Propiolate‐Terminated Polybutadiene‐Based Network Binders for Solid Propellants via Catalyst‐Free Azide‐Alkyne Cycloaddition

We developed the new preparation method of polybutadiene‐based binders, which has been widely used in solid composite propellants, under the triazole curing system formed by the Huisgen azide‐alkyne cycloaddition (AAC) without any promotors. Firstly, polybutadiene terminated with propiolate, alkyne adjacent to electron‐withdrawing group −C(=O)O−, PKPB(propiolate‐terminated polybutadiene), was prepared followed by the 1,3‐cycloaddition with trivalent azide curatives leading to form the polybutadiene binder cured via triazole linkages. Unexpectedly, compared to the conventional urethane‐cured binders, higher temperature and long time were required to cure the polybutadiene binder and the mechanical properties, especially tensile strength was not as good as that of binder formed under urethane curing system. For the triazole‐cured polybutadiene binder to exhibit the better mechanical properties, an asymmetric difunctional chain‐linker end‐capped with an alkyne and an isocyanate, respectively was introduced to modify the end‐groups of hydroxyl‐terminated polybutadiene (HTPB) with propiolates, ester alkynes, resulting in forming the propiolate‐terminated polyurethane butadiene (PTPUB). The triazole‐cured polyurethane butadiene‐based binders obtained from the click reaction of PTPUB with tri‐azide curatives conveyed the excellent mechanical properties as well as considerable shortening of reaction time, compared to PKPB‐based binders. Finally, both of triazole cured binders showed the good low‐temperature properties, Tg, available for solid propellants.