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    Photoinitiation of Polymerization by Chloro-o.xobis(2,4- pentanedionato)vanadium(v)
    (Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1974, 70 (11), 1974) Aliwi, S. M.; Bamford, Clement H.
    Chloro-oxobis(2,4-pentanedionato)vanadium(V)[VO(acac)2Cl] sensitizes the polymerization of methyl methacrylate when irradiated by wavelengths in the near ultra-violet. Under the experimental conditions employed ([VO(acac)2Cl]<10–4 mol dm–3) no retardation occurs and the rate of initiation is independent of monomer concentration (with benzene as diluent). The quantum yield for initiation at λ= 365 nm is 2.07 × 10–2. Analysis of the polymers formed shows that initiation occurs predominantly through scission of chlorine atoms from VO(acac)2Cl. Spectral changes accompanying irradiation are consistent with the formation of VO(acac)2 as the final product. Rates of photodecomposition of VO(acac)2Cl have been measured spectrophoto-metrically over a range of monomer concentrations [M] with benzene as diluent and found to increase linearly with [M]. At [M]= 0, the rate of decomposition is equal to the (constant) rate of initiation at finite [M], but for [M]>0, the rate of photodecomposition exceeds the rate of initiation. A reaction mechanism is proposed based on an intramolecular photo-oxidation-reduction process which leads to the primary formation of a VIV chelate and a chlorine atom. In addition, monomer is considered to undergo an insertion reaction into the V—Cl bond of photo-excited VO(acac)2Cl, resulting in decomposition of the chelate by a non-radical route. Relevant kinetic parameters are evaluated.
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    Polymerization of Ethylene on Chromium Oxide Catalysts: Part 4.—Infra-red Study of the Adsorption of Nitric Oxide and Ammonia on Active Catalyst
    (Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1973, 69 (3), 1973) Eley, D. D.; Rochester, C. H.; Scurrell, M. S.
    Nitric oxide adsorbs on reduced supported chromium(VI) oxide catalyst to give infra-red bands at 1740, ca. 1800, and ca. 1860 cm-1. The band at ca. 1800 cm1 has been assigned to nitric oxide molecules coordinatively chemisorbed on Cr4i ions in the surface. The band at 1740 cm-1 is considered to result from a combination of separate bands at 1743 and 1738 cm-1 due to nitric oxide covalently bound to Cr3+ and Cr5+ sites respectively. The band at ca. 1860 cm 1 is similarly assigned to nitric oxide chemisorbed on two types of site. The adsorption of ammonia gave infra-red bands due to coordinatively bound ammonia at 3400 and 3300 cm-1 which were insensitive to the extent of reduction of the catalyst. Correlations between the intensities of the bands due to adsorbed nitric oxide and the activities of catalyst samples for the polymerization of ethylene support the conclusion that Cr5i ions are the active sites in the polymerization process. The polymerization reaction was poisoned by the pre-adsorption of nitric oxide or ammonia.
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    Telomerization of Methyl Methacrylate with Bromotrichloromethanc
    (Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1972, 68 (9), 1972) Barson, C. A.; Luxton, A. R.
    The photoinitiated reaction between methyl methacrylate and bromotrichloromethane has been studied at 30°C. The products have been analyzed by gel permeation chromatography and the relative proportions of the smaller individual telomers have been estimated. The average degrees of polymerization have also been determined by end-group analysis, using 14C-labelled bromotrichloromethane as photoinitiator. Values of the transfer constants for the first seven radical intermediates have been obtained; these undergo an increase in size over the first three propagation steps to a constant value equal to that of the transfer constant for polymeric radicals.
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    Photo-initiation of Polymerization by Manganese(III) Chelates
    (Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1972, 68 (7), 1972) Bamford, C. H; Ferrar, A. N
    Manganese(lII) acetylacctonatc (Mn(acac)3) and manganese(III) tris(l,l,l-trifluoroacetyl- acetonate) (Mn(facac)3) photosensitize (A = 365 nm) the free-radical polymerization of methyl methacrylate and styrene. Photolysis of the chelates in benzene and cyclohexane solutions is shown to yield acac* or facac* radicals, which undergo hydrogen abstraction reactions. Initiation of polymerization occurs with low quantum yields, and, in bulk monomer, does not depend on the nature of the monomer. In the latter respect it therefore differs markedly from thermal initiation by Mn(facac)3, which is strongly monomer-selective. The rate of photodecomposition of Mn(acac)3 exceeds the rate of initiation, the difference being proportional to the monomer concentration. On the other hand, photo-decomposition and initiation proceed at similar rates with Mn(facac)3. Photo-initiation of the polymerization of methyl methacrylate by Mn(facac)3 is subject to marked solvent effects, being less efficient in benzene than in ethyl acetate solutions, particularly at low monomer concentrations. No similar behaviour is encountered with Mn(acac)3. A mechanism involving exciplex formation between Mn(facac)3 and methyl methacrylate or ethyl acetate is proposed.
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    Effects of Salts of Metals on Vinyl Polymerization: Part 8. Polymerization of Vinyl Chloride in the presence of Ferric Chloride
    (Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1972, 68 (10), 1972) Bengough, W. I.; Chawdry, N. M.
    The polymerization of vinyl chloride in dimethylformamide, initiated with l,l'-azobisisobutyro- nitrile, and retarded with ferric chloride, has been investigated at temperatures from 40 to 70°C. A 6.65 M monomer concentration was used for most of the work, but some polymerizations were carried out using 2.66 M vinyl chloride. At ferric chloride concentrations of >10~3 M termination proceeded entirely by reaction with ferric chloride, but at lower concentrations some mutual termination of growing polymer radicals occurred. Rates of initiation, the activation energy for the initiation reaction, and values of the ratio Kp/Kx, where kx is the rate constant for the reaction between polyvinyl chloride) radicals and ferric chloride, were measured at 40, 50, 60, and 70°C.