The effect of stabilizers, additives, and low molecular weight fractions on cavitation during tensile drawing was studied in polypropylene. The additives were extracted from compression molded samples by critical CO 2 and also by a mixture of nonsolvents. The extract was an oily liquid composed of antioxidant, processing stabilizer, and a spectrum of low molecular weight fractions of polypropylene. Purified polypropylene exhibited surprisingly more intense cavitation than pristine polypropylene as it was determined by small-angle X-ray scattering and volume strain measurements. Intensification of the cavitation process in the purified samples was explained by the changes in the amorphous phase, namely, the changes in free volume by eliminating low fractions and soluble additives. An increase in free volume was probed with positron annihilation lifetime spectroscopy. Intense formation of cavitation pores in purified polypropylene proves that initiation of cavitation in polypropylene has a homogeneous nature.

Studies of positron annihilation accompanied by EPR technique were undertaken for sodalite and lazurite and their synthetic counterparts (synthetic sodalite and ultramarines). Results of measurements performed by two techniques of positron annihilation spectroscopy (angular correlation of annihilation radiation, ACAR, and positron annihilation lifetime) revealed the undoubted influence of free radicałs on positron annihilation mechanism but both inhibition of positronium formation by them and the effect of filling cages ought to be taken into account. The distinct differences between ACAR curves for sodalites, lazurites and ultramarines probably reflect the presence of different radicals in their cages and chemical heterogeneity as well as the disorder in Al, Si-site ordering in case of ultramarines. Comparison of the results of ACAR measurements with the ones of the EPR studies indicates that there is correspondence between them. Similarly to three families of the ACAR curves, different likes of EPR lines were obtained for three groups of samples; sodalites, lazurites and ultramarines. It is possible that the annihilation of positrons takes place mainly with unpaired electrons recorded by the EPR technique.PACS numbers: 61.90.+d, 71.60.+z, 76.30.-v, 78.70.-g (29) 30 A. Baranowski et al.

Positron annihilation phenomenon has been studied in chloropolystyrenes. PAL and ACAR measurements have been performed in air and at room temperature for amorphous samples of different chlorine content. The increase in the latter is followed by the decrease in both the intensity of the narrow component of ACAR curves and the intensity of the longest-lived component (I) in PAL spectra. The latter one, related to the ortho-posi troniurn intensity in polystyrene I: , changes according to the formula: 1~/ 1~1 1 + (1 9. 9 3 *~)~.~~1-~ where C denotes the number of C1 atoms per unit of the polymer. The inductive effect produced by the chlorine in chloropolystyrenes is assumed to be the reason of the inhibition of the positronium formation in them. In general the chlorine reactivity towards positrons seems to depend on its position in the polymer structure. The numerical Laplace inversion technique /1/ has been applied to PAL data to recover the radius distribution of free volumes for each sample of the second series. A tendency towards decrease in mean radius of free volumes is seen when chlorine content increases in studied samples. The only exception is the sample in which the highest amount of chlorine atoms has been substituted at a-carbons in the aliphatic chain.

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Positron annihilation experiments using both lifetime spect,roscopy and Doppler broadening of the annihilation lineshape technique are performed for various pure zeolites nnd for mordenite impregnated with highly dispersed gold particles. Changes in the annihilation parameters are tentatively correlated with the properties of the samples and, in case of impregnated samples, attributed t o the presence of gold particles in the matrix of the zeolite.Positronenannihilationsexperimente werden mittels Lebensdauerspektroskopie und Dopplerverbreiterungs-Linienformanalyse fur verschiedene reine ,,Zeolite und Mordenite, die mit hochdispersen Goldteilchen impragniert werden, durchgefuhrt. Anderungen der Annihilationsparameter werden versuchsweise mit den Eigenschaften der Proben korreliert und in Fallen impragnierter Proben der Anwesenheit von Goldpartikeln in der Zeolitmatrix zugeordnet.