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 (Σi[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: ΔH_p = -13.8 kJ mol^-1 and ΔS_p° = -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.