A recyclable catalytic system for ionic polymerization under ambient conditions is still undoubtedly a challenging issue that needs to be addressed for industrial production. In this study, a metal-free cationic ring-opening polymerization of glycidol (GD) using tris(pentafluorophenyl)borane (B(C6F5)3, BCF) as a catalyst affords a well-controlled branched cyclic polyglycidol (BC-PGD) structure and a recycling polymerization process was achieved using unpurified reagents and ambient conditions. Although homogeneous catalysts cannot usually be readily recycled during polymerization, the growing PGD chains in nonpolar solvents induces self-precipitation in catalyst solutions with increasing molecular weight and hydrophilicity, causing a phase separation of PGD with a uniform molecular weight distribution. Specifically, the recycling polymerization process is successfully performed by repeating the simple sequence of decantation and addition of the unpurified monomer. The unique structure of the obtained PGDs was confirmed by 1H NMR, inverse-gated 13C NMR analyses, SEC, and MALDI-ToF-MS. Based on the green and recyclable BCF-catalyzed cationic ring-opening polymerization, more intriguing examples with simple and well-reproducible polymerization techniques are anticipated for challenging industrial applications.
