Effect of the amide units in soft segment and urea units in hard segment on microstructures and physical properties of polyurethane elastomer

A new amino-terminated oligomer with amide units was synthesized by polycondensation reaction of diethyl oxalate and amino-terminated polypropylene oxide of 400 g/mol, which was used to prepare novel polyurethane elastomer containing amide units in soft segments and urea units in hard segments (PU-A2000). To explore the effects of amide and urea units on the physical properties and microstructures of polyurethane elastomers (PUEs), amino-terminated polypropylene oxide and polypropylene glycol based polyurethane elastomers (PUD2000 and PU-PPG2000 respectively) were prepared and investigated. Characterization results exhibited that the urea units in the hard segments could distinctly enhance the mechanical properties of PUEs at elevated temperatures. Especially, the tear strength retention rate at 120 degrees C of PU-D2000 was 18.8% higher than that of PU-PPG2000 with only urethane based hard segments. More significantly, the tear and tensile strength of PUD2000 and PU-A2000 with urea units in hard segments were invariable for nearly 3 h at 100 degrees C in comparison with the gradual decline in tear strength of PU-PPG2000. The amide units in the soft segments effectively weakened the intermolecular interaction between soft segments and hard segments and promoted the micro phase separation, which further induced remarkably improved mechanical properties at high temperatures of PUEs, specifically, the tear strength retention rate at 120 degrees C of PU-A2000 was 17% higher than that of PU-D2000. On the whole, the tear strength retention rate of PU-A2000 at 120 degrees C was 35.6% higher than that of conventional PU-PPG2000, indicating that it is a promising strategy to enhance the mechanical properties at high temperatures of PUEs by incorporating urea units into the hard segments and amide units into the soft segments.