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Title: Hexamethylene-N, N' bis (tert-butyl peroxycarbamate) as a crosslinking agent for elastomers
Authors: Ogunniyi, David
Issue Date: 1985
Publisher: © David Sunday Ogunniyi
Abstract: The synthesis of a new bisperoxycarbamate based on a reaction between hexamethylene-1,6 diisocyanate and tertiary butyl hydroperoxide was undertaken. In addition, studies were carried out on an earlier research bisperoxycarbamate based on methylene bis(4-cyclohexylisocyanate) and tertiary butyl hydroperoxide. The equation showing the preparation of the new material is shown below: [Equation not shown] The new material - hexamethylene-N,N' bis (tertiary butyl peroxycarbamate) is shown to be able to crosslink a wide range of elastomers, namely -BIIR, NR, SBR, NR/BR, CR, FKM, NBR, Q, ECO, GPO. However, it has been found to give best results in fluorocarbon rubber which was examined in further detail. The material is shown to be versatile by using it to cure different grades of fluorocarbon rubber (mainly copolymers of vinylidene fluoride and hexafluoropropylene). The physical properties obtained with the new material as curing agent are comparable with those obtained using standard crosslinking agents for fluoroelastomers. Since carbon dioxide is evolved when bisperoxycarbamates are heated, calcium hydroxide was included in most formulations to act as an absorber system. Calcium oxide and magnesium oxide were found to be suitable metallic oxides to react with any acidic gases (such as hydrogen fluoride) evolved during curing of fluoroelastomer compounds. It was ii observed that the state of cure was- poorer when lead oxides were used (e.g. litharge PbO); also, the use of dibasic lead phosphite as acid acceptor appeared to interfere with HBTBP cure. Compounding studies, solvent extraction methods and nitrogen tests, and crosslink density measurements were used to postulate possible routes of crosslink formation. These routes of crosslink formation were based on homolytic decomposition of the bisperoxycarbamate, radical abstraction, interaction of a reactive intermediate, and radical­radical interaction. Additional information was obtained from stress relaxation measurements which indicated that new crosslinks were formed during postcuring of fluorocarbon vulcanizates and that this process continued in the initial stages of heat-ageing of postcured FKM vulcanizates.
Description: A Doctoral Thesis. Submitted in partial fulfilment of the requirements for the award of Doctor of Philosophy of Loughborough University.
URI: https://dspace.lboro.ac.uk/2134/25499
Appears in Collections:PhD Theses (Materials)

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