The thermal-oxidative degradation of polypropyleneoxide

Abstract

IT WAS pointed out in reference [1] that the degradation and stabilizatioxt of polyalkyleneoxides has reccived little study. In addition to studies of the thermal degradation of polypropyleneoxide [2], some ilfformation is given on the stability of this polymer in papers dealing with its synthesis [3-5]. The thermal-oxidative degradation of polyformaldehyde, the first member of this class of polymers, has been studied in some detail (see ibr example references [6] and [7]). As a characteristic of the process of oxidation of polypropyleneoxide (PPO), for the present work the induction period was chosen, and a s tudy was made of the dependence of this on a number of factors. The starting material was synthesized by catalytic polymerization of I)ropylene on ferric chloride and was purified by reprecipitation for times by water from acetone solution acidified with hydrochloric acid. The molecular weight of the polymer was 40,000 and the melting point 69 °. The method of determination of the induction period is described in reference [1]. In the oxidation of PPO a well defined induction period is always observed, followed by rapid absorption of oxygen. The length of the induction period is dependent on the temperature of oxidation. Figure la shows tim dependence of the induction period, r, on temperature at an oxygen pressure of 340 mm. For determination of the apparent energy of activation for the oxidation of PPO these results are represented in the form of a plot of log ~ against 1/T (Fig. 2). The activation energy found from the slope of this line is 22 kcal/molc. An induction period was still obtained when the initial oxygen pressure was increased. Figure lb shows the results obtained at 121 °. At oxygen pressures above 250 mm the induction period varies little ~Sth pressure, as was observed in the oxidation of polyethyleneoxide [1]. All this indicates that PPO, like polyethyleneoxide has comparatively little resistance to thermal-oxidative (legr~dation. The effect on the induction period of the addition of various antioxidants was also studied. The investigation was carried out at 137 ° and an oxygen pressure of 340 ram. The additives were 2,2-methylene-bis-(4-methyl-6-tert-butylphenol), N-phenyl-N'cyclohexyl-p-phenylenediamine, N,N'-di-octyl-p-phenylenediamine and propyl gallate.