Oxidative degradation of poly (vinyl acetate) and poly ( ε-caprolactone) and their mixtures in solution

Abstract

The oxidative degradation of the poly ( ε-caprolactone) (PCL), poly (vinyl acetate) (PVAC) and their mixtures in dichlorobenzene has been investigated at various temperatures (70–130°C) in the presence of benzoyl peroxide. The interaction between the polymers is quantified by monitoring the molecular weights of individual polymers using gel-permeation chromatography. The various physical mixtures employed in the present investigation are 20 80 , 50 50 and 80 20 wt%/wt% PCL/PVAC. Experimental data indicated that the degradation is random without cross-linking and repolymerization. An optimum in degradation temperature (corresponding to maximum degradation rate) of 105°C was observed for the entire range of polymer compositions (0–100% PCL) investigated. This optimum temperature of degradation is characteristic mostly of the initiator and only to a small extent of the degrading polymer system. The experimental results of the mixtures indicated that the degradation rates of PVAC are significantly enhanced, while the degradation rates of PCL are decreased in the physical mixture. This can be attributed to the proton-accepting and proton-donating nature of PCL and PVAC, respectively. A radical mechanism for the oxidative degradation of pure polymers and their mixtures has been proposed and a model based on continuous distribution kinetics was developed considering the interaction of the polymers through hydrogen abstraction and the parameters were evaluated numerically. The activation energies for the peroxide attack for the PCL and PVAC are 10.5 and 10.6 kcal mol −1 , respectively. The activation energies for the random chain scission of PCL and PVAC are 10.6 and 14.5 kcal mol −1 , respectively.