Chain Transfer in the Polymerization of Methyl Methacrylate. I. Transfer with Monomer and Thiols. The Mechanism of the Termination Reaction at 60°¹

Radical-Scavenging Activity of Thiols, Thiobarbituric Acid Derivatives and Phenolic Antioxidants Determined Using the Induction Period Method for Radical Polymerization of Methyl Methacrylate

“…This suggested that the polymerization of MMA did not involve thiyl radicals. The chain transfer constant of ME for growing poly(MMA) radicals is reported to be 0.62, although the value for aliphatic thiols such as ME is smaller than that for aromatic thiols [7]. This indicates that for a higher concentration of ME, the chain transfer reaction of this compound could occur during polymerization of MMA.…”

“…ME (structure: HS-CH 2 CH 2 OH) at the indicated concentrations acted as an inhibitor due to H abstraction from the -SH group in the ME molecule by free radicals (Figure 2). The weakness of the S-H bond and the high reactivity of the thiyl radical (RS*) are the two crucial parameters for a chain transfer agent [7,8]. Nucleophilic thiyl radicals are expected to be more reactive toward the α,β-unsaturated carbonyl group in the MMA molecule because of their higher electrophilicity.…”

“…Therefore, the negative value of IP for 1 and 7 may have been derived from their consumption of dioxygen in a DSC sample pan. On the other hand, the possibility that can not be completely excluded is that the small effect of 1 or 7 on the IP value may be due to their interaction of the surface of an alumina DSC sample pan because thiobarbituric acid derivatives showed a potent adhesion of resin to noble metals (Au, Ag, Pd) as well as base metals [7]. However, in the present study, 1 or 7 acted as a chain transfer agent for polymerization of MMA initiated by the thermal decomposition of AIBN (Table 4).…”

“…Quantitative inhibition of auto-oxidation by various synthetic and natural phenols and organic sulfur compounds has been investigated by many researchers [1][2][3][4][5][6][7][8][9]. Burton and Ingold studied the radical-scavenging activity of various phenolic compounds using the induction period method in a chlorobenzene-styrene system initiated by AIBN, and found that phenolic compounds act as potent chain-breaking antioxidants [1].…”

“…However, there have been few kinetic studies of these compounds. Also, thiols such as 2-mercaptoethanol and 2-mercaptothioxanthone have been previously reported to act as chain transfer agents in radical polymerization [6,7]. The high efficiency of organic sulfur compounds for control of chain length has attracted considerable attention in the field of radical polymerization, since the mechanical properties of the polymers obtained are dependent on their molecular weight.…”