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

The ring opening polymerisation of L,L-lactide using an equimolar complex o f 2-ethylhexanoic acid tin(II) salt Sn(Oct)(2) and triphenylphosphine P(phi )(3) as catalyst shows for the first time a reactivity providing a polymeri sation propagation rate fast enough to imagine a continuous single-step rea ctive extrusion process for bulk polymerisation. The ring opening polymeris ation has been realised on a corotating closely intermeshing twin-screw ext ruder, using a specially designed screw concept to provide sufficient energ y 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 wit h 25 mm diameter and a L/D-ratio of 48, the influence of different processi ng 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 . (C) 2000 Elsevier Science Ltd. All rights reserved.