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.

No abstract

An extremely sensitive instrument for ESR measurements in liquid media was developed on the basis of a new principle of registration of the ESR signals. By means of this device the spectrum of macroradicals of polymerizing styrene was recorded, and the stationary concentration of growing chains was measured quantitatively. Thus the first direct data for the chain propagation constant of the radical polymerization of styrene were obtained. ZUSAMMENFASSUNG:Fur ESR-Messungen an fliissigen Systemen wurde ein a d e r s t empfindliches Gerat mit einer neuartigen Registriermethode entwickelt. Hiermit wurde das ESR-Spektrum der Makroradikale in polymerisierendem Styrol registriert ; aus diesem wurde die stationare Konzentration der wachsenden Ketten quantitativ bestimmt. Dies sind die ersten, unmittelbar bestimmten Werte fur die Kettenwachstumskonstante bei der Polymerisation von Styrol.

The use of a sensitive electronic paramagentic spectrometer permits one to obtain a number of new quantitative and qualitative data regarding the kinetics of polymerization and behavior of macroradicals with large polymerization depths. In particular, it is shown that in the photopolymerization of methyl methacrylate in a block of considerable number of sequestered macroradicals accumulates in the final stages. On the basis of an investigation of the change of the spectra in the heating of the polymer some assumptions are made concerning the secondary reactions of the radicals and concerning the influence of low-molecular impurities on the velocity of these reactions.

The formation of macroradicals in the mechanical degradation of polymers gives the means for the direct kinetic determination of macroradical reactivity (reaction of the macroradicals with each other and with various low molecular substances). The free radical concentration was determined by means of EPR spectroscopy. With the aid of this method a study was made of the characteristic reactions such as removal of a hydrogen atom, addition, etc.