Low Risk Synthesis of Energetic Poly(3‐Azidomethyl‐3‐Methyl Oxetane) from Tosylated Precursors

Abstract

Azidated oxetanic polymers such as poly(3‐azidomethyl‐3‐methyl oxetane), are under investigation as “energetic” binder to be used as an alternative to polybutadiene in solid rocket propellants. The classic synthetic route for the production of the polymer is through an azidated monomer where the N3− functionality has been previously introduced by nucleophilic displacement of a suitable, usually a halogen, leaving group. However, this could involve critical steps with manipulation of a highly unstable liquid monomer. Here it is shown that the azidation can be performed as the final step of the preparation by substitution of the tosyl group in a preformed polymer. The procedure assures good yield and purity of the product and satisfactory rate of reaction, being the energetic functionality always kept in a safe form, which shows low shock and friction sensitivity. Poly(3‐azidomethyl‐3‐methyl oxetane) was prepared by azidation of poly(3‐tosyloxymethyl‐3‐methyl oxetane) in dimethylsulfoxide, testing several operating conditions. Moreover, hypothesizing a second order kinetics, the rate constant and the activation energy for the azidation step have been estimated.

Homo- and copolymers of 3-tosyloxymethyl-3-methyl oxetane (TMMO) as precursors to energetic azido polymers

“…The conditions and the kinetics of the azidation of pTMMO were deeply investigated and reported in a previous paper [5]. Analogously to pAMMO, the copolymer p(AMMO-co-BAMO) was obtained by displacement of bromine and tosyloxy groups by azide groups.…”

“…The main limit of this synthetic route is related to safety, as it involves the handling and storage of azide-oxetanes which are considerably more unstable and shock-sensitive than the corresponding polymers. For this reason, we recently synthesized azide polymers, such as pAMMO and the random copolymer p(GA-co-BAMO), by direct azidation of their polymeric precursors poly(3-tosyloxymethyl-3-methyl oxetane) (pTMMO) and poly(epichlorohydrin-co-3,3-bis(bromomethyl)oxetane) p(ECH-co-BBrMO), rather than by polymerization of the azide monomers (Barbieri et al [4], [5]). …”

Synthesis and Characterization of Poly(3‐azidomethyl‐3‐methyl oxetane) by the Azidation of Poly(3‐mesyloxymethyl‐3‐methyl oxetane)

“…The solid rocket propellant using energetic thermoplastic elastomers (ETPEs) as binderh as manya dvantages,s uch as reuse, recycle, and recovery,w hich has caused wide concern in the field of energetic materials [1,2].T he ETPEs based on the azidepolymers such as glycidyl azidepolymer (GAP) and poly(3,3-bisazidomethyl oxetane/3-azidomethyl-3-methylo xetane) [P(BAMO/AMMO)] have been focus of research in recent years, because of their positive heat of formation, low glass transition temperature, and insensitivity [3][4][5][6].B ut ETPEs based on GAP have poor mechanical properties compared with theE TPEs based on P(BAMO/AMMO) at low temperature. P(BAMO/AMMO) is the preferred next generation ETPE energetic binder [6].…”

New insights into copper-mediated polymerization and polymer topologies

“…Most literature procedures for the reaction of -Br polymer end-groups with NaN 3 to produce an azide end-group use organic solvents (e.g. DMF) and takes between 12 to 24 h. 24,[38][39][40] This is due to the low solubility of NaN 3 . For example, in DMF the solubility is 4.9 mg/mL at 95 °C) and by changing the solvent to DMSO at this temperature not only did the solubility increase to 52 mg/mL but there was a dramatic increase in the rate of azidation.…”

“…For example, in DMF the solubility is 4.9 mg/mL at 95 °C) and by changing the solvent to DMSO at this temperature not only did the solubility increase to 52 mg/mL but there was a dramatic increase in the rate of azidation. 40 At first sight, from the hydrolysis data above, significant hydrolysis in water of PNIPAM-Br should occur prior to formation of azide end-groups. The in situ addition of NaN 3 (~20 eq to halide end-group) in water immediately after the polymerization for azidation of 2a reached ~92% EGF after only 30 s measured by MALDI-ToF ( Figure 5.2A), and the EGF did not change after 10 min (see Figure A5.2 in Appendix).…”