Single-step reactive extrusion of PLLA in a corotating twin-screw extruder promoted by 2-ethylhexanoic acid tin(II) salt and triphenylphosphine

The ring opening polymerisation of l,l-lactide using an equimolar complex of 2-ethylhexanoic acid tin(II) salt Sn(Oct)2 and triphenylphosphine P(φ)3 as catalyst shows for the first time a reactivity providing a polymerisation propagation rate fast enough to imagine a continuous single-step reactive extrusion process for bulk polymerisation. The ring opening polymerisation has been realised on a corotating closely intermeshing twin-screw extruder, using a specially designed screw concept to provide sufficient energy input and mixing for further enhancement of the propagation rate, without detrimentally enhancing depolymerisation or transesterification reactions. Using one chosen screw and processing concept on a twin-screw extruder with 25 mm diameter and a L/D-ratio of 48, the influence of different processing parameters on the resulting molecular parameters of the Polylactide (PLA) has been determined. Furthermore, the mechanical property profile of the generated PLA-polymers is discussed and related to the molecular parameters.