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..

A new method for the photochemical initiation of polymerization of vinyl compounds in aqueous solution is described. The photochemically active species is an ion pair complex of the formula Fe3+X−(X− = OH−, CI−, N−3, etc.). The light absorption by the ion pair leads to an electron transfer causing reduction of the cation and oxidation of the anion to an atom or free radical X. The latter leads to the initiation of polymerization in accordance with X + CH2CHR→XCH2CHR. The kinetics of the reaction were studied by the measurement of: (a) ferrous ion formed (colorimetrically), (b) monomer disappearance (by titration and by weighting the polymer), (c) the chain length of the polymer (in the case of methyl methacrylate). The dependence of the quantum yield on the light intensity, light absorption fraction, and the concentration of vinyl monomer and ferrous ion added initially was investigated. A complete mechanism, both with regard to the formation of free radicals and the polymerization reaction, was put forward involving: (1) light absorption, (2) a primary dark back reaction, (3) dissociation of the primary product, (4) a secondary dark back reaction, (5) initiation of polymerization by free radicals, (6) propagation of polymerization, and (7) termination by recombination of active polymer endings. The mechanism was verified by the experimental results and some constant ratios were estimated quantitatively.

SynopsisA systematic kinetic study of the thermal polymerization of methyl methacrylate, methyl acrylate, and acrylonjtrile initiated by ceric ion in aqueous perchloric, nitric, and sulfuric acid solutions, has been made. The polymerization experiments were conducted in the dark a t 35OC. under conditions of negligible oxidation of water by ceric ion. The polymerization was found to proceed without an induction period, and the stesdy-etate rate waa attained in a short time. The rate of monomer disappearance (followed by gravimetry) was found to bear a square dependence on monomer concentration and is independent of both the ceric and hydrogen ion concentrations. The rate of ceric disappearance (followed by titrimetry or spectrophotometry) waa found to be directly proportional to the ceric, monomer, and hydrogen ion concentrations. The chain lengths of the polymers (determined viscometrically) were directly proportional to the monomer concentration and inversely to the ceric and hydrogen ion concentrations. Initially added cerous ion had negligible effect on the rates. Increase in ionic strength caused a slight increase in the rates. From experiments conducted at different temperatures, the activation energies for the various procesees in the reaction were calculated. Most of the experimental results were suitably explained by a kinetic scheme involving initiation and termination by ceric ion in the unhydrolyzed Ce4+ form.

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Supplementary Material Available: Tables SI and SII, listing electronic absorption spectra and 13C NMR data, respectively, for nickel(II) compounds (2 pages). Ordering information is given on any current masthead page.