Determination of the Propagation Rate Coefficient of Vinyl Pivalate Based on EPR Quantification of the Propagating Radical Concentration

Abstract

The propagation rate coefficient (kp) of the vinyl pivalate (VPi) has been determined from an EPR quantification of the concentration of propagating radicals. The polymerizations followed first‐order kinetics with respect to the monomer, and the concentration of propagating radicals did not vary with time. The chain lengths were estimated to be sufficiently large to not affect kp. The resulting Arrhenius parameters for kp of VPi in heptane are Ap = 1.39 × 107 dm3 · mol−1 · s−1 and Ep = 20.5 kJ · mol−1. They are very similar to those of vinyl acetate as previously determined by the PLP method. The present results thus indicate that EPR gives consistent kp values for vinyl esters.magnified image

Novel Access to Propagation Rate Coefficients of Radical Polymerization by the SP-PLP-EPR Method

“…Usually, EPR measurements in highly polar solvents such as D 2 O suffer from poor signal‐to‐noise quality due to the dielectric loss of microwave energy . The signal quality for TMAEMA is however well above the one of radicals in organic solvents because of the high radical concentration of 2.63 × 10 −5 mol L −1 …”

“…These stationary experiments, which are performed over a wider conversion range, suffer from the disadvantage that the microwave energy stored in the cavity and thus signal intensity may vary due to changes in dielectricity of the sample and may affect the accuracy of k p determination. For example, methyl methacrylate (MMA) homopolymerization up to high conversion is accompanied by an increase in signal intensity by a factor of three . The novel instationary method may be applied in the initial polymerization period and thus under conditions, for which EPR calibration is more easily and accurately carried out.…”

Chain‐Length‐Dependent Termination of Vinyl Acetate and Vinyl Pivalate Bulk Homopolymerizations Studied by SP‐PLP‐EPR

“…Peroxides and benzoyl peroxides have been successfully used in vinyl ester polymerizations. [ 34,44,45 ] To ensure identical initiation rates of both primary radical species and because of the relatively high extinction coeffi cient at the laser wavelength of 351 nm, DCP [ 46 ] has been selected for the SP-PLP-EPR studies into VAc. The absorption spectrum of DCP is given in the Supporting Information.…”

“…[ 27,34,44 ] Shown in Figure 3 are EPR spectra measured on VAc at a pulse repetition rate of 25 Hz at 60 °C with DCP acting as the photoinitiator. Even at this elevated temperature, no indication of mid-chain radicals can be seen with either VAc or VPi.…”

“…The propagation rate coeffi cient of VPi was taken from literature [ 44 ] and the density was measured to be: ρ (VPi)/g mL −1 = 0.8918−0.00107 Θ /°C (see Supporting Information). From fl uidity measurements between 10 and 60 °C, E A ( η −1 ) = (10.6 ± 0.1) kJ mol −1 has been obtained.…”