Investigating the Impact of Systematic Hard Segment Modulation on Performance of Hydroxyl Terminated Polybutadiene (<scp>HTPB</scp>) Thermoset Polyurethane Elastomers

ABSTRACT Despite the versatility and extensive applications of hydroxyl‐terminated polybutadiene (HTPB)‐based thermoset polyurethanes (PUs), research on tailoring their performance through hard‐segment modulation is limited. In this study, the impact of hard segment (HS) content modulation (20%–50%) on the properties of two series of HTPB‐based thermoset PU elastomers at R (NCO/OH) 1.5 and 1.6 was investigated. The effect of increasing the HS content on processability, structural confirmation, physico‐mechanical properties, thermal properties, and crystallinity was evaluated through rheological analysis, Fourier‐transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and x‐ray diffraction (XRD). Both series showed 19% and 23% increases in the hydrogen bonding index (HBI) with HS modulation. The pot life at R = 1.5 decreased from 373 to 284 min and at R = 1.6, from 265 to 210 min. The crosslink density, glass transition temperature, and thermal stability increased for both series with higher HS content. At R = 1.5, the tensile strength increased by 105% and the maximum elongation increased to 40% HS before decreasing. At R = 1.6, the tensile strength increased by 81%, and the maximum elongation increased to 30% HS before decreasing. These findings clarify how hard‐segment modulation affects thermosetting PU structure, processing, and performance.