Effect of crosslinking point structures on properties of polyurethane end-crosslinked PBT elastomers

Exploration of the effect of crosslinking point structures on elastomer properties is significant in the formulation design and performance optimization of elastomers. In the work, we used an equal molar random copolyether of hydroxyl terminated 3,3-bis(azidomethyl)oxetane and tetrahydrofuran (PBT) as a prepolymer, and two PBT elastomers with different crosslinking point structures were prepared by reacting PBT with polyfunctional isocyanate compound N100 and TMP/HDI. FTIR spectrum analysis and swelling tests indicated that N100 crosslinked elastomer S0 and TMP/HDI crosslinked elastomer S4 had an identical chemical crosslinking network. For elastomer S0, hydrogen-bonded urea carbonyl and hydrogen-bonded carbamate carbonyl existed simultaneously, whereas only hydrogen-bonded carbamate carbonyl existed for elastomer S4. Low-field nuclear magnetic resonance measurements analysis indicated that hydrogen-bonding association was among elastomer crosslinking points. Dynamic mechanical analysis showed that the stronger urea carbonyl hydrogen bonding among crosslinks provided elastomer S0 with a lower glass transition temperature (− 37 °C) and a lower modulus loss factor. Elastomer S4 with weaker carbamate carbonyl hydrogen bonding among crosslinking points yielded a higher glass transition temperature (− 30 °C) and higher modulus loss factors. Elastomer S0 presented a higher tensile modulus, and elastomer S4 presented a higher tensile strength and elongation-at-break. These findings provided an experimental and theoretical basis for adjusting mechanical properties of end-crosslinked elastomer by constructing different crosslinking point structure. Graphical abstract