Abstract
Organocatalyzed ring-opening polymerization (ROP) of cyclic esters was developed into a stage that demanding translation of the academic success into commercially viable production. An industrial relevant development of the organocatalysis in ROPs required bulk polymerizations at high temperatures up to 180 degrees C. Organic phosphoric acid was one of the few organocatalysts workable under these conditions that devoid of otherwise commonly appeared transesterification, epimerization, and decarboxylation in the ROPs. A commercial dibutyl phosphate (DBuP), which was inexpensive and available by hundreds of tons as antistatic agent, was firstly evaluated as a catalyst. Well-defined polyesters catalyzed by DBuP were obtained with narrow dispersities (D-m 1.08-1.31) and predicted molecular weights from 2.1 to 55 kg mol(-1). Series of homopolymers, diblock copolymers and end-functionalized polymers of epsilon-caprolactone (CL), delta-valerolactone (VL), trimethylene carbonate (TMC), and L-lactide (LA) were synthesized. H-1 NMR, C-13 NMR, SEC, and MALDI-ToF MS analyses indicated that the obtained polyesters were exactly the designated ones. NMR titration experiments confirmed that the ROP proceeded a bifunctional activation mechanism. The cytotoxicity test using MTT assay showed biosafety of the polyesters. The experimental results suggested that dibutyl phosphate is a commercial organocatalyst widely useful in all major cyclic ester monomer toward commercial relevant ring-opening polymerizations.