Next Generation of Zinc Bisguanidine Polymerization Catalysts towards Highly Crystalline, Biodegradable Polyesters

Polylactide and polycaprolactone are both biodegradable polymers produced from cyclic monomers through metal-catalyzed ring-opening polymerization. For a truly sustainable lifecycle of these polymers it is essential to replace the industrially used cytotoxic catalyst tin(II) bis(2-ethylhexanoate) [Sn(Oct) 2' ] with non-toxic alternatives, while exhibiting the same or even better activity in the polymerization reaction. Here, we report the fastest known robust catalyst in the polymerization of lactide and e-caprolactone. This zinc guanidine catalyst can polymerize non-purified technical rac -lactide and e-caprolactone in the melt at different [M]/[I] ratios with fast rate constants, high molar masses around 150 000 g mol -1 and high yields in a short time leading to colorless, transparent polymer. Moreover, we report that by zinc-guanidine complexes produced polylactide and polycaprolactone have favorably high crystallinities. In fact, the obtained polylactide shows a more robust degradation profile than its Sn(Oct) 2 -catalysed equivalent due to a higher degree of crystallinity, ideal for long-exposure biological applications.