Food Sweetener Saccharin in Binary Organocatalyst for Bulk Ring‐Opening Polymerization of Lactide

Polylactic acid or polylactide (PLA) is the leading commercialized bio‐based polyester widely used in biomedical apparatus and disposable food packaging materials, among others. Desirable features of green and environmentally friendly ring‐opening polymerization (ROP) of lactide (LA) by organocatalysts were bulk ROP at high temperature; the organocatalyst should be inexpensive, readily available, and biosafe in the produced PLA; and the ROPs should afford PLA of precisely controlled molecular weights with no transesterifications, nor epimerizations. An organocatalyst that met all these desirable merits has, to the best of our knowledge, not been reported to date. We proposed pyridinium saccharinate binary organocatalyst for industrially feasible ROPs of lactide, carbonates, and lactones. Pyridinium saccharinates of three commercial pyridines including 4‐dimethylaminopyridine (DMAP), 4‐pyrrolidinopyridine, and pyridine were prepared in one step by quantitative yields. An optimal DMAP saccharinate (DMAP ⋅ Sac) as the catalyst successfully promoted ROPs of l‐lactide (LLA) and δ‐valerolactone (VL) with benzyl alcohol (BnOH) as an initiator. The bifunctional DMAP ⋅ Sac coordinated to living polymer chain‐end with enolate oxygen to hydrogen of the hydroxyl, and to monomer with pyridinium N−H to oxygen of the carbonyl that successfully catalyzed efficient polymerization of LLA. High relative growth rate (RGR>90%) of the DMAP ⋅ Sac containing poly(l‐lactic acid) (PLLA) ensured the desirable biocompatibility and biosafety.