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

Abstract

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 À C(=O)OÀ , PKPB(propiolate-terminated polybutadiene), was prepared followed by the 1,3cycloaddition 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 tria-zole-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, T g , available for solid propellants.

Eco‐friendly chemically crosslinked solid composite propellants via catalyst‐free azide‐alkyne cycloaddition

“…In our previous study on PTPB-based polymeric binder [31], it was observed that PTPB-based solid propellants exhibited a remarkably slow curing rate at 70 °C, even displaying tardy curing over a week, as depicted in Figure 15. Additionally, a significant number of bubbles were observed within the PTPB-based solid propellants, as shown in Figure 15.…”

“…Another azide polymer, GAP, was purchased from EURENCO under the trade name of PGA diol. Two types of alkyne (propiolate)-terminated polybutadienes, propiolate-terminated polybutadiene (PTPB) and propiolate urethane-terminated polybutadiene (PUTPB) were also prepared as described in our earlier work [31].…”

“…Both propiolate-terminal curatives for azide-terminated polymers and azide-terminal curative for propiolate-terminated polybutadienes in Figure 3 were synthesized and used, as described previously [31,32]. In addition, another triazide-terminated PCL from the azidation of PCL triol(purchased from Union Carbide, TONE 0310, 500 g/mol) was used as a trivalent azide crosslinker together divalent propiolate curatives.…”

“…Along with IPDI, polyfunctional isocyanate curative Desmodur N-100 pluriisocyanate (N-100, Thorson Chemical) was used in the preparation of urethane-cured solid propellants. As a chain extender for preparing PUTPB, propiolic urethane isophorone mono-isocyanate (PUIMI), asymmetric difunctional compound, prepared as described in our earlier paper was used [31]. All curatives, crosslinkers and chain-extenders used are described in Figure 4.…”