Rational design of a novel NDI-based thermoplastic polyurethane elastomer with superior heat resistance

Thermoplastic polyurethanes (TPUs) hold immense developing potential in engineering products. However, the poor heat-resistance property restricts its large-scale application. 1,5-Naphthalene diisocyanate (NDI) is a rigid aromatic diisocyanate with highly symmetric structure, and the synthesized NDI-based polyurethane has been proved to perform excellent thermal dynamic mechanical properties. In view of this, the development of a new TPU based on NDI and poly(tetramethylene ether) glycol (PTMG) proves to be important. To our best knowledge, it is the first investigation to focus on NDI-based TPU with high heat resistance for 3D printing materials. Moreover, the structure-property behavior of variations in the molecular weight of soft segment (SS) and the content of hard segment (HS) is investigated. It is found that, as the concentration of HS becomes higher or SS becomes shorter, the hydrogen bonding interaction becomes stronger, together with the glass transition temperature, storage modulus, softening temperature and hardness becoming higher. Meanwhile, the peak value of tan δ becomes lower with a higher HS content or longer SS. The results of WAXD indicate the NDI-based TPU exhibit strain-induced crystallization and orientation after deformation, which reinforces the TPU. The results of SAXS and AFM show HS are well-dispersed in the matrix and in nanoscale. This NDI-based TPU is superior to recently reported high-performance TPU materials in terms of heat resistance and can be used as 3D printing materials. The exceptional comprehensive properties, especially high temperature resistance of the proposed NDI-based TPU, provide a new horizon in the development of high-performance elastomer and will contribute to better design of NDI-based TPU.