Analysis of the mechanical behavior of polyurethane thermoset elastomers based on hydrogen bonding between different crosslinking point structures

To reveal the effect of polyurethane crosslinking point structures on the mechanical properties of polyurethane thermoset elastomers, using amorphous prepolymer poly (azide glycidyl ether) (GAP) as a binder, polyisocyanate cross-linker N100 and hexamethylene diisocyanate (HDI) as curing agents, trimethylolpropane (TMP) as a crosslinking agent, two GAP polyurethane thermoset elastomers that have similar chemical crosslinking network density, elastomer S0 prepared from GAP and N100 and elastomer S4 prepared from GAP and HDI/TMP, were selected to study in detail. DSC and XRD analysis indicated that two GAP polyurethane thermoset elastomers both exhibit stable amorphous aggregation structure below 80 °C. Mechanical properties test showed that thermoset elastomer S0 gives higher tensile modulus, lower tensile strength and elongation rate, while thermoset elastomer S4 gives lower tensile modulus, higher tensile strength and elongation rate. In-situ FTIR and low field nuclear magnetic resonance (LF-NMR) analysis suggested that there exists stronger urea carbonyl hydrogen bonding structure within thermoset elastomer S0, while weaker urethane carbonyl hydrogen bonding structure within thermoset elastomer S4. The different strength of the hydrogen bonding between crosslinking points imparts different segment mobility to S0 and S4. Dynamic thermodynamic analysis (DMA) indicated that, stronger urea carbonyl hydrogen bonding has suppressed segments mobility and thermoset elastomer S0 present lower loss modulus and loss factor, while thermoset elastomer S4 present higher loss modulus and loss factor because there just exist weaker urethane carbonyl hydrogen bonding interaction between crosslinking points.