Browsing by Author "Lee, Munam"

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    Living ” Radical Polymerizations of Vinyl Monomers Initiated by Aged “ Cr2 --BPO ” in Homogeneous Solution
    (Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1978, 74 (07), 1978) Lee, Munam; Morigami, Tadashi; Minoura, Yuji
    Monomer is added to chromium(II) acetate (Cr2+) and benzoyl peroxide (BPO) previously treated at 10°C in dimethylformamide (DMF)(the ageing process), and polymerizations are performed. It is found that the degree of polymerization of poly(methyl methacrylate)(PMMA) obtained at 30°C or below increases with an increase in monomer conversion and the single peak of a molecular weight distribution curve shifts with monomer conversion. These results suggest that a “living” polymerization occurs in the homogeneous polymerization of MMA initiated by the aged “Cr2++ BPO” system. The polymerizations of various vinyl monomers with this initiator system are carried out at 25°C. The polymerization activity is relatively high for MMA, acrylonitrile, methyl acrylate and acrylamide but low for styrene, vinyl acetate and vinyl chloride. The molecular weights of polyacrylonitrile and poly(methyl acrylate) also increase with the monomer conversion. By copolymerizing MMA with acrylonitrile, it is found that polymerizations with aged “Cr2++ BPO” proceed via a free radical intermediate. The polymerization rates (Rp) of MMA at 25 and 30°C are expressed by the following relation, Rp= const.[aged “Cr2++BPO”]0.7–1.0[MMA]. The mechanism of a “living” radical polymerization is discussed in terms of a transition metal complex with free radicals.
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    Polymerization of Vinyl Monomers Initiated by Chromium(n) Acetate-i-Organic Peroxides
    (Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1978, 74 (07), 1978) Lee, Munam; Minoura, Yuji
    The redox initiator systems consisting of chromium(II) acetate (Cr2+) and organic peroxides are studied in dimethylformamide (DMF) at low temperatures. The second-order rate constants of reduction of benzoyl peroxide (BPO) with Cr2+ are 0.65, 0.24 and 0.075 dm3 mol–1 min–1 at –10, –20 and –28°C, respectively. The activity of organic peroxides for the redox polymerization of methyl methacrylate (MMA) at –28°C decreases in the following order; hydroperoxide > diacylperoxide > perester = dialkyl peroxide. The kinetics of polymerization of MMA are different from that of a conventional free-radical polymerization. The dependence of the initial rate of polymerization (Rp) on the concentrations of initiator components, Cr2+ and BPO, is very small; the kinetic orders are 0.1 and 0.2, respectively. However, Rp is proportional to the square of the concentration of MMA. This result is explained in terms of a primary radical termination. The polymerization of MMA with the Cr2++ BPO system is found to occur continuously without a dead end polymerization after red Cr2+ changed to blue Cr3+, i.e., after Cr2+ was consumed by the redox reaction with BPO. The degree of polymerization of PMMA obtained by this initiator system below 30°C increases with an increase in monomer conversion.