Polyperoxides from cyclic monomers: synthesis, characterization, and high-pressure kinetics study

Abstract

This study reports on the free-radical-initiated polymerization of various cyclic monomers, including 2,3-dihydro furan (DHF), 2,3-dihydro-5-methyl-furan (MDHF), benzo[b]furan (BF), and indene (I), conducted under high oxygen (O₂) pressure at 50 °C in toluene. Kinetic experiments were performed at different O₂ pressures to identify the saturation oxygen pressure, beyond which polymerization rates remain unaffected. The overall activation volume (ΔV‡) was calculated from the oxidative polymerization rates (Rₒ₂) derived from oxygen uptake (Δp) over time. The electron-donating group and heteroatom in the monomers play a crucial role in polymerization rates. Density functional theory (DFT) calculations support the experimental oxidative polymerization rates, showing the order BF < I < DHF < MDHF. Elemental analysis, NMR spectroscopy, and O₂ content determination confirmed the alternating sequences of cyclic monomers with repeating peroxy bonds (−[O−O]−) in the polymer backbone. Thermogravimetric analysis assessed the thermal stability of polyperoxides, and degradation products were characterized by mass spectrometry. Differential scanning calorimetry revealed an exotherm linked to thermal degradation of the peroxy bonds in the polymer. These results broaden the scope of polyperoxide synthesis from cyclic monomers and offer insights into the high-pressure kinetics of oxidative radical polymerizations.