Structure-Property Relationships of Multi-Armed Glycidyl Azide Polymer Binders

Despite extensive research efforts to improve the mechanical properties of glycidyl azide polymer (GAP), the potential of multi-armed polymers remains underexplored. In this study, we synthesized branched GAP binders using initiators with increasing arm numbers: 2,2-diethyl-1,3-propanediol (DEP) (two-arm), trimethylolpropane (TMP) (three-arm), and pentaerythritol (PE) (four-arm). A linear two-arm 1,4-butanediol (BDO)-derived GAP served as the control. This study focused on how the initiator architecture impacts the viscoelastic and mechanical properties of the GAP binders, with and without N-butyl-N-(2-nitroxy-ethyl) nitramine (Bu-NENA) plasticization. The results showed that, despite having similar hydroxyl values, the GAP binder derived from the branched DEP initiator had lower crosslink densities compared to that derived from the linear BDO initiator, highlighting the influence of branched initiators on network formation. Crosslink densities increased with more initiator arms, leading to improved creep resistance, tensile strength, glass transition temperature, and hardness, but reduced elongation at break. The Bu-NENA plasticizer's effectiveness varied with the initiators. Due to the resistance to plasticizer percolation in more crosslinked networks, DEP-GAP was the most plasticized, while PE-GAP was the least. Tensile strength correlated linearly with crosslink density, while elongation followed a power-law relationship.