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

Abstract

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.