Furthermore, HTPB used as prepolymer binder cured with
toluene diisocyanate (TDI) to have required mechanical properties.
During curing, hydroxyl groups of HTPB react with NCO
groups of TDI to form urethane linkages, i.e., NHC( O) O . The
polyurethane linkage decomposes into smaller molecules during
the digestion with nitric acid and a clear solution was obtained.