Cationic Ring-Opening Polymerization of Epichlorohydrin in a Nonsolvent: A Cheaper, Cleaner, and Industrially Ready Process

Abstract

The cationic ring-opening polymerization of epichlorohydrin in a nonsolvent (NS-CROP) is presented as a greener alternative to solution polymerization. In this original process, conventional hydrocarbons (n-hexane, methylcyclohexane, petroleum ether, or dodecane), used as dispersion media, solubilize the monomer and the catalyst (BF3×OEt2), but not the initiator (3-chloro-1,2-propanediol) and the polymer. This approach enables rapid CROP initially in small initiator droplets, where the polymer slowly builds up. Only a fraction of the starved-feed monomer swells this dispersion, thereby (i) favoring the activated monomer mechanism, (ii) preventing the conventional temperature runaway observed in solution polymerization, and (iii) maintaining a high polymerization rate. Well-defined poly(epichlorohydrin) diols with controlled molar masses (Mn up to 4000 g·mol–1), low dispersity (Đ ≤ 1.25), and near-quantitative number-average functionality (Fn(OH) ∼ 2.0) were hence generated. No stabilizer is used in the NS-CROP of epichlorohydrin, so stopping the agitation promotes fast phase separation and direct extraction of polyepichlorohydrin. The dispersion solvent, which ultimately contains only traces of catalyst (<2 mol %), was directly reused in at least four consecutive polymerization cycles without any deleterious effects on the properties of the synthesized polymer.