HIGHLY CRYSTALLINE AS-POLYMERIZED POLY(L-LACTIDE)

Two new lactone polymerization catalysts, tin(II)-bis(2,4-pentanedionato-O,O') (Sn(Acac)2) and zinc-bis(2,2-dimethyl-3,5-heptanedionato-O,O') (Zn(DMH)2), together with tin(II)-2-ethylhexanoate (Sn(Oct)2), were used to study the effect of the catalyst in the L-lactide polymerization on the nascent polymer structure. Using Zn(DMH)2 and ultra high crystalline polymer was obtained with a DELTA-H(m) of 100 J.g-1. Independent of the catalyst and the crystallinity the structure of the crystalline polymer was a pure alpha-structure as revealed by WAXS-measurements. SAXS-measurements showed a long period for both the Sn(Oct)2 and the Zn(DMH)2 polymer of about 33 nm., the latter revealing a more complex highly regular structure with up to fourth-order reflections. SEM micrographs showed a fibrillar like structure for the Zn(DMH)2 polymer.