Equilibrium polymerizations of 1.3-dioxolane and some related cyclic formals have been studied in benzene solution by using boron fluoride ethyl ether complex as a catalyst. From the relation between equilibrium monomer concentration and polymerization temperature, the thermodynamic parameters of the polymerization of these cyclic formals were evaluated as follows:AHp = -3.6 f 0.6 kcal/mole, AS: = -14 f 2 cal/mole.deg. AHp = -3.2 f 0.5 kcal/mole, AS: = -9.3 f I .4 cal/mole*deg. 0.8 kcal/mole, AS: = -9.3 f 1.4 cal/mole-deg. ZUSAMMENFASSUNG: Die Gleichgewichtspolymerisation von 1.3-Dioxolan und einiger abgeleiteter cyclischer Formale wurde unter Anwendung des Bortriiluorid/~thylither-Komplexes als Katalysator in benzolischer Losung untersucht. Aus der Beziehung zwischen Gleichgewichtskonzentratiori des Monomeren und Polymerisationstemperatur wurden die thermodynamischen Polymerisationsparameter wie folgt ermittelt : 1.3-Dioxolan: AHp = -3,6 f 0,6 kcal/mol, AS: = -14 f 2 cal/mol.grad 1.3-Dioxepan: AHp = -3,2 f 0,s kcal/mol, AS: = -9,3 f 1,4 cal/mol-grad 1.3.6-Trioxocan: AHp = -5,3 rt 0,8 kcal/mol, AS: = -9,3 f 1,4 cal/mol*grad * ) Revised manuscript, December 12th, 1967.

Human urokinase was immobilized on an ethylene vinyl acetate copolymer surface. Soluble urokinase showed its maximum activity at pH 8.5, while the immobilized enzyme was most active at pH 9.0. Apparently, the shift in optimal pH was due to the polyanionic nature of the carrier surface on which the enzyme was immobilized. Optimal temperatures of soluble urokinase and immobilized enzyme were identical, i.e., 37 degrees C. The stability of immobilized enzyme against thermal degradation was several times higher than that of the soluble enzyme. Its stability at higher temperatures is one of the main reasons for the clinical use of immobilized urokinase as an antithrombotic material.

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A copolymer composition equation including the depropagation reaction was derived and applied to the cationic copolymerization of 3.3-bischloromethyl oxacyclobutane and tetrahydrofuran. The observed decrease of the number of tetrahydrofuran units incorporated in the copolymer with increase of the polymerization temperature or with decrease of the monomer concentration was well explained by the equation. Differences between the catalyst systems, BF3. EtzO, EtsOBF4, PhNzPF6, and AlEt3-HzO were also observed. ZUSAMMENFASSUNG:Fur die kationische Copolymerisation von 3.3-Bischloromethyl-oxacyclobutan und Tetrahydrofuran wurde eine Gleichung fur die Zusammensetzung des Copolymeren, bei der auch die Depolymerisation berucksichtigt wurde, abgeleitet und angewendet. Der mit steigender Polymerisationstemperatur oder mit Abfall der Monomerenkonzentration beobachtete Abfall der Anzahl der Tetrahydrofuraneinheiten, die in das Copolymere eingebaut werden, wird durch die Gleichung gut erklart. Es wurden auch Unterschiede in der Wirksamkeit der Katalysatorsysteme BF3 .(CzH5)20, ( C~H~) Z O B F~, C~H~N Z P F G und Al(CsH5)s-H20 beobachtet.

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