BLOCK-COPOLYMERS OF POLY(L-LACTIDE) AND POLY(EPSILON-CAPROLACTONE) ORPOLY(ETHYLENE GLYCOL) PREPARED BY REACTIVE EXTRUSION

Blends of poly(L-lactide) (PLLA) and poly(epsilon-caprolactone) (PCL) were prepared in a corotating twin screw miniextruder (40 rpm, 200 deg rees). It was attempted to prepare multiblock copolymers by allowing a controlled number of transesterification reactions. Various catalysts (n-Bu(3)SnOMe, Sn(Oct)(2), Ti(OBu)(4), Y(Oct)(3), para-toluene sulpho nic acid) were introduced to promote these transesterification reactio ns. However, PLLA degradation by ring-closing depolymerization was the dominant reaction in every case. Alternatively, after showing that L- lactide can be conveniently polymerized in the extruder, L-lactide and hydroxyl functionalized prepolymers of PCL or poly(ethylene glycol) ( PEG) were fed to the extruder in the presence of stannous octoate. Mon omer conversions of over 90% and effective transformation of all hydro xyl end groups present were generally reached. Di- and triblock copoly mers could be prepared in this way with characteristics very similar t o polymers prepared in a batch-type process, but with considerably red uced reaction times in a fashion, which is, in principle, scaleable to a continuous process for the production of such block copolymers. (C) 1996 John Wiley & Sons, Inc.