Curing of Glycidyl Azide Polymer (GAP) diol using isocyanate, isocyanate-free, synchronous dual, and sequential dual curing systems

Abstract

Glycidyl azide polymer (GAP) is an important energetic binder candidate for new minimum signature solid composite rocket propellants, but the mechanical properties of such GAP propellants are often limited. The mechanical characteristics of composite rocket propellants are mainly determined by the nature of the binder system and the binder-filler interactions. In this work, we report a detailed investigation into curing systems for GAP diol with the objective of attaining the best possible mechanical characteristics as evaluated by uniaxial tensile testing of non-plasticized polymer specimens. We started out by investigating isocyanate and isocyanate-free curing systems, the latter by using the crystalline and easily soluble alkyne curing agent bispropargylhydroquinone (BPHQ). In the course of the presented study, we then assessed the feasibility of dual curing systems, either by using BPHQ and isophorone diisocyanate (IPDI) simultaneously (synchronous dual curing), or by applying propargyl alcohol and IPDI consecutively (sequential dual curing). The latter method, which employs propargyl alcohol as a readily available and adjustable hydroxyl-telechelic branching agent for GAP through thermal triazole formation, gave rise to polymer specimens with mechanical characteristics that compared favorably with the best polymer specimens obtained from GAP diol and mixed isocyanate curatives. The glass transition temperature (Tg) of non-plasticized samples was heightened when triazole-based curing agents were included, but when plasticized with nitratoethylnitramine (NENA)plasticizer, Tg values were very similar, irrespective of the curing method.