Four intrinsically different methods for the determination of the number of active centers were employed in propylene polymerization catalyzed by the typical heterogeneous system TICI, /AlEt,Cl: (i) determination of M, (GPC method) and calculation of number of macromolecules therefrom; (ii) quenching with BuOT and determination of tritium in the polymer; (iii) quenching with CO or CO, and determination of carbonyl groups in the polymer (IR spectroscopy); (iv) quenching with SO, and determination of sulfur in the polymer. The first two methods exhibited a reasonable agreement for the number of active centers. Method (iii) gave much lower values, whereas method (iv) was found to be virtually unsuitable due to a high extent of side reactions of SO, with the polymer. A similar comparison of the methods was made in ethylene polymerization catalyzed by the typical homogeneous systems Cp,TiEtCl/AIEtCl, and Cp,TiEtCl/alumoxane. Method (ii) gave a much lower number of active centers than method (i), due perhaps to a low extent of alcoholysis of the Ti-C bond or to a high kinetic isotope effect. CO, appeared to be entirely inert as a quenching agent and CO had been reported to show side reactions. It follows that none of the above quenching methods have universal application and thus literature data should be considered with caution.

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SynopsisThe effect of titanium compounds on thermooxidation stability of stabilized polypropylene was studied. It was found that the presence of titanium compounds shortens the induction period of PP oxidation. This phenomenon is brought about by the thermal reactions of titanium compounds with antioxidants which take place during polymer processing. The first step is the reaction of Ti-Cl with OH groups of phenolic antioxidant, which gives rise to a colored titanate and HCl. Hydrogen chloride functions as a Friedel-Crafts catalyst for degradation and dealkylation of phenolic antioxidants. The products of degradation have a very low stabilization efficiency. Hydrogen chloride acceptors suppress antioxidant degradation and increase the polymer stability even in the presence of small amounts of titanium compounds.

SynopsisThe photooxidative degradation of the films of an atactic polymer effected with a mercury discharge tube was studied. The formation of carbonyl and hydroxyl groups in the polymer was followed by infrared spectroscopy. The conversion curves of both oxidation products are exponential. The following energies of activation for formation of car-bony1 and hydroxyl groups were found: E = o = 14.7 kcal./mole, E = 15.9 kcal./mole. The biradical termination of RO;: radicals is proved. A reaction mechanism of formation of carbonyl and hydroxyl groups is suggested.

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