The application of simultaneous chemiluminescence and thermal analysis for studying the glass transition and oxidative stability of poly(<i>N</i>‐vinyl‐2‐pyrrolidone)

Abstract

Abstract A computer‐controlled chemiluminescence (CL) instrument incorporating a differential scanning calorimeter was used to simultaneously acquire photochemical and enthalpic data for poly( N ‐vinyl‐2‐pyrrolidone) (PVP). Samples were subjected to a linear temperature ramp under nitrogen and their luminescence response recorded. The resultant dynamic CL peak is attributable to the decomposition of hydroperoxide groups and the subsequent mutual termination of secondary polymer peroxyl radicals. It is shown that dynamic CL can be used to characterize the level of oxidation in PVP, which in commercial samples, may be partly related to the level of residual polymerization inititor and to the drying process. The temperature at which maximum CL emission occurs correlates with the glass transition temperature ( T g ) of the polymer and increases with increasing molecular weight. A marked increase in the T g of PVP occurs after it is aged in air for 24 h at 120°C. This is due to the loss of adsorbed moisture from the polymer which was confirmed by thermogravimetric analysis. Oxidation profiles of PVP were obtained by plotting the integrated CL peak area as a function of aging time. The profiles are compared with data obtained from isothermal CL and viscosity measurements. Gas perturbation experiments suggest that when drying PVP under nitrogen at elevated temperatures significant populations of longlived macroalkyl radicals are formed which can peroxidize the polymer on exposure to air. © 1993 John Wiley &amp; Sons, Inc.