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Polymers 2012, 4(2), 1025-1036; doi:10.3390/polym4021025
Article

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

1,*  and 2
1 Institute of Biomaterials and Bioengineering, Tokyo Medical and Dental University, Kanda-surugadai, Chiyoda-ku, Tokyo 101-0062, Japan 2 Meikai University School of Dentistry, Sakado, Saitama 350-0283, Japan
* Author to whom correspondence should be addressed.
Received: 27 February 2012 / Revised: 2 April 2012 / Accepted: 5 April 2012 / Published: 16 April 2012
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Abstract

The radical-scavenging activities of two thiols, eight (thio)barbituric acid derivatives and six chain-breaking phenolic antioxidants were investigated using the induction period method for polymerization of methyl methacrylate (MMA) initiated by thermal decomposition of 2,2’-azobisisobutyronitrile (AIBN) and monitored by differential scanning calorimetry (DSC). The induction period (IP) for the thiols 2-mercaptoethanol (ME) and 2-mercapto-1-methylimidazole (MMI) was about half that for phenolic antioxidants. Except for the potent inhibitor 5,5-dimethyl-2-thiobarbituric acid (3), the IP for thiobarbituric acid derivatives was about one tenth of that for phenolic antioxidants. The IP for 1,3,5-trimethyl-2-thiobarbituric acid (1) and 5-allyl-1, 3-dimethyl-2-thiobarbituric acid (7) was less than that of the control, possibly due to inhibition by a small amount of atmospheric oxygen in the DSC container. The ratio of the chain inhibition to that of chain propagation (CI/CP) for the thiols and thiobarbituric acid compounds except for 1, 3 and 7 was about 10 times greater or greater than that for phenolic compounds. A kinetic chain length (KCL) about 10% greater than that of the control was observed for 1, suggesting that 1 had chain transfer reactivity in the polymerization of MMA. The average molecular weight of polymers formed from thiobarbituric acid derivatives is discussed.
Keywords: organic sulfur compounds; phenolic compounds; radical polymerization; AIBN; MMA; induction period; initial rate of polymerization; chain inhibition; chain propagation organic sulfur compounds; phenolic compounds; radical polymerization; AIBN; MMA; induction period; initial rate of polymerization; chain inhibition; chain propagation
This is an open access article distributed under the Creative Commons Attribution License (CC BY 3.0).
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Kadoma, Y.; Fujisawa, S. Radical-Scavenging Activity of Thiols, Thiobarbituric Acid Derivatives and Phenolic Antioxidants Determined Using the Induction Period Method for Radical Polymerization of Methyl Methacrylate. Polymers 2012, 4, 1025-1036.

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