Mechanism of Ring-Opening Polymerization of 1,5-Dioxepan-2-one and l-Lactide with Stannous 2-Ethylhexanoate. A Theoretical Study

Abstract

A theoretical study of the ring-opening polymerization (ROP) mechanism of 1,5-dioxepan-2-one (DXO) and L-lactide (LLA) with stannous(II) 2-ethylhexanoate (Sn(Oct)2) is presented. The B3LYP density functional method has been used for the quantum chemical calculations. Our results support a coordination-insertion mechanism initiated by a tin-alkoxide species formed prior to the ROP. The ratedetermining step in the ROP was the nucleophilic attack of the alkoxide on the carbonyl carbon of the monomer. The activation energy for the ROP of DXO with Sn(Oct′)2 has been determined to be 19.8 kcal/mol and for L-lactide 20.6 kcal/mol. At normal reaction temperatures, a ligand may dissociate as Oct′H during propagation. An excess of carboxylic acid hinders the coordination of monomer to the initiating/propagating complex.

Synthesis and structure-property relationships of biodegradable polyurethanes

“…In the next step, the acyl-oxygen bond (between the carbonyl group and the endocyclic oxygen) of the lactide is broken, making the lactide chain open to insert into the tin-oxygen bond (alkoxide) of the catalyst. The following propagation is induced by an identical mechanism and continues as additional lactide molecules are inserted into the tin-oxygen bond [43][44][45][46]. The insertion-coordination mechanism of lactide polymerization is supported by a Matrix-Assisted Laser Desorption/Ionization Time-of-Flight (MALDI-TOF) mass spectrum showing molecular peaks that correspond to the oligomeric PLLA chains connecting with tin residues, which are propagating species formed with the Sn(Oct) 2 /lauryl alcohol system [39,47].…”

An Overview of the Synthesis and Synthetic Mechanism of Poly (Lactic acid)

“…Stannous(II) 2-ethylhexanoate (Sn(Oct) 2 ) is one of the catalysts most widely used as a compound that starts the ring opening polymerization (ROP) of various lactones and lactides [40][41][42].…”

Molecular Weight and Structural Properties of Biodegradable PLA Synthesized with Different Catalysts by Direct Melt Polycondensation

“…However, direct condensation polymerization of L-lactic acid like bulk polymerization, azeotopic dehydration, and enzymatic polymerization have been known to produce PLA with a molecular weight in the order of only ~10 4 g/mol due to the unfavorable reaction equilibrium constant of L-lactide [3]. In comparison with the well-established method for the catalytic ring-opening polymerization of L-lactide [4][5][6][7], the direct polycondensation of L-lactic acid has received much less attention. Studies of direct polycondensation of L-lactic acid with various catalysts [8,9], melt/solid polycondensation [10], and direct condensation polymerization of L-lactic acid in bulk state [11] have been conducted in order to investigate the production of PLA with a high molecular weight.…”