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

Abstract

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.

Effects of crosslinking degree and carbon nanotubes as filler on composites based on glycidyl azide polymer and propargyl‐terminated polyether for potential solid propellant application

“…It showed uniform distribution of the components, and indicated that the crosslinked GAP/PTMP resulted in no great ‐ scale phase separation. What's more, the composite materials did not contain any bubbles or other discontinuities, which affected the quality and safety of the GAP/PTMP materials, as there are no side reactions to prepare the triazole during the curing process by Huisgen reaction when compared to the GAP‐urethane cured polymers.…”

Review of novel energetic polymers and binders – high energy propellant ingredients for the new space race

“…Azido groups from GAP react with polyfunctional alkynes to yield 1,2,3-triazoles. GAP cured with bis-propargyl succinate (BPS) has shown better mechanical properties to diisocyanate cured urethane counterpart [21][22][23][24][25][26][27][28][29].…”

“…Several triazoles cured polymer suffers from various degrees of swelling and may require a careful mixture of ratios and other solutions [23][24][25][26][27]. A recent study cured poly-butadiene with GAP using Propargyl terminated polybutadiene(PTPB) in a 2:1 ratio, respectively.…”

“…PTPB-GAP binder shows promising properties with good mechanical properties and glass transition temperature [27]. Other groups have developed an alternative to BPS in the triazole curing of GAP using Bis-propargyl hydroquinone(BPHQ) and dimethyl 2,2-di(prop-2-ynyl)malonate (DDPM) and appear to show better mechanical properties than the BPS cured formulation [25,28].…”

Mechanical Characteristics and Thermal Decomposition Behaviors of Polytetrahydrofuran Binder with Glycerol Propoxylate (Mn=1500) as a Crosslinking Agent

“…A propellant with a high burning rate can supply a large impulse; therefore, a high-burning-rate propellant is required when developing high-performance rocket motors. The application of an energetic binder is one approach that could improve propellant performance, and many studies on energetic binders have been conducted [1][2][3][4][5][6][7][8]. To date, such energetic binders have not been used for practical applications because they are expensive and difficult to manufacture industrially.…”