The ionic polymerizations of methyl glyoxylate

Methyl glyoxylate has been polymerized in CH₂Cl₂ solution either cationically or anionically to give the corresponding polyacetal. Thermodynamic and kinetic results of the polymerizations initiated by CF₃SO₃H, BF₃OEt₂, and NEt₃ are reported here. Monomer conversion was followed by UV and active centers concentrations were determined through phosphorus end-capping. A ceiling temperature of 26°C was observed for M_eq=l mol.H (T_c = 109°C for bulk) with ΔH°=?29.5 kJ.mo^?1 and ΔS°=?99 J.mo^?1.K^?1. Both initiations were found instantaneous and quantitative, and no termination was observable within the time scale of the reaction (second to hour). Cationic propagation appears to take place essentially on free ions (k_p+ ≈ 60 l.moH.s^?1 at ?20°C) in equilibrium with a larger amount (K_d ≈ 6.7.10^?6 mol.^?1) of much less reactive ion-pairs (k_p± ≈ 0.16 ± 0.03 1.mo^?1.s^?1). A stopped-flow device was used to follow the much more rapid anionic polymerization (k_p,app ≈ 8 ± 2.10³ 1.mo^?1.s^?1 at ?20°C).