Polyperoxides from Cyclic Monomers: Synthesis, Characterization, and High-Pressure Kinetics Study

Herein, we report free-radical-initiated polymerization of various cyclic monomers such as 2,3-dihydro furan (DHF), 2,3-dihydro-5-methyl-furan (MDHF), benzo[b]furan (BF), and indene (I) under high oxygen (O2) pressure at 50 °C in toluene. Kinetic studies of all the cyclic monomers have been performed at various O2 pressures to determine the saturation oxygen pressure, the pressure beyond which the rate of polymerization is invariant on the O2 pressure. The overall activation volume (ΔV#) was evaluated from the rates of oxidative polymerization (Rp), obtained from the slope of oxygen uptake (Δp) against the time plot. Interestingly, the electron-donating group and heteroatom play a crucial role in the rates of polymerization. Density functional theory calculations have been carried out to support the experimental rate of oxidative polymerization, which increased in the order: BF < I < DHF < MDHF. Elemental analysis, NMR spectroscopy, and active O2 content determination study have been used to establish the alternating sequences of a cyclic monomer with repeating peroxy bonds (−O–O−) in the polymer main chain. Thermogravimetric analysis was employed to study the thermal stability of the polyperoxides, and the degradation products have been characterized from a mass spectroscopic study. Additionally, differential scanning calorimetry exhibited an exotherm associated with the thermal degradation of the peroxy links of the polymer. These results not only expand the scope of polyperoxide synthesis from cyclic monomers but also pave a way to examine the high-pressure kinetics of oxidative radical polymerizations.