Ring-Opening Polymerization of d,l-Lactide Using Rare-Earth μ-Oxo Isopropoxides as Initiator Systems

Abstract

Introduction.Polylactides are important biodegradable materials having biomedical, pharmaceutical, and environmental applications. [1][2][3][4][5] These polymers can be synthesized by ring-opening polymerization of lactides using anionic, cationic, or coordinated type initiators. [6][7][8][9][10] In order to obtain polymers with controlled characteristics (structure, molecular weight), initiators leading to a living type process are desirable. Ideally, they should also promote rapid polymerization.Anionic initiators such as alkali-metal alkoxides lead to some side reactions. 6,11 Aluminum alkoxides can be used for controlled polymerization, but they exhibit a relatively low activity. 8,9 The livingness of the polymerization systems was discussed in terms of the selectivity of the involved elementary reactions. 12 It was reported recently that rare-earth alkoxides show a very high reactivity for the polymerization of lactones and lactides. [13][14][15][16][17][18] A living type behavior was observed for some of them. Yttrium oxo isopropoxide is presently a commercially available compound. Stevels et al. 19,20 have recently studied the kinetics and mechanism of L-lactide polymerization with commercial yttrium oxo alkoxide and with other yttrium alkoxides prepared in situ from exchange reaction between the bulky tris(2,6-di-tert-butylphenoxy)yttrium and various alcohols. The rate of polymerization with the latter initiators was found to be several orders of magnitude higher than that observed with the commercial yttrium oxo isopropoxide.Originally, the synthesis and the characteristics of yttrium oxo isopropoxide Y 5 (µ-O)(OiPr) 13 was described by Poncelet et al. 21 It is a cluster compound in which five yttrium atoms are linked to a single central oxygen atom.In this paper we describe the results of the polymerization of D,L-lactide using different rare-earth oxo alkoxide clusters of Ln 5 (µ-O)(OiPr) 13 type where Ln is La, Sm, Y, and Yb. Previously, only the polymerization of L-lactide with commercial yttrium oxo isopropoxide was reported. 17,20 Experimental Section. All µ-oxo isopropoxide initiators were prepared according to the procedure described by Poncelet et al. 21 for yttrium. Commercial yttrium oxo isopropoxide (Aldrich, France) was also used after washing with toluene, removal of insolubles by filtration, and drying in vacuo. D,L-Lactide (Purac Biochem b.v., Gorinchem, the Netherlands) was purified by sublimation under vacuum. Dichloromethane was distilled from calcium hydride and toluene from sodium

Ring-opening polymerization of ?-caprolactone and ?-valerolactone using new Sm(III) ?-halo-bis(trimethylsilyl)amido complexes

“…Polylactones are of interest as biodegradable material for various medical applications. [1][2][3][4][5][6] The applications of new initiators, based on the lanthanide elements, has led to the production of several new macromolecular architectures like telechelic and block polymers incorporating poly(-caprolactone) (PCL) segments. [7][8][9][10] .…”

Ring-opening polymerization of lactides using heterobimetallic yttrocene complexes

“…McLain et al have introduced the yttrium alkoxide Y(OCH 2 CH 2 NMe 2 ) 3 as a highly active initiator for the living ring-opening polymerization of L-lactide (L,Ldilactide) 3) . Subsequently, a series of other rare earth alkoxides such as Ln 5 (l 5 -O)(O i Pr) 13 (Ln = Y, La, Sm, Yb) have been studied and found to constitute a promising class of efficient initiators [4][5][6][7] . More recently we have found that the heterobimetallic yttrocene derivatives containing two linked amido-cyclopentadienyl ligands Li[Y(g 5 : g 1 -C 5 R 4 SiMe 2 NCH 2 CH 2 OMe) 2 ] (Scheme 1) are capable of efficiently polymerizing e-caprolactone.…”

Synthesis and Application of Bimetallic Zinc(II) Phenoxy-Imine Complexes as Initiators for Production of Lactide Polymers

“…3,4 There is a great number of metal-based catalysts able to perform ROP reactions via coordination-insertion mechanism. However, some of these catalysts are toxic and difficult to remove from the reaction mixtures, preventing applications of the resulting polymers in biomedical and pharmaceutical areas.…”