Kinetics of radical polymerization-XIX. study of the reactivities of phenols towards polyvinyl acetate radicals

Kinetics of vinyl polymerization initiated by the redox system thiourea-Mn3+ were investigated in the temperature range 30–40°C in sulfuric acid, and the rates of polymerization Rp and disappearance of Mn3+ have been measured. The effect of certain water-miscible organic solvents and anionic surfactant on the rates of polymerization was investigated. A mechanism involving the formation of a complex between Mn3+ and thiourea whose decomposition yields the initiating free radical with the polymerization terminated by mutual intraction of growing radicals is suggested.

Polymerization of Acrylonitrile Initiated by the Thiourea-Mn3+ Redox System

Publisher Summary This chapter discusses some of the particular kinetic problems of hydrogen atom abstractions from O–H bonds in the context of questions of general interest. The chapter aims to make unsolved problems explicit rather than giving final solutions. It seems desirable to realize explicitly that many of the theories and treatments are entirely empirical resembling the empirical origin of the rate constant. Radicals are chemical species having a free valence in classic chemical terms, or having an electron of uncoupled spin in terms of the quantum theory. Short-lived radicals have to be continuously generated for a steady concentration to be maintained. Radical reactions are classified in different ways. Firstly they can be selected according to the phase they are studied in. This chapter deals almost entirely with liquid-phase reactions. Arrhenius parameters, the limited liquid phase data are complemented by those taken from gas phase reactions.

The Hydrogen Atom Abstraction Reaction from O-H Bonds

Transfer Constants to Monomers, Polymers, Catalysts and Initiators, Solvents and Additives, and Sulfur Compounds in Free Radical Polymerization

The kinetics of the polymerization of arylonitrile with ceric ammonium sulfate in the presence of 2-propanethiol as the redox initiator system in aqueous solution has been investigated. The rate of polymerization was found to be proportional to the square root of both ceric ion and thiol concentrations, and the monomer exponent was close to 1.5. Spectral studies indicated that there is a complex formation between ceric ion and the monomer acrylonitrile. A kinetic scheme, based on initial formation of this complex and its subsequent reaction with the thiol to produce the free radicals (RS.) responsible for initiation has been postulated to account for the observed results. The activation energy and different kinetic and transfer constants for the system have also been evaluated.

Polymerization of Acrylonitrile with Ceric lon-2-Propanethiol as Initiator System

The polymerization of acrylonitrile (AN) was studied in aqueous solution with hydrogen peroxide (H2O2) as catalyst and thiourea (TU) as cocatalyst at 30°C. Since the polymerization was carried out at a relatively low temperature, AN was not polymerized by hydrogen peroxide alone. Upon addition of TU to the reaction system, polymerization occurred immediately, and the rate of polymerization increased with increasing TU concentration. In order to obtain the overall polymerization equation, the dependence of polymerization rate on H2O2 and AN concentration was studied kinetically. It was found that the overall polymerization rate Rp was represented by the equation: Rp = K[TU]frac12;[H2O2]frac12;[AN], where K is the rate constant. The acceleration in the presence of TU might be attributed to a redox reaction between H2O2 and TU which would produce free radicals rapidly. The effect of substituents was investigated by use of various N-substituted derivatives of TU. The polymerization rate increased linearly with the σ* constants of the substituents as electron-withdrawing substituents were added. The polymerization mechanism is discussed on the basis of the results.

Effect of thiourea on the radical polymerization of vinyl monomers. Part I. Polymerization of acrylonitrile with the hydrogen peroxide–thiourea catalyst system

The effect of phenol, o-cresol, m-cresol, and p-cresol on the polymerization of styrene in solution and emulsion was studied.

It was stated that the inhibition effect is caused by remaining oxygen in these system. In the case of polymerization under oxygen free conditions (i.e. vacuum), no inhibition and retardation effect was seen. The chain transfer constants, Ctr, became smaller in the order: o-cresol > p-cresol > m-cresol > phenol. It was assumed that there exists a linear relationship between Ctr and HAMMETT's σ because the phenolic substances are little dissociated. In other words, it was considered to follow the order of the value of pKa. In the case of co-existence of oxygen and phenolic substances, no retardation effect was seen, but inhibition effect was noticed, while, the relation, [I.P.] = k [phenols]0.7, was recognized between the concentration of each phenols and induction period [I.P.]. Also, the relationship between the value of k and HAMMETT's σ was plotted along with the regression line defined by following equation: log k/k0 = ρσ and ρ value was −2.5. The results were discussed.

The effect of phenol and cresols on the polymerization of styrene

フェノール,およびo-,m-,p-クレゾールがスチレンの重合に及ぼす影響について研究を行なった。これらのフェノール類の作用を溶液重合および乳化重合で検討し,残存する酸素に影響されることを知った。酸素の存在しない場合には,禁止および抑制効果は見られなかったが,連鎖移動が認められ,その連鎖移動定数ctrはo-クレゾール＞p-クレゾール＞m-クレゾール＞フェノールの順で小さくなり,ctrとHammettのσとの間に直線関係があり,フェノール性物質の解離しにくさに関係する。すなわち解離定数pKaの大きさの順に大きくなるものと考えられた。酸素共存の場合は,抑制作用はないが禁止効果が認められ,個々のフェノール類の濃度[Phenols]と誘導期間[I.P]の間に[I.P]=k[phenols]0.7なる関係があった。また,このk値とHammettのσとの間に直線関係があり,ctrの場合と同様pKaの大きさの順(o-クレゾールを除く)になっていた。これらの結果より酸素共存下におけるフェノールの禁止効果について考察した。

Effects of Phenol and Cresol on the Polymerization of Styrene

天然ゴム- メタクリル酸メチル系グラフト重合物を合成し, オゾン分解によって分枝のポリアクリル酸メチルを取出した。粘度測定による分子量決定で, 遊離のポリメタクリル酸メチルも分枝のそれも数平均重合度が等しいことがわかった。

Noboru Yasumoto

Papers

Effect of thiourea on the radical polymerization of vinyl monomers. Part I. Polymerization of acrylonitrile with the hydrogen peroxide–thiourea catalyst system

The effect of phenol and cresols on the polymerization of styrene

Effects of Phenol and Cresol on the Polymerization of Styrene

The Number and Length of Branches on Natural Rubber-Methyl Methacrylate Graft Copolymer