Supercritical fluid extraction of cyclic oligomers from depolymerizing PBT

Cyclic oligomers of polyester show great potential for a reaction‐injection‐molding process, because of their initial low viscosity and rapid ring‐opening polymerization at low temperatures (180°C) without exothermic reaction or condensates. In this work, we report the synthesis of cyclic oligo(butylene terephthalate) (COBT) from linear poly(butylene terephthalate) by a formation–extraction process employing supercritical fluids (SCF) CO₂ and pentane at T = 230°C and P = 250 bar. Following this, depressurization of SCF leads to easy recovery of the COBTs. When compared with SCF CO₂, SCF pentane is found to be an attractive solvent because of its higher solubilizing capacity (0.8 mg COBT dimer/g pentane) for the COBTs. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 4487–4492, 2006