thermoplastic polyurethane elastomer containing bi‐soft segment

In this work, we investigated the microphase separation, mechanical, and dynamic mechanical properties of thermoplastic polyurethane elastomers (TPUs) with one‐soft segment (polypropylene glycol, PPG, or hydroxyl‐terminated polybutadiene, HTPB) or bi‐soft segment (PPG and HTPB) using FTIR, XRD, SAXS and amplitude modulated‐frequency modulated viscoelastic mode of AFM (AM‐FM mode AFM) methods. The results showed that the microphase separation process of hard and soft segments (HS and SS) in TPU containing PPG and HTPB soft segments (PPG‐HTPB‐PU) was restricted by randomly alternated bi‐soft segments, which results in formation of a low content of irregular‐shaped hard domain (HD). In addition, the microphase separation of PPG‐HTPB‐PU induced a triple‐phased structure of HD, HTPB rich phase and mesophase. The mesophase of PPG‐HTPB‐PU was formed of HS, PPG and HTPB segments which were excluded out of HD and HPTB rich domains during microphase separation process. The damping temperature range (at tan δ greater than 0.3) of PPG‐HTPB‐PU was from −14.6 to 32.1°C (46.5°C) which was more broad than that of TPU containing HTPB soft segment (HTPB‐PU). The broad damping temperature range of PPG‐HTPB‐PU is mainly attributed to the enhanced energy consumption caused by the frictional motions of mixed segments of mesophase.