Bulk Polymerization of L-Lactide with Dibenzoylmethane Sn(II) Compounds

초록

The bulk polymerization behavior of L-lactide monomer using dibenzoylmethane (DBM)-based Sn(II) compounds (DBM)Sn(OBu) (2) and (DBM)(2)Sn (3) is investigated. Compounds 2 and 3 were prepared from the reaction of Sn(OBu)(2) (1) with 1 or 2 equiv of DBM, respectively. X-ray diffraction studies revealed that, while 2 exists as a dimeric form linked by 1-butoxide bridges, 3 is monomeric in the solid state. The Sn(II) centers in both compounds adopt distorted square-pyramidal geometry. Ring-opening polymerization of L-lactide with 1-3 efficiently produced poly(L-lactide)s with high molecular weight and narrow polydispersities (PDI < 2). The catalytic activity was found to be in the order 1 > 2 > 3, indicating that the DBM ligand causes a sluggish coordinative insertion of the lactide monomer into the Sn(II) center. In particular, the addition of dodecanol (DDO, 0.1 mol%) substantially improved the catalytic activity for all compounds. The comparative polymerization using Sn(Oct)(2) (Oct = 2-ethylhexanoate) in the absence and presence of DDO further showed that 1 is higher in activity than Sn(Oct) 2 and that Sn(II) alkoxides are the actual active species in the polymerization of L-lactide.

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