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The way in which the decomposition reaction of a persulfate initiator is influenced by the nature of reactants of the polymerization medium and by the working conditions during the semicontinuous polymerization and copolymerization of vinyl acetate is studied. The rate of the splitting reaction of potassium persulfate is higher in the aqueous phase containing a protective colloid and surfactant. The splitting rate is smaller in the presence of vinyl acetate. The presence of hydrophobic comonomers decreases the rate ofinitiator decomposition. An increase of the addition rate of monomers leads to an increase of the obtained polymer and of the splitting rate of the initiator. Semikontinuierliche Emulsionspolymerisation von Vin.dacetat. IX. Zer.~etziingsreuktion rles InitiatorsDer EinfluD der Reaktanten im Polymerisationsmedium und der Reaktionsbedingungen auf die Zersetzungsreaktion eines Persulfatinitiators wird untersucht. Die Geschwindigkeit der Spaltungsreaktion von Kaliumpersulfat steigt bei Anwesenheit eines Schutzkolloids und einer oberflkhenaktiven Substanz in der wPDrigen Phase. in Gegenwart von Vinylacetnt ist die Spaltungsgeschwindigkeit niedriger. Bei Anwesenheit hydrophober Comonomere nimmt die Zersetzungsgeschwindigkeit dcs Initiators ab. Ein Anstieg der Zufiihrungsgeschwindigkeit der Monomere erhoht die Menge an erhaltenem Polymer und die Spaltungsgeschwindigkeit des Initiators. DONESCU and FUSULAS: Scmicontinuous emulsion polymerizntion of vinyl acetate. 1X Systcm')Acta Polymcriu 42 (1Wl) Nr. 10

dModification of clay with biopolymers has been of high interest in recent years. These new materials may be used for drug delivery systems and as biomaterials due to their high biocompatible properties and because they have the advantage of being biodegradable. The modification of montmorillonite (MMT) with chitosan was done in solution, at ratio 1 : 2 and at room temperature, or at stages of high temperature, and subjected to a microwave treatment. The influence of pH was observed upon the intercalation process.The obtained materials were characterized through X-ray diffraction (XRD), thermogravimetrical analyses (TGA), Fourier transform infrared spectroscopy (FTIR), atomic force microscopy (AFM), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Using such a mixed treatment, the basal distance of modified MMT increased up to 3.6 nm. The results show the intercalation of chitosan between the layers of MMT and obtaining of intercalated and partial exfoliated nanocomposites.