Systematic Control of Epoxidation in Low-cis Hydroxyl-Terminated Polybutadiene (HTPB) and Its Impact on Polyurethane Properties

Hydroxyl-terminated polybutadiene (HTPB) is widely used in polyurethane binders, adhesives, and elastomers, but its low polarity and unsaturated backbone limit adhesion and long-term stability. Epoxidation presents a promising approach to addressing these limitations. However, most prior studies have focused on high-cis polybutadiene (PB), and systematic tuning of epoxidation in industrial low-cis HTPB has not been thoroughly examined. In this work, the epoxidation conversion of low-cis HTPB was systematically controlled by varying the equivalent amount of 3-chloroperbenzoic acid (<i>m</i>-CPBA). Conversion was governed solely by oxidant stoichiometry, while reaction time, concentration, and temperature had minimal effect, consistent with rapid, mixing-controlled epoxidation. Selective modification of 1,4-cis and 1,4-trans units enabled direct evaluation of how epoxidation degree influences polyurethane network formation and performance. Polyurethanes derived from epoxidized HTPB (EHTPB-PU) exhibited a clear correlation between epoxidation degree and network formation. Mechanical, adhesion, and chemical-resistance measurements revealed optimal performance at 10% epoxidation, where polarity and network compactness are effectively balanced. At this level, polyurethanes showed enhanced tensile strength, broad substrate adhesion, and increased resistance to acidic, basic, polar, and nonpolar environments, along with reduced water uptake. These results identify moderate epoxidation as a practical and efficient strategy for improving HTPB-based polyurethane materials.