Monomer−Linear Macromolecules−Cyclic Oligomers Equilibria in the Polymerization of 1,4-Dioxan-2-one

1,4-Dioxane-2-one (DX) was polymerized in 1,4-dioxane as solvent or in bulk by means of the tin octoate/butyl alcohol (Sn(Oct)2/BuOH) mixture as an initiating system, in the range of temperatures from 80 to 120 °C. Size exclusion chromatography (SEC) and MALDI TOF mass spectrometry measurements of the crude reacting mixtures revealed that in the thermodynamically equilibrated systems a relatively high fraction of cyclic oligomers (DX(i)) appear. The molar concentration of cyclic oligomers (∑i[DX(i)]eq) increased with increasing temperature and monomer concentration in the feed and reached a maximum value equal approximately to 1 mol L-1 for the polymerization in bulk. On the other hand, the mass fraction (f) of cyclic oligomers after passing a maximum (f = 40% at [DX]0 ≈ 4.0 mol L-1, 100 °C) decreased with increasing [DX]0, and eventually for bulk polymerization f < 10% (f = 8% at 80 °C) was reached. The equilibrium monomer concentration, determined by means of SEC, increased with increasing [DX]0 until [DX]0 ≈ 4.0 mol L-1 when it became constant value ([DX]eq). The temperature dependence of thus-determined [DX]eq gave the following thermodynamic parameters of polymerization: ΔHp = −13.8 kJ mol-1 and ΔSp° = −45.0 J mol-1 K-1. Thermodynamic parameters of polymerization of cyclic oligomers (DX(i), i = 3−8) have also been determined in a similar way.