Kinetics and Mechanism of ε-Caprolactone Polymerization Using Yttrium Alkoxides as Initiators

Abstract

ε-Caprolactone polymerization using an initiating system comprising tris(2,6-di-tert-butylphenoxy)yttrium and 2-propanol was first-order in monomer and initiator. A propagation rate constant of 1.65 L·mol-1·s-1 was determined in dichloromethane. The reaction proceeds via a three-step mechanism. In the first step the large 2,6-di-tert-butylphenoxy ligands are exchanged for the smaller 2-propanol. In the second step the polar alkoxide is able to attack the carbonyl group and form the thermodynamically favored ring-opened product. After the first two initiating steps, the polymerization can proceed until complete conversion of monomer is reached. Evidence for these three steps is provided by 1H and 13C NMR spectroscopy of the reaction products of each single step. The kinetic behavior of commercially available yttrium isopropoxide was more complicated. 2-Propanol could be used as an effective chain transfer agent for this initiator.

Rare earth metal initiated ring-opening polymerization of lactones

“…Other Ln isopropoxides (M = Er, Sm, Dy, La) were also found to be effective ROP initiators for lactones even at -64 8C. All isopropoxide groups were established to be active as initiators in the CL polymerization and end group analysis of low molecular weight PCL (M -n a 10 000) by means of 1 H NMR spectroscopy suggests a coordination insertion mechanism with acyl-oxygen bond cleavage 78,79) . Structural rearrangement processes involving partial or complete disassembly of the O-bridged initiator upon the coordination of monomer and/or polymer giving the actual active catalyst species is proposed.…”

New Aryloxy and Benzyloxy Derivatives of Titanium as Catalysts for Bulk Ring‐Opening Polymerization of ϵ‐Caprolactone and δ‐Valerolactone

“…[6,[11][12] The coordination-insertion ring-opening mode of polymerization is the most popular because of its capability in producing high polymers with narrow MWDs. [1,11,[13][14][15][16][17][18][19][20][21][22][23][24] Group 4, the most versatile in homogeneous olefin polymerization catalysis [25][26][27] , has been exploited in the ring-opening polymerization of cyclic esters.…”

Controlled ring-opening polymerization of -pentadecalactone with yttrium isopropoxide as an initiator

“…Glycolide, lactides and e-caprolactone are among the most used monomers for the synthesis of biodegradable polymers by ring-opening polymerization, and several efficient catalyst systems for their preparation have recently been developed [1][2][3][4][5][6][7]21) . In contrast to the ring-opening polymerization of small and medium-membered lactones, polymerization of large-membered lactones has received less attention.…”