Beneficial effect of triphenylphosphine on the bulk polymerization of L,L-lactide promoted by 2-ethylhexanoic acid tin (II) salt

The ring-opening polymerization of L,L-lactide has been studied in bulk using 2-ethylhexanoic acid tin (II) salt, Sn(Oct)2, as a catalyst over a wide range of temperature and monomer to Sn(Oct)2 molar ratio. Although Sn(Oct)2 was known to initiate a fast polymerization, it is reported now that some Lewis bases, particularly triphenylphosphine (P()3), can increase further the polymerization rate, without any detrimental effect on the polylactide thermal stability. In order to optimize the balance between propagation and competing depolymerization reactions, the experimental conditions, i.e., temperature and concentration of Sn(Oct)2 and P()3 have been optimized. The up-scaling of the laboratory experiments to reactive extrusion has proved to be feasible, which demonstrates the efficiency of this catalytic system to produce polylactide in a continuous one-stage polymerization process.