Epichlorohydrin (ECH) was polymerized through a cationic ring-opening polymerization reaction using hydroxyl-terminated polybutadiene as an initiator. ECH was very slowly added to the reactant mixture containing a Lewis acid catalyst to promote an activated monomer mechanism (AMM) rather than an active chain-end mechanism (ACM). The triblock copolymer PECH-PB-PECH was separated from the resulting polymers using a fractional precipitation method; however, unlike previous reports of the preparation of a fully azidated PECH-PB-PECH, the substitution of the chlorine moiety in PECH with an azide moiety at high temperatures was not completely accomplished due to the entanglement of the partly azidated PECH-PB-PECH and unreacted PECH-PB-PECH.

수산기로 말단 변성된 폴리부타디엔을 개시제로 사용하여 에피클로로히드린을 양이온 개환 반응에 의하여 중합시켰다. 촉매는 루이스 산을 사용하였으며, 단량체인 에피클로로히드린을 천천히 반응물에 투여하여, 활성 사슬말단 메커니즘보다는 활성 단량체 메커니즘에 의하여 중합이 이뤄지도록 하였다. 반응 후, 분별 침전방법에 의하여 생성물에서 삼중블록 공중합체인, 폴리에피클로로히드린-폴리부타디엔-폴리에피클로로히드린을 분리하였다. 하지만, 위 삼중블록 공중합체의 고온에서의 아지드화 반응 시, 반응 완료되기 전, 부분적으로 아지드화된 삼중블록 공중합체와 아지드화가 안된 삼중블록 공중합체들간 반응에 의하여 고분자 사슬들이 엉켜 생성물 내에서 젤화 현상이 일어나, 최종적으로 아지드화 반응을 종결시킬 수 없었다.

Keywords: cationic ring opening polymerization, hydroxyl-terminated polybutadiene, azidation, azide-alkene reaction

Glycidyl azide polymer (GAP), prepared via the cationic polymerization of epichlorohydrin followed by the azidation of the resulting polymer, has generated significant interest for its positive effects on the flame temperature and burn rate of nitrate ester plasticized solid propellants due to the presence of the highly exothermic azide (-N₃) pendent group in the polymer chain.¹ GAP is also useful as a solid fuel for air-breathing propulsion systems because its monopropellants provide excellent combustion properties.²
In addition to a propellant’s performance and vulnerability to hazard stimuli during manufacturing, the environmental impact of a propellant’s combustion byproducts must be considered. Ammonium perchlorate (AP) has been widely used as an oxidizer for the production of solid propellants; however, AP releases toxic chlorine products during combustion. Ammonium nitrate may be used in place of AP; however, the resulting propellants frequently display undesirable performance properties. The unique thermal properties of GAP cir-cumvent the performance reductions typically observed in propellants that are manufactured using ammonium nitrate instead of AP while avoiding toxic combustion products, thereby rendering GAP an eco-friendly chlorine-free and smokeless propellant.³ Despite its excellent thermal properties, GAP-based solid propellants do not display good mechanical or low-temperature properties compared to conventional hydroxyl-terminated polybutadiene (HTPB)-based solid propellants.
In an effort to address these problems in the field, we previously demonstrated that the introduction of flexible linear polymers, such as polyethylene glycol (PEG) and polycaprolactone (PCL), into GAP-based propellant formulations improved the mechanical and low-temperature properties of the propellant.^4-6 Another approach has involved using HTPB, which displays excellent mechanical and low-temperature properties, as an initiator for the cationic polymerization of epichlorohydrin, a polymeric precursor to GAP.^7,8
We prepared a GAP-PB-GAP triblock copolymer according to the reported procedures; however, the reaction conditions failed to yield the triblock copolymer because the reactants appeared to become entangled (“gelated”) during the azidation reaction of the polyepichlorohydrin (PECH)-PB-PECH. Here, we investigated the causes underlying the entanglement during the azidation reaction. The triblock copolymer (PECH-PBPECH) prepared by the cationic polymerization of ECH was characterized using precipitation methods, ¹H nuclear magnetic resonance (NMR), and gel permeation chromatography (GPC).