Isocyanate‐Free and Dual Curing of Smokeless Composite Rocket Propellants

Bis‐propargylhydroquinone (BPHQ) is an alkyne functionalized isocyanate‐free curing agent for hydroxyl terminated azido polymers. Conventionally, glycidyl azide polymer (GAP) is cured by isocyanate based curatives, which are toxic and hygroscopic in nature. The reaction between hydroxyl end group of GAP and isocyanate is highly sensitive to moisture causing voids in the propellant, leading to poor mechanical properties. Herein, an alternate approach was adapted to exploit 1,3‐dipolar cycloaddition reaction between azido group of GAP and the triple bond (–C≡CH) of BPHQ without catalyst at 50 °C forming triazole crosslinked polymer. The curing behavior of GAP‐BPHQ system was studied by rheological method and based on the results the gel time was determined. In addition, the reaction between GAP and BPHQ was carried out with various GAP/BPHQ ratios (0.9 to 2.5) and effects on mechanical properties of resulting triazole polymers were investigated. Post curing hardness of GAP‐BPHQ binder system was tested by surface Shore‐A hardness measurement. The compatibility of BPHQ with energetic oxidizers such as ammonium dinitramide (ADN) and hydrazinium nitroformate (HNF) were also studied by differential scanning calorimetery (DSC) technique and showed good compatibility. The activation energy (Ea) of cured GAP‐BPHQ binder was evaluated by DSC using Ozawa and Kissinger methods and are found to be 33.55 and 33.16 kcal mol–1, respectively. The advantage of this curing system between GAP and BPHQ is unaffected by moisture as compared to isocyanate based urethane systems and also no need to control humidity during the processing of propellant. The experimental results reveal that triazole crosslinked polymer system could be a better choice to develop novel energetic binder systems for explosives as well as propellants composition with improved performance and eco‐friendly nature.

Section: Introductionmentioning

confidence: 91%

Isocyanate‐Free Curing of Glycidyl Azide Polymer with Bis–propargylhydroquinone

Sonawane

Anniyappan

Athar

et al. 2016

“…Huisgen azide-alkyne cycloaddition (AAC) has been gradually studied as the most promising replacement of urethane reaction for elastomeric matrix of solid composite propellants [12,[15][16][17][18]. Nowadays, AAC reaction is similarly considered as the "click" reaction using metal catalysts such as copper (Cu) and ruthenium (Ru).…”

Section: Introductionmentioning

confidence: 99%

In‐situ Robust Polymeric Networks Prepared via Facile Uncatalyzed Huisgen Cycloaddition of Alkyne‐terminated Polyurethane with Terminal Azides

Min

Kim

et al. 2019

We carried out catalyst – and solvent‐free Huisgen azide‐alkyne cycloadditon (AAC) to develop the polyurethane‐based networks crosslinked through triazole moieties at chain‐ends. An asymmetrical divalent compound carrying the hydroxyl and electron‐deficient alkyne as terminal groups was newly synthesized to prepare the alkyne‐terminated polymer containing urethane moieties within polymer backbone. Additionally, three kinds of terminal‐azide crosslinkers were introduced to react with alkyne‐terminated polyurethanes without any promoters. Kinetics of the uncatalyzed AAC were monitored by using real‐time FT‐IR technique at 50 °C temperature. The rate of AAC using aromatic azide dipole was faster than other dipoles. Compared to the non‐polyurethane‐based networks crosslinked via either urethane or triazole moieties at chain‐ends, triazole chain‐ends crosslinked polyurethane networks conveyed the excellent mechanical properties. However, thermal properties at low temperature were not as good as those of non‐polyurethane networks. Especially, Tg of polyurethane networks formed by an oligomeric azide crosslinker was much higher than others.

“…ADN has been strongly regarded as the most promising replacement of AP, which is widely used in solid rocket propellant and releases hydrogen chloride in combustion. Under urethane curing systems, which have been a long‐used technology in conventional solid propellants, ADN draws serious compatibility problems with isocyanate curing agents, resulting in evolving gaseous products during the curing reaction 8–11.…”

Section: Introductionmentioning

confidence: 99%

Study on Curing Reaction Thermokinetics of Azide Binder/Bispropargyl Succinate by Microcalorimetry

Zhao

Luo

et al. 2015

The thermokinetics of the curing reactions between poly‐(3‐azidomethyl‐3‐methyloxetane) (PAMMO) and bispropargyl succinate (BPS) were studied using a microcalorimeter. On the basis of experimental and calculated results, three thermodynamics parameters (the activation enthalpies, the activation entropies, the activation free energies), the rate constant, three thermokinetic parameters (the activation energies, the pre‐exponential constant, and the reaction order) and the enthalpies of the curing reactions between PAMMO and BPS in the temperature range of 50–65 °C were obtained, showing that the main reaction leading to a triazole structure easily took place in the studied temperature range. The linear relationship between lnk and the molar ratio of triple bonds to azide groups was found. Furthermore, the corresponding kinetic equation describing the curing reaction between PAMMO and BPS was dα/dt=10−4.48(1−α)0.962 at 333.15 K.