Enhancement of toughness and ductility to 1,2,3-triazole Click-cured elastomers via regulation of molecular network and microphase separation

Abstract

Huisgen-click curing systems of 1,3-dipolar cycloaddition are widely employed in solid propellant binders due to their humidity insensitivity and gentle reaction conditions. However, curing systems of multi-azide and alkyne usually suffer network defects due to uncontrollable reaction equivalents and intramolecular cyclization of multi-azide. Moreover, the formed rigid triazole rings further lower mechanical performance by impeding molecular mobility. Herein, a strategy based on a polymeric curing agent with fixed multi-azide functionality and flexible chain was proposed to cure alkyne terminated binder for regulation of the network structure. Meanwhile, the urethane group near the terminal alkyne was introduced into the binder regulating the spatial distribution of rigid triazoles, forming microphase separation, and improving intermolecular forces. A parabolic relationship between mechanical properties and the molar ratio of alkyne/multi-azide was illustrated with peaking near the stoichiometric ratio, which indicates controllable reaction equivalent and prevention of intramolecular cyclization to optimize the network structure. Furthermore, the toughness and elongation at the break of the cured system respectively increased by 781.25% and 524.24% due to the incorporation of urethane. The introduced urethane group induced microphase separation via aggregating hard segments and improving molecular mobility. This strategy depending on the optimization design of molecular network and microphase separation significantly enhances the mechanical properties of solid propellants and shows promising applications in energetic material systems.