Highly Flexible Polyether for Solid Propellants: Synthesis, Room Temperature Curing, Thermal Analysis, and Mechanical Properties

The nitrile oxide-alkene curing system has attracted attention in the solid propellant field due to its byproduct-free, catalyst-free ligation and room temperature curing. For the propellant field, the design and synthesis of alkenyl-terminated adhesives are extremely important, where controllable distribution and quantity of alkene groups improve the integrity of the cross-linked network of the cured elastomers. Compared with traditional adhesives for propellants such as poly(ethylene glycol) (PEG) and polybutadiene (PB), poly(propylene glycol) (PPG) is both highly flexible and polar due to the presence of ether linkages and methyl groups. In this study, PPGs of different number-average molecular weights were used as raw materials and further modified by esterification and carbamate reactions to successfully obtain two types of alkenyl-terminated polymers, 1-PPG and 2-PPG. Based on the nitrile oxide-alkene click cycloaddition reaction, elastomers were then obtained at room temperature. Strikingly, due to the interaction of rigid and highly flexible structures, all of the elastomers exhibited excellent low-temperature mechanical properties (at −40 °C), particularly in terms of elongation at break (up to a maximum of 1126%). This research introduced different kinds of alkenyl-terminated adhesives in the propellant field, providing options for formulation design and promoting further application of the nitrile oxide-alkene curing system.