Research progress of nitrate ester binders

Nitrate ester binders are a unique class of energetic binders containing nitrate ester (-ONO2) pendant groups attached to the polymeric backbones, which have been extensively employed in solid propellant formulations to improve overall energy output and oxygen balance. Both polymerization of nitrate ester monomers and chemical modification of inert polymers are commonly used methods for constructing such binders. Poly(glycidyl nitrate) [PGN] and poly(3-nitratomethyl-3-methyloxetane) [PNIMMO] are well-investigated nitrate ester pre-polyethers formed by cationic ring-opening polymerization (CROP) from nitrate ester monomers, and their synthesis, properties, chemical modification and applications in solid propellants are discussed in detail. It is worth noting that PGN and PNIMMO as soft blocks can further generate energetic thermoplastic elastomers (TPEs) by polyurethane addition polymerization, which have emerged as potential energetic binder candidates for thermoplastic propellants and melt-cast explosives. Therefore, the recent advances of PGN-based TPEs and PNIMMO-based TPEs are subsequently presented. Finally, the synthesis, properties and applications in propellants of several nitrate ester-modified polymers such as cellulose-based nitrates, nitrated hydroxyl‑terminated polybutadiene (NHTPB) and polyvinyl nitrate (PVN), obtained by direct/indirect nitration of inert polymers, are briefly described.