SynopsisPolymerization of the monomers, methyl acrylate (MA) and methyl methacrylate (MMA) was carried out in sulfuric acid medium at 15°C. with the redox initiator system, ceric ammonium sulfate-malonic acid. There was no induction period, and a steady state was attained in a short time. There was found to be no polymerization even after 1 hr. in the absence of the reducing agent R. The initiation was by the radical produced from the Ce4+-malonic acid reaction. The rate of monomer disappearance was proportional to [MI l.6, [R]0.5, and [Ce4+]0.a--0.6, and the rate of ceric disappearance was directly proportional to [R] and [Ce4+]. Chain lengths of the polymers were directly proportional to [MI and inversely to [R] 'Iz and [Ce4 +] '1%. The experimental results were explained by a kinetic scheme involving the following steps: (a)oxidation of the substrate to give the primary radical which reacts with Ce4 + to give the products, ( b ) initiation by the primary radical, (c) propagation, and ( d ) termination of the growing polymer radicals by the mutual type. For the polymerization of acrylonitrile (AN) by the redox system, ceric ammonium sulfate-cyclohexanone (CH), in sulfuric acid at 15OC., the scheme was modified to include linear type of termination by Ce4 +, along with the mutual termina, tion to explain the results especially under conditions with [Ce4+] > [CHI..

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Ceric perchlorate/formaldehyde (F)redox couple initiated polymerisation of the monomer methyl acrylate (MA), acrylonitrile (AN), and methyl methacrylate (MMA) in perchloric acid (25OC) was carried out. The rate of polymerisation was directly proportional to [MI2 and [F] for all the systems. The rate was independent of [Ce4+] for the systems with MA or AN, but inversely proportional to [Ce4+] with MMA as the monomer. The rate of ceric disappearance was directly proportional to [Ce4+], [F], and [MI. The results were explained by a kinetic scheme involving the oxidation of the substrate by Ce4+ to give the primary radical and further reaction of the latter with Ce4+ to give the final product, and initiation of polymerisation both by Ce4+ and the primary radical, propagation followed by termination by the metal ion. Only with MMA as the monomer, the initiation by Ce4+ was found to be negligible compared to that by primary radicals. In the system with the reducing agents t-butanol and n-butanol, there was found to be 1 : 1 complex formation between the substrate and Ce4+. Otherwise the scheme is similar to that proposed for the Ce4+/ HCHO/HC104/AN (MA) systems. ZUSAMMENFASSUNG: Die vom Ceriperchlorat/Formaldehyd-Redoxpaar gestartete Polymerisation von Methylacrylat, Methylmethacrylat und Acrylnitril wurde in waRriger Perchlorsaure bei 25 O C ausgefiihrt. Die Polymerisationsgeschwindigkeit in allen Systemen war direkt proportional zu [F] und [M]2. Bei Methylacrylat und Acrylnitril war die Geschwindigkeit von der Cerionenkonzentration unabhangig ; beim Methylmethacrylatsystem war sie dagegen umgekehrt proportional der Ce4f-Konzentration. Die Geschwindigkeit des Umsatzes der Ce4+-Ionen war direkt proportional zu [Ce4+], [F] und [MI. Die Ergebnisse werden folgender-mal3en erklart : Oxydation des Substrats durch Ce4+-Ionen zu Primirradikalen, die teaweise mit weiteren Ce4+-Ionen abbrechen. Start der Polymerisation sowohl durch Ce4+-Ionen als auch durch Primkadikale. Der Abbruch erfolgt durch Metallionen. Nur im Fall des Methylmethacrylats wurde gefunden, dal.3 der Start durch Ce4+-Ionen i m Vergleich zum Start durch Primarradikale vernachlassigbar war. I n Systemen mit t-Butanol und n-Butanol als Reduktionsmitteln erfolgt eine Komplexbildung (1 : 1) zwischen AUcohol und Ce4+-Ionen; sonst gilt dasselbe Reaktionsschema wiefiir die Systeme mit Formaldehyd.