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

Abstract

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.

Improved dynamic properties of thermoplastic polyurethanes made fromco‐monomericpolyester polyol soft segments based on azelaic acid

“…At the same NCO/OH ratio, TPUs based on BDAZSA and BDAZAA had relatively lower concentration of HS as indicated by its molecular structures (Scheme 3) in comparison to TPUs based on BDSA, BDAA, and BDAZ (Scheme 4). Similar observation was reported by Liu et al, 34 whereby TPU made from bi‐soft segment (polypropylene glycol‐hydroxyl‐terminated polybutadiene based TPU, PPG‐HTPB‐PU) exhibited lower tensile strength and Shore A hardness compared with TPU made from one‐soft segment (hydroxyl‐terminated polybutadiene based TPU, HTPB‐PU). In addition, due to extensive crystallinity of the BDSA SS, a yield in tensile strength was observed in the TPU, indicating a thermoplastic behavior.…”

“…At the same NCO/OH ratio, TPUs based on BDAZSA and BDAZAA had relatively lower concentration of HS as indicated by its molecular structures (Scheme 3) in comparison to TPUs based on BDSA, BDAA, and BDAZ (Scheme 4). Similar observation was reported by Liu et al,34 whereby TPU made from bi…”

“…[37][38] The obtained data were normalized to the area of deconvoluted aromatic peak at 1600 cm −1 . Using formula disclosed by Liu et al 34 and data in Table 3, relative contents of the bonded urethanes for TPUs can be arranged in the following order: BDSA (68.7%) > BDAZSA (60.0%) > BDAZ (51.5%) > BDAZAA (50.5%) > BDAA (44.6%). According to Liu et al, 34 the CO (carbonyl) groups of TPUs can be divided into four types based on a degree of hydrogen bonding, that is, free CO groups from soft domain (1730 cm −1 ), disordered hydrogen bonded CO groups from soft domain or interphase between hard domain and soft domain (1716 cm −1 ), ordered hydrogen bonded CO groups from hard domain (1704 cm −1 ) and ordered hydrogen bonded CO groups from crystalline phase (1690 cm −1 ).…”

Application of blocked isocyanate in preparation of polyurethane(urea) elastomers

“…The degree of microphase separation and the domains morphology play a key role in the properties of polyurethane. 26 The linear structures are beneficial to the slip between molecular chains in stress-induced, and the crystalline structures prove the aggregation and regular arrangement of the phases, which lead to microphase separation. 27,28 In addition, Strong hydrogen bonds provide pseudo-cross-linked network structures between highly linear polyurethane chains, which make the polymer possess the physical properties and mechanical behaviors, (such as, strength and high elasticity) of covalent cross-linked network at room temperature.…”

“…We imaged that polyurethane (urea) with high linear structures and good crystallinity was expected to solve this problem. The degree of microphase separation and the domains morphology play a key role in the properties of polyurethane 26 . The linear structures are beneficial to the slip between molecular chains in stress‐induced, and the crystalline structures prove the aggregation and regular arrangement of the phases, which lead to microphase separation 27,28 .…”