Hock cleavage - The cause of main-chain scission in natural rubber autoxidation

Boon A. J., . Hock cleavage - The cause of main-chain scission in natural rubber autoxidation. pp. 90-106. ISSN 0127-7065

The possibility that acid-catalysed decomposition of ailylic hydroperoxides known as Hock cleavage is responsible for the autoxidative chain scission of natural rubber has been investigated. A hydroperoxidised peroxide vulcanisate was prepared by the ene reaction of a peroxide vulcanisate with singlet oxygen. Treatment of this rubber with various acids caused scission and produced a reduction in the hydroperoxide content. Several vulcanisates containing sodium carbonate or Proton Sponge (N N N N-tetramethyl-l 8-naphthalenediamine) were prepared and the retentions in their tensile properties after ageing in air at 100C were compared with the corresponding vulcanisates containing no base. The incorporation of base produced a dramatic reduction in the loss in tensile properties for a semi-efficient vulcanisate; a smaller reduction was observed for a conventional sulphur vulcanisate. By contrast the reduction in tensile properties of a peroxide vulcanisate was unaffected by base. These results provide support for the theory that Hock cleavage is responsible for main-chain scission during autoxidation of natural rubber particularly protected sulphur vulcanisates. Hock cleavage also adequately explains the many discrepancies discovered in the currently accepted scission mechanism which involves peroxyl radical cyclisation.

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Abstract

The possibility that acid-catalysed decomposition of ailylic hydroperoxides known as Hock cleavage is responsible for the autoxidative chain scission of natural rubber has been investigated. A hydroperoxidised peroxide vulcanisate was prepared by the ene reaction of a peroxide vulcanisate with singlet oxygen. Treatment of this rubber with various acids caused scission and produced a reduction in the hydroperoxide content. Several vulcanisates containing sodium carbonate or Proton Sponge (N N N N-tetramethyl-l 8-naphthalenediamine) were prepared and the retentions in their tensile properties after ageing in air at 100C were compared with the corresponding vulcanisates containing no base. The incorporation of base produced a dramatic reduction in the loss in tensile properties for a semi-efficient vulcanisate; a smaller reduction was observed for a conventional sulphur vulcanisate. By contrast the reduction in tensile properties of a peroxide vulcanisate was unaffected by base. These results provide support for the theory that Hock cleavage is responsible for main-chain scission during autoxidation of natural rubber particularly protected sulphur vulcanisates. Hock cleavage also adequately explains the many discrepancies discovered in the currently accepted scission mechanism which involves peroxyl radical cyclisation.

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Item Type:	Article
AGROVOC Term:	Natural rubber
AGROVOC Term:	Oxidation
AGROVOC Term:	Peroxides
AGROVOC Term:	Vulcanization
AGROVOC Term:	Oxygen
AGROVOC Term:	Acids
AGROVOC Term:	sodium
AGROVOC Term:	Sulphur
AGROVOC Term:	Sodium bicarbonate
AGROVOC Term:	Biochemical reduction
Depositing User:	Ms. Suzila Mohamad Kasim
Last Modified:	24 Apr 2025 06:28
URI:	http://webagris.upm.edu.my/id/eprint/23549

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