Chlorinated Solvent-Free Living Cationic Ring-Opening Polymerization of Epichlorohydrin Using BF3•OEt2 as Co-Initiator: Toward Perfectly Functionalized Poly(epichlorohydrin) Diols

Abstract

The cationic ring-opening polymerization of epichlorohydrin co-initiated by BF3•Et2O has been investigated here. Fast synthesis of pure poly(epichlorohydrin) diols (Fn(OH) ≈ 2.0) with controlled molar mass (Mn up to 4000 g mol–1) and low dispersity (Đ < 1.25) was performed both in toluene and in bulk. An original approach was developed here, consisting of first generating in situ the initiator through the BF3•Et2O-catalyzed reaction of ECH with water, leading to a mixture of oligomers with better solubility in the reaction medium than conventional initiators previously used. Then, through a second monomer starved-feed step, polymerization proceeds exclusively through the activated monomer mechanism, allowing perfect control of the polymer growth. The developed procedure was successfully upscaled to 100 g of polymer to validate a future industrial production of PECH, as well as its derivative glycidyl azide polymer (GAP), the most important energetic binder for solid propellants. Additionally, a separate study was performed to elucidate the reasons for coloration of the polymer observed in the course of polymerization and/or under storage