Study of radical polymerization by means of ESR, 2. Homogeneous polymerization of methyl methacrylate and vinyl acetate

Abstract

A very efficient ESR spectrometer was applied to the measurement of the stationary concentration of macroradicals in homogeneous polymerization. From these data the rate constants of chain propagation and chain termination for the polymerizations of methyl methacrylate and vinyl acetate were found in a direct way. Activation energies of these elementary reactions were measured. ZUSAMMENFASSUNG:Fur die Bestimmung der stationaren Konzentration von Makroradikalen bei der homogenen Polymerisation wurde ein sehr wirksames ESR Spektrometer eingesetzt. Aus den erhaltenen Daten wurden die Geschwindigkeitskonstanten des Kettenwachstums und Kettenabbruchs fur die Polymerisationen von Methylmethacrylat und von Vinylacetat auf direktem Weg erhalten. Die Aktivierungsenergien dieser Elementarreaktionen wurden gemessen.

Molecular Aspects of Radical Polymerizations—The Propagation Frequency

“…Bresler et al reported for the first time in 1972 the application of ESR for the determination of the Arrhenius relation of the propagation rate constant for the bulk polymerization of styrene initiated with dibenzoyl peroxide and a few years later the corresponding data for MMA and vinyl acetate. [21,22] The results for styrene were later confirmed over a wide temperature range (between 0 and 130 8C) with UV initiation and different thermal initiators. [23] The k p values for other monomers have also been determined, such as for n-butyl methacrylate, [24] vinyl chloride, [25] and MMA.…”

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

“…To this end, a previously not investigated monomer, vinyl pivalate (VPi), was chosen ( Figure 1). Among the vinyl esters, vinyl acetate (VAc, Figure 1) has been subjected to k p determination using the EPR method, [29,30,73] the rotating sector method, [74] and PLP-SEC, [75] but the k p values obtained were not in agreement. The k p of vinyl neo-decanoate has been determined by PLP-SEC.…”

“…Straight lines are least squares fits. ------), [3,6,75] and for VAc determined by the EPR method in ethyl acetate (&) [82] and in bulk (~, [30] &, [82] and [73] ).…”

“…The very similar k p Arrhenius relationships obtained for the structurally similar monomers VPi (present study) and VAc (PLP-SEC) [3,6,75] thus suggest that consistent k p values for VPi have been obtained by the EPR method. The Arrhenius Equation of k p for VAc (45-80 8C) was reported based on EPR quantification of the propagating radical concentration for the first time more than 30 years ago, [73] and the k p values for VAc were determined as 1 700…”

Search for highly resolved electron spin resonance spectra of the transient radical in radical polymerization

“…However, these conditions for measurement are far different from practical conditions for radical polymerization. Although Bresler and coworkers 13,14 observed ESR spectra of propagating radicals of styrene and methyl methacrylate (MMA) with a specially designed cavity, the resolution of the spectra still was not good enough to understand the structure and electronic state of the propagating radicals because of their insufficient hfc's.…”