The reinforcing effect of cyclic binary secondary amine chain extenders on the cryogenic performance of thermoplastic polyurethane elastomers

• Published in: Journal of applied polymer science 2022-07, Vol.139 (27), p.n/a
• Main Authors: Geng, Yanfei, Wang, Meng, Li, Wenke, Yi, Pengcheng, Ji, Yumei, Stewart, Callum, Yang, Yike, Liu, Feng
• Format: Article
• Language: English
• Subjects: Chains; elastomers; glass transition; Glass transition temperature; Homology; Imidazoline; Low temperature; Materials science; Mechanical properties; Polymers; polyurethane; Polyurethane resins; Prepolymers; Segments; structure‐property relationships; Tensile strength; Thermodynamic properties; Urethane thermoplastic elastomers
• ISSN: 0021-8995; 1097-4628
• DOI: 10.1002/app.52500

The poor cryogenic performance of thermoplastic polyurethanes (TPU) severely restricts their extensive application in low‐temperature fields as elastomers. Chain extenders are one of the adjustable items for TPUs to optimize cryogenic performance. In this contribution, three cyclic amine homologs of imidazoline, piperazine and 2‐methylpiperazine are selected as bi‐functional chain extenders. The corresponding TPU elastomers, TPU‐IM, TPU‐PP, and TPU‐2P with identical soft segments, are synthesized by the prepolymer method. All TPUs' structure, morphology and thermodynamic properties were investigated. The results showed that the cyclic amine structure embedded in TPU hard segment can effectively promote microphase separation through hydrogen‐bonded crosslink and polar aggregation on the molecular scale, achieving a glass transition temperature (Tg) as low as −103.9°C for resisting low temperatures. The mechanical properties also demonstrated a 23‐fold improvement compared to the control TPU‐BD. The elastomer TPU‐PP possessed the best all‐around performance with an ideal Tg of −98.4°C and tensile strength of 18.1 MPa. We believe that these TPUs will have potential applications in cryogenic engineering. The low‐temperature resistance and mechanical properties of all modified TPU elastomers are enhanced simultaneously by employing cyclic amine chain extenders. TPU‐IM exhibits a Tg as low as −103.9°C, achieving excellent low‐temperature resistance the theoretical limit. The best comprehensive performance, including an ideal Tg of −98.4°C and the strongest tensile strength of 18.1 MPa, is provided by piperazine‐embedded TPU‐PP.