Enzymatic Synthesis and Chemical Recycling of Aromatic Polyesters via Cyclic Oligomers

Aromatic polyesters were synthesized by the lipase-catalyzed polymerization of a diacid and diol via cyclic oligomers as a green process. A series of cyclic oligomers was synthesized by the condensation of dimethyl terephthalate or dimethyl isophthalate and alpha, omega-alkanediol in a dilute toluene solution using immobilized lipase from Candida antarctica (lipase CA). The cyclic oligomer was polymerized by ring-opening polymerization (ROP) in a concentrated anisole solution using lipase CA to produce a series of poly (alkylene terephthalate)s and poly (alkylene isophthalate)s with M(w)s of 81,000 similar to 102,000. Also, poly (benzenedimethanol-adipate)s with M(w)s of 104,000-107,000 were prepared from dimethyl adipate and 1,4- or 1,3-benzenedimethanol under the same conditions. The thermal and mechanical properties were dependent on the position of the substituents on the aromatic ring and the number of methylene groups. The chemical recycling of the aromatic polyesters were also evaluated by their degradation into the corresponding cyclic oligomers using lipase CA in dilute solution. The produced cyclic oligomers were repolymerized in a concentrated solution using lipase CA to produce aromatic polyesters having an M similar to the initial polymer.