Synthesis, characterization and rheology of tetrafunctional glycidyl azide polymer vis-à-vis difunctional GAP

Glycidyl azide polymer (GAP) with hydroxyl functionality of two is a potential energetic binder for explosive and propellant formulations. To improve its curing behavior and mechanical properties, the synthesis of multifunctional GAP has been attempted. In the present paper, a tetrafunctional GAP (t-GAP) was synthesized by epoxidation of linear difunctional polyepichlorohydrin (PECH-diol) having molecular weight ~1700 and then epoxy ring opening in the presence of water to obtain tetrafunctional PECH (t-PECH) followed by azidation with sodium azide in presence of aprotic solvent. Both t-PECH and t-GAP were characterized by FTIR, NMR, molecular weight, viscosity and hydroxyl value. The viscosity built up and curing reaction with different curator was monitored by rheometer. Viscosity of t-GAP was found to be higher as compared to difunctional GAP. The decomposition pattern of t-GAP, as determined by DSC, was similar to GAP-diol with exothermic decomposition at 254 °C. Clean and void-free curing of t-GAP was achieved using IPDI only as a curator and the curing profile was recorded on rheometer. The curing of t-GAP has been compared with GAP-diol which was cured with mixture of IPDI and triisocyanate (Desmedour N-100). It was observed that t-GAP gave clean and void-free curing with single isocyanate, where as difunctional GAP did not cure with single isocyanate without additive. The mechanical properties for both the cured samples were determined and compared. The t-GAP showed almost fourfold increase in tensile strength when compared with difunctional GAP cured with mixed isocyanate.