Some thermodynamic, kinetic, and mechanistic aspects of the ring-opening polymerization of 1,4-dioxan-2-one initiated by Al(OⁱPr)₃ in bulk

1,4-Dioxan-2-one (PDX) was polymerized in bulk by means of aluminum triisopropoxide (Al(OⁱPr)₃) as initiator. Thermodynamic parameters and ceiling temperature were determined from the temperature dependence of the monomer conversion over the range from 60 to 150 °C. It highlights that the thermodynamic equilibrium monomer conversion depends strongly on the final amorphous or crystalline state of poly(1,4-dioxan-2-one) (PPDX), at least below its melting temperature. The kinetics of the PDX polymerization for various monomer-to-Al(OⁱPr)₃ ratios at 80 °C is typically first order in both monomer and initiator and characterized by an absolute rate constant of 0.08 L mol^-1 s^-1. Molecular weight increases regularly with monomer conversion and initial monomer-to-Al ratio, while polydispersity is kept quite narrow all along the polymerization (M_w/M_n < 1.3). Mechanistic investigations proved that Al(OⁱPr)₃ is an efficient initiator for promoting the ring-opening polymerization that proceeds through a coordination-insertion mechanism with a selective rupture of the acyl-oxygen bond of the monomer.