sample thickness and structural changes in thermo-oxidative degradation of polybutadiene

the thermo-oxidative degradation of two viscous liquid resins of 1,2- poly-butadiene  (1,2-pbd) and 1,4- polybutadiene  (1,4-pbd) have been studied by differential scanning calorimetry (dsc) and thermogravimetry analy-sis  (tga). to  study  further,  the  effect of flm  thickness on oxidation kinetics was periodically studied by tracing the weight of the samples to make comparison with dsc results at constant temperature of 100°c under atmospheric pressure. finally, the structural changes of 1,4-pbd were investigated by carbon-13 nuclear magnetic resonance spectroscopy (13c nmr). the results from 13c nmr from 1,4-pbd show that after heat treatment new carbon peaks are obtained for an epoxide carbon at 58.6 ppm, an adjacent methylene carbon of epoxide group at 24.0 ppm and a peroxide methine carbon group at 86.7 ppm. the results from tga and dsc studies conclude that 1,2-pbd do not age due to its structure. the results from nmr spectroscopy indicate that besides structural changes, increase in mass is due to radical addition to double bond while, epoxide groups are one of major products of thermal oxidation which can be identifed from their 13 c nmr peaks.