Studies on mechanism of tetrahydrofuran polymerization initiated by a heteropolyacid

摘要

Polymerization mechanism of tetrahydrofuran initiated with H_3PW_(12)O_(40) in the presence of ethylene oxide (EO) was studied by means of NMR, GC and GPC. The polymerization stopped after complete consumption of EO, but could be re-initiated when a further portion of EO was added. A part of EO was converted into dioxane in the beginning of polymerization in the presence or absence of water, but the formation of dioxane was suppressed by addition of a low molecular weight diol. All the polymer chains were started with EO moieties, and the percentage of hydroxyl group attached to EO moieties at the polymer chain ends was higher than 50 of the total hydroxyl end groups and increased with conversion. Kinetic experiments were performed with successive addition of EO, indicating that the concentration of propagating species and the chain propagation rate constant remained unchanged during polymerization after each addition of EO. The rate constant of the reaction of EO with the propagating species in EO homopolymerization was determined by GC to be 3.6 * 10~(-2) L (centre dot) mol~(-1) (centre dot) s~(-1) at 0deg C. The high reactivity of EO offered the possibility of tetrahydrofuran polymerization via dormant dioxanium species. The molecular weight distribution index of the product decreased with conversion, in some runs it was lower than 1.3 at a conversion as high as 46.9.