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

Abstract

Poly(3-azidomethyl-3-methyloxetane) and its copolymers with 3,3-bis(azidomethyl)oxetane were synthesized by cationic polymerization from 3-tosyloxymethyl-3-methyl oxetane and 3,3-bis(bromomethyl)oxetane, using a polyol as initiator and boron trifluoride complex as catalyst, followed by azidation. The final objective is the synthesis of an energetic binder to be used for rocket propellants and therefore the effects of different initiator/catalyst systems on important properties, like, i.e., the molecular weight distribution and the functionality of the polymer, were investigated. It was found that, even though both the operating conditions and the catalytic system were chosen in order to grant the living character of the polymerization, the latter seems to be prevalently driven by an "active chain end" mechanism. In particular, this may lead to the undesired formation of a small quantity of oligomers and to the presence of non-hydroxylic chain-end functionalities. Nevertheless, the average number of OH groups can be strictly controlled when boron trifluoride tetrahydrofuranate is used as catalyst.

Azidated Ether-Butadiene-Ether Block Copolymers as Binders for Solid Propellants

“…This technique of azidation is almost "universal" and in the last decades many researchers, which tested several solvents and operating conditions as well as many different leaving groups, described it. In our research group, it was previously used to substitute chlorine, bromine and tosyl groups, in either DMF or DMSO, with temperatures ranging from 90 up to 150 °C [37,38,40,43]. Pisharat and Ang azidated PECH in DMF, at 120 °C for 12h [39], while Manser suggested DMSO at 80 °C also for the azidation of the oxetanic monomers [33].…”

“…Side reactions, including cyclization, are strongly reduced in AMM and well-defined linear products can be obtained [7]. However, it must be emphasized that it is not easy to drive the reaction toward the desired mechanism and often both mechanisms may be present at the same time [37,38].…”

“…The polymers were also subjected to preliminary characterizations in lab-scale propellant formulations [41,42]. The same research group studied also the use of the tosylated precursor of AMMO to prepare PAMMO [43] and p(AMMO-r-BAMO) copolymers [38].…”

Synthesis of GAP and PAMMO Homopolymers from Mesylate Polymeric Precursors

“…In this case the side reactions, including cyclization, should be minimized [6]. However, it must be underlined that it is not easy to drive the reaction toward the desired mechanism and often both mechanisms may be present at the same time [31,35].…”

“…Other suggested polymeric azides are poly(3,3 bis(azidomethyl)oxetane-co-ε-caprolactone) [25], 3,3 bis(azidomethyl)oxetane-tetrahydrofuran [26,27], polyglycidylazide-bpoly(azidoethyl methacrylate) [28] and polyoxetanes [6,[29][30][31][32][33][34][35], first synthesised by Manser [36][37][38], such as 3-nitratomethyl-3-methyl oxetane (NIMMO), 3,3-bis-(azidomethyl)oxetane (BAMO) and its analog monofunctional 3-azidomethyl-3-methyl oxetane (AMMO). In the first synthesis, the chlorinated or tosylate monomer was azidated and then subjected to cationic ring-opening polymerization by using a diol and a Lewis acid as catalyst.…”